I

MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY, BHOPAL

DEPARTMENT OF ARCHITECTURE AND PLANNING

DECLARATION

This dissertation, entitled RESIDENTIAL BUILDINGS ON SLOPING SITES is

being submitted in subject in ARC 426, Research Principles and Dissertation as part

of requirement for eighth semester of Bachelor of Architecture by the undersigned for

evaluation.

The matter embodied in this dissertation is either my own work or compilation of

others work, acknowledged properly. If, in future, it is found that the above statement

is false, then the institute may take any action against me as per rules.

Deepa Sharma

Scholar Number: 101110047

May 2014

II

ACKNOWLEDGEMENT

I would like to gratefully and sincerely thank Dr. Manmohan Kapshe for his

guidance, understanding, patience, and most importantly, his friendship during my

dissertation research study. He encouraged me to grow as an instructor and an

independent thinker. I am not sure many graduate students are given the opportunity

to develop their own individuality and self-sufficiency by being allowed to work with

such independence.

The writing of this dissertation has been one of the most significant academic

challenges I have ever taken. Though the following dissertation is an individual work,

I could never have reached the heights or explored the depths without the help of

books published by various authors, the e-books available on the internet, the research

papers published by various authors and the various organizations and websites

providing information related to my dissertation topic.

My very special thanks to my colleagues for their support and suggestions for my

research and all the other respective sources for helping me.

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LIST OF CONTENTS

DECLARATION ....................................................................................................... I

ACKNOWLEDGEMENT ........................................................................................ II

LIST OF CONTENTS .............................................................................................. II

LIST OF FIGURES .................................................................................................. V

LIST OF TABLES ................................................................................................. VII

Chapter-1. INTRODUCTION ................................................................................... 1

1.1. Justification ..................................................................................................... 1

1.2. Need of the topic ............................................................................................. 2

1.3. Aim .................................................................................................................. 3

1.4. Objectives ........................................................................................................ 3

1.5. Scope ............................................................................................................... 4

1.6. Limitations ...................................................................................................... 5

1.7. Methodology ................................................................................................... 6

Chapter-2. UNDERSTANDING THE TOPOGRAPHY OF SLOPING

LANDFORMS AND DESIGN PRINCIPLES .............................................................. 8

2.1. Types of sloping landforms ............................................................................. 8

2.2. Buildings on slope: the implications and solutions ....................................... 11

2.3. Clustering of houses ...................................................................................... 16

2.4. Scenic opportunities ...................................................................................... 17

2.5. Conclusion ..................................................................................................... 18

Chapter-3. BUILDING TYPOLOGIES, CONSTRUCTION TECHNIQUES AND

SERVICES 19

3.1. Residential building typologies prevalent in North India ............................. 19

3.2. Residential building typologies prevalent in North East India ..................... 20

IV

3.3. Construction techniques to be adopted while designing the building in

sloping sites .............................................................................................................. 21

3.4. Roads: ............................................................................................................ 26

3.5. Practical considerations (landslide or slope stability) ................................... 32

3.6. Recommended practices ................................................................................ 35

3.7. Conclusion ..................................................................................................... 35

Chapter-4. LANDSCAPING ON SLOPING LANDFORMS ................................. 36

4.1. Planning a landscape on slope ....................................................................... 36

4.2. Landscaping principles on sloping sites ........................................................ 39

4.3. Ways of landscaping a sloping site ............................................................... 44

4.4. Erosion control for residential hillsides ........................................................ 48

4.5. Conclusion ..................................................................................................... 51

Chapter-5. CASE STUDIES OF DIFFERENT BUILDINGS ON SLOPING SITES

52

5.1. Car park house, Los Angeles......................................................................... 52

5.2. Family house, Prague .................................................................................... 53

5.3. Apartment block, North-East Italy ................................................................ 54

5.4. Stepped house, Spain..................................................................................... 56

5.5. Conclusion ..................................................................................................... 57

REFERENCES ........................................................................................................ 58

ANNEXURE............................................................................................................ 60

V

LIST OF FIGURES

Figure 2.1: Up slope (left) and Down slope (right) (Tweed Shire Council) ................. 9

Figure 2.2: Side slope (left) and Rolling slope (right) (Tweed Shire Council) .......... 10

Figure 2.3: Building on flat site (left) and moderate slope (right) (Tweed Shire

Council)........................................................................................................................ 11

Figure 2.4: Building on steep slope (left) and extreme slope (right) (Tweed Shire

Council)........................................................................................................................ 11

Figure 2.5: Design principles that must be taken care of (HRO) .............................. 15

Figure 2.6: Over excavation and creation of artificial plateau should be avoided

(North Tipperary County Council, 2009) .................................................................... 15

Figure 2.7: Step building design (Tweed Shire Council) ............................................ 16

Figure 2.8: Standard large lot residential layout, mixed single family layout with open

spaces, mixed density layout with open spaces ( from left to right) (City of Vernon-

Hillside Guidelines 2008, 2008) .................................................................................. 17

Figure 3.1: RC moment resisting frame with unreinforced masonry infill walls (left)

and open ground storey structure (right) (Assessment Project Group of IIT Bombay,

IIT Guwahati, IIT Kharagpur, IIT Madras, IIT Roorkee, 2013) .................................. 20

Figure 3.2: Cut and fill construction (left) and stilts construction (right)

Basements/Retaining walls (Tips for building on a sloped terrain, 2014) (How to

Build on a Sloping Site) ............................................................................................... 22

Figure 3.3: Basement construction on sloping sites (Tips for building on a sloped

terrain, 2014) ................................................................................................................ 23

Figure 3.4: Typical retaining wall construction, Gabion wall and rock buttress (from

left to right) (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME

ROADS BMPS) ........................................................................................................... 24

Figure 3.5: Common types of retaining structures (Slope Stabilization and Stability

of Cuts and Fills- LOW-VOLUME ROADS BMPS).................................................. 24

VI

Figure 3.6: Construction detail for retaining wall of height upto 2 m (left) and 5 m

(right) (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS

BMPS).......................................................................................................................... 25

Figure 3.7: Typical rock wall construction for smooth backfill (left) and face with

steps (right) (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME

ROADS BMPS) ........................................................................................................... 25

Figure 3.8: Two lane road (left) and split level access road (right) (California Coastal

Commission) ................................................................................................................ 27

Figure 3.9: Single lane road with pullouts (left) and bridge (right) (California Coastal

Commission) ................................................................................................................ 28

Figure 3.10: Culvert (left) and Arizona crossing (right) (California Coastal

Commission) ................................................................................................................ 29

Figure 3.11: Balanced cut and fill for most of the construction on hill slopes (Slope

Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS) ....... 30

Figure 3.12: Full bench cuts for slopes exceeding 60% (Slope Stabilization and

Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS) ................................... 30

Figure 3.13: Through cut (Slope Stabilization and Stability of Cuts and Fills- LOW-

VOLUME ROADS BMPS) ......................................................................................... 31

Figure 3.14: Typical fill (Slope Stabilization and Stability of Cuts and Fills- LOW-


Figure 3.15: Benched slope fill with layer placement (Slope Stabilization and Stability

of Cuts and Fills- LOW-VOLUME ROADS BMPS).................................................. 31

Figure 3.16: Reinforced fill. These can be used as an alternative for retaining wall

(Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)

...................................................................................................................................... 32

Figure 3.17: Through fill (Slope Stabilization and Stability of Cuts and Fills- LOW-


Figure 3.18: Contour graded slope (left) and Steep geogrid slope (right) (California

Coastal Commission) ................................................................................................... 34

VII

Figure 4.1: Ground covers for steep slopes (Alders) .................................................. 42

Figure 4.2: Steep sidewalk grades are a significant barrier to access for many

pedestrians (left), If he side walk grade exceeds 5% level landings should be provide

at regular intervals (right) (Federal Highway Administration, Updated: 02/10/2014)

...................................................................................................................................... 44

Figure 4.3: Gardens showing terracing (Washburn) .................................................. 45

Figure 4.4: Construction of tiered garden (Alpha Landscapes Design ltd.) ............... 46

Figure 4.5: Rock landscaping (DIY network) .............................................................. 47

Figure 4.6: A sloping site, made up of semicircular layers. The key stone is the largest

stone. Subsequent stones get progressively shallower so that they disappear into the

ground at the sides of the site. (Rock Landscaping Ideas Flat and Sloping Sites) ... 48

Figure 5.1: Car park house built on sloping site (ArchInspire) .................................. 52

Figure 5.2: Conceptual sketches developed by the architect (Grido Architektura and

Design) ......................................................................................................................... 53

Figure 5.3: View of the house (top), timber frame construction (bottom left), sections

(bottom right) (Grido Architektura and Design) ......................................................... 54

Figure 5.4: The three-storey Dolomitenblick building (Plazma Studio) ..................... 55

Figure 5.5: Tiered home on sloping site in Spain (left), view showing arrangement of

spaces (right) (Eva Designs, 2014) .............................................................................. 56

Figure 5.6: Side view of home showing stepped appearance (Eva Designs, 2014) .... 56

LIST OF TABLES

Table 1 : Common stable slope ratios for varying soil/rock conditions (Slope

Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS) ....... 60

VIII

Table 2 : Relation between number of levels and number of gabions for flat backfill


...................................................................................................................................... 61

Table 3 : Relation between number of levels and number of gabions for face with

steps (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS

BMPS).......................................................................................................................... 61

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CHAPTER-1. INTRODUCTION

The housing we build today will not only help to shape our environment in the

immediate future, it will also be determining the environmental quality of spaces. This

study describes the contributions to quality and sustainability of the design of new

residential developments on sloping sites.

The context given in the report is aimed at achieving attractive and functional places

through better design, better construction techniques and services, proper use of

building materials, suitability of landslopes for different buildings to promote:

1. The wider context of the local setting, the characteristics of the site for

development

2. More sustainable patterns of living and working

3. More effective integration between topography and built up

4. The creation of attractive places in which people are happy to live, work and

take their leisure.

5. Greater responsiveness to site and setting in the layout of new development to

achieve a better balance between requirements and other factors.

The creation of attractive residential environments with a genuine sense of place is a

prerequisite to achieving sustainability. The quality of where we live depends not just

on the design of buildings, but on their layout and landscaping, the arrangements

made for access, and in particular, how they relate to their surroundings. It is intended

to encourage the interconnection of design considerations of the setting, landscape

design, circulation patterns and buildings to form a coherent design structure.

1.1. Justification

In global context, each and every piece of land should be praised to its individuality.

At designing point of view, each site has got its own potential in terms of its richness,

fertility, texture, ability to bear, nearby features like deep valleys, water bodies,

hillocks, ridges and soaring mountains.

Designing of building on sloping sites while avoiding the cut and fill construction

techniques is cumbersome process because of change in ground levels. But spaces

should be carved out respecting the character and physical behavior of site, thus

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achieving the better functional space. These techniques are only employed when

necessary.

Designing on sloping spaces is a move away from typical standards of flat sites to a

more integrated and functional approach to achieve high quality and sustainable

designs. Most of the sloping sites due to its beautiful and admiring surrounding

features, the user can enjoy the nature upto its full expanse.

Spaces designed in sloping sites may differs from those of in flat or less sloping sites

(where presence of contours can be neglected) in terms of their approach, dimensions,

geometry, proportions, views, etc. Those spaces may prove inconvenient or

exhaustive for physically challenged people, but that can also be avoided by following

some design criteria, thus making the space more functional and universal.

The execution principles, services utilized for construction of buildings are quite

different from those adopted in flat sites. Also the ambient climatic conditions reaches

extreme in most of the regions having uneven landforms. These places are also

vulnerable to other natural calamities like seismic activities, storms, snowfall, hail,

etc.

Some of the buildings are constructed using locally available materials and techniques

which may not be prevailing in other regions because there, the transport of building

materials proves laborious.

So, the study would help architects/ designers to get the complete idea of

perspective of spaces and designing according to the requirement of user and

exploring the site upto its full extent.

1.2. Need of the topic

1. To understand the way that how spaces should be carved out respecting the

site potential, field patterns, townscapes and landscapes.

2. To lessen the impact of seismic impacts, wind loads, and other dynamic

loadings on building and its surroundings.

3. To design spaces according to the extreme of climates

4. To minimize the cut and fill construction techniques, adopting sustainable and

green building principles as far as possible.

5. To make the space more functional for physically challenged people.

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6. Development designed to emphasis a sense of place and community with

proper movement networks.

7. Move away from conventional standards to more interesting approach for

achieving high quality and functional spaces.

8. To enhance the importance of views and vistas.

9. Protection of existing trees and other important natural and topographical

features.

10. Considers the wider context of the local setting, the characteristics of the site

for development, and strategies for the overall design character of a proposal.

11. Giving guidance on the main elements needed to achieve high quality design,

from the overall landscape and urban design considerations to the layout of

dwellings, means of access and patterns of movement.

12. Integrate with existing patterns of movement.

1.3. Aim

The main purpose of the study is to contribute to the methodologies and principles

employed for carving out spaces in sloping sites. The study is also intended to

contribute to the better understanding of terrain and opportunities for creating spaces

which have greater responsiveness to site.

To establish design principles for different typologies of residential buildings on

sloping sites.

1.4. Objectives

Residential development on sloping sites must complement the scenic hillside

character by integrating unique or special natural features such as landforms, rock

outcroppings, viable existing stands of trees and vegetation, ravines, water features,

hilltops and ridgelines; protect wildlife habitat; avoid unstable or hazardous sites and

protect lives and property from hazardous conditions, such as rock falls, storm runoff,

erosion, etc.; provide safe year round access for residents, visitors and service

providers;

1. Suitability of land slopes for different buildings and design criteria

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Sloping landforms can be classified on the basis of direction of slope and amount of

slope. Each site has its individuality on which a particular type of arrangement of

spaces can be done. This further requires analysis of some of the other parameters. A

thorough investigation and assessment of ground conditions and stability is essential

to determine whether a site is suitable for building on, where the best place may be to

locate a building and the type of structural system that will be required.

2. How sloping landforms can be best accomplished for getting functional and risk

free spaces

Sloping sites are generally prone to soil erosion, landslides, debris flow, seismic

activities, etc. These are also burdensome for physically challenged people. But

incorporating some of the design criteria, spaces can be made more functional and

risk free. Natural character of the hillside should be preserved as well as provide

scenic views from a hillside site.

3. Design principles, construction techniques, materials and services

Design solutions/construction techniques like step building design, cut/fill

construction techniques, raising the building on stilts/poles, retaining wall

construction, drainage issues, seepage problems should be incorporated which

respects the site potential upto its full expanse and lessen the impact of seismic

loading and other dynamic loadings.

4. Scope of landscaping on sloping sites

Landscapes on sloping sites will certainly take a little more thought and effort than for

a normal flat site but the results can be very interesting by playing with change in

levels, creating stepped appearance, terracing, tiering, etc. The biggest concern is

usually the risk of erosion. Additionally, planting and maintaining plants on inclines

can be a difficult undertaking. However, there are many ways to successfully

landscape a slope and create an attractive incline.

1.5. Scope

The study is intended for use in the design of all the proposals for residential

buildings of all typologies in global context having uneven terrains from small scale

housing projects to major housing projects on large sites satisfying the climatic

5

conditions, culture and heritage of the region and also respecting the landform.

Nevertheless, the principles in the report will be used by architects as a basis for

assessing any proposal.

The study also have emphasis on landscaping features(decks, patios, pavers, pergolas,

entryways, walkways, plants, retaining walls, lighting, water bodies, etc.), process of

landscaping in slopes, hardscaping and softscaping.

Preservation of slopes or hillside erosion control, importance of heights and

proportions, designing open spaces, protection of existing trees, and other important

natural and topographical features is also included in report.

Study also includes construction of houses using modern building materials and

techniques as well as vernacular materials and techniques.

The study also includes the construction technologies, materials, services (water

supply, sewage disposal, gas, electricity, lighting and telecommunication) and study

about vehicular and pedestrian networks.

Seismic vulnerability assessment of building types is also included in study.

Cost factors are not taken into consideration in this study.

The study also not includes designing in largely steep slopes, inaccessible sites, places

having frequent landslides, other natural calamities like heavy snowfall, hail storm,

etc.

The study also not includes the interior designing of the spaces and elements (wall

treatments, finishes, flooring, ceiling, etc.)

1.6. Limitations

The study will be helpful for architects and designers for proposals of all types of

residential buildings but not commercial, industrial, recreational buildings like

shopping malls, large office buildings, sports complexes and stadiums.

The study includes information about construction techniques and materials employed

for particular type of landform but not project management and construction

management of execution, materials, time taken for execution, labours and cost.

6

The scope of study could be very vast and very much extensive in nature involving all

constructional techniques and structural aspects. But, sighting the specific need and

the other constraints such as time etc., we should draw a limit to our area of

exploration. No live case studies are done because of time constraint.

1.7. Methodology

The study encompasses the information on topics from detailed research referring

journals, documents, literature reviews, case studies, in each and every objective of

the study.

Detailed analysis of the visual character of the local setting, topography, field patterns

(using topographical survey techniques), landmarks, historic features and nature

conservation interests is done to provide a source of inspiration for the design.

Maps and aerial photographs can provide useful indicators of visual character and

help to highlight the character of the local landscape or townscape.

Topographic survey is done to get the necessary data to produce a topographic map of

the earths surface. This map will include contour lines, location of natural features,

such as streams, gullies, and ditches and man-made features like bridges, culverts,

roads, fences, etc. which are needful for detailed planning. The best practical method

of presenting topography is by means of contour maps.

Analysis of the local landscape and townscape is important to help relate the

development more sensitively to its surroundings. Such analysis should include

patterns of landscape and townscape, spatial characteristics and building forms, and

the results should be illustrated on plan.

The analysis also includes the visual characteristics of building forms and related

elements, such as: aspect and orientation; proportion; the balance of solid to void; the

shapes and details of roofs, chimneys, windows and doors and the materials used.

7

Primary studies about the type of geography of different places in global context from various websites and its response to the building and

building's response to the site

Study about the behavior of building in particular type of landform through case studies and browsing illustrations of buildings in sloping sites to get the

perspective of spaces

Collection of information about different typologies of residential buildings and their design principles referring various journals and literature reviews

Study of construction techniques, services, circulation patterns, vulnerability assesment, scope

of landscaping from various literature reviews, journals, documents, videos and documentaries

Assimilation of information in proper hierarchy and preparation of report

reviews

Preparation of final report

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CHAPTER-2. UNDERSTANDING THE TOPOGRAPHY OF

SLOPING LANDFORMS AND DESIGN PRINCIPLES

Hillsides are defined as lands in their natural state that have a slope angle of 12% or

greater for a minimum horizontal distance of 10 meters. Landforms may be extremely

sloped or almost flat. The steepness of slopes can also be described in degrees;

however, for the purpose of land development it is defined as either a percent or a

ratio.

Engineered structural slopes are required in all fill locations where roads, utilities or

buildings are being supported. These slopes can be as steep as 100%, or 1:1,

depending on materials used and compaction methods. The use of geotextiles as part

of a structurally engineered design can further increase the maximum slope attainable.

Typical engineered slopes are 67% or 1.5:1. 1.5:1 slopes, though they may be

structurally acceptable, are generally too steep to properly retain the minimum depth

of topsoil of 150mm necessary to enable re-growth of native plant species. Minimum

finished slopes that will consistently retain topsoil are 50% (2:1) or flatter. (Design

Ideas for sloping sites)

Sloping sites offer unique opportunities including great views, access to cooling

breezes and often result in more interesting building forms where the design

accommodates the slope. They do however require more design consideration than a

flat block to balance house design, excavation and potential amenity impacts on

neighboring properties. On a sloping site, off the shelf designs which have been

specifically designed for a flat block should be avoided to get interested spaces

incorporated in and to achieve greater responsiveness to site. Key importance of slope

development is the preservation of land which provides natural space, buffering and

habitat for native plants and animals. (Design Ideas for sloping sites)

2.1. Types of sloping landforms

There can be diverse types of landforms in sloping sites which are listed below based

on the direction and amount of slope which decides the type of spaces in residential

buildings.

(Tweed Shire Council)

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2.1.1. Classification based on direction of slope of the site

Landslopes can be classified on the basis of direction of slope as Down slope, Up

slope, Side slope and Rolling slope

2.1.1.1. Up slope

1. Site rises up from road. (see Figure 2.1)

2. Generally require more cut allowing for lower level/garage.

3. Garage doors and driveways are generally more visually dominant from the

street on up slope lots. A projecting balcony over the garage reduces this

visual impact.

4. A level transition off the street level into the elevated living areas should be

aim at.

2.1.1.2. Down slope

1. Site falls away from road. (see Figure 2.1)

2. Garage carports are easier to build closer to the street.

3. An extra storey at the rear should be avoided which significantly increases the

buildings height and bulk from the rear.

Figure 2.1: Up slope (left) and Down slope (right) (Tweed Shire Council)

2.1.1.3. Side slope

1. Site rises/falls away from side boundaries. (see Figure 2.2)

2. House with the garage at lower level with living space above can be designed.

3. Site benching and large retaining walls at property boundaries which can

lead to overshadowing, overlooking and drainage issued should be avoided.

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2.1.1.4. Rolling slope

1. Site rises/falls in two or more directions. (see Figure 2.2)

2. Level change within the building design by splitting the house over different

floor levels can be designed.

3. Unsightly retaining walls outside of the building envelope should be avoided.

Figure 2.2: Side slope (left) and Rolling slope (right) (Tweed Shire Council)

2.1.2. Classification based on direction of slope of the site

Landforms may be flat, having moderate slope, steep slope or extreme slope

depending upon the terrain which decides the construction techniques to be adopted

(whether single slab, post and beam construction or pole construction should be

employed)

2.1.2.1. Flat sites

Single slab on ground construction are only appropriate up to a slope incline of 4 or

7 as the cut/fill required becomes excessive (over 1.5m). Slopes between 4-6 should

accommodate some level change within the building footprint. (see Figure 2.3)

2.1.2.2. Moderate slope

On slopes of 6-12, single slab construction should be avoided (up to 1:5). Two or

more slabs or part slab/part post and beam construction techniques should be adopted.

(see Figure 2.3 )

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2.1.2.3. Steep slope

On slopes over 12-18 (1:5-1:3) post and beam construction which steps with the

site. This may include a lower part level which may be a concrete slab. (see Figure

2.4)

2.1.2.4. Extreme slope

On slopes over 18 (1:3), suspended or pole construction is required. This degree of

slope is more suited to a downslope configuration. Driveway access is generally

difficult on upslope lots which require large retaining walls and a curving driveway.

(see Figure 2.4)

Figure 2.3: Building on flat site (left) and moderate slope (right) (Tweed Shire Council)

Figure 2.4: Building on steep slope (left) and extreme slope (right) (Tweed Shire Council)

2.2. Buildings on slope: the implications and solutions

If a site is flat, the topography may not influence the location and layout of the

building, but on a sloping site, the topography is likely to be a significant design

factor. The slope of a site and adjacent surroundings may affect access to sun and

views. For example, an east-facing hillside will have reduced afternoon and evening

sunlight, particularly in winter, and depending on the height and steepness, a south-

facing site may receive little or no sun during the winter months. The position of a

new house in undulating and hilly areas needs to be carefully considered to achieve a

practical design which does not look out of place. (Design Ideas for sloping sites)

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2.2.1. Level changes

On a sloping site, a split level floor plan is the most cost effective way to develop a

site. However, this will usually involve several small sets of stairs between levels and

this can add to costs. Multiple levels may also limit the appeal of a property to

households with elderly, disabled, or young members. Changes in level can, however,

add considerably to the interest and appeal of the space, for instance, a change in floor

level can be used as an informal way of defining different areas within an open plan

space, as an alternative to using partition walls which restricts the appeal of the

openness of the space.

2.2.2. Upside down living

A sloping site often means that there is a view. One of the best ways of taking

advantage of this view is to reverse the accommodation to bring the living areas to the

top with the sleeping areas to the lower floors. The garage can be a complicating

factor in all of this. If the road is at the higher level, then the solution is for the garage

to be designed over the rest of the residential spaces. If the road is at the lower level

then there might be no alternative but for it to remain. However, it is likely that in

those circumstances the entrance accommodation will also have to share the lower

floor.

2.2.3. Building regulations

Building Regulations relating to disabled access can sometimes affect the design of a

house on a sloping site. Externally, they require that access ramps for slopes up to 1 in

15 should not be longer than 10 meters, and those for gradients up to 1 in 10, no

longer than 5 meters. Steeply sloping sites can, in the absence of a ramp, employ steps

at least 900mm wide with a rise no greater than 150mm and a distance between

landings of no more than 1,800mm. Additionally, if there are more than three risers,

handrails must be provided to at least one side. Internally the entrance floor must

contain a WC accessible by wheelchair.

2.2.4. Design guidelines for different amount of slopes

All development including grading on natural slopes below fifteen percent (15%)

should be designed according to the following guidelines (HRO) :

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1. Building should be oriented with the contours utilizing the natural slopes. (see

Figure 2.5)

2. All development should be sited to avoid potentially hazardous areas and

environmentally sensitive areas as identified in the open space as well as to

avoid dislocation of any unusual rock.

3. The need for excavation or fill increases complexity of the construction as

well as adds on the cost.

4. For steeply sloping sites (e.g. in excess of 1:5) consider suitable split level

(stepped) schemes that relate more closely to existing ground levels should be

considered. Land should be carefully spaced around the building so that it

blends more successfully with the surroundings while creating further shelter.

(see Figure 2.7)

5. Excess fill should be either removed or carefully graded around the building to

suit the natural slope of the land.

6. Natural slope should dictate the form. Over excavation and creation of

artificial plateau should be avoided. (see Figure 2.6)

7. Natural drainage courses should be preserved, enhanced, and incorporated as

an integral part of the project design to the extent possible. Where required,

drainage channels should follow the existing drainage patterns to the extent

possible. They should be placed in inconspicuous locations and receive a

naturalizing treatment including native rock and landscaping, so that the

structure appears as an integral part of the environment.

8. Grading should be limited to the extent possible and designed to retain the

shape of the natural landform. Grading must be designed to preserve natural

features such as knolls or ridgelines. In no case should the top of a prominent

hilltop, knoll, or ridge be graded to create a large building pad; circulation

should be aligned to conform to the natural grades as much as possible. (see

Figure 2.5)

9. The use of retaining walls, plantable walls, and terraced retaining structures is

encouraged when use of these can eliminate the need for extensive cut or fill

slopes. Retaining walls should typically have a height of five (5) feet or less.

Plantable walls should be used instead of retaining walls above six (6) feet in

14

height. Terraced retaining structures should be considered when their use can

avoid the need for extensive manufactured slopes and retaining walls. (see

Figure 2.5)

10. Slopes steeper than two to one (2:1), appropriately designed by a geotechnical

engineer,

15

Figure 2.5: Design principles that must be taken care of (HRO)

Figure 2.6: Over excavation and creation of artificial plateau should be avoided (North Tipperary County

Council, 2009)

Development including grading on natural slopes between fifteen percent (15%) and

twenty-five percent (25%) should be designed according to the following guidelines

(HRO):

1. Grading should be utilized only for the construction and installation of roads,

utilities, garage

2. Deck construction with excessively high distances between the structure and

grade should be avoided.

3. Rear yard should not exceed twenty (20) feet measured parallel to the slope if

such yard requires a grading exemption.

4. Single-level residential structures should be oriented such that the greatest

horizontal dimension of the structure is parallel with, and not perpendicular to,

the natural contour of the land. The slope of the roof should be oriented in the

same direction as the natural slope. (see Figure 2.5)

Development including grading on natural slopes of thirty-five percent (25%) or over

should be designed according to the following guidelines (HRO):

1. Extensive manufactured slopes and retaining walls should be avoided.

2. Landscaping should be utilized to recreate the linear silhouette and to act as a

backdrop for structures. Trees that grow to at least one and a half times the

16

height of the structure should be planted between buildings to eliminate the

open gap and blend the rooflines into one continuous silhouette.

Figure 2.7: Step building design (Tweed Shire Council)

2.3. Clustering of houses

Clustering allows large portions of the original development to be retained in its

undisturbed natural state. To ensure that clustering of units does provide the open

space desired (City of Vernon- Hillside Guidelines 2008, 2008):

1. Small and larger lot detached housing (reduced yard setbacks);

2. Zero-lot line development (the equivalent of duplexes and townhouses but

with each unit owned in fee simple);

3. Multiple family development (e.g., duplex, triplex, etc, townhouse apartment);

and

4. Single-family strata development (any of the above where common areas are

collectively owned by two or more residents).

17

Figure 2.8: Standard large lot residential layout, mixed single family layout with open spaces, mixed density

layout with open spaces ( from left to right) (City of Vernon- Hillside Guidelines 2008, 2008)

2.4. Scenic opportunities

Scenic view opportunities from hillsides are recognized as valuable to both hillside

residents and the community as a whole. It is important, however, not to compromise

the geotechnical or environmental integrity of the slope to achieve views. View

corridors must be identified and strictly maintained for all lots to enable re-vegetation

in non-view locations on each lot. Additional criteria include (City of Vernon-

Hillside Guidelines 2008, 2008):

1. Buildings should be located to face the view and minimize interference with

the views of nearby residences. Buildings should be staggered where

appropriate to provide views between units that may otherwise limit the field

of view.

2. Buildings should be located so that upslope buildings have views over down

slope buildings. If massive grading of the slope is necessary to achieve this

concept, it may be necessary to reconfigure the subdivision or layout. The

priority is to avoid disruption of the terrain.

3. Development areas must be sited lower than the ridgeline so that the roof line

does not protrude into the ridgeline. Placement of roads, cuts and large or

continuous buildings near or over ridgelines should be avoided. Where gaps or

interruptions in the ridgeline are unavoidable due to road network

requirements, plant trees and vegetation in front of and behind the disturbance

to screen and restore a naturally appearing ridgeline. For grassland areas

where native trees are limited or nonexistent clusters of viable native trees

must be established to provide screening.

4. Development on ridgelines or the top of knolls is not supported and these

areas must be integrated as open spaces. Development should be sited and

18

designed in a way so as not to alter, disturb or remove significant scenic or

environmentally functional features of a parcel.

2.5. Conclusion

This chapter concludes that building should positively respond to the site and explore

the full potential of site. This chapter also tells about the implications and principles

of building design on different amount of slope to avoid the grading as much as

possible.

19

CHAPTER-3. BUILDING TYPOLOGIES, CONSTRUCTION

TECHNIQUES AND SERVICES

Most of the sloping landform in India lies in Northern region and North-Eastern

region. There large number of construction technologies is employed to suit the

terrain. Some buildings are constructed using locally available materials while some

are constructed using RCC. Thus there are large numbers of building typologies

prevalent in those regions.

3.1. Residential building typologies prevalent in North India

(Assessment Project Group of IIT Bombay, IIT Guwahati, IIT Kharagpur, IIT

Madras, IIT Roorkee, 2013)

1. Thathara with timber plank partitions and light weight sloping roof

2. Thathara with Dhajji-Diwari partitions and light weight sloping roof

3. Thathara with infills of stone masonry in mud mortar and light weight sloping

roof, dry stone and light weight sloping roof, brick masonry in cement mortar

and light weight sloping roof

4. Kath-Kunni walls with stone packing and light weight sloping roof,

heavy/stone sloping roof.

5. Mixed Kath-Kunni construction

6. Mixed rammed earth construction

7. Rubble stone (field stone) in mud/lime mortar or without mortar (usually with

timber roof)

8. Dressed stone masonry with cement mortar

9. Adobe block walls with sloping roof

10. Unreinforced brick masonry in cement mortar, cement mortar with reinforced

concrete floor/roof slabs, mud/lime mortar.

11. Unreinforced concrete block in lime/cement mortar (various floor/roof

systems)

12. Masonry mixed structure with reinforced concrete

13. Confined brick/block masonry with concrete posts/tie columns and beams

20

14. RC moment resisting frame with unreinforced masonry infill walls (see Figure

3.1), flat slab structure, open ground storey structure (see Figure 3.1), load

bearing masonry, open intermediate storey structure, mixed infills.

15. RC mixed structure with composite timber, bamboo and others

16. Dry rubble stone masonry with flat slab

17. Mixed dry rubble stone masonry

Figure 3.1: RC moment resisting frame with unreinforced masonry infill walls (left) and open ground storey

structure (right) (Assessment Project Group of IIT Bombay, IIT Guwahati, IIT Kharagpur, IIT Madras, IIT

Roorkee, 2013)

3.2. Residential building typologies prevalent in North East India

(Assessment Project Group of IIT Bombay, IIT Guwahati, IIT Kharagpur, IIT

Madras, IIT Roorkee, 2013)

1. Random rubble stone with mud/lime mortar

2. Dressed stone masonry with cement mortar

3. Mud walls with horizontal wood elements

4. Unreinforced brick masonry in mud/lime mortar, mud mortar with vertical

posts, cement mortar, cement mortar with reinforced concrete floor/roof slabs,

5. Unreinforced brick masonry in cement mortar with lintel bands (various

floor/roof systems)

6. Masonry mixed structure with timber, bamboo and other wood elements

7. RC moment resisting frame designed for gravity loads only, seismic features,

unreinforced masonry infill walls, flat slab structure, open ground storey

structure, composite steel

8. Steel moment resisting frame with brick masonry partitions, light weight

partitions

21

3.3. Construction techniques to be adopted while designing the building

in sloping sites

Design solutions/construction techniques like step building design, cut/fill

construction techniques, raising the building on stilts/poles, retaining wall

construction, drainage issues, seepage problems should be incorporated which

respects the site potential upto its full expanse and lessen the impact of landslide and

other issues.

3.3.1. Cut and Fill

This describes the process of carving out a level plinth on a sloping site in order to

build a space that is essentially designed for use on a level site. Any spoil that is cut

from the bank is reserved in order for it to be brought back to make up the levels on

the lower edge. With the cut-and-fill technique, material is removed from the uphill

part of the site and placed on the downhill portion to form a level surface (see Figure

3.2). The fill material may compact and settle later, and cause cracking of foundations

and walls. The extra load of a building may trigger a slope failure on unrestrained fill.

Retention walls and pre-compaction of fill may lessen the potential for that type of

slope failure. (How to Build on a Sloping Site)

3.3.2. Stilts/Poles

Building on stilts is one way of addressing steeply sloped sites (see Figure 3.2). This

avoids the need for expensive foundations and also negates the requirement for

tanking. The other benefit is that it leaves the ground untouched, allowing planting to

take place over much more of the site. It could also be implemented on multiple

levels. (How to Build on a Sloping Site)

22

Figure 3.2: Cut and fill construction (left) and stilts construction (right) Basements/Retaining walls (Tips for

building on a sloped terrain, 2014) (How to Build on a Sloping Site)

3.3.3. Basement and Retaining wall construction

When creating basements on sloped terrain, the walls are often subject to a lot of force

from the surrounding banks of land and therefore becoming retaining walls. Basement

construction (see Figure 3.3) may have to be strong enough to hold back

considerable banks of ground in which walls behave as retaining walls. In other

situations, such as building on a level plinth beside a natural or carved out bank, it

may be necessary to construct separate retaining walls. In certain circumstances it

may be cheaper, and visually more attractive, to construct a series of lower retaining

walls with the ground stepped between them. Structural engineers should be consulted

to be involved in the design of these structures, and detail design stage is important to

ensure good water proofing. Another option is stepping the ground by using low level

retaining walls, or gabion walls which are wire cages filled with stone or interlocking

concrete blocks that are subsequently filled with soil. (see Figure 3.4)

Retaining structures are relatively expensive but necessary in steep areas to gain

roadway space or to support the roadbed on a steep slope, rather than make a large cut

into the hillside. They can also be used for slope stabilization. Figure 3.5 presents

information on common types of retaining walls and simple design criteria for rock

walls (see Figure 3.7) where the base width is commonly 0.7 times the wall height.

Different construction principles are employed for retaining walls of different heights.

(see Figure 3.6). Figure 3.5 and Figure 3.4 shows the Gabion structures which are

commonly used for walls up to 5 meters high, particularly because they use locally

available rock and are labor intensive. These are commonly used for low gravity

retaining structure because they use locally available rock and are relatively

23

inexpensive. (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME

ROADS BMPS)

The use of retaining walls is not encouraged. These are only supported where they

preserve native undisturbed areas, address unstable native slopes or rock faces, or

form part of the neighborhood character. Where provided, the following criteria

should be considered in their design (Slope Stabilization and Stability of Cuts and

Fills- LOW-VOLUME ROADS BMPS):

1. Retaining walls should respect the natural character of the site and not present

a large uniform wall face that overpowers the site and disrupts animal

movements.

2. Retaining wall height should not exceed 3.0 m for roads and site specific

works, 1.2 m for yards. Higher walls may be appropriate where they are

articulated, have a surface texture/pattern, or where sufficient landscaping is

provided to screen the wall.

3. Smaller stepped retaining walls are employed instead of a large uniform wall.

The height and depth of the wall steps should be consistent with the natural

terrain or with the slope above and below the walls. For stepped retaining wall

systems, the walls must be designed to permit landscaping of the terraces that

will screen the wall, including irrigation to all terraces. Landscaping of the

terraces using mixed hardy native shrubs or trees is required. Width of each

terrace proposed must be sufficient to enable the landscaping required and

permit access for maintenance.

4. Retaining walls must be set back from utilities and the traveled portion of

roads to enable planting of screening landscaping.

Figure 3.3: Basement construction on sloping sites (Tips for building on a sloped terrain, 2014)

24

Figure 3.4: Typical retaining wall construction, Gabion wall and rock buttress (from left to right) (Slope

Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)

Figure 3.5: Common types of retaining structures (Slope Stabilization and Stability of Cuts and Fills- LOW-

VOLUME ROADS BMPS)

25

Figure 3.6: Construction detail for retaining wall of height upto 2 m (left) and 5 m (right) (Slope Stabilization

and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)

Figure 3.7: Typical rock wall construction for smooth backfill (left) and face with steps (right) (Slope


3.3.4. Storm water management and Drainage system

Implement methods for collection, conveyance, control and treatment of storm water

is employed that mitigates potential impacts and emulates the areas natural water

cycle. This is required to limit runoff from new development based on the soil

capacity and sensitivity for ground recharge.

Having a sloping site may involve extra costs with drainage and. If site slopes down

from a road in which the sewer is fairly shallow then, pumped sewage system can be

used. But if the sewer is quite deep, then the slope may actually represent a saving in

cost, as the resulting house drainage will not have to be as deep. Sloping down from

the road means that surface water can collect around the base of the lower floor. This

may mean having to install a drainage channel to divert the water to soak ways.

26

Sloping up from the road may at first seem the best option, but many local authorities

will not allow surface water to go into the public sewers and many require that

precautions are taken to ensure that surface water does not flow onto the road. (Slope


3.4. Roads:

Road designs are typically site specific and may require input from geotechnical

engineers and engineering geologists. Slope failures, or landslides, typically occur

where a slope is over-steep, where fill material is not compacted, or where cuts in

natural soils encounter groundwater or zones of weak material. Good road location

can often avoid landslide areas and reduce slope failures. When failures do occur, the

slide area should be stabilized by removing the slide material, flattening the slope,

adding drainage, or using stabilizing structures. Failures near streams and channel

crossings have an added risk of impact to water quality. Certain points to be taken

care of while designing road on sloping sites (Slope Stabilization and Stability of Cuts

and Fills- LOW-VOLUME ROADS BMPS):

1. Grading for the construction of access roads or drainage ways shall be

minimized so that the visual impacts associated with said construction are

mitigated to the greatest extent possible;

2. The construction of access roadways or driveways should be accompanied by

sufficient berming and landscaping/erosion control so that visual impacts

associated with said construction are promptly mitigated.

3. If the city engineer determines that no hazard to pedestrian or vehicular traffic

will be created, a garage or carport may be built to within five (5) feet of the

street right-of-way line.

3.4.1. Classification of access routes

Depending upon the terrain conditions, access routes may be classified as:

(California Coastal Commission)

3.4.1.1. Two-Lane Access Road

(see Figure 3.8)

1. Ingress and egress provided by 1 road.

27

2. Merges easily with existing access and conventional roadway designs.

3. 9' minimum width for each lane, required for fire safety.

4. On steep slopes, disturbed area for cut and fill will extend far beyond limits of

road bed and shoulders.

5. Careful drainage controls needed along road and modified slopes.

6. Broad road area may be visible from great distances.

7. Additional road may be required for emergency access.

3.4.1.2. Split Level Access Road

(see Figure 3.8)

1. Ingress and egress provided by 2 roads.

2. 9' minimum width for each lane, required for fire safety.

3. Split roads can be "stacked" to minimize visual impact, cut and fill can be

reduced.

4. Careful drainage controls needed along road and modified slopes.

5. Separate roads may provide emergency back-up when secondary access is

required.

Figure 3.8: Two lane road (left) and split level access road (right) (California Coastal Commission)

3.4.1.3. Single Lane with Pullouts

(see Figure 3.9)

1. One road providing ingress and egress.

2. Minimum width for lane should be 10' with turnouts, required for fire safety.

3. Land form alteration for cut and fill can be minimized.

4. Periodic road widening needed for pull-outs and turn-around.

28

5. Not suitable for high-density vehicle use.

6. May require secondary, back-up road for emergency situations.

3.4.1.4. Bridge

(see Figure 3.9)

1. Can span stream bed and most riparian habitat, if stream is narrow.

2. Most appropriate for high-use roads which cross perennial streams.

3. Structures can be expensive, need to assure sufficient width, turning angle and

height for emergency vehicles.

4. If bridge can be built without supports in stream, can avoid impacts to flow

and habitat.

5. Design must consider high flood events

6. A large bridge structure may dominate visual character of area.

Figure 3.9: Single lane road with pullouts (left) and bridge (right) (California Coastal Commission)

3.4.1.5. Culvert under Road

(see Figure 3.10)

1. Stream flow is channeled into a culvert and roadbed is constructed on top.

2. Only suitable for intermittent or low-flow streams or as part of area-wide

drainage plan for directing surface flow.

3. Road could provide primary access.

4. For stream crossings, a culvert will disturb banks.

29

3.4.1.6. Arizona Crossing/Ford

(see Figure 3.10)

1. Roadbed built directly into stream bed.

2. Stream bank and habitat at crossing will be disturbed by road.

3. Road should be a low volume road or secondary access.

4. If used for primary access, a secondary access should be provided for flash

flood events.

5. Due to low-profile, fords rarely alter visual character.

Figure 3.10: Culvert (left) and Arizona crossing (right) (California Coastal Commission)

Design criteria that should be considered while planning for sidewalks include (Slope

Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS):

1. Sidewalks must be set back from the road a minimum of 1.5 m to

accommodate snow storage (for cold regions).

2. Sidewalks are to be located on the same side of the road due to the winding

nature of hillside roads. The location for sidewalks must be set to maximize

the function as a safe pedestrian corridor through the development and provide

scenic views where possible.

3. Sidewalks on both sides of the road may be required for short distances to

provide walking linkage between roads and to provide improved sight

distances for road crossings.

4. The requirement for sidewalks on local cul-de-sac roads may be waived where

low traffic volume is generated, provided alternate off street pedestrian

facilities exist.

5. Curvilinear or meandering sidewalks and pathways may be used where they

eliminate long sustained grades. Varying offsets between the road and the

30

sidewalk may also be considered where it will save a significant feature or

reduce grading requirements.

3.4.2. Cut slope design options

In this technique, earth is cut from one pat and filled to other part to make access

route. For most of the hillside construction (slope between 0-60 percent), balanced cut

and fill (see Figure 3.11) is adopted because it can be done for most of the soil types.

In case of rocky terrains, a full bench cut (see Figure 3.12) is adopted for slope more

than 60 percent and through cut is adopted for slope between 0-60 percent. (see

Figure 3.13)


Figure 3.11: Balanced cut and fill for most of the construction on hill slopes (Slope Stabilization and Stability

of Cuts and Fills- LOW-VOLUME ROADS BMPS)

Figure 3.12: Full bench cuts for slopes exceeding 60% (Slope Stabilization and Stability of Cuts and Fills-

LOW-VOLUME ROADS BMPS)

31

Figure 3.13: Through cut (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS

BMPS)

3.4.3. Fill slope design options

Fill slope design solutions include typical fill (see Figure 3.14), benched slope fill

(see Figure 3.15), reinforced fill (see Figure 3.16), through fill (see Figure 3.17).


Figure 3.14: Typical fill (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS

BMPS)

Figure 3.15: Benched slope fill with layer placement (Slope Stabilization and Stability of Cuts and Fills-

LOW-VOLUME ROADS BMPS)

32

Figure 3.16: Reinforced fill. These can be used as an alternative for retaining wall (Slope Stabilization and

Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)

Figure 3.17: Through fill (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS

BMPS)

3.5. Practical considerations (landslide or slope stability)

The steepness does not necessarily correlate with the stability of slopes. Slope

stability depends on factors such as geologic materials, soils, moisture content and

vegetation cover. A comprehensive geotechnical investigation is required for

developments on slopes to provide the detailed information necessary to ensure slope

stability. Various studies have found that soil slips, which cause avalanche failures,

commonly initiate on slopes greater than 33%; slower moving earth flows occur most

often on slopes 30% to 60%. Nevertheless, serious erosion can occur on much

shallower slopes and the potential for erosion is greatest in the period between

removal or disturbance of vegetation and re-establishment of new vegetation.

Decisions on suitable methods for slope stabilization first require an evaluation of the

hazard. Deep mass movements (deep landslides) are difficult to control and require

engineering solutions. Shallower mass movement (shallow landslides) and erosion

processes are more suitable for control using bioengineering or eco engineering.

Bioengineering techniques combine engineering methods with natural or living

materials to protect or restore slopes and reduce erosion like using brush matteresing,

and the planting of shrubs, plants and trees to stabilize the soil.

33

Methods include the use of stone, steel, concrete and geosynthetics to stabilize or

shore up slopes that are liable to landslides. These methods should, where possible, be

combined with use of plants and trees to enhance the urban green space. (California

Coastal Commission)

There are various construction techniques by which landslide stability can be

achieved on slopes (California Coastal Commission):

3.5.1. Conventional Buttress Fill Slope

1. Extensive grading is required for steep slopes, since fill must be designed at

2:1 or 1.5:1 (horizontal to vertical).

2. Extensive surface disturbance and loss of habitat from fill area.

3. Finished slope does not blend with natural terrain min steep slope areas can be

varied to blend with natural terrain.

4. Surface and subsurface water flows must be controlled as long as fill slope

exists.

5. Drainage must be maintained; water cannot be directed to a modified slope.

3.5.2. Contour Graded Slope

(see Figure 3.18)

1. Extensive grading required if natural slope is steep; slope must conform to

local grading standards.

2. Some disturbance of surface area and habitat.

3. Finished slope can be varied to blend with natural terrain.

4. Surface and subsurface flows need to be controlled, as long as slope exists.

5. Portions of natural vegetation can be maintained.

3.5.3. Steep Geogrid Slope

(see Figure 3.18)

1. Slope can be constructed with little grading, even in steep terrain.

2. Finished slope can be steeper than a conventional buttress fill, up to 1:1.

3. Surface and subsurface flows need to be controlled as long as slope exists.

4. Can be constructed where space is limited.

5. Finished slope can be varied to blend with natural terrain.

34

3.5.4. High Retaining Wall

1. Can be constructed with very little grading.

2. Structures can be expensive, need to be carefully designed and constructed.

3. Drainage behind wall must be controlled as long as wall exists.

4. Useful for areas with limited construction space.

5. Rarely blends with natural terrain; surface treatments are possible.

6. Can be used for some landslide remediation.

3.5.5. Several Low Retaining Walls

1. Can be constructed with very little grading.

2. Only suitable for small slope instabilities, or for small cuts or fills.

3. Drainage behind walls needs to be controlled, as long as walls exist.

4. Small walls can be camouflaged be vegetation and often can blend into natural

terrain.

3.5.6. Gravity Wall/Crib Wall

1. Walls require more disturbance than retaining walls, but less than a buttress.

2. Since structure is open, surface and subsurface flows can go through the

structure; little drainage control needed.

3. Can be used for some landslide remediation.

4. Facing will not blend with natural terrain; some planting between the facing

elements may be possible.

Figure 3.18: Contour graded slope (left) and Steep geogrid slope (right) (California Coastal Commission)

35

3.6. Recommended practices


1. On steep ground (>60% slope) full bench construction should be adopted. A

narrow, single lane road with turnouts is constructed to minimize excavation

but road should not be much narrow so that it causes accidents

2. Cut slopes should be constructed in most of the soils using a cut slope ratio of

3/4:1 to 1:1 (horizontal: vertical). Flatter cut slopes should be constructed in

coarse granular and unconsolidated soils, in wet areas, and in soft or clay-rich

soils. Cut slopes in rock should have a ratio of 1/4:1 to 1/2:1.

3. Vertical cuts (1/4:1 or steeper) should be adopted only in stable rock or in very

well cemented soils, such as cemented volcanic ash or in-place decomposed

granite soil, where the risk of surface erosion is great and the risk of local

failures in the steep cut is low.

4. Unsuitable or excess excavation material should be disposed in locations that

will not cause water quality degradation or other resource damage.

5. Fill slopes should be compacted well in sensitive areas or when the fill is

constructed with erosive or weak soils to avoid landslides.

6. Retaining structures should be placed only upon good foundation materials,

such as bedrock or firm, in-place soils

3.7. Conclusion

This chapter tells about the residential building typologies prevalent in Northern and

North Eastern region of India and construction techniques to be adopted while

designing the building on sloping sites. This section focuses on cut/fill construction

techniques, construction of building on stilts, retaining wall construction, rock wall

construction, etc.

Road design criteria are also discussed focusing on cut/fill slope design options.

Landslide or slope stability is also taken into consideration.

36

CHAPTER-4. LANDSCAPING ON SLOPING LANDFORMS

Slopes offer a great challenge than flat ground when it comes to landscaping. The

biggest concern is usually the risk of erosion. Additionally, planting and maintaining

plants on inclines can be a difficult undertaking and take a little more thought and

effort than for a normal 'flat' garden but the results can be very unusual - and a much

more interesting garden can be created.

If slopes are very steep or complicated, landscape architect must be preferred, who

can advise on this aspect of your garden design, and make sure the design and the

works are structurally safe and sound.

4.1. Planning a landscape on slope

Planning a garden with slopes will surely be a challenge, but changes of level

certainly give any garden added interest, and add an extra aspect to sloping landform

design. Sloping garden designs will need to be very carefully thought about at the

planning a garden stage.

Designing a garden on sloping landform will depend on:

1. The severity of the slope (degree of slope or steepness of slope)

2. The size of the garden

3. Features to be included

Factors to be considered while planning a landscape on slope (Anderson) :

4.1.1. Drainage

If water drains to the down of the slope, water channel clues and channels are narrow,

then the erosion control will be a problem and slope may be more unstable than

required. This is something to keep in mind when landscaping is done slope

stability. To check this, a hole is dug and filled with water and time taken by water to

drain is noted. If drainage occurs within an hour or so, slope is relatively stable. If it

takes several days to drain, then slope is highly unstable. Water accumulation on the

slope is controlled because wet soil and mud on a steep hill can cause erosion and

slide issues.

37

4.1.2. Soil

Proper analysis of type of soil and is water holding capacity should be done. It will

decide the type of planting material that will best grow here and better secure the

slope. To check the type of soil, a hole should be dug somewhere on the slope,

preferably where landscaping is to be done and result is noted down. If soils on top

slides down the slope easier, then the soil is rocky or clayey. (Anderson)

4.1.3. Access and maintenance

Access to gardens on slope is necessary for maintenance, weeding, pruning and

watering, and can take different forms. If a very small garden, access can be made

from the edges. Larger gardens require access via paths, walkways or steps. Steps and

paths down the slope can be used to more appropriately access the terraced gardens.

(Anderson)

4.1.4. Rainwater and runoff management

Rainwater and runoff management is interrelated with irrigation, plant selection and

erosion control. Rainwater can prove harmful for a hillside garden. If unchecked, it

can cause serious erosion. Rain running down the hill and off the landscaped area into

the residential spaces is a problem. Rain can become an asset with proper design.

Terraces accomplish this inherently by providing level garden areas for the rain to

soak in and not runoff. Where a slope is not terraced, berms across the hillside with

narrow swales behind, and winding stone-lined creek beds can slow the movement of

water, allowing it to soak in. Garden at the bottom of the slope allows the last of the

runoff to gather and irrigate plants assembled there.

If there is a slope uphill from the residence, berms can also be used there to send

surface water around the house for use in lower gardens.

Aesthetically pleasing ground cover is also an easy solution to control water runoff. If

the slope is not too steep, a ground cover creates a clean appearance that is easy to

maintain. Ground covers such as Blue Rug Juniper, Baltic English Ivy and buffalo

grass are low maintenance and well suited to sloped areas. There are also flowering

ground covers for inclines like Creeping Phlox, Vinca Minor vines and Sweet

Woodruff. (Anderson)

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Boulders or rocks should be strategically placed around the plants to slow down any

water runoff. Stones offer a natural appearance, but they also trap the earth and

moisture within it.

4.1.5. Irrigation

Since hand watering of a landscaped area on slopes is not very convenient, there is a

need to install drip irrigation. Alternatively, on a low-water slope landscape, drought

tolerant plants can be selected; hand watering them first two summers can be done,

rather than installing irrigation.

Plants put at the top of a slope will get the least water, those in the middle somewhat

more, and those near the bottom the most, as water running downhill section is

soaking in more and more. Accordingly; top, middle and bottom regions are planned.

The most drought tolerant should go toward the top, and those that can tolerate more

water closer to the bottom. Exposure plays a factor too. And the direction the slope

faces will impact plant selection; southern and western exposures are hotter, and

northern and eastern can take plants that can stand less direct sun. (Anderson)

In addition to normal gardening issues mentioned above, particular challenges hillside

gardening must also be considered while planning a landscape on sloping site:

1. Erosion control and retaining the hillside

2. Rainwater and Runoff

3. Structural safety for landscape design

4. Plant selection and locationfor erosion control and relating to water needs

and exposure

5. Zoning and water behavior on slopes

6. Accessibility to the beds or plantings for maintenance and moving

7. Steepness of paths and steps, and safety aspects

Design considerations for gardens sloping up away from the house (or sloping

down towards the house)

A garden that slopes up from the home is one that can be seen to an even greater

degree than a flat site. It becomes a garden that can be terraced so as to bring

aesthetical values to the residence.

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1. Patio on a higher part of the garden, away from the house may look

interesting. Raised wooden decks can be attractive and they can be constructed

in such a way as to allow light to filter down to the windows of lower storeys.

2. The rest of the garden could be a series of attractive terraces probably with

steps.

3. Professional advice on structure should be taken and as to avoid water running

down the slope and collecting near the house. (Sloping Garden Design Ideas,

2014)

Design considerations for gardens sloping down away from the house (or sloping

up towards the house)

1. High level decking may look interesting.

2. The rest of the garden could be terraced with steps, and attractive planting and

groundcover to make space look aesthetically pleasing.

3. Advantage of great views. (Sloping Garden Design Ideas, 2014)

4.2. Landscaping principles on sloping sites

Hillside landscaping is the most challenging of all residential design problems.

Whether it is a natural undisturbed slope or one composed of cut-and-fill, there are

five essential principles that should be taken care of while designing on slopes.

(Gilmer)

1. Views should be preserved while solving problems.

Residence built within forested hillsides often cleared to increase the view. The trees

have vast roots that have held the soil in place for a long time, and when trees are cut

down the roots die and the soil becomes vulnerable. For this reason it is far better to

keep trees living whenever possible.

All the new trees, shrubs and structures proposed between the house and top of slope

should be taken care of. If trees are too large these can interfere with the view.

Trees planted on the slope itself can over time exceed the height of the slope to

encroach into the view. This is more important where a terrace may be graded into the

slope further down where trees are planted for shade. Trees with a low spreading

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canopy should be planted rather than an upright conical form such as a fir tree to

avoid repeated topping in the future. (Gilmer)

2. Slopes should be taken up gradually as possible.

A very gentle slope is not much different than a flats garden, but a steeper slope

certainly is.

Any time a slope is cut its integrity is compromised, therefore its more better if less

slope is cut. Cutting into a slope removes topsoil to expose subsoil, often heavy clays

or shale that are poorly drained or lack microbial action of a living topsoil. This is

why the planting on so many cut slopes and home pads on exposed subsoil are prone

to failure.

To preserve the slope, grading is done with a series of shorter terraces rather than one

or two very large ones graded with cut and fill. The larger terraces may require

extreme erosion control measures on the cut slope and a substantial retaining wall

must be specially engineered to hold the fill. Such walls are constructed with footings,

sometimes extending down to bedrock. Residences on moderate to extreme slopes are

prone to mudslides and slope failures in extreme weather. (Gilmer)

3. Plants with extensive root system should be used to bind the slope deep

underground.

Erosion and depth of the soil can be issues in a sloping garden, so choosing the right

plant for the right spot is the key. Slope is composed of different soil layers. When the

slope has been altered to create building pads, the natural binding of layers may be

lost or compromised. When extreme weather such as heavy rains falls on these sites

the water may travel through weaker seams to saturate layers deeper down. When

they become wet enough they lose their cohesive qualities and slough off in layers.

This is usually the cause of slope failures during rainy seasons.

When planting is done on slope, trees are selected with a deep network of fine roots.

The larger the root system the better, so trees are highly effective at binding subsoil

layers, with their extensive roots. There has been a great deal of study on the use of

fast growing drought resistant trees such as acacia, planted on slopes. They were

topped every year or two to force growth energy into expanding the roots for more

effective soil binding. Thought effective, the maintenance required by this technique

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precluded widespread use, but it is still recommended as a powerful tool for solving

site specific problems. (Gilmer)

What to plant on a sloping landform and where on the slope to plant various species

are key considerations. Shrubs require less maintenance than perennials, and in

addition, generally have a more extensive root system. Attractive foliage or flowers

can be chosen, and mix and matched to create attractive mounds of color and texture.

Plants like geraniums and begonias can be planted to protect slopes from being

washed away by rain. Good plants for a slope also include California lilac, Creeping

juniper, Purple coneflower, Rattlesnake master, Russian sage, Snowberry, Star

jasmine, common periwinkle, Siberian carpet cypress. Add plants that strengthen and

bind the soil while adorning the slope. (Anderson)

Shrubs which can be planted on slopes include Arctostaphylos, Ceanothus, Erica,

Helianthemum and Euonymous. Drought tolerant plant selections include Baccharis

pilularis 'Twin Peaks', Cistus, Correa, Grevillea, Mahonia, Rhamnus and Rosmarinus.

Ground cover plants are a perfect solution for covering sloping areas. Using ground

cover plants on any slope helps retain or hold the soil on the slope. Additionally,

groundcovers fill the area and crowd out weeds, making it easier to maintain. Hardy

perennials and shrubs can also be included as groundcover plants like hostas, sage and

snowberry. Ground cover plants such as Aubrietia are excellent for steep banks; they

suppress weeds, help stabilize the soil and needs low maintenance. (See Figure 4.1)

Planting pockets near the large boulders should be created for seasonal color or

creeping shrubbery like Cotoneaster or vinca. The stones can be treated with the moss

and to give them a weathered and time-elapsed effect. A small stream can also be put

in with for sound and visual effect.

While putting larger trees on slopes, certain things should be taken care of. Area

where the trees are to be planted should be leveled off so the tree stands on level and

not on a slope. A retaining wall can be put behind the tree to prevent dirt from

washing over the roots too much. Decorative stones can also be used to turn it into a

focal point. Too many upright plants should be avoided because they block the view.

Larger trees, shrubs and plants should be planted vertically, not pointing out of the

hillside. A small half well on the bottom side of the plant should be built to help retain

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water and allow it to soak into the soil around the plant. Smaller plants and ground

covers can be planted to fill in while larger plants take hold with the hillside.

Composting the soil usually proves helpfulcertainly if hillside soil is sandy or clay.

Hillside gardens, like all gardens should be well mulched. But the choice of mulch is

more critical. Things like straw, small bark or cocoa hulls will wash away easily.

Finely shredded redwood, or the coarser shredded rather than chipped mulches tend to

knit together into a mass, and are less (but not completely) susceptible to being

pushed downhill by rain. (Anderson)

Figure 4.1: Ground covers for steep slopes (Alders)

Certain points should be taken care of regarding landscaping on slopes:

1. Retain all trees, hedgerows and other existing features (e.g. streams, rock

outcrops) to provide a framework for the garden. Create new hedgerows of

mixed native species

2. Avoid large expanses of manicured lawns and suburban style gardens with

exotic species, these usually appear alien to their surroundings and do not

provide habitats for wildlife.

3. Plant the space between the house and the front boundary with trees in

informal clumps.

4. Trees and shrubs which are locally native will be easier to establish than more

exotic species, and in keeping with the character of the area.

5. On exposed sites, consider more substantial shelter planting of native trees to

help reduce the effects of cold winds and driving rain, whilst also increasing

privacy.

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4. Surface soils should be protected from rain spatter and runoff.

When rain falls on the slope, each drop that falls on bare earth dislodges particles of

soil. As runoff runs down slope, the velocity causes more particles to be scoured from

the surface of the soil. This is the basic cause of erosion. Anything that slows the

speed of runoff such as rocks or plants reduces scouring and protects the soil. Slopes

are planted to cover soil and to slow the runoff velocity.

Freeway slope planting is the most widespread example of how a single monoculture

of spreading plants such as ice plant or African daisy is used to protect the surface.

Although

dissertation_residential buildings on sloping sites

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