단지계획 14강EARTHWORK & UTILITIES

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PRESENTATION ORDER

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I. Overview

• General process of earthworks

• Construction documents

II. Earthwork

• Earthwork

• Earth-moving machines

• Grading criteria

• Representing elevations

• Cut and fill calculations

• Profiles

• Grading plans

III. Utilities

• Storm drainage

– Elements of the system

– Flow of water

– Gradients

– System layout

– Computation of pipe size

– Culverts

• Sanitary drainage

– Sewage disposal

– Dry disposal

• Water supply

– Capacity

• Electric power

• Lighting

• Other utilities

• Solid waste

• Utility plan

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I. Overview

• “Infrastructure” – pavements, curbs, foundations, grading, sewer

pipes, power lines – is the central concerns of site construction,

and their specification is the meat of the working drawings.

• Normal construction process: 1) Identify the accurate location

of property and construction boundaries; 2) Strip off the topsoil

from the working area and store in heaps; 3) Locate principle

structure (roads, buildings, underground utilities); 4) Lay

foundations and trench in pipes; 5) Complete major structures; 6)

Grade the exposed topsoil to its new shape; 7) Install the road

base & surfacing and above-ground features 8) Replace the

topsoil and put in new plant materials

• This normal process will often be modified

e.g.) When new grades are very different from the old ?

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I. Overview

Construction documents

• Contents and preparation order of construction documents

1. Precise plan layout (layout of the roads and buildings in plan)

2. A profile of each road or other critical linear feature

3. Spot elevations of critical points & a grading plan

4. A plan layout of all utilities

5. A landscaping plan

6. A series of detailed drawings of street elements (manholes, inlets,

curbs, seats, lights, and walls)

7. A set of written specifications to control the quality and installation

• However, working details are not just the mechanical consequence of a

design idea. Designers should develop them in a looping and iterative

game

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II. Earthwork

Earthwork

• Grading has a strong influence on cost, utility, and appearance of the

completed project

• Use of grade stakes

• The ratio of cut and filled earth volumes: This is only a first guess!!

1) Not compacted + 15~25%;

2) Compacted - 10%;

3) Normally, - 5%

Grade stakes

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II. Earthwork

Earthwork

• Degree of compaction: dense enough not to settle after the occupation,

yet loose enough not to destroy internal drainage

Where settlement is not critical the fill can be dumped as it comes

Where settlement must be controlled the composition of the fill

will be selected; its moisture content will be set; the fill will be pressed

Where greater stability is required the fill will be placed in thin

layers, each of which is independently moistened and compacted

Where to be replanted break up the top layers of the regraded

soil by plowing and harrowing before the topsoil is respreaded.

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II. Earthwork

Earthwork

• Other disturbances during the grading process (by surface erosion)

Valuable organic material is lost by mixing topsoil and subsoil

A loss of soil

The pollution of downstream rivers and ponds

• Countermeasures

dam at the lower edges of all newly graded areas with

temporary berms of earth

quick replanting

spraying new ground with water, seed, and liquid fertilizer

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II. Earthwork

Earth-moving machines

• Designers should know something of the capabilities of various types

of earth-moving machines

Tracked bulldozers are used wherever a push or pulling force is

needed, have 3.5~6m turn radius, and work on slope up to 85%

Huge wheeled scrapers take up earth from their undersides and

carry it along to be released at will, can operate on slopes up to

60% longitudinal and 25% traverse

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II. Earthwork

Earth-moving machines

• Designers should know something of the capabilities of various types

of earth-moving machines

Huge wheeled graders are used for final shaping of a surface

Power shovels handle weak or broken rock, excavate hills, rock

faces, and other volumes at their elevation or higher

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II. Earthwork

Earth-moving machines

• Designers should know something of the capabilities of various types

of earth-moving machines

Draglines useful for large cuts and channels below the level of

the machine and for making valleys, mounds, slopes and banks

Rollers and scarifiers to compact or break up the ground

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II. Earthwork

Earth-moving machines

• Cost rules for areas larger than 5 acres

Curves of new contours should not be sharper than the

minimum radii of the expected equipment

Equipment cannot work on too steep slopes or work

economically in confined spaces

Fussy shapes and shallow cuts and fills are to be avoided

Undulating hill and valley forms are cheaper than terracing

Repeated landforms are cheap

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II. Earthwork

Grading criteria

• New grades are kept as close to preexisting grades as possible

• Agricultural value of the land should be conserved even in urban

development … one therefore avoids unnecessary, shallow cuts in

particular

• The basic criteria for any new surface are its fitness for the purposes of

its occupants and its ability to be maintained as part of a stable system

• Imagine acting and moving over it check it for its plant cover, for

erosion and for drainage

• Grass slopes … below 25% (ivy up to 100%); wet clay and silt … 30%; wet

sand … 80%↔ crib or terrace or drainage at its top might be helpful

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II. Earthwork

Grading criteria

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II. Earthwork

Grading criteria

• Drainage … water should flow away from buildings and roads, and not

be directed into valleys and swales not prepared for the additional flow

• To have a pleasing visual form (simple, smoothly curving, visually

stable), the new ground shape must be imagined from many

viewpoints … and mostly, it will be studied in a model

• Common difficulties in a grading plan: excessive or unbalanced cut

and fill; drainage pockets in the land, on the roads or against the sides

of buildings; steep grades; a poor visual or functional relation between

a building or a road and its surroundings; the destruction of existing

trees by changes in the ground level; the loss of good agricultural soil;

frequent use of expensive and undesirable steps and retaining walls

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II. Earthwork

Representing elevations

• The new surface is usually represented by a drawing showing the new

contour lines in relation to the old ones, supplemented by spot

elevations at key points

• The new form as the best transition between the set of fixed points

(the roads, buildings, sewers and special landscape features) and the

existing land at the site boundaries or at the edge of construction

• The new form as a sculpture

• In either case, contour sketch are designer’s language and he must be

fluent

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II. Earthwork

Representing elevations

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II. Earthwork

Cut and fill calculations

• Methods of cut and fill calculation

Contour-area method

End-area method: used for a long, connected

can

Use of elevations at grid corners

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II. Earthwork

Profiles

• The vertical dimension of the plan

• Begin with the design of the road profile

• The horizontal scale is that of the road layout; the vertical scale is

exaggerated ten times

• Draw a series of straight tangents over the profile of the existing

ground

• Search for a new line whose grades are neither too steep nor too flat,

minimizing and balancing cut and fill

• Then draw the necessary vertical curves at the intersections of the

tangents

• Profile vs. grading plan

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II. Earthwork

Profiles

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II. Earthwork

Grading plans

• Connect Spot elevations at other critical

points – such as … floors in the principle

buildings or those at the base of existing

trees to be saved (and roads) – with freehand

smooth curves

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II. Earthwork

Grading plans

• How to draw the road cross-sections where a new

contour will cross

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II. Earthwork

Grading plans

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III. Utilities

Storm drainage

• A substitute for the natural surface drainage

• Unnecessary in low-density (fewer than 5 families/ha)

• Storm water & pollutants

• Recharge pits or retention basins made in pervious soil

and big enough to hold water from the worst storm

economize on the length of main drainages but they many

not very handsome because of fluctuation

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III. Utilities

Storm drainage

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III. Utilities

Storm drainage

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III. Utilities

Storm drainage

• Heavy runoff from the development

1) overloads downstream channels

2) imposes cost for artificial drainage works

3) lowers the water table

• Underground drainage system’s problems: 1) expensive 2) cause

difficulties in the grading plan

• Ways to minimize the underground drainage system:

Low density development; decrease of paved surfaces; increase of

planted surfaces; careful grading to ensure gentle slopes and

positive flow; rely on ditches

• Separation of storm water drainage from sanitary drainage

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III. Utilities

Storm drainage / Elements of the system

• The storm system: a drainage surface (a set of open gutters and ditches);

a series of underground pipes made of vitrified clay; manholes; inlets

• Large sewers over 1m in diameter are made of concrete

• For all sizes of sewer lines, the radius is not less than 30m ( for

maintenance) and the vertical grade is constant

• Manholes – man-sized circular pits – are used to enter the lines for

inspection and maintenance … placed at the upper end of lines and at

every change in horizontal or vertical direction or curvature … place no

more than 100 to 150 m apart for cleaning apparatus

• Recharge manholes: designed to deliver storm water back to the ground

… made with porous sides and … set in pits filled with gravel

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III. Utilities

Storm drainage / Elements of the system

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III. Utilities

Storm drainage / Flow of water

• Keep the surface water moving but not so fast to cause erosion

• Allowable slopes depends on 1) volume of water 2) surface finish 3) the

amount of damage expected by local flooding

• Minimum grades: planted areas and broad paved areas 1%; streets and

other paved surfaces with exact elevations 0.5%; land within 3m from all

buildings 2%; Planted drainage swales 2% (no more than 10% or 5% if

the area drained is over 0.2 hectares); Lawns and grass bank maximum

25%; unmown planted banks maximum 50%

• The designer must be aware of the quantity of flow entering his site

from the outside and of how it may change in the future … any water

leaving his site should not be greater than before

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III. Utilities

Storm drainage / Flow of water

• Surface flow will begin to cut small rivulets within 150m it should be

concentrated in man-made channels

• Check dams, paved channels or piped drains may be installed to

prevent erosion

• Gutter flow must be picked up at least once on each block, at the

lowest corner, or be carried under the crossroad in culvert

• Gutter flow should not run more than 250 to 300m, turn a sharp corner

or meet a sudden obstacle

• Inlets finally cut the flow

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III. Utilities

Storm drainage / Flow of water

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III. Utilities

Storm drainage / Gradients

• Sewer lines must be covered deeply enough to prevent breakage and

freezing but no more than 6m

• L:ine slope … minimum 0.3% (0.6m/s) … not over 3m/s

• Changes in slope can be made only at man holes

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III. Utilities

Storm drainage / System layout

• The storm sewer system is initially laid out in plan, with the 1st inlets

located as far down the slopes as possible within the limit for open

gutter flow. Then, the pattern of converging sewers is arranged … to

minimize the length of line and the number of manholes

• The manholes must be in the R.O.W. but the sewer lines may run

through easements separate from the R.O.W.

• It is easier to draw the preliminary profile upward from the

discharge point

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III. Utilities

Storm drainage / Computation of pipe size

• Required pipe size depends on the slope of the pipe; the volume to

be carried; the size of the area being drained; the coefficient of runoff

(0.9 for roofs and pavements, 0.1 for wooded land); intensity of storm

(“year of the storm” + the time since the storm began); retention basins

• The minimum diameter of a sewer that drains a street is 300mm

• The velocity of flow within any pipe should be between 3 and 0.6m/s

the slope of very large pipes vs. very small pipes?

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III. Utilities

Storm drainage / Culverts

• Culvert: A short length of pipe inserted under a road or other barrier to

carry storm water or a small brook

• The gradient just below the outlet must be at least as steep as the

slope just above the inlet to prevent silting

• The size of culverts is calculated in the same way as the size of sewer

pipes

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III. Utilities

Sanitary drainage

• “Sanitary” wastes, such as those from sinks and toilets, are kept out of

the storm drains

• Sanitary drainage is typically a converging system of manholes and

straight pipes of gentle horizontal curvature, leading to a disposal plant

• Continuous over large areas … sometimes pumping is needed …

Pumping is avoided if possible at the site planning scale

• The layout is rarely controlling in site planning

• Unlike storm sewers, sanitary sewers form a closed drainage system

• The branch lines leading to houses connect into the main all along its

course rather than just at manhole

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III. Utilities

Sanitary drainage

• The street main must be set low enough to receive the house laterals …

at least 2m down and more where the land slopes down from the

street or … deep basement

• Minimum size of sanitary sewer: 200mm for main or laterals and

150mm for house branches

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III. Utilities

Sanitary drainage / Sewage disposal

• When a public disposal plant is not within reach, it is possible to

construct a private disposal plant and this plant should be set 100m

from any house and could be economically designed to serve 50~500

houses

• Where the soil is pervious and the ground water low, it is possible to give

each unit a septic tank discharging into an underground drain field …

Drain field must be kept 30m from any surface water or well, and should

not be heavily shaded, or crossed by any vehicles, or installed with a

slope over 15% … Absorption rate is important (Table 4)

• Private disposal plants vs. individual septic tanks

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III. Utilities

Sanitary drainage / Sewage disposal

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III. Utilities

Sanitary drainage / Sewage disposal

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III. Utilities

Sanitary drainage / Dry disposal

• The two water-borne systems are expensive, wasteful of a resource and

can pollute huge volumes of ground and surface water

• Alternative system using no or very little of water … the pit privy …

water table should be at least 7.5m below the bottom of the pit

(1~2m deep) … the pit must be at least 30m away and downhill from

any well … the soil not impermeable, nor yet so extremely permeable

… made tight for half a meter below … unlined below … the waste

materials of the privy filled is left underground for at least a year before

it is removed or used as fertilizer.

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III. Utilities

Sanitary drainage / Dry disposal

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III. Utilities

Sanitary drainage / Dry disposal

• More expensive aqua privy may be preferable where there is danger of

groundwater contamination … a water-tight tank, filled with water,

located directly under the toilet or squatting plate … connected to an

overflow drain … sludge falls to the bottom and scum floats on top.

The sludge I pumped very several years, while the scum is restrained by

a baffle from entering the overflow drain … 7 liters of water per person

(everyday) should be added to maintain the level and a sufficient

degree of dilution of the wastes … the tank must have a capacity of

about 120~150 liters for each person

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III. Utilities

Sanitary drainage / Dry disposal

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III. Utilities

Sanitary drainage / Dry disposal

• Anaerobic digester is a bulky sealed tank in which water, vegetable

waste, and excreta are held for 30~ 80days, producing methane gas

and a safe, fertilizing sludge … work only in a warm climate … best

suited to a tropical agricultural settlement

• Aerobic digester … decomposes the same mix of vegetable matter and

excreta in a large ventilated bin, from which odors and water vapors are

drawn off by a flue … A safe fertilizer can be removed from the

bottom of the bin in about 30~50days … No water is used; odors and

flies are controlled; no risk of disease; by-product is useful

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III. Utilities

Sanitary drainage / Dry disposal

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III. Utilities

Water supply

• Clean water is the most critical utility, a necessity even in the most

primitive settlement

• Water lines must be located in a public R.O.W.

• Water lines vs. Sewers

• Two basic distribution layouts

1. Treelike pattern – minimize length of line … cheapest

2. A loop or interconnected network – avoids the drop in pressure …

at the ends of long branches, and the difficulty of keeping the

dead-end pipes clear

• One most seriously affected by frost … laid under 1.5m(in New

England)

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III. Utilities

Water supply

• Valves … placed in house branches where they leave the mains and in

the mains at points necessary to cut off section in the event of breaks

(no more than 300m apart)

• Fire hydrant … all parts of buildings within 100m from one or two

hydrants … not closer than 7.5m and preferably 15m from any

structure

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III. Utilities

Water Supply / Capacity

• The minimum diameter for water mains is 150mm, or 200mm in high-

value areas

• In U.S. cities, average demand varies from 450 to 900 liters per capita

per day

• A private group water supply, composing of a well, ore group of wells, a

pump, and pressure or gravity tanks … can serve development of 50 to

500 houses … a threshold in cost at about 200 houses

• The principal cost is in the distribution system rather than in the pump

or well

• A large, professionally operated public water system is still the

preferable solution

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III. Utilities

Water Supply / Capacity

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III. Utilities

Electric power

• Power plants primary high-voltage lines transformers low-

voltage lines the points of use

• Secondary lines should be shorter than 120m

• Branching patterns vs. a loop distribution

• Overhead distribution vs. underground distribution (cost, breaks,

maintenance)

• Overhead system … a risk to building repairmen and adventurous

children … pole space 40m or less … esthetical problems … power poles

are useful for mounting street lights, telephone lines, signs, and

callboxes

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III. Utilities

Lighting

• Standard mounting heights for lights are 9m over roadways at spacings

of 45~60m … 10 lux on arterial roads or large parking lots, or 5 lux on

local roads

• Lamps on walkways are normally 3.5m high … the critical factors are the

quality of the light and the psychological sense of safety. Thus shrubs,

recesses, doorways, steps, and intersections should be well lit … 50 lux

• Power and light poles are intrusions in the daytime visual scene

• Night lighting can structure a darkened landscape so that people find

their way and recognize the familiar daytime features

Symbolic landmarks vs. ordinary buildings

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III. Utilities

Other utilities

• Gas is piped underground by a system similar to the water distribution

network … danger of leakage or explosion and so these lines are not

laid under or close to buildings except where they enter them, nor are

they put in the same trench with electric cable

• Telephone lines … overhead on the electric power poles or easily laid

in underground conduit

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III. Utilities

Other utilities

• In case of central heating, the location of the heating plant is preferably

in the middle of the development but on low ground to facilitate the

return of condensate …

• The choice between central heating plants and individual ones depends

on the type and number of dwelling units, the attitude of residents,

maintenance costs, relative efficiency of plants, and the relative cost of

coal, gas, oil, and electricity

• The choice has an important effect on the site plan.

A central plant may be appropriate for 100~200 or more families

Individual plants need provision for the delivery and storage of fuel

(coal, oil, gas or electricity)

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III. Utilities

Solid waste

• Organic material, combustible and noncombustible rubbish

• Use of incinerators; Separation for recycling; Burial of noncombustible

material

• For group collection stations, they are screened and drained

• For separate collection, a drained and protected area must be provided

for the waste cans, convenient to the dwelling unit and as close to the

curb as possible

• Compactors and duct systems

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III. Utilities

Utility plans

• Once the grading plan has been completed, the layout of utilities is

made

• Usually, begin with the storm drainage

• Check if no critical problems of elevations or sizing will occur

• Check the layout of all utilities together and in three dimensions

• Where curves or grades permit, it is desirable to keep utilities in a

uniform location relative to the street, particularly underneath the

planting strip

• The layout of all utilities may be shown on one sheet, or it may be

more convenient for the storm drainage to be shown on the grading

plan