geotechnical report 01 witthout borehole

8/11/2019 Geotechnical Report 01 Witthout Borehole

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GROUP:

Geotechnical Exploration and Evaluation Report of

Gymnastic and Meeting Building Florida

CLIENT

The Parks and Recreation Department of Relax City, Florida

Dale: _____________


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M/s The Parks and Recreation Date. 27-11-2013

Department of Relax City,

Florida

Subject: Geotechnical Exploration and Evaluation Report of Gymnastic and Meeting Building,

Near City Hall, Florida

Dear Sir,

Reference your request regarding the geotechnical investigation for the subject site; enclosed

please find copy of the geotechnical investigation report. The 'Geotechnical Investigation

Report' has been prepared for the foundation design of proposed Gymnastic and Meeting

Building, near City Hall, Florida. The report includes information regarding subsoil stratigraphy,

field as well as laboratory determinations of soil characteristics and foundation design

recommendations.

We hope that the investigation results presented in this report will provide all the necessary

information for the construction of the subject facility. In case there is any query, please do

not hesitate to contact the undersigned.

Best Regards,

(Student Name)


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Table of Contents

1. INTRODUCTION 3

2. PROJECT DESCRIPTION 3

3. THE SITE GEOLOGY AND SEISMICITY 3

3.1. The Site Geology 3

3.2. The Seismicity at the Site 4

4. THE SCOPE OF WORK 4

5. THE INVESTIGATION DETAILS 4

5.1. Drilling Of Bore Holes 4

6. THE SUBSURFACE CONDITIONS AT THE SITE 5

6.1. Site Conditions 56.2. Subsoil Conditions (Stratigraphy) 5

6.3. Groundwater 5

7. FOUNDATION DESIGN CONSIDERATION 6

7.1. General 6

7.2. Selection Of Foundation Types 6

7.3. Depth of Foundation 6

8. THE EARTHWORK 9

8.1. Clearing, Grubbing, Leveling And Grading 9

8.2. Excavations 9

8.3. Fill Materials 10

9. CONSTRUCTIONAL ASPECTS 10

10. INSPECTION AND MONITORING 10

11. SUMMARY OF RECOMMENDATIONS 11

11.1. Type Of Foundation 11

11.2. Minimum Depth Of Foundation 11

11.3. Bearing Pressure 11

12. GENERAL COMMENTS 11

13. APPENDIX - A 12


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1. Introduction

This report present the results of geotechnical investigation for the foundation design of

proposed Gymnastic and Meeting Building, Near City Hall, Florida.

The principal objective of the investigation was to evaluate the surficial and subsurface

conditions at the site, select appropriate geotechnical parameters and to make

recommendations for the design and construction of foundation including the selection of

most appropriate foundation type, foundation depth and the allowable bearing pressure for

design of the foundations.

This report on geotechnical investigation covers the reporting requirement stipulated in the

scope of work. The report contains the main text together with 1 Appendix A (containing

tables, chats, figures, and borehole).

The main text of the report presents description of the site, a general geotechnical assessment

of the project area, details of the investigation performed and an appreciation of the

subsurface conditions as well as recommendations and conclusions with respect to the

foundation design for the proposed structure based on the investigation results. The report

also includes recommendations on earthwork including grading, excavation, fill and

compaction.

2. Project Description

The project site is located in Florida near City Hall. The proposed area is rectangular in shape,

and has width of 175 ft and length of 300 ft. the total gross area of the proposed site is 52,500

square feet.

Based on the plan provided, the proposed construction is to build a Gymnastic and Meeting

Building. The height of the proposed building is approximately 45 feet. It is noticed that project

site is at final grade elevation and no mass excavation or fill is required.

3. The Site Geology And Seismicity

3.1.The Site Geology

It is known from the investigation that the geology at the site is characterized by sandy soil

underneath is lime stone loose to medium rock strata.

The geology of Florida is composed of a thick section of mostly unreformed carbonate rocks.

This carbonate platform has been developing since the late Triassic opening of the North

Atlantic. The rocks generally deposited in shallow water are undeformed. Floridan plateau is

associated with the Bahaman platform to the east; contiguous until later development of


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Florida straits. Rocks gently dip to south. The deepest wells have penetrated up to 18,000 ft of

sedimentary rocks in South Florida Basin

3.2. The Seismicity at the Site

The City Florida is located on the North American Plate passive margin. This active margin isconfined by faults that cause earthquakes when there is movement along them. This is the

major reason that Florida has a particularly low incidence of earthquakes. In a highly unusual

event, some Floridians felt a strong (Magnitude 5.8) earthquake that occurred on September

10 at 10:56 a.m. Eastern Daylight Time in the Gulf of Mexico, about 250 miles (405 km) south-

southwest of Apalachicola, Florida.

4. The Scope Of Work

The purpose of the investigation was to determine the subsoil conditions and to evaluate the

subsoil parameters for the foundation design of proposed Gymnastic and Meeting Building,Florida.

Specifically the scope of work included:

Field exploration, in-situ testing and sampling.

Laboratory testing

Analyses of data gathered through field and laboratory investigations and preparation of

report including recommendations for:

a. Bearing capacity for proposed foundation.

b.

Construction aspects

5. The Investigation Details

5.1. Drilling Of Bore Holes

The field investigation included drilling of 05 bore holes at the locations specified by the client.

The locations of the boreholes are marked on Figure - 1. Boreholes were drilled down to a

depth 25 ft below the existing ground level.

Exploratory borings of 2 feet long diameter and 2 inch split spoon sampler were drilled using

straight rotary technique. Standard Penetration Tests (SPTs) were performed in accordance

with ASTM D-1586 at surface and at 0.5 ft depth intervals below the existing ground level up to

the final depth explored. SPT Resistance values (N values) are shown on boring logs attached in

AppendixA (Figure 3 to 7). Figure 2 represents legends and symbols used on boring logs.


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Estimates of relative density of soils and consistency of the cohesive soils given on the boring

logs, in general, are based on the SPT resistance as recommended by Terzaghi and shown in

Table 1.

6. The Subsurface Conditions at The Site

6.1. Site Conditions

The site for the design of proposed Gymnastic and Meeting Building is located near City Hall,

Florida. At present the site is an open piece of land surrounded on three sides by buildings and

the front side by main road. The site is nearly even and is at final grade elevation adjacent to

road level. The site is covered by grass, shrubs and vegetation.

6.2. Subsoil Conditions (Stratigraphy)

The ground surface of the site is covered by grass and few trees. The subsoil conditions are

fairly uniform and consist of deposits consisting of silica sand with trace of fragmented

limestone. In general the subsurface strata exist in a medium dense to dense condition of

compactness. The natural sub soil can be broadly divided into the following stratum:

Stratum # 1: In general the top stratum starts off below a thick cover of dense dark brown

silica sand consisting of sand mixed with fragmented limestone. The dark sand consists of

limestone fragmented particles and in general extends to a depth of about 10 ft below the

existing ground level. The top stratum exists in a medium dense to dense condition of

compactness with SPT values ranging from 13 to 45. The soil can in general be classified as SP.

In borehole No 05, gray concrete fill with brown sand of 02 feet layer is encountered.

Stratum # 2:This stratum underlying stratum # 2 consists of tan fragmented limestone and

extends to the final depth explored. In borehole No 01 & 03, again tan sand with fragmented

limestone of depth 5 ft is encountered. This stratum is rock and exists in a soft to medium

dense condition of compactness with SPT value ranging 14 to 40 ft.

The actual thicknesses and occurrence of different soil/rock layers at different depth horizons

observed during drilling are documented in borehole logs attached at figure 08 & 09 in

AppendixA.

6.3. Groundwater

The groundwater level was established at a depth of about 07 ft below the existing ground

level during drilling operations. The static groundwater is ranges from approx. el +0 to el+3

based on experiences. It is important to mentioned that tidal and seasonal variation in the

above given limit is expected.


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7. Foundation Design Consideration

7.1. General

In order for the foundations to be safe, the load carrying strata must be competent to sustain

the imposed loading without undergoing shear failure and at the same time any settlements of

the foundations must not exceed the tolerable limits. Therefore, the load carrying

characteristics of the strata must be evaluated from these two considerations.

7.2. Selection Of Foundation Types

Considering the competence of the strata, as evaluated from the investigation results and the

type of the structures to be constructed, any type of shallow foundation (isolated, strip or mat)

would be technically feasible and economical in construction; provision of deep foundation

will not be required. However taking into consideration the presence of sandy soils it is

recommended that if isolated foundations are used. The foundations should be tied to reducethe chances of differential settlement.

The preference of a type of the shallow foundation over the other for a particular structure

must be carefully evaluated, considering the resistance of a foundation type to the shear

stresses and deformation characteristics of the bearing soils, as well as consideration for the

economy of construction.

The settlement of a structure among other factors is also a function of the type of foundation

system adopted. A spread footing is more sensitive to the variations in the subsurface

conditions, and therefore may settle more than a strip footing, which has the ability ofbridging over the relatively weaker zones between adjacent columns and thereby adding

significant rigidity to the foundation system. The mat foundation provides even more

advantage in this respect.

7.3. Depth of Foundation

Regardless of the foundation type adopted for a particular structure, the foundations must be

laid at a sufficient depth, below the depth of seasonal variation zone of the subsoil.

The depth of foundation among other factors is also governed by the lateral stability

requirements and presence of surficial debris, organic matter and chemically deleterious

materials, all of which, if within the zone of influence of foundation must be replaced by a

competent material and the foundations be placed well below such materials so that these can

transmit the pressure directly onto the competent load bearing strata.

It is our understanding that the proposed structure will consist of a three storey building

without a basement. It is recommended that the foundation of the structure should be placed


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at a minimum depth of 3 ft below the existing ground level on well compacted soil. However

keeping in mind the limitations of investigation it is strongly recommended that before placing

the foundations a senior qualified engineer should inspect the foundation level after

excavation and make sure that the foundation rests on well compacted soil.

7.3.1. Settlement and Allowable Bearing Pressures

The allowable bearing pressure for the design of foundations must not exceed more than the

allowable bearing capacity of the load carrying soil with respect to shear failure. At the same

time the settlement corresponding to the allowable bearing pressure must not exceed the

maximum allowable limit of settlement for the particular foundation / structure system,

therefore the load carrying capacity of the soil has to be checked against both shear and

settlement. The lesser of the two (shear and settlement) will determine the allowable bearing

pressure for design of foundations. In order to recommend allowable bearing pressure for

design of foundations, it is first necessary to establish the allowable settlement criteria for thestructures to be constructed at the site.

The allowable total settlement for structures as reported in the literature varies between the

classical Terzaghi criteria of 1 inch (25 mm) to more than 4 inch (100 mm). Generally 2 inch (50

mm) total settlement is recommended for mat foundation. It is however to be noted that it is

usually the differential settlement, rather than the total settlement that is of concern in the

design of foundations. A state of the art criteria for tolerable settlements is developed on the

basis of the distortion that a structure can tolerate, which is then related to the differential

and total settlements which a structure can tolerate depending upon various loading

conditions and subsurface characteristics.

Typical soil parameters used for the calculations of settlement and bearing pressure for

foundations are presented in Table 2.

7.3.2. Settlement Calculations

The settlement of square isolated footings of different dimensions has been calculated using

the following relationship given by Timoshenko and Goodier (Reference Foundation Analysis

and Design 5th Edition by Joseph E. Bowles):

Where


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H = Allowable Settlement

q = Allowable Bearing Pressure

B' = Least lateral dimension of the foundation

If= Influence factor for reduction of settlement when foundation is placed at some depth "D"in the ground.

Is= Influence factor which depends upon L/B, thickness of stratum H and Poisson's ration 0.3.

Es= Elastic soil parameter.

7.3.3. Allowable Bearing Capacity

The allowable bearing capacity is smaller of the safe bearing capacity (foundation should not

fail in shear) and the bearing capacity calculated on the bases of tolerable settlement.

Therefore, the load carrying characteristics of the strata must be evaluated from these twoconsiderations. The width of the foundation along with other factors generally controls the

allowable bearing capacity, as the width of the foundation increases it is the allowable

settlement of foundation rather than shear failure of the ground which will govern the

assignment of the allowable bearing pressure for design of foundation.

Generally the allowable settlement for framed building structures supported on square / strip

footing is taken as 25mm.

Terzaghi Ultimate Bearing Capacity Theory

Qu= c Nc+ D Nq+ 0.5 B N

= Ultimate bearing capacity equation for shallowstrip footings, (kN/m2) (lb/ft

2)

Qu= 1.3 c Nc+ D Nq+ 0.4 B N

= Ultimate bearing capacity equation for shallowsquare footings, (kN/m2) (lb/ft

2)

Qu= 1.3 c Nc+ D Nq+ 0.3 B N

= Ultimate bearing capacity equation for shallowcircular footings, (kN/m2) (lb/ft

2)

Where:

c =Cohesion of soil (lb/ft2),

= effectiveunit weight of soil (lb/ft3)

D = depth of footing (ft)

B = width of footing)(ft),

Nc=cot(Nq1)

Nq=e2(3/4-/2)tan/ [2 cos2(45+/2)],
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N =(1/2) tan(kp/cos2- 1)

e = Napier's constant = 2.718

kp= passive pressurecoefficient

=angle of internal friction (degrees).

Taking into consideration the above described criteria the net allowable bearing pressure hasbeen calculated at 3 ft (1 m) depth below the existing ground surface. The recommended

allowable bearing pressure values in general are as follows:

Depth of

Foundation

Type of

Foundation

Least lateral

Dimension

of

Foundation

Net

Allowable

Bearing

Pressure

3 ftIsolated

Square5.25 ft 6,564 Ib/ft

2

The actual net bearing pressure value for any particular Isolated Square foundation can be

seen from Table 03.

8. The Earthwork

8.1. Clearing, Grubbing, Leveling And Grading

Prior to any construction activity at the site, it must be cleared of all debris, and surface

vegetation. This can be carried out by graders/dozers. For leveling and grading, stakes should

be installed on a grid marked by Surveying Crews. The required levels to be attained through

cut or fill at the grid points must also be identified.

The leveling and grading can be carried out by normal earth moving machine. As

predominantly sandy soils will be encountered in excavation throughout the project area, no

special problems are anticipated in excavating and moving these soils with excavators,

scrappers and dozers.

8.2.

ExcavationsThe excavations for construction of foundations, other substructures or for trenches for utility

lines can be made by using conventional earth moving machinery including scrappers, dozers

and trenchers etc. All the excavations should be properly sloped or supported to avoid any

stability failure as well as movement in the adjacent structures.
http://www.geotechnicalinfo.com/lateral_earth_pressure_coefficient.htmlhttp://www.geotechnicalinfo.com/angle_of_internal_friction.htmlhttp://www.geotechnicalinfo.com/angle_of_internal_friction.htmlhttp://www.geotechnicalinfo.com/lateral_earth_pressure_coefficient.html


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After reaching the designed foundation level and before placing the foundation, it is

recommended that the soil should be well compacted by using an appropriate roller or

equivalent.

8.3. Fill Materials

The on-site materials after removing about 1.5 ft. of topsoil can be used for general backfilling

at the site. However preferably the backfill material should be granular and the quantities of

fines should limit to the recommended values.

9. Constructional Aspects

We recommend the following measures for long-term stability of the structures.

Well compact the bottom of the excavation using appropriate compaction equipment (such

as tamping plates) before placing the foundations.

A pad of at least 6 inches of 1:4:8 PCC (well compacted) should be placed on the prepared

ground before placing foundations.

Engineering fill (A-1-a, A-1-b or A-3) should be used as a back fill material. The commonly

available back fill material is A-3 (sand).

Plinth protection slab sloping away from the buildings should be provided around the

structure to reduce ingress of water to foundation soils.

Proper surface drainage should be provided in the project area and the area should be

graded to keep the surface runoff away from the structure. The ingress of water from any

source should be avoided.

10.Inspection And Monitoring

It is necessary that all the geotechnical aspects of foundation construction and earthwork be

monitored by competent construction supervision staff including qualified and experienced

engineers. For this purpose a comprehensive inspection and monitoring program should be

prepared. The program must specifically address the following aspects.

1. Inspection of all stripping work to ensure that the undesirable topsoil containing refuse

and organic material has been adequately removed.

2.

Making sure that all the stripped off material and other unwanted materials from thesite are disposed off in designated disposal area without any environmental hazard.

3. Identification of in-situ conditions of the subsurface during foundation excavation and

preparation of sub grades, so that over excavation is avoided. Senior engineer should

ensure that the foundation has been placed on well compacted soil.


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4. Identify the areas on the excavated slopes requiring protection, and provide suitable

remedial measures, where required to ensure stability of slopes during construction.

5. Special precautions should be observed during excavation and proper protection

should be provided to neighboring structures. Full time monitoring by an experienced

engineer should be ensured.

11.Summary Of Recommendations

11.1. Type Of Foundation

Shallow foundation Isolated Square type can be used; however foundations should be tied to

reduce chances of differential settlement.

11.2. Minimum Depth Of Foundation

Minimum depth of foundation should be 3 ft below the existing ground level on well

compacted soil.

11.3. Bearing Pressure

The recommended allowable bearing pressure values in general are as follows:

Depth of Foundation Type of Foundation

Least lateral

Dimension of

Foundation

Net Allowable

Bearing Pressure

3 ft Isolated Square 5.25 ft 6,564 Ib/ft2

12.General Comments

Foundation should be placed on well compacted soil; a senior qualified engineer should

inspect the site before placing foundations and should ensure that the foundation has been

placed on well compacted soil.

Sulphate Resistance cement should be used for the foundation works.

Special precautions should be observed during excavation and proper protection

should be provided to neighboring structures. Full time monitoring by an experienced

engineer should be ensured.


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13.APPENDIX - A

Tables

Bore Hole Logs


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TABLE-1

Empirical Values For , Qu, Drand Unit Weight Of Soils Based on The SPT

Table-2

Soil Parameters Used In The Analysis Of Settlement and Bearing Pressure

DESCRIPTION OF PARAMETER VALUE OF PARAMETER

Bulk unit weight 120 Ib/ft3

Corrected average N-value 25 blows/1 ft

Angle of internal friction of top soil 33o

Cohesion , c 0


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Table-3

Calculation of Foundation Width

Given

bearing pressure from building = 180,000 lbs/ft2

unit weight of soil, = 120 lbs/ft

3

Cohesion, c = 0

angle of Internal Friction, = 33 degrees

footing depth, D = 3 ft

Solution

Try a width, B = 5.25 foot

Use a factor of safety, F.S = 3

Determine bearing capacity factors N, Ncand Nq. See typical bearing capacityfactorsrelating

to the soils' angle of internal friction.

Ng= 31

Nq= 33

Nc= 49

Solve for ultimate bearing capacity,

Qu= c Nc+ D Nq+ 0.4 B N strip footing eq.

Qu= 0(49) + 120lbs/ft3(3ft)(33) + 0.4(120lbs/ft3)(5.25ft)(31)

Qu=19,692 lbs/ft2

Solve for allowable bearing capacity,

Qa= Qu

F.S.
http://www.geotechnicalinfo.com/bearing_capacity_factors.htmlhttp://www.geotechnicalinfo.com/bearing_capacity_factors.htmlhttp://www.geotechnicalinfo.com/bearing_capacity_factors.htmlhttp://www.geotechnicalinfo.com/bearing_capacity_factors.html


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Qa=21645lbs/ft2= 6564lbs/ft

2 o.k.

3

Since Qa> 180,000/5.252= 6530 lbs/ft

2bearing pressure, Use B=5.25 ft

Conclusion

Footing shall be 5.25 feet wide at a depth of 3 feet below ground surface. Many engineers

neglect the depth factor (i.e. D Nq= 0) for shallow foundations. This inherently increases the

factor of safety.

geotechnical report 01 witthout borehole

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