Soil Investigation

FOR INTERNAL CIRCULATION ONLY

user’s manual of Construction

Soil Investigation

&

Foundations

Construction Management

Power Grid Corporation of India Limited

CHAIRMAIN

&

MANAGING DIRECTOR’S MESSAGE

It gives me immense pleasure to learn that Construction Management has come out with further four volumes of User’s Manual of Construction : ‘Soil Investigation & Foundations’, ‘Pile & Well Foundations’, ‘Contracts Management’ and ‘Transformers & Reactors’.

The various changes in the wake of rapid advances in technologies and growing competition on global basis has made it imperative to conceptualise the methods for optimizing our resources; the 5M’s namely men, money, machines, materials and methods. They are the basics to realize a construction project and time, cost & quality are its critical parameters. The construction of transmission line is a wide canvas and complex in nature that needs a multi disciplinary approach. However, no standard guidelines or manuals in consolidated form are available for its various construction activities.

I compliment the Construction Management team for bringing out these manuals wherein the main focus of the authors has been to combine the theoretical & practical aspects drawn from their respective experience in transmission lines construction, academic institutions and industry. An attempt has been made to explain the fundamentals in a simple & lucid language. I am convinced that these manuals will act as guidelines and serve the needs of our practicing Managers & site Engineers.

I should be our endeavour to follow these systems and procedures to enhance the quality of construction management in transmission and quality power. More such User’s Manuals covering the other related fields should be prepared for the benefit of the ultimate users at our remote sites as well as for the younger generation inducted in POWERGRID.

CONTENTS

SECTION-I

SOIL INVESTIGATION

SL. NO. DESCRIPTION PAGE NO.

1.0 INTRODUCTION 1

1.1 PURPOSE OF SOIL INVESTIGATION 1

1.2 TYPE OF TESTING 3

1.2.1 BORING 3

1.2.2 SHELL AND AUGER BORING 3

1.3 SAMPLING 4

1.3.1 GENERAL 4

1.3.2 DISTURBED SAMPLE 4

1.3.3 UNDISTURBED SAMPLE 5

1.3.4 UNDISTURBED SAMPLING IN COHESIVE SOIL 6

1.3.5 UNDISTURBED SAMPLING USING PISTON SAMPLER 6

1.3.6 UNDISTURBED SAMPLING IN COHESIONLESS SOILS 7

1.3.7 TYPES OF SAMPLERS 7

1.4 INSITU PERMEABILITY TEST 7

1.4.1 PUMP-IN TEST 8

1.5 STANDARD PENETRATION TEST 9 1.6 STATIC CONE PENETRATION TEST 11 1.7 DYNAMIC CONE PENETRATION TEST 12

1.8 VANE SHEAR TEST 12

1.9 PLATE LOAD TEST 13

2.0 TRIAL PIT 15

2.1 GROUND WATER 18

2.2 ELECTRICAL RESISTIVITY TEST 19 2.3 FIELD INVESTIGATION ROCK 20

2.4 LABORATORY TESTING 24

2.5 REPORT 29

2.6 RATES & MEASUREMENTS 37 2.7 SPECIFIC REQUIREMENTS FOR GEOTECHNICAL

INVESTIGATION AT RIVER CROSSINGS

39

2.8 SUMMARY OF RESULTS OF LABORATORY TEST ON SOIL AND WATER SAMPLES

40

2.9 TOOLS AND PLANTS FOR SOIL INVESTIGATIONS 42 3.0 GUIDELINES FOR CONDUCTING SOIL INVESTIGATION

IN TRANSMISSION LINE

SECTION-II

TOWER FOUNDATIONS

CHAPTER-1

GENERAL

SL. NO. DESCRIPTION PAGE NO.

1.0 TOWER FOUNDATIONS

1.1 LOADS, SAFETY FACTORS AND SETTLEMENT

1.2 CLASSIFICATION OF SOILS

1.3 PROPERTIES OF SOILS

1.4 DATA FOR FOUNDATION DESIGN

CHAPTER-2

TYPES OF FOUNDATIONS

SL. NO. DESCRIPTION PAGE NO.

2.0 INTRODUCTION

CHAPTER-3

CLASSIFICATION AND STUB SETTING

SL. NO. DESCRIPTION PAGE NO.

3.0 LINE CONSTRUCTION

3.1 INVESTIGATION AND SURVEY

3.2 TRANSPORTATION

3.3 FOUNDATION

3.4 PREPARATION OF FOUNDATION SITE

3.5 TYPE OF FOUNDATION TO BE ADOPTED

3.6 PIT MARKING

3.7 SHORING AND SHUTTERING

3.8 DEWATERING

3.9 EXCAVATION IN ROCK

3.10 PROCEDURE FOR SETTING STUBS OF SITE BY COMBINED STUB SETTING

CHAPTER-4

TYPES OF FOUNDATIONS

SL. NO. DESCRIPTION PAGE NO.

4.0 CONCRETE TYPE 4.1 MIXES 4.2 SIZES OF AGGREGATES 4.3 GRAVEL SUB-BASE 4.4 REINFORCEMENT 4.5 FORM WORK

4.6 MIXING, PLACING AND COMPACTING OF CONCRETE

4.7 BACK FILLING

4.8 CURING

CHAPTER-5

PROTECTION OF FOUNDATION

SL. NO. DESCRIPTION PAGE NO.

5.0 CONCRETE TYPE

5.2 REVETMENT

5.3 BENCHING

5.4 PROTECTION OF FOUNDATION AGAINST CHEMICAL WATER

5.5 MEASUREMENT OF VOLUME FOR REVETMENT AND BENCHING

CHAPTER-6

CONCRETE TECHNOLOGY

SL. NO. DESCRIPTION PAGE NO.

6.1 INTRODUCTION

6.2 PROPORTIONING CONCRETE MIXTURES

6.3 FRESH CONCRETE

6.4 HANDING AND BATCHING CONCRETE MATERIALS

6.5 BATCH PLANTS AND MIXERS

6.6 READY MIXED CONCRETE

6.7 MOVING AND PLACING CONCRETE

6.8 CONSOLIDATING CONCRETE

6.9 RECOMMENDED VIBRATION PRACTICES

6.10 FINISHING AND CURING CONCRETE

6.11 PLACING CONCRETE IN COLD WEATHER

6.12 PLACING CONCRETE IN HOT WEATHER

CHAPTER-7

MECHANISED CONSTRUCTION

SL. NO. DESCRIPTION PAGE NO.

7.0 INTRODUCTION

7.1 MECHANICAL CONSTRUCTION EQUIPMENT & THEIR APPLICATIONS

7.2 WORK STUDY ON CONSTRUCTION EQUIPMENT

7.3 PLANT PURCHASE VERSUS PLANT HIRE

7.4 SAFETY PROGRAMME

7.5 WHY MECHANICAL CONSTRUCTION EQUIPMENT?

7.6 PRODUCTION OUT PUTS

7.7 PRODUCTION TRIAL

7.8 ECONOMIC LIFE

CHAPTER-8

STANDARD FIELD QUALITY PLAN

8.0 STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES

CHAPTER-9

GUIDELINES

SL. NO. DESCRIPTION PAGE NO.

9.0 PIT MARKING

9.1 STUB SETTING

9.2 CONSTRUCTION MATERIALS

9.3 INSTALLATION OF REINFORCEMENT STEEL & FORM BOXES

9.4 MIXING, PLACING AND COMPACTING OF CONCRETE

CHAPTER-10

CHECK FORMAT

SL. NO. DESCRIPTION PAGE NO.

1.0 CHECK FORMAT FOR PIT MARKING

2.0 CHECK FORMAT FOR FOUNDATION CLASSIFICATION

3.0 CHECK FORMAT FOR STUB SETTING

4.0 CHECK FORMAT FOR CONSTRUCTION MATERIALS

5.0 CHECK FORMAT FOR INSTALLATION OF REINFORCEMENT STEEL & FORM BOXES

6.0 CHECK FORMAT FOR MIXING, PLACING AND COMPACTING OF CONCRETE

ANNEXURE-IA : TOOLS & PLANTS FOR EXCAVATION, STUB SETTING AND CONCRETING

ANNEXURE-IB : MANPOWER FOR EXCAVATION, STUB SETTING & CONCRETING GANG

ANNEXURE-IC : REINFORCED CONCRETE RETAINING WALLS

SECTION-1

Soil Investigation

___________________________________________________________________________

SECTION ONE

___________________________________________________________________________

SOIL INVESTIGATION Back to contents page

1.0 INTRODUCTION

Back to contents page

An investigation of sill is essential for judging its suitability for the proposed engineering works and for preparing adequate and economic design. In general, the purpose of soil investigation is to obtain necessary information about the soil and to know the engineering properties of soil which will be affected.

Earlier, the soil investigation of locations of transmission line towers was not very popular and general practice had been to adopt 4to 5 types of standard design foundations for different classes of soils encountered. Only special foundations in river beds necessitating huge volumes of concrete were investigated for properties of soils. Now the soil investigation of normal foundations is also felt necessary in good number of locations in the 400 kv transmission lines which helps in better choice of standard foundation & development of new designs to achieve overall cost, economy and minimise chances of failure.

1.1 Purpose of soil investigation:

Back to contents page

b) Economic Consideration

a) Technical Considerations : An inadequate design or a conservative

choice of standard foundation can lead to a failure causing long outage of transmission line. In modern practice, a large variety of standardised foundations are being pre-designed with different sets of properties attached to forseeably encountered soils. Aarge varity of soils are encountered as length of transmission lines are increasing with voltage llevels going up. To obtain optimal choice of pre-designed standard foundations,it is very much necessary to have a proper scientific knowledgfe of properties of soil against the back-drop of increasing sizes of towers, foundations, loads, thereby minimising the risk of fail-ures of foundations.

b) Economic Considerations : Among site erection activities, the

foundations form the major chunk of the cost. The cost of foundations constitures 50 to 70% of the toral cost of erection depending upon terrain conditions. It forms 10 to 15% of the total cost of transmission line. A considerable saving in the foundation cost can be achieved by having detailed knowledge of soil properties and making wide usage of them in designing the foundations in sufficient types and classification of the foundations in field to match the most optimum size and type of foundation.

1.2

Types of Testing :

Back to contents page

1.2.1

Boring : Bore holes are generally taken at specified locations to obtain information about the sub soil profile, its nature and strength and to collect soil

samples for strata identification and conducting laboratory tests. The minimum diameter of the bore hole shall be 150 mm and boring shall be carried out in accordance with the provision of IS:1892. Casing pipe is used in the bore hole to support its side when a side fall is suspected to occur inside the borehole. When casing pipe is used, it shall be ensured that its bottom end is at all times less than 15cms above the bottom of the borehole and not below the level at which the test has to be conducted or sampling has to be done. In case of cohesion less soils the advancement of the casing pipe shall be such that it does not disturb the soil to be tested or sampled. The casing shall be advanced by slowly turning the casing pipe and not by driving.

1.2.2

Shell and Auger Boring: Cylindrical augers and shells with cutting edge on teeth at the lower end can be used for making deep boring. Hand operated rings are used for depths up to about 25m and the mechanized rings up to 50m. Shell and auger boring can be used in all types of soil free from boulders. For cohesion less soil below ground water table, the water table in the borehole shall always be maintained at or above the ground water level. The use of chisel bit is permitted in hard strate with SPT-N value greater than 100.Chisel bits are also used to extend the borehole through local obstructions such as old construction boulders, rocky formation etc. The various activities to be conducted during the boring include standard penetration test, collection of undisturbed and disturbed samples of soil at various depths, logging of different layers of soil, depth of subsoil water and preparation of data sheets. Further a series of tests have to be conducted on the disturbed and undisturbed samples of soil at laboratory.

1.3

Sampling :

Back to contents page

1.3.1

General :

Back to contents page

(a) Sufficient number of soil samples shall be collected. Disturbed soil samples shall be collected for field identification and conducting tests such as sieve analysis, index properties, specific gravity, chemical analysis etc. Undisturbed sample shall be collected to estimate the physical strength and settlement properties of the soil. All the accessories required for sampling and the method of sampling shall confirm to IS:2132.

(b) All the samples shall be identified with date, bore hole and trial pit number, depth f sampling etc. It is also essential to mark and arrow pointing towards the top surface of the sample as the soil was in-situ. Care shall be taken to keep the core samples and box samples vertically with the arrow directing upwards . The tube samples shall be properly trimmed at one end and suitably caped and sealed with molten paraffin wax.

1.3.2

Disturbed Sample

Back to contents page

a) Disturbed soil samples shall be collected in bore holes at regular

itervals.Jar samples weighing approximately 10N shall be collected in boreholes at 0.5m intervals starting from a depth of 0.5 m below ground level and at every identifiable change of strata to supplement the boring

records. Samples shall be immediately stored in air tight jars and shall fill the jar as far as possible.

b) In elevated areas, if superficial material is available in plenty, then bulk samples from a depth of about 0.5m below ground level shall be collected to establish all the required properties to use it as a fill material. Disturbed samples weighing about 250 N shall be collected at shallow depths and immediately stored in polythene bags as per IS:1892. The bags shall be sealed properly to avoid any change in moisture content and they shall be kept in wooden boxes.

1.3.3

Undisturbed Sample :

Back to contents page

In each borehole undisturbed sample shall be collected at every change of strata and depths of 1.0 4.0 7.0,10.013.0,15.5m and water at regular intervals of 3.0m and as directed by the Engineer. The depth interval between the top levels of undisturbed sampling and standard penetration test shall not be less than 10.m. Undisturbed samples shall be of 100m dia and 450 mm length. Samples shall be collected in such a manner that the structure of the soil and its moisture content do not get asserted. The specifications for the accessories required for sampling and the sampling procedure shall conform to IS:1892 and IS:2132. Undisturbed sampling in sand shall be done using compressed air technique mentioned in IS:8763. Thin walled sampler shall be used to collect undisturbed samples by pushing the tube into the soil. The sampling tube shall have a smooth finish on both surfaces and minimum effective length of 450mm. The area ratio of sampling tubes shall be less than 12.5%. However, in case of very stiff soils, area ratio up to 20% shall be permitted. Area ratio

should be as low as possible. In no case it should be greater than 25%. The inside clearance of the sampler should lie between 1 to 3 percent and the outside clearance should not be much greater than the inside clearance. 1.3.4 Undisturbed Sampling in Cohesive Soil

Back to contents page

Undisturbed samples in soft to stiff cohesive soils shall be obtained using a thin walled sampler. In order to reduce the wall friction, suitable precautions such as oiling the surfaces shall be taken.

1.3.5

Undisturbed Sampling using Piston Sampler

Back to contents page

Undisturbed samples in very loose saturated sandy and silty soils and very soft clays shall be obtained by using a piston system. In soft clays and silty clays, with water standing in the casing pipe, piston sampler shall be used to collect undisturbed samples. During this method of sampling expert supervision is called for. Accurate measurement of the depth of sampling, height of sampler, stroke and length of sample recovery shall be recorded. After the sampler is pushed to the required depth, both the sampler cylinder and piston system shall be drawn up together ensuring that there shall not be any disturbance to the sample which shall then be protected from changes in moisture content.

1.3.6

Undisturbed Sampling in Cohesion less Soils

Back to contents page

Undisturbed samples in cohesionless soils shall be obtained as per the procedure given in IS:8763. Compressed air sampler shall be used to take samples of cohesionless soils below water table.

1.3.7

Type of Samplers:

Back to contents page

Samplers which shall be used commonly at sites are open drive sampler, stationary piston sampler, and Rotary samplers depending upon the mode of operation. Open drive types can be both the thick and thin wall samplers and the stationary piston and the rotary types are thin wall sampler - depending upon the area ratio (Fig.1 & Fig.2)

D22 _{- D1}2

Area ratio = --- X 100 Percent D12

D3 - D1

Inside Clearance = --- X 100 percent D1

D2 - D4

Outside Clearance = --- X 100 percent D4

1.4

In situ permeability test : In situ permeability test shall be conducted to determine the water percolation capacity of overburden soil. The specification for the equipments required for the test and the procedure of testing shall be in accordance with IS: 5529, part -1. When it is required to carry out the permeability test for a particular section of the soil strata above the ground water table, bentonite slurry shall not be used while boring.

Back to contents page

1.4.1 Pump-in test:

Pump-in test shall be conducted in the bore hole/trial pit by allowing water to percolate into the soil. Choice of the method of testing shall depend on the soil permeability and prevailing ground water level.

a) Constant Head Method ( in bore hole):

This test shall be conducted in boreholes where soils have a high permeability i.e. it shall be allowed into the borehole through a metering system ensuring gravity flow at constant head so as to maintain a steady water level in the borehole. A reference mark shall be made at a convenient level which can be easily seen in the casing pipe to note down the fluctuations of water level. The fluctuation shall be counteracted by varying the quantity of water flowing into the borehole. The elevation of water shall be observed at every 5 minute interval. When three consecutive readings show constant value, the necessary observations such as flow rate, elevation of water surface above test depth, diameter of casing pipe etc. Shall be made and recorded as per the proforma recommended in IS:5529, PART-I, Appendix-A.

b) Falling head method ( in bore hole)

This method shall ve adopted for relatively less permeable soils where the discharge is small and where the soil can stand without casing. The test section shall be seated by the bottom of the borehole and a packer at the top of the test section. If the test has to be conducted at an intermediate section of a prebored hole then, double packer shall be used . Access to the test section through the packer shall be by means of a pipe which shall extend to above the ground level. Water shall be

filled into the pipe upto the level marked just below the top of the pipe and water allowed to drain into the test section. The water level in the pipe shall be recorded at regular intervals as mentioned in IS:5229,part-I, Appendix- B. The test shall be repeated till constant records of water level are achieved.

1.5 Standard penetration Test :

Back to contents page

The test shall be performed in a clean hole, 55 to 150 mm in diameter. A casing or drilling mud shall be used to support the sides of the hole. The test shall be conducted at depth of 2.0, 3.0, 5.0, 6.0, 8.0, 9.0, 11.0, 12.0, 14.0, m and at 3.0m intervals and every change of strata and as per the direction of the Engineer-in-charge. A standard thick wall split-tube sampler, 50.8 mm shall be driven into the undisturbed soil at the bottom of the hole under the blows of a 65 kg drive weight with 75 cm free fall. The minimum open length of the sampler should be 60 cm. The sampler shall be first driven through 15 cm as a seating drive. It shall be further driven through 30cm or until 100 blows are applied. The number of blows required to give the sampler 30 cm beyond the seating drive, is termed as penetration resistance N. This test shall be discontinued when the blow count is equal to 100 or the penetration is less than2.5 cm for 50 blows whichever is earlier. At the location were the test is discontinued the penetration and the number of blows shall be reported. Sufficient quantity of disturbed soil samples shall be collected from the split spoon sampler for identification and laboratory testing.

Following Tables give some of the empirical correlation of the soil properties with the penetration resistance corrected for depth and for fine saturated sand.

Table (1) Penetraqtion resistance and Empirical correlations for cohesionless soils. Penetration Resistance N (Blows) Approx.  (Degrees) Density Index (%) Description Approx. Moist Density (t/m2) -4 10 30 50 25-30 27-32 30-35 35-40 38-43 0 15 35 65 85 Very Loose Loose Medium Dense Very dense 1.12-1.6 1.44-1.84 1.76 –2.08 1.76 –2.24 2.08 –2.40

Table (2) : Penetration resistance and empirical correlations for cohesive soils Penetration Resistance N (blows) Unconfined Compressive Strength (t/m2₎ Saturated Density (t/m3₎ Consistency 0 2 4 8 16 32 0 2.5 5 10 20 40 -1.6 - 1.92 1.76 -2.08 -1.92 - 2.24 -Very soft Soft Medium Stiff Very stiff Hard 1.6

Static cone penetration test : Static cone penetration test shall be conducted

to know the soil stratification and to estimate the various soil propertie such as density, undrained shear strength etc. The cone penetrometer shall be advanced by pushing and the static forcr required for unit penetration shall be determined. The test shall be conducted upto the specified depth or refusal whichever is earlier. For this test ‘refusal’ means meeting a very hard strata which can’t be penetrated at the rate of at least 0.3cm/sec even when the

equipment is loaded to its full capacity. The specifications for the equipment and accessories required for performing the test, test procedure, field observations and reporting of results shall conform to 1S: 4968, Part 111. Only 100 kN capacity mechanically operated equipment shall be used. At the ground level, preboring upto 0.5 m depth shall be permitted if the overlying strata is hard. Continuous record of the penetration resistance shall be maintained.

Back to contents page

1.7 Dynamic cone penetration test: Dynamic cone penetration test shall be conducted to

predict stratification, density, bearing capacity etc of soils. The test shall be conducted upto the specified depth or refusal whichever is earlier. Refusal shall be considered when the blow count exceeds 150 for 300mm penetration. The specification for the equipment and accessories re- quired for performing this test, test procedure, field observations and reporting of results shall conform to 18:4968 Part-ll. The driving system shall comprise of a 650 weight having a free fall of 0.75m. The cone shall be of 65 mm diameter provided with vents for'continuous flow of bentonite slurry through the cone and rods in order to avoid friction between the rods & soil. On completion of the test, the result shall be presented as a continuous record of the number of blows required for every 300mm penetration of the cone into the soil in a suitable chart supplemented by a graphical plot of blow count for 300 mm penetration vs. depth.

Back to contents page

1.8

Vane shear test: Field vane shear test shall be performed inside the borehole

to determine the undrained shear strength of cohesive soil -especially of soft and sensitive clays, which are highly susceptible to sampling disturbance. The vane shear test consist of four thin steel plates called vanes, welded

orthogonally to a steel rod (Fig.3) .The test shall be conducted by advancing this four winged vane of s~itable size (as per the soil condition) into the soil upto the desired depth and measuring the torque required to rotate the vane. The torque shall be measured through a torque measuring arrangements such as calibrated torsion spring, is attached to the steel rod which is rotated by a worm gear and worm wheel arrangement. The specification for the equipments and accessories required for conducting the test, the test procedure and field observations shall correspond to IS: 4434. Tests mayalso be conducted by direct penetration from ground surface. On completion of the test the results shall be reported in an approved proforma as specified in IS: 4434, Appendix-A.

Back to contents page

1.9

Plate Load Test: Plate load test shall be conducted to determine the ultimate

bearing capacity of soil, and the load/settlement characteristics of soil at shallow depths by loading a plane and leveled steel plate kept at the desired depth and measuring the settlement under different loads, until a desired settlement takes place or failure occurs. The specification for the equipment and accessories required for conducting the test, the test procedure, field observations and reporting of results shall conform to IS:1888. The test pit shall be made five times the width of the plate. At the centre of the pit, a small square hole shall be dug whose size shall be equal to the size of the plate and the bottom level of which correspond to the level of actual foundation (Fig.4) .

The loading to the test plate shall be applied with the help of a hydraulic jack. The reaction of the hydraulic jack shall be borne by either of the following two methods:

a) Gravity loading platform method b) Reaction truss method.

In case of gravity loading method a platform shall be constructed over a vertical column resting on the test plate and the loading shall be done with the help of sand bags, stones or concrete blocks. The general arrangement of the set up for this method is shown in Fig. 5 & 6.

If the water table is at a depth higher than the specified test depth, the groundwater shall be lowered and maintained at the test depth for the entire duration of the test.

1.9.1 A seating load of 70 gm/sq.cm shall be applied and after the dial gauge readings are stabilized , the load shall be released and the initial readings of the dial gauges recorded after they indicate constant reading. The load shall be increased in stages. These stages shall be 20, 40, 70, 100, 150, 200, 250, 300, 400, 500, 600 and 800 KN per sq.m. or as directed by the Engineer. Under each loading stage, record of Time vs Settlement shall be kept as specified in IS: 1888.

The load shall be maintained for a minimum duration of one hour or till the settlement rate reduces to 0.02 mm/ min whichever is later. No extrapolation of settlement rate from periods less than one hour shall be permitted.

1.9.2 Loading shall be carried out in stages as specified above till one of the following conditions occurs.

a) Failure of the soil under the plate i.e. the settlement of the plate at constant load becomes progressive and reaches a value of 40 mm or more.

b) Total settlement of the plate is more than 40 mm.

c) Load intensity of 800 KN/Sq.m is reached without failure of the soil.

1.9.3 Dial gauge readings for settlement shall generally be taken at

1,2.25,4,6.25,9,16,25,60,90 and 120 minutes from the commencement of each stage of loading. Thereafter the readings shall be taken at hourly intervals upto a further 4 hours and at two hours intervals thereafter for another 6 hours .

2.0

Trial pit

Back to contents page

2.0.1 Trial pits shall be of minimum 2mx2m size at the bottom so as to permit easy access

for visual examination of walls of the pit and to facilitate sampling and insitu testing operations. pits shall be upto 4 m deep or as per the directions of the Engineer. Precautions shall be taken to ensure the stability of pit walls including provision of shoring, if necessary, as per IS: 4453: Precautions shall be taken to prevent surface water draining into the pit. Arrangements shall be made for dewatering if the pit is extended below water table. Trial pits shall be kept dry and a ladder shall be provided for easy access to the bottom of the pit. In-situ tests shall be conducted and undisturbed samples shall be collected immediately on reaching the specified depth so as to avoid substantial changes in moisture content of the subsoil. Arrangements shall

be made for barriers, protective measures and lighting necessary for the period the pits remain open.

2.0.2 A note on the visual examination of soil strata shall be prepared. This should include

the nature, colour, consistency and visual classification of the soil, thickness of soil strata, groundwater table, if any, etc.

2.0.3 Undisturbed samples shall be collected at 1.0, 2.0, 3.0 m depth and at the termination

depth in all the pits.

a) Chunk Samples

In cohesive soils, undisturbed samples of regular shapes shall be collected. The samples shall be cut and trimmed to a suitable size (0.3x0.3x0.3m). A square area (0.35x0.35m) shall be marked at the centre of the leveled surface at the bottom of the pit. Without disturbing the soil inside the marked area, the soil around this marking shall be carefully removed upto a depth of 0.3Sm. The four vertical faces of the soil block protruding at the centre to be trimmed slowly so that its size reduces to 0.3mx0.3m. Wax paper cut to suitable size shall be wrapped uniformly covered with two layers of thin cloth over all the S exposed surfaces of the soil block and sealed properly using molten wax. A firmly constructed wooden box of size 0.3Sx0.35x0.35m (internal dimensions) with the top and bottom open shall be placed around the soil block and held such that its top edge protrudes just above the surface of the block. The space between the soil block and the box shall be filled uniformly and tightly with moist sawdust. The top surface shall also be covered with saw dust before nailing the wooden lid to cover the box firmly taking care that the soil block is not

disturbed. The area of contact between the bottom portion of the block and the ground shall be reduced slowly by removing soil in small quantities using small rods, so that the block can be separated from the ground slowly without disturbance. After inverting the wooden box along with the soil block, the bottom portion shall be trimmed and covered with wax paper, cloth and sealed with molten wax. A wooden lid shall be nailed to the box after providing proper saw dust cushion below it. An arrow mark shall be made on the vertical face of the wooden box to indicate the top surface along wi th the coordinates and depth of sampling .

b) Tube Samples

Undisturbed tube samples may also be obtained by means of a l00mm diameter sampling tube with a cutting edge. The sampler shall be slightly oiled or greased inside and outside to reduce friction. The sampler shall be pushed into the soil and while doing so, soil around the tube shall be carefully removed. In case it is not possible to push the sample, it may be driven by light blows from a "monkey".

2.0.4 In each trial pit the soil in-situ density shall be determined by the sand replacement method. The specifications, equipments, accessories required for the test and test procedure shall be as per IS: 2720, Part- XXVIII. No separate payment shall be made for this test.

2.1 Ground Water

2.1.1 One of the following methods shall be adopted for determining the ground water table

in bore holes as per IS: 693 5 and as per the lnstructions of the Engineer.

a) In permeable soils, the water level in the hole shall be allowed to stablise after depressing it adequately by bailing. When the water level inside the bore hole is found to be stable, the depth of water level below ground level shall be measured. Stability of sides and bottom of the bore hole shall be ensured at all times.

b) For both permeable and impermeable soils, the [following method shall be suitable. The bore hole shall be filled with water and then bailed out to various depths. Observations on the rise or fall of water level shall be made at each depth. The level at which neither a fall nor a rise is observed shall be considered as the water table elevation. This shall be established by three successive readings of water level taken at an interval of two hours.

2.1.2 In case any variation in the groundwater level is observed in any specific boreholes,

then the water level in these I boreholes shall be recorded daily during the course of the field investigation. Levels in nearby wells, streams, etc., if any, shall also be noted whenever these readings are taken.

2.1.3 Sub-soil Water Samples

a) Sub-soil water samples shall be collected for carrying out chemical analysis thereon. Representative samples of groundwater shall be collected when it is first encountered in bore holes before the addition of water to aid boring or drilling.

b) Chemical analysis of water samples shall include determination of pH value; turbidity, sulphate, carbonate, nitrate and chloride contents; presence of organic matter and suspended solids. Chemical preservatives maybe added to the sample for cases as specified in'the test method/IS codes. This shall only be done if analysis cannot be conducted within an hour of collection and shall have the prior written permission and approval of the Engineer.

2.2

Electrical Resistivity Test

Back to contents page

This test shall be conducted to determine the Electrical resistivity of soil required for designing safety grounding system for the entire switch yard area. The specifications for the equipments and other accessories required for performing electrical resistivity test, the test procedure, and reporting of field observations shall conform to 1S:3043. The test shall be conducted using Wanner's four electrode method as specified in 1S:1892,Appendix-B2.Unlessotherwisespecified, at each test location, the test shall be conducted along two perpendicular lines parallel to the coordinate axes. On each line a minimum of 8 to 10 readings shall be taken by changing the spacing of the electrodes from an initial small value of 0.5m upto a distance of 10.0m.

2.3Field Investigation Rock

Back to contents page

2.3.1 Rock Drilling

a) Boring shall be continued in large hard fragments or natural rock beds like but not limited to igneous, sedimentary and metamorphic formations. The equipments, method and the procedure for drilling

operation shall conform to IS:1892. The starting depth of drilling in rock shall be certified by the Engineer. The portion drilled in rock shall be backfilled with cement and sand (1:3) grout.

b) Drilling shall be carried out with NX size tungston carbide (TC) or diamond tipped drill bits depending on the type of rock and as per IS:6926. Suitable type of drill bit (TC/Diamond) and core catchers shall be used to ensure continuous and good core recovery. Core barrels and core catchers shall be used for breaking off the core and retaining i t when the rods are withdrawn. Double tube core barrels shall be used to ensure better core recovery and to pick up cores from layers of bed rock. Water shall be circulated continuously down the hollow rods and the sludge conveying the rock cuttings to the surface shall be collected. A very high recovery ratio shall be aimed at in order to get a satisfactory undisturbed sample. Core of minimum 1.5m length shall be aimed at. Normally TC bit shall be used. Change over to a diamond bit shall require the specific written approval of the Engineer and his decision whether a TC or a diamond bit is to be used shall be final and binding on the Contractor.

c) No drilling run shall exceed 1.5m in length. If the core recovery is less than 80% in any run the length of the subsequent run shall be reduced to 0.75m. During drilling operations observations on return water, rate of penetration, etc., shall be made and recorded as per IS:5313.

i) The colour of return water at regular intervals, the depth at which any change of colour of return water is observed, the

depth of occurrence and amount of flow of hot water, if encountered, shall be recorded.

ii) The depth through which a uniform rate of penetration was maintained, the depth at which marked change in rate of penetration or sudden fall of drill rod occurs the depth at which any blockage of drill bit causing core loss, if any, shall be recorded.

iii) Any heavy vibration or torque noticed during drilling should be recorded together with the depth of occurrence.

iv) Special conditions like the depth at which grouting was done during drilling fluid, observation of gas discharge with return water etc., shall also be observed and recorded.

v) All the observations and other details shall be recorded as a daily drill and reported in a proforma as given in IS:5313. d) Core samples shall be extracted by the application of a continuous

pressure at one end of the core with the barrel held horizontally without vibration. Friable cores shall be extracted from the barrel directly into a suitable sized half round plastic channel section. Care shall be taken to maintain the direction of extrusion of sample same as while coring to avoid stress reversal.

e) Immediately after withdrawl from the core barrel, the cores shall be placed in a tray and transferred to boxes specially prepared for the purpose. The boxes shall be made from seasoned timber or any other durable material and shall be indexed on top of the lid as per IS : 4078. The cores shall be numbered serially and arranged in the boxes in a

sequential order. The description of the core samples shall be recorded as per IS : 4464. Where no core is recovered, it shall be recorded as specified in the standard. Continuous record of core recovery and RQD to be mentioned in the corelog as per IS : 11315 Part-II.

2.3.2 Permeability Test

Permeability Test shall be conducted in bedrock inside the drilled holes by pumping in water under pressure to determine the percolation capacity of the rock strata. This test shall be conducted in uncased and ungrouted sections of the drill hole and the use of bentonite slurry during drilling is strictly prohibited when this test has to be conducted.

Clear and clean water shall be used for the purpose of both drilling and testing. The equipments required and the procedure to be followed for conducting the test shall conform to IS : 5529, Part-II. The length of the test section shall be either 1.5m or 3.0 m as per field conditions and the directions of the Engineer. The level of water table, if any, in the drill hole shall be recorded and the drill hole shall be cleaned before beginning the test. Depending upon the depth of the test section, single packer or double packer method shall be adopted. Care shall be taken to see that all joints and connections are watertight during the test.

a) Single Packer Method

This method shall be adopted when the bottom elevation of the test section is the same as the bottom of the drill hole and where it is considered necessary to know the permeability values during drilling itself. This test shall be useful where the full length of the hoe cannot stand uncased or ungrouted. The packer shall be fixed at the top level

of test section such that only the test section lies below the packer. Water shall then be pumped through a pipe into the test section under a particular pressure and maintaining it till a constant quantity of water intake is observed. The amount of water percolating through the hole shall be recorded at every 5 mm intervals. The test shall be repeated by increasing the pressure at regular intervals upto a pressure limit as specified in IS : 5529, Part-II. The details and observations during the test shall be suitably recorded in a proforma recommended in IS : 5529, Part-II, Appendix-B.

b) Double Packer Method

This method shall be used when the permeability of an isolated section inside a drill hole has to be determined. Packers shall be fixed both at the top and bottom of the test section such that their spacing is exactly equal to the length of the test section.

2.4Laboratory Testing

Back to contents page

2.4.1 Essential Requirements

a) Depending on the type of sub strata encountered, appropriate laboratory tests shall be conducted on soil and rock samples collected in the field. Laboratory tests shall be scheduled and performed by qualified and experienced personnel who are thoroughly conversant with the work. Tests indicated in the schedule of items shall be performed on soil, water and rock samples as per relevant IS: codes. One copy of all the laboratory test data records shall be submitted to the Powergrid progressively every week. Laboratory tests shall be carried out concurrently with field investigation

since initial laboratory test results could be useful in planning the later stages of fieldwork. A schedule of laboratory tests shall be established by the Contractor to the satisfaction of the Engineer within one week of completion of the first borehole.

b) Laboratory tests shall be conducted using approved apparatus comply in with the requirements and specifications of/'Indian Standards or other approved standards for this class of work. It shall be checked that the apparatus are in good working condition before starting the laboratory tests./Calibration of all the instruments and their accessories shall be done carefully and precisely. The tests shall be conducted at an approved laboratory.

c) All samples, whether undisturbed or disturbed, shall be extracted, prepared and examined by competent personnel properly trained and experienced in soil sampling, examination, testing and in using the apparatus as per the specified standards.

d) Undisturbed soil samples retained in lines or seamless tube /samplers shall be taken out without causing any disturbance to the samples using suitably designed extruders just prior to actual testing. If the extruder is horizontal, proper support shall be provided to prevent the sample from breaking. For screw type extruders, the pushing head shall be free from the screw shaft so that no torque is app11ed to the soil sample in contact with the pushing head. For soft clay samples, the sample tube shall be cut by mean of a high speed hacksaw to proper test length and placed over the mould before pushing the sample into it with a suitable piston.

e) While extracting a sample from a liner or tube, care shall be taken to see that its direction of movement is the same as that during sampling to avoid stress reversal.

2.4.2 Tests

Tests as indicated in this specification and as called for by the Engineer shall be conducted. These tests shall include but not be limited to the following. a) Tests on Undisturbed and Disturbed Samples

- Visual and Engineering Classification - Sieve Analysis and Hydrometer Analysis - Liquid, Plastic and Shrinkage Limits - Specific Gravity

- Chemical Analysis

- Swell Pressure and Free Swell index determination - Proctor Compaction test

- California Bearing Ratio b) Tests on Undisturbed Samples

- Bulk Density and Moisture Content

- Relative Density (for sand)

- Unconfined Compression Test - Box Shear Test (in case of sand)

- Triaxial Shear Tests: (depending on the type of soil and field conditions on undisturbed or remoulded samples )

i) Unconsolidated undrained,

ii) Consolidated Undrained Test with the Measurement of Pore Water Pressure.

iii) Consolidated Drained.

- Consolidation

c) Tests on Rock Samples - Visual Classification

- Moisture Content, Porosity and Density Specific Gravity Hardness - Slake durability

- Unconfined Compression test (both saturated and at insitu water content ) -Point load strength index

- Deformability test (both saturated and dry, samples) d) Chemical Analysis of Sub soil water

2.4.3 Salient Test Requirements

a) Remoulded soil specimen, whenever desired, shall be fully reworked at field density and moisture content . For conducting CBR test and triaxial test for dyke and road material the sample shall be remoulded to 95% of standard proctor density.

b) Triaxial shear test shall be conducted on undisturbed soil samples, saturated by the application of back pressure. Only if the water table is at sufficient depth so that chances of its rising to the base of the footing are meagre or nil, the triaxial tests shall be performed on specimens at natural moisture content. Each test shall be carried out on a set of three test specimens from one sample at cell pressures equal to 100, 200 and 300 KN/sq.m. or as required depending on the soil conditions .

c) Effective stress triaxial shear test could be either consolidated drained or consolidated undrained with pore water pressure measurement. The test shall be conducted at cell pressure of 100,200 and 300 KN/ sqm.

increased in stages of 50 KN/sqm. ensuring complete consolidation at each stage.

d) Direct shear test shall be conducted on undisturbed soil samples. The three normal vertical stresses for each test shall be l00, 200 and 300 KN/sq.m. or as required as per the soil conditions .

e) Consolidation test shall have loading stages of 10, 25,50,75,100,200, 400and800KN/Sq.m. Rebound curve shall be recorded for all the samples by unloading the specimen at the in-situ stress of the specimen. Additional rebound curves shall also be recorded whenever desired by the Engineer.

f) Chemical analysis of sub-soil shall include determination of pH value; carbonate, sulphate (both SO3andSO4) , chloride and nitrate contents; organic matter; salinity and any other chemical harmful. to the foundation material. The contents in soils shall be indicated as percentage ( % ) .

g) Chemical analysis of sub-soil water sample shall include the determination of the properties such as colour, odour, turbidity, pH value and specific conductivity both at 25 deg.C and chemical contents such as Carborates, Surphates(both SO3 and SO4), Chlorides, Nitratesm Organic matter and any

other chemical harmful to the founmdation material. The contents such as Sulphates, etc. shall be indicted as ppm by weight.

h) The lab CBR test shall be performed on undisturbed and remoulded sample for soaked and unsoaked condition.

2.5Report

2.5.1 General

a) On completion of all the field and laboratory work, the Contractor shall submit a formal report containing Geological information of the region, procedure adopted for investigation, field observations, summarised test data, conclusion and recommendations. The report shall include detailed borelogs, subsoil sections, field test results, laboratory observations and test results both in tabular as well as graphical form, practical and theoritical considerations for the interpretation of test results, the supporting calculations for the conclusions drawn, etc. Initially, the Contractor shall submit three copies of the report in draft from for the Owner's review.

b) The Contractor's qualified Geotechnical engineer shall visit the Owners Corporate office for a detailed discussion on the Owners comments on his draft report. During the discussions, it shall be decided as to the modifications that need to be done in the draft report. Thereafter the Contractor shall incorporate in his report the agreed modifications and after get ting the amended draft report approved, ten copies of the detailed final report shall be submitted alongwith one set of reproducibles of the graphs, tables, etc .

c) The detailed final report based on field observations, in-situ and laboratory tests shall encompass theoretical as well as practical considerations for foundations for different types of structures envisaged in the area under investigation. The Contractor shall acquaint himself about the type of structures, foundation loads and other information required from the Engineer.

2.5.2 Data to be Furnished

The report shall also include but not be limited to the following :

a) A plot plan showing the locations and reduced levels of all field tests e.g. boreholes, trial pits, static cone penetration tests, dynamic cone penetration tests, plate load tests 1 etc. properly drawn to scale and dimensioned with reference to the established grid lines.

b) A true cross section of all individual boreholes and trial pits with reduced levels and coordinates shown in the classification and thickness of individual stratum, position of ground water table, various in-situ tests conducted and samples collected at different depths and the rock stratum, if met with.

c) A set of longitudinal and transverse soil/rock profiles connecting various boreholes in order to give a clear picture of the variation of the subsoil strata as per IS:6065.

d) Geological information of the area such as geomorphology, geological structure, lithology, stratigraphy and tectonics, core recovery and rock quality designation, etc.

e) Past observations and historical data, if available, for the area or for other areas with similar soil profile or with similar structures in the surrounding areas.

f) Plot of Standard Penetration Test (N values both uncorrected and corrected) with depth for identified areas.

g) Results of all laboratory tests summarised (i) for each sample (as per Table-I) as well as (ii) for each layer along with all the relevant charts,

tables, graphs, figures, supporting calculations, conclusitions and photographs of representative rock cores.

h) For all triaxial shear tests stress vs strain diagrams as well as Mohr’ s circle envelopes shall be furnished. If back pressure is applied for saturation, the magnitude of the same shall b~ indicated. The value of modulus of elasticity, E shall be furnished for all tests alongwith relevant calculations.

i) For all consolidation tests, the following curves shall be furnished : e vs log p

e vs p and

Compression vs log t or

Compression vs square root of t (depending upon the shape of the plot for proper determination of co-efficient of consolidation).

The point showing the initial condition (eo, po) of the soil shall be marked on the curves.

j) The procedure adopted for calculating the compression index from the field curve and settlement of soil strata shall be clearly specified. The time required for 50% and 90% primary consolidation alongwith secondary settlements, if significant, shall also be calculated.

k) For pressuremeter tests, the following curves shall be furnished : Field pressure meter, creep and air calibration curves indicating Po' Pf and Pi.

Corrected pressure meter and creep curves indicating Po, Pf', Pi alongwith calculation for the corrections.

l) From the pressure-meter test results the values of cohesion, angle of internal friction, pressuremeter modulus, shear modulus and coefficient of subgrade reaction shall be furnished alongwith sample calculation. Calculation for allowable bearing pressures and corresponding total settlements, for shallow foundations and capacity calculation of piles in various modes shall also be included.

2.5.3 Recommendations

Recommendations shall be given area wise duly considering the type of soil, structure and foundation in the area. The recommendations shall include but not be limited to the following :

a ) Type of foundations to .adopt for various structures, duly considering the sub soil characteristics, water table, total settlements permissible for structures and equipments. Minimum depth and width of foundation shall also be recommended. The provision in relevant IS: Codes indicated in clause 4.0 shall be considered.

b) For shallow foundations the following shall be indicated with comprehensive supporting calculations.

i) Net safe allowable bearing pressure for isolated square footings and continuous strip footings of sizes 2.0,3.0 and 4.0m at three different founding depths of 1.0, 2. 0 and 4.0m below ground level considering both shear failure and settlement criteria, giving reasons for type of shear failure adopted in the calculation.

ii) Net safe allowable bearing pressure for raft foundations of widths greater than 6m at 2.0m , 3.0m and 4.0m below ground level considering both shear failure and settlement criteria. iii) rate and magnitude of settlement expected of the structure. iv) Net safe bearing capacity for foundation sizes mentioned above,

modulus of subgrade reaction, modulus of elasticity from plate load test results alongwith time settlement curves and load settlement curve in both natural and log graph, variation of Modulus of subgrade reaction with size, shape and depth of foundation.

c) If piling is envisaged, the following shall be indicated with comprehensive supporting calculations:

i) Type of pile and reasons for recommending the same duly considering the soil characteristics.

ii) Suitable founding strata for the pile.

iii) Estimated length of pile for 500 KN (400 mm dia), 750 KN (450 mm dia), 1000 KN (500 mm dia) and 4500 KN (1070 mm dia) capacities. End bearing and frictional resistance shall be indicated separately. iv) Magnitude of negative skin friction, if any, to be

considered in pile design.

2.5.4 Additional Recommendations

a) Coefficient of permeability of various sub soil and rock strata based on in-situ permeability tests.

b) Cone resistance, frictional resistance, total resistance, relation between cone resistance and Standard Penetration Test N Value, and settlement analysis for different sizes of foundation as specified based on static cone penetration test.

c) Electrical resistivity of sub-soil based electrical resistivity tests including electrode spacing vs cumulative resistivity curve.

d) Suitability of the soil for construction of roads and pavements, their stable slopes for shallow and deep excavations, active and passive earth pressures at rest and modulus of elasticity as a function of depth for the design of underground structures.

e) Suitability of locally available soils at site for filling and back filling purposes.

f) If expansive soil is met with, recommendation on removal or retainment of the same under the foundation etc. shall be given. In the latter case, detailed specifications of any special treatment required including specifications for materials to be used, construction method, equipments to be deployed, etc. shall be furnished.

g) Protective measures based on chemical nature of soil and ground water with due regard to potential deleterious effects on concrete, steel and other building materials, etc. Remedial measures for sulphate attack and acidity shall be dealt in detail. Susceptibility of soil to termite action and remedial measures for the same.

h) Susceptibility of sub soil strata to liquifaction in the event of earthquake. If so, recommendation for remedial measures.

i ) Any other information of special significance like dewatering schemes, etc. which may have a bearing on the design and construction ,

j) Recommendations for additional soil investigation beyond the scope of the present work if the Contractor considers such investigation is necessary.

2.6

Rates and Measurements

Back to contents page

The clauses below shall apply for item rate contracts only. They shall not be applicable to turn key and lumpsum contracts, except for work beyond the scope of such contracts.

2.6.1 Rates

a) The item of work in the Schedule of Quantities describes the work very briefly. The various items of the Schedule of Quantities shall be read in conjunction with the corresponding sections in the technical specifications including amendments and additions, if any. For each item in the Schedule of Quantities, the bidder's rates shall include for the activities covered in the description of the item as well as for all necessary operations in details described in this technical specification. b) The unit rates quoted shall include minor details which are obviously

and fairly intended, and which may not have been included in these documents but are essential for the satisfactory completion of the work. c) The bidders quoted rates shall be inclusive of providing all plant equipments, men, materials, skilled and unskilled labour; making observations establishing the ground level and coordinates at location of each borehole, test pit, etc. by carrying levels from one established

bench mark and distances from one set of grid lines furnished by the Owner. Also, no extra payments shall be made for conducting the Standard Penetration Test; collecting, packing, transporting of all samples and cores; recording of all results and submitting them in approved formats.

d) No claims shall be entertained if the details are shown on the released for construction drawings differ in any way (e.g .location and depth for tests, number of tests, etc.) from those shown on the tender drawings.

2.6.2 Measurements

a) All measurements shall be in SI Units.

b) Lengths shall be measured in meters (m) correct to two places of decimals. Areas shall be worked out in square meters (m2) and volume in cubic meters and which may not have been included in these documents but are essential for the satisfactory completion of the work. c) The bidders quoted rates shall be inclusive of providing all plant equipments, men, materials, skilled and unskilled labour; making observations establishing the ground level and coordinates at location of each borehole, test pit, etc. by carrying levels from one established bench mark and distances from one set of grid lines furnished by the Owner. Also, no extra payments shall be made for conducting the Standard Penetration Test; collecting, packing, transporting of all samples and cores; recording of all results and submitting them in approved formats.

d) No claims shall be entertained if the details are shown on the released for construction drawings differ in any way (e.g. location and depth for tests, number of tests, etc.) from those shown on the tender drawings.

2.6.2 Measurements

a ) All measurements shall be in SI Units

b) Lengths shall be measured in meters (m) correct to two places of decimals. Areas shall be worked out in square meters (m2) and volume in cubic meters (m3), rounded off to two decimals.

c) Certain tests have to be conducted in bore holes, trial pits, etc. Such boreholes, trial pits, etc., shall be measured only once and not again just because of a tests are conducted therein.

2.7

Specific Requirements for Geotechnica1 investigation at River Crossings

Back to contents page

The entire soil investigation work shall be carried ~ out in accordance with the relevant parts of the specification for geotechnical investigation. Standard Penetration test at River Crossings and special locations shall be carried out at the interval of 2.0, 3.0, 5.0, 7.0, 10.0 and thereafter at the rate of 3m intervals to 40m. However in each bore holes undisturbed samples shall be collected at every change of strata and at depths as follows: 1.0m, 4.0m, 7.0m, 11.0m and thereafter at the rate of 3m intervals up to 38m. The spacing between the top levels of undisturbed sampling and standard, penetration testing shall not be less than 1.0m. The boreholes shall generally be executed to, specified depth as per specifications or as shown in the drawing. If refusal strata is reached (i.e. SPT-N Value is greater than 100 continuously for 5m depth) the borehole may be terminated at shallower depth i.e. at 5m in refusal strata.

2.8 Summary of Results of Laboratory Tests on Soil and Water Samples B O R E H O L E/ T RI A L PI T N O. D E P T H ( m ) T Y P E O F S A M P L E DENSITY (KN/Cu.m.) Bulk Dry W A T E R C O N T E N T ( % )

PARTICLE SIZE (%) CONSISTANCY PROPERTIES

SOIL

GRAVEL SAND SILT CLAY L.L. P.L. P.I. CLA SSIF ICA TIO N – IS D E S C R I P T I O N S P E C I F I C G R A V I T Y Notations :

I. For type of sample II. For Strength Test

DB Disturbed Bulk Soil sample PMT Pressuremeter Test

DP Disturbed SPT soil sample SCPT Static Cone Penetration Test DS Disturbed Samples from cutting edge UCC Unconfined Compression Test

Of Undisturbed soil sample VST Vane Shear Test

RM Remoulded soil sample Tuu Unconsolidated Undrained Triaxial Test UB Undisturbed soil sample Tcu Consolidated Undrained

US Undisturbed Soil Sample by Sampler Triaxial Test with Pore Pressure W Water Sample Ted Consolidated Drained Triaxial Test

STRENGTH TEST CONSOLIDATION TEST TYPE C  ec pc Cc P mv Cv S H RI N K A G E LI M IT ( %)

SWELL TEST COMPACTION TEST S. Pr F S M.D.D. O.M.C. C.B.R. R E L A T I V E D E N SI T Y ( % ) P E R M E A B I L I T Y ( m / h o u r ) R E M A R K S

III. For Others Cv Coefficient of consolidation (sq.m./hr) LL Liquid Limit (%) MDD Maximum Dry Density (KN/Cu.m.) PL Plastic Limit (%) OMC Optimum Moisture Content (%) PI Plasticity Index (%) CBR California Bearing Ratio (%) C Cohesion (KN/Sq.m.) IV. For Chemical Test

 Angle of Internal friction (degrees)

S. Pr. Swelling Pressure (KN/Sq.m.) pH pH value FSI Free Swell Index (%) Cl Chlorine Content ec Initial Void Ratio SO3 Sulphate Content

Pf Preconsolidation Pressure (KN/Sq.m.) NO4 Nitrate Content

Cc Compression Index CO3 Carbonate Content P Pressure range (KN/Sq.m.)

2.9 Tools and Plants for Soil Investigations.

Back to contents page

A. Sampling, S.P.T.

i) Tripod

ii) Shell and Augar

iii) Augar and wash boring

iv) Pump

v) Casing

vi) Chaintong vii) Drill rod viii) Pipes

ix) Monkey weight (For S.P.T.)

x) Winch (Man/Mechanically operated) xi) Cathead

xii) Sockets xiii) Samples

a) Open drive thin wall sampler b) Tube Sampler

c) Split Spoon Sampler

d) Piston sampler (Bishop Sampler) xiv) Polythin Packet

B. Other Test Apparatus

i) Vane Shear (4 blade vane)

iii) Static cone (apex angle 60 Deg. & bore diameter 35.7 mm)

C. Pressure Meter Test

i) Menard Pressuremeter

D. Rock Drilling

i) Rotary drilling Machine with supporting equipments

a) Casing

b) Drilled c) Core Barrel

d) Drilling bid (T. C bit/Diamond bit)

E. Resistivity Test i) Meggar Test F. Other Equipments i) Power Winch ii) Pulley iii) Chain iv) Buckets

v) Tents, water drums, camping cots, tables, chairs & petrox.

G. Transport Requirement

i) Motor Cycle ii) Jeep

H. Safety Equipments

i) Safety Helmets ii) First Aix Box iii) Hand Gloves iv) Shoes

NOTE :

a) The quantities and capacities of the equipments will depend upon the nos. of bore hole, depth of the bore hole and completion schedule.

b) Additional equipments may be required depending upon site conditions.

3.0

Guidelines for Conducting Soil Investigation in Transmission Line

Back to contents page

Provision is made in Tower Package Specification for conducting soil investigation at various tower locations. However, it was observed in past that there were doubts about the selection of locations for conducting soil investigation. In view of the above to facilitate the procedure, the locations where the soil investigation is to be conducted are described below :

The soil investigation is to be conducted at the following locations :

1. Fissured rock is encountered with sub-soil water within 1.5 meter depth from ground level.

2. Hard rock in combination with sub-soil water within 1.5 meter depth from ground level.

3. Fissured rock in combination with water is encountered at the bottom of the pit with black cotton soil at top.

4. Hard rock is encountered at the bottom with water and black cotton soil at top.

5. Dry pure sand encountered in the pit.

6. Predominantly silty sand mixed with clay or other soils (without sub-soil water).

8. Predominantly silty sand mixed with clay or othersoils encountered with sub-soil waters.

9. Pure clay encountered with sub-soil water. 10. If soil considered bad/trencherous.

11. At the locations falling in back waters of a tank or reservoirs where there will be stagnation of water.

12. River crossing locations.

13. Tower used with 18M/25M extensions for power line crossings. 14. Railway crossings.

Soil investigation may be done at the locations mentioned above. It is not required to be done at the locations wherever soil could be easily classified and one of standard approved types of foundations could be adopted.

SECTION-II

Tower Foundation

CHAPTER-1

General

___________________________________________________________________________

CHAPTER ONE

___________________________________________________________________________

GENERAL Back to contents page

1.0 Tower Foundations

Back to contents page

The tower foundations cost approx. 10 to 30 percent of overall cost of tower, or 5 to 15 percent of the cost of transmission lines, depending on the type of soil.

Experience shows that while an inadequate foundation may lead to collapse of tower, an over design may prove very uneconomical. It is a good practice to check the tower for permissible deflection at the top. Since differential foundation settlement also causes tower deflection at the top, and if the total deflection at the top of the tower is to be restricted, the permissible deflection has to be carefully apportioned between the structure deflection and that caused by the differential foundation settlement.

The design of a safe and economical foundation is based on soil properties, knowledge of soil structure interaction and settlement analysis of tower foundation.

1.1 Loads, Safety Factors and Settlement

Back to contents page