Draft For Comment Only
Doc. WRD 05(455 ) July 2006
BUREAU OF INDIAN STANDARDS Draft Indian Standard SUBSURFACE EXPLORATION FOR CANALS AND CROSS DRAINAGE WORKS – CODE OF PRACTICE (First Revision) (Not to be reproduced without the permission of BIS or used as a STANDARD)
Last date for receipt of comments is 30-9-06
FOREWORD (Formal clauses will be added later) This Indian Standard was published in 1985. The present revision is proposed to reflect the experience gained on the subject since then. In India, canal systems have been constructed since historic times. With the improvement of the techniques of construction of canals and cross drainage structures, the necessity of detailed soil investigations are felt, before taking up the actual construction. To prevent loss of valuable water through the canal bed and banks passing through alluvial or fissury reaches, costly protection works, such as lining, etc, have to be provided. Reaches are to be avoided where damages can occur to the surrounding cultivated lands, due to water logging. Canal embankments often get breached and flood vast areas if not properly designed. Therefore, adequate subsurface exploration is needed before the canal system is designed and constructed. Similarly, to construct a big aqueduct or syphon across a canal, detailed foundation investigations are required, for the safety of these structures. Subsurface explorations, therefore, form a very important part in the planning and designing of canals and cross drainage structures. The term subsurface exploration as used herein covers all types of exploration connected with determination of the nature and extent of the soil and/or rock along the alignment of the proposed canal and its distributaries and also the foundation condition at the sites of the proposed cross drainage structures. It is not possible to lay down the required extent of exploration to cover all types of cases. The standard provides guidelines for planning the exploratory works through various stages of the project development. These recommendations may have to be modified for individual cases, depending upon the site conditions and other characteristics peculiar to each of them.
Draft Indian Standard SUBSURFACE EXPLORATION FOR CANALS AND CROSS DRAINAGE WORKS – CODE OF PRACTICE (First Revision)
1. SCOPE 1.1 This standard provides guidance on the type, extent and details of subsurface explorations needed in connection with the following items of work : a) Canals - Stability of banks and bed in: i) cutting, and ii) filling. b) Canals - Water loss due to seepage and water logging in the command area. c) Canals - Selection of lining with reference to the characteristics of bed material, permeability, subsoil water table and salinity. d) Cross drainage structures - Design and construction of the foundation for head regulators, cross-regulators syphons, aqueducts, level crossings and bridges. e) Borrow area investigations for the suitability of material to be used for canal embankments and necessary compaction procedure.
2. REFERENCES 2.1 The Indian Standards listed in Annex A contain provisions which through reference in this text constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision and parties to agreements based on these standards are encouraged to investigate the possibility of applying the most recent editions of the standards indicated as under: IS No. IS 1498:1970 IS 1892:1979 IS 2131:1981 IS 2720(Part 1):1983 IS 2720(Part 2):1973 IS 2720(Part 5):1985 IS 2720(Part 7):1980 IS 2720(Part 13):1986
Title Classification and identification of soils for general engineering purposes (first revision) Code of practice for subsurface investigations for foundations (first revision) Method for standard penetration test for soils (first revision) Method test for soils – Part 1 : Preparation of dry soil samples for various tests (second revision) Method test for soils – Part : 2 Determination of water content (second revision) Method test for soils – Part : 5 Determination of liquid and plastic limit (second revision) Method test for soils – Part : 7 Determination of water contentdry density relation using light compaction (second revision) Method test for soils – Part : 13 Direct shear test (second
IS 2720(Part 14):1983 IS 2720(Part 21):1977 IS 2720(Part 28):1974 IS 4434:1978 IS 4453:1980 IS 4464:1985 IS 4968(Part 1):1976 IS 4968(Part 2):1976 IS 4968(Part 3):1976 IS 5529(Part 1):1985 IS 5529(Part 2):1985 IS 6403:1981 IS 6065(Part 1):1985
IS 6926:1996 IS 7422(Part 1):1974
revision) Method test for soils – Part : 14 Determination of density index (relative density) of cohesionless soils (first revision) Method test for soils – Part : 21 Determination of total soluble solids (first revision) Method test for soils – Part : 28 Determination of dry density of soils inplace, by the sand replacement method (first revision) Code of practice for in-situ vane shear test for soils (first revision) Code of practice for subsurface exploration by pits, trenches, drifts and shafts (first revision) Code of practice for presentation of drilling information and core description in foundation investigation (first revision) Method for subsurface sounding for soils: Part 1 dynamic method using 50 mm cone without betonity slurry (first revision) Method for subsurface sounding for soils – Part 2 : Dynamic method using cone and bentonite slurry (first revision) Method for subsurface sounding for soils – Part 3: Static one penetration test (first revision) Code of practice or in-situ permeability test: Part 1 Test in overburden (first revision) Code of practice for in-situ permeability tests : Part 2 Tests in bedrock (first revision) Code of practice for determination of bearing capacity of shallow foundations (first revision) Recommendations for the preparation of geological and geotechnical maps for river valley project: Part 1 Scales (first revision) Diamond core drilling – Site investigation for river valley projects – Code of practice (first revision) Symbols and abbreviations for use in geological maps, sections and subsurface exploratory logs : Part 1 Abbreviations
3. GENERAL CONDITIONS 3.1 The type and extent of exploration should be commensurate with the size and importance of the project and will depend upon the size of canal system or the cross drainage structure. This should be neither too little, resulting in inadequate data, nor too much, resulting in excessive cost and time . 3.2 Subsurface explorations in connection with a canal would cover suitable alternative alignments for the main canal and its distributaries and will be carried out to a specified depth, preferably up to a few metres below the proposed bed of the canal. In case of cross drainage structures, the exploration should cover also, the alternative suitable sites and up to the critical depth below the proposed bottom of the foundation. A complete programme of exploration should be able to give information regarding the following aspects: a) Canals and distributaries:
i) Shearing properties, that is, cohesion and angle of internal friction of the bed and bank material; ii) In situ moisture content and density of the bank and bed: material; iii) Seepage characteristics or permeability of bed and bank material; iv) Chemical test on ground water; v) Ground water table, both in dry and monsoon season, along the alignment; and vi) Grain size distribution of the material at the bed for calculating the critical velocity and rugosity of the canal. b) Cross drainage structures: i) Cohesion, angle of internal friction and density of the material up to critical depth below the proposed foundation level; ii) Bearing capacity of the soil or rock at the proposed foundation level; iii) Ground water table at the site of the proposed structures; iv) Possibility of liquefaction, if any, of the sandy material in foundation, under seismic condition; and v) Silt factor for assessing scour depth. 4. STAGES OF EXPLORATION 4.1 The extent of foundation exploration required for a canal or a cross drainage structure of given size varies greatly from site to site, depending on the Subsurface conditions and cannot be adequately visualized in advance. The exploration generally proceeds in stages, the details of each stage growing out of the one before. 4.2 Explorations can be, however, generally sub-divided into four stages as given in 4.2.1 to 4.2.4. 4.2.1 Reconnaissance or Prefeasibility Stage This shall comprise of selection of suitable alternative alignments of the canal and suitable alternative sites for the cross drainage works on the basis of regional and local geology, relative impermeability of the area, economy of excavation and filling and foundation conditions. The geophysical methods for investigations during the reconnaissance stage may be deployed to assess the thickness of overburden and bedrock configuration on various alternatives under consideration. The investigations in this stage will consist of a general field inspection by a qualified engineering geologist and an engineer, for assessment of the overall aspects of feasibility, economy and safety. On the basis of information gathered at this stage and evaluations made about the expected seepage in the canal, cost of excavation and filling, type and cost of foundation of cross drainage structures, etc, planning of the detail field work will be made. 4.2.2 Preliminary Investigation or Feasibility Stage 188.8.131.52 Objectives and types and methods of exploration
During this stage, certain essential data regarding the canal and cross drainage structures would be collected. The coverage of exploration should be adequate for examination of the feasibility, which includes estimation of the cost, expected seepage losses in the canal and stabilityof canal banks and cross drainage structures. This stage would also include studies for preliminary choice of the canal alignment, selection of the type of lining and the choice of the type and depth of foundation for the cross drainage structures. The stage of exploration will include the following methods: a) Exploration by test pits; b) Exploration by augering/drilling; c) Determination of the depth of water table, evaluation of field permeability and determination of salinity of the ground; d) Field penetration and field density tests at the sites of the foundation of the cross drainage structures and along the alignment of the canal; and e) Laboratory tests on the disturbed and undisturbed samples for the determination of engineering properties of the canal bed and bank material, borrow materials for embankment and proposed foundation material of the cross drainage structures. 184.108.40.206 Choice of methods Normally, for, canals and cross drainage structures of moderate size, exploration by trial pits and drill or auger holes would be sufficient. Some field tests of permeability and penetration would also be necessary. 220.127.116.11 Spacing For canals, exploration by pits at a spacing of 500 m depending upon the nature of the soil may be necessary. However, wherever there is an apparent change of characteristics, the pits may be dug at even 200 m to 300 m spacing or closer if required. Under the major cross drainage structures the holes or pits should be selected at specific points, where the proposed piers, wells and abutments are to be rested. 18.104.22.168 Location Explorative holes and pits should follow the central line of the proposed canal alignment and also the axis of the cross drainage structures. 22.214.171.124 Depth of exploration a) In case of canals, exploration should reach at least 3 m below the proposed bed of the canal. If the canal is to be in a rocky reach, this depth may be reduced at the discretion of the Engineer-in-Charge. If the strata appears to be changing, the depth of exploration should go up to an extent of canal depth below the bed level. b) In case of cross drainage structures, the depth of the holes or pits should be up to the bottom of the expected bulb of pressure under the abutments or the piers or down to the hard firm strata or rock, if available. In case of well
foundations, however, the depth of exploration should reach the stable strata, which can support the foundation safely.
4.2.3 Detailed Investigation or Detailed Project Report(DPR) Stage 126.96.36.199 In this stage of investigation, the data required for detailed design and preparation of construction drawings should be collected. Close coordination is essential between work of the organizations for exploration, geology design and construction. The design engineer and the geologist should be closely associated with the exploration and they should be required to prepare an outline of the scope and extent of exploration. 188.8.131.52 Investigations at this stage would comprise the following: a) Intensive exploration for specific difficult reaches of the canal, where the banks need special protection against land slides, breaches, water logging, seepage, etc. b) Additional drillings of the foundation of the cross drainage structures, to determine the actual condition of the foundation of each and every component of the structures. The possibility of high submergence, sudden drawdown of the embankments, seismic effects, etc, have to be kept in mind at this stage. c) Ascertaining the relative merits and demerits between the open foundation and well, raft or pile foundation under the piers and abutments special field shear tests may be used wherever necessary. d) Compaction methods to be determined for canals in filling, from the reach by reach borrow material testing. 184.108.40.206 The engineer-in-charge should be consulted to get an idea of the type of foundation that was likely to be provided at a later stage and accordingly the depth of exploration should be fixed. 4.2.4 Construction Stage Construction stage exploration should aim at making available data generally, for the evolution of specific foundation problems and preparation of the foundation after excavation and special precautions to be taken along the canal as and when the project is under actual execution. 5. METHODS OF EXPLORATION 5.1 The following categories of methods may be used for subsurface exploration for canals and cross drainage works:
a) Trial pits, b) Borings ( auger boring and core drilling ), c) Field tests in situ, and d) Geophysical methods.
6. EXPLORATION BY PITS 6.1 Shallow or deep trial pits may be used, according to the size of the canal, to investigate the engineering properties of the material, salinity of the ground, water table, seepage rate, etc, along the canal alignment. Similar investigation may be performed at the proposed foundation of the cross drainage structures of minor nature. 6.2 At the surface near the pit, the excavated material shall be placed in an orderly manner around the pit and marked stakes shall be driven to indicate depth of pit from which the material is removed, in order to facilitate logging and sampling. 6.3 The level of the water table and the level, location and rate of seepage flow in the test pit should be recorded date wise. 7. EXPLORATION BY BORINGS 7.1 Borings provide the simplest method of subsurface investigation and sampling. They may be used to indicate the subsurface strata and to collect samples from each of the strata. 7.2 Borings may be made by several methods depending upon the importance of the work and on the nature of the sub-soil strata. They are as below :
For Soils i) Post hole auger ii) Shell and auger boring ( see IS : 1892) iii) Wash boring ( see IS: 1892) iv) Rotary drilling ( see IS : 1892) 7.3
For Rocks i) Bore drilling ( see IS : 6926) ii) Short drilling ( see IS: 1892 )
7.3.1 Post Hole Auger Hand operated post hole augers 100 mm to 300 mm in diameter may be used for exploration up to about 6 m. However, with the aid of tripod, holes for greater depths can be excavated. Depth of auger investigations are limited by ground water table and also by the presence of gravels and boulders.
220.127.116.11 Mechanically operated augers are also available and may be used in case of deep borings in difficult strata. 18.104.22.168 An auger boring is made by tuning the auger to desired depths into the soil, withdrawing it and removing the soil for examining and sampling. The auger is inserted in the hole again and the process is repeated. Holes are usually bored without addition of water in loose, moderately cohesive moist sand. But in hard dry soils or cohesion less sands the introduction of a small amount of water into the hole will very much facilitate the drilling and sample extraction. 7.3.2 Shell and Auger Borings - Pipe casing or shell is required in .unstable soil, in which the bore hole collapses and especially where the boring is extended below the ground water level. Stabilisation of the hole ,by means of bentonite slurry, can also be done. The inside diameter of the -casing should be slightly larger than the diameter of the auger used. Boring up to 200 mm dia and 25 m depth can be done with manual operation. The casing is driven to a depth not greater than the top of the next sample and is cleaned out by means of the auger. 7.4 Core Drilling 7.4.1 Core drilling should be done in accordance with IS : 6926. 7.4.2 The accuracy and dependability of the records furnished by diamond drilling depend largely upon the size of the core in relation to the kind of material drilled, the percentage of core recovery and experience of the drill crew. Recovery of core is much more important than :the rapid progress in drilling the hole. When drilling in soft materials, .the water circulation should be reduced or stopped entirely and the core recovered ‘dry’. 7.4.3 Detailed history of mechanical operation of drilling including observations on the loss of returned water and its reappearance, difficulties encountered should be included in the drilling report. 7.4.4 Percolation tests under specified pressure may be done in drill holes, if needed, using packers as the drilling progresses. 8. FIELD TESTS 8.1 Field tests ( in situ) are those in which material is tested without actual removal of the material from its existing position. Those applicable to stability of canal banks and foundation of cross drainage, structure are the following: a) Strength tests: i) Penetration tests; and ii) Shear tests. b) Measurement of density of foundation material; c) Permeability tests.
8.1.1 The necessity and the number of each type of test to be conducted, depend on the type of material and its degree of variability. 8.2 Strength Tests 8.2.1 Penetration Tests 22.214.171.124 These tests [see IS : 2131, IS: 4968 (Part 1 ), IS : 4968 ( Part 2)and IS: 4968 (Part 3 ) ] consist of measuring the resistance to penetration under static or dynamic loading of different shaped tools. The tests are empirical and have been developed from experience. They should be performed carefully in the prescribed manner. 126.96.36.199 Static and dynamic penetration tests provide simple means of comparing the results of different bore holes on the same site and for obtaining an indication of the bearing value of the soils and of the state of densification of non-cohesive soils. Corelation between the number of blows obtained in standard ( dynamic) penetration tests with relative density of non-cohesive soils and consistency of soil (that is, soft, medium, stiff, etc, ) in cohesive soil (see IS: 2131 ) and between penetration resistence in static penetration tests with bearing capacity and relative density of non-cohesive soils are given in several publications(see also IS : 6403). 188.8.131.52 The number of tests should be fairly large to cover the entire critical foundation area. 8.2.2 Shear Tests These tests (see IS : 4434) measure the in situ strength of cohesive soils, which are too soft or sensitive for sampling. 8.3 Permeability Tests 8.3.1 Permeability of a soil gives the measure of the rate, by which water can flow through unit area of it under unit hydraulic gradient. A knowledge of the permeability of the soil is necessary in estimating seepage through the canal banks in permeable soils or fissured rock and in determining the type and necessity of lining the canal. 8.3.2 Permeability is usually determined by in situ pumping in and pumping out tests [see IS : 5529 (Part 1) and IS: 5529 ( Part 2 )] in holes or wells. This test is very important where loss of water from the canal is not at all desirable and also where it may cause water logging in the neighbourhood. 8.4 Measurement of Density of Foundation Material 8.4.1 In situ density of canal banks and of foundation material is used in stability analysis. It also offers information on the state of compaction and to decide whether further compaction is needed. 8.4.2 The sand density method is used to determine the in-place density by excavating a hole from a horizontal surface, weighing the material excavated and determining the volume of the hole by filling it with calibrated sand [see IS : 2720 ( Part 28 )]. The
water content [see IS : 2720 (Part 2 )] of the soil at the place of determination of in situ density is needed to calculate the dry density of the soil. Other methods, such as core cutter method and surface nuclear gauge may be used. 8.4.3 This test is applicable to very shallow depths only, or to the depths of pits and trenches, where it is possible to perform the test up to the depth excavated. The density determination at depth should be made from undisturbed samples obtained from depths , or by deep penetration tests in non-cohesive soils. 9. SAMPLING 9.1 The methods employed for enabling for enabling collection of samples for visual examination and for performance of laboratory tests thereon have already been described in 6 to 8. 9.2 To take undisturbed samples from bore holes, properly designed sampling tools shall be used. These differ for cohesive and non-cohesive soils and for rocks. Special samplers like piston samplers and/or freezing or grouting techniques may have to be employed in cases where samples are to be collected from cohesion less sand which cannot be sampled by ordinary equipment and methods, particularly those existing below ground water level. 9.3 Sufficient quantity of representative undisturbed samples shall be collected for carrying out the necessary tests. 9.4 While boring small diameter bore holes in foundation area of cross drainage works or along the canal alignment, the total material recovered as core should be collected and stored in core boxes ( see IS : 4078 ). Samples of soil and rock should be collected and preserved in sealed bars to retain their natural water content. Samples should be representative of the material, as it is found in the area. 9.5 Samples collected in the process of routine exploration are not as a rule satisfactory for determination of properties of soil in its natural condition. For this purpose, undisturbed samples should be collected from large diameter bore boles (100 mm to 150 mm dia minimum), or from the open pits. 9.5.1 Bore hole samples should be 450 mm to 600 mm long and should open pit samples 250 mm to 300 mm cubes. Every effort be made to preserve such samples as nearly in their natural condition as possible.
10.2 Tests for Soils 10.2.1 Visual and Manual Examination This would give general description of the soil or rock in terms of colour, consistency, structure, etc, to help in general classification of the material.
10.2.2 Natural Moisture Content It helps in assessment of pore pressure in the foundation and backfill. 10.2.3 Liquid and Plastic Limits Liquid and plastic limits are measures of water absorption qualities of clay. They give an indication of the cohesiveness of soil and are also useful in soil classification [ see IS : 2720 ( Part 5 )]. 10.2.4 Particle Size Distribution A knowledge of particle size distribution is of use for soil classification and in understanding its specific features such as density, permeability, etc. 10.2.5 Bulk Density In case of canal banks and foundation of cross drainage works, it is essential for computing their stability. 10.2.6 Permeability A knowledge of permeability of the canal banks and of the foundation strata of the cross drainage structures is necessary, for estimating the seepage loss, uplift, grouting requirements, etc. 10.2.7 Consolidation Characteristics These are required for estimating the magnitude and rate of settlement due to consolidation in the canal banks and also in the foundation of the cross-drainage structure. 10.2.8 Swelling Tests Swelling tests are useful for clays present in the embankment to assess the likely pressures the clay would exert on saturation. These tests should be conducted at the lowest moisture content that may be obtained in the field.
10.2.9 Strength Characteristics Strength characteristics of soil may be determined by unconfined compression test [ see IS : 2720 ( Part 1)], direct shear test [see IS : 2720 ( Part 13 )] and triaxial shear test. 10.2.10 Compaction Test Compaction test may be required for comparison with in situ densities [ see IS : 2720 ( Part 7 )] . 10.2.11 Relative Density
For cohesionless soil to assess the degree of compaction of the soil in situ [see IS 2720 (Part 14) ] 10.2.12 Chemical Analysis Chemical test may be performed on soil samples from areas suspected to be saline, to determine soluble salt content [see IS: 2720(Part 21)]. 11. RECORDING AND REPORTING OF DATA 11.1 General Information collected from the explorations should be recorded and presented in a systematic manner suitable for convenient use. The locations of the canal and crossdrainage structures and points of exploration should be clearly indicated on a map. Trial pits and different types of bore holes should be indicated on the location maps using suitable symbols, in accordance with IS: 7422 . 11.1.1 The scales used for maps should be in accordance with IS :6065( Part 1 ). 11.2 Logging of Pits and Holes 11.2.1 Location Every pit and hole should be definitely located on a map by being tied to a co-ordinate grid system. The top elevations should also be recorded in the map. 11.2.2 Identification The holes and pits should all be numbered normally in the order in which they are drilled and with suitable symbols, as given in IS : 7422 . 11.2.3 Logs A standard and exhaustive log form should be used giving as much information as possible ( see IS : 4453 ) and IS : 4464.
11.2.4 Description of Soils The soils should be described in the logs and in the records according to IS : 1498 .
11.3 Subsurface Sections in Foundations of Cross-drainage Structures Sections showing subsurface conditions believed to exist should be prepared. The locations of the sections should be selected in a manner such that the information is presented in the best possible way. In the sections, different information like type and nature of subsurface material, C, φ , natural moisture content, density, etc, may be shown for the different strata.