SOIL MECHANICS AND FOUNDATION ENGINEERING-II (CE 311)

TEXT/ REFERENCE BOOKS 1.SOIL MECHANICS by T WILLIAM LAMBE & ROBERT V. WHITMAN, Wiley ASTERN 2.FOUNDATION ANALYSIS & DESIGN by JOSEPH E. BOWLES, Mc Graw Hills 3.GEOTECHNICAL ENGINEERING by SHASHI K GULHATI & MANOJ DATTA, TATA Mc Graw Hill 4.SOIL MECHANICS AND FOUNDATION ENGINEERING by B C PUNMIA, A K JAIN & A K JAIN, Laxmi Publications Pvt. Ltd.

SOIL & ROCK INVESTIGATIONS  The purpose of the investigation is to find out what are types of soils and rocks at the site at various locations as well as various depths. What are the properties of soils and rocks The properties can be determined by conducting TESTS IN THE FIELD or by bringing the soil samples and TESTING IN THE LABORATORY. To get samples from different depths or conduct field tests the BORE HOLES are to be drilled.

SOIL & ROCK INVESTIGATION (Contd.) 1.How many bore holes should be drilled? 2.Where should the bore holes be located? 3.How deep should the bore hole be? 4.With what equipment should the bore holes be drilled? 5.At what depth intervals should soil samples be taken? 6.What type of samples and sampling techniques should be used? 7.Which samples should be subjected to laboratory tests? 8.What laboratory tests should be conducted? 9.What field i.e. in-situ tests should be conducted? 10.Where should the in-situ tests be conducted?

SOIL & ROCK INVESTIGATION (Contd.) INVESTIGATION METHODOLOGIES  Geophysical and Remote sensing Methods  Drilling Bore Holes and Sampling  Pits, Trenches & Shafts  In-Situ Testing  Laboratory Testing

INVESTIGATION METHODOLOGIES GEOPHYSICAL AND REMOTE SENSING METHODS  Enables us to obtain information about the soil profile by using the fact that different soils have different resistivities or that a wave generated by in impact load will travel through different soils with different velocities. These methods are referred as Geophysical Methods.  They are useful when we are interested in obtaining a macro view of the soil profile over a relatively large area.  Method based on wave velocity is referred as SEISMIC METHOD which is useful in determining the depth of various bedrocks.  ELECTRICAL RESISTIVITY METHOD is useful in determining the depth of water below the ground surface.

INVESTIGATION METHODOLOGIES GEOPHYSICAL AND REMOTE SENSING METHODS (Contd.)  Interpreting Areal Photographs gives nature of surface soils, drainage pattern, land use, geological features, topography etc.  These are called REMOTE SENSING TECHNIQUES.

INVESTIGATION METHODOLOGIES DRILLING BORE HOLES AND SAMPLING  Most powerful technology for site investigation available to the Consulting Geotechnical Engineer is that of drilling bore holes, taking samples from various depths and subjecting them to careful scrutiny and testing in the laboratory.  Over the years, we have learnt that the process of drilling and sampling can disturb the soil and that properties determined using disturbed soil samples can be different from the properties as they exist in the natural state in the field.  This leads to refine the techniques of drilling, sampling, transporting, storing, retrieving and testing. Thus evolution of Correction Techniques.

INVESTIGATION METHODOLOGIES PITS TRENCHES AND SHAFTS  When we need to investigate only to shallow depths, PITS are excavated for a close look. Undisturbed soil samples are taken by simply using hands. Typically, pits have base area of 1.2 x 1.2 m.  When bedrock is at shallow depth, TRENCHES can be dug along the entire length and breadth of the area to determine the profile of the bedrock as well as to examine the condition of bedrock.  In deposits of Cobble and Boulders, large diameter shafts are excavated to see profile with depth.

INVESTIGATION METHODOLOGIES IN-SITU TESTING  In general we can not obtain undisturbed samples of coarse grained soils such as SAND. Numerous field test have been developed.  Some are conducted in the bore holes at different depths.  Some are conducted without drilling bore holes by merely pushing PROBES into the soil deposits to desired depths.  Apart from coarse grained soils, deposits of CLAY having very high sensitivity are also require In-Situ Testing.

INVESTIGATION METHODOLOGIES LABORATORY TESTING  Samples collected from bore holes are carefully sealed labeled before transporting them to the laboratory.  This is backbone of the Investigation Methodologies.  In the laboratory, the Engineer prepares a testing programme specifying which samples are to be subjected to what tests.  These tests are used to validate the visual classification as well as to find both the physical and engineering properties required for analysis and design.

DRILLING TECHNOLGIES  AUGER DRILLING  PERCUSSION DRILLING  JET DRILLING AND WASH DRILLING  HIGH SPEED ROTARY DRILLING

DRILLING TECHNOLOGIES AUGER DRILLING  TYPES OF AUGERS  POST HOLE AUGER

AUGER DRILLING TYPES OF AUGER  HELICAL AUGERHOLLOW HELICAL AUGER

AUGER DRILLING  The augers can be rotated and pushed into the ground manually and by using motorized system.  Using manually operated augers, bore holes of 100 mm diameter and depth upto 20 m depending upon the type of soils.  The auger drilling is effective in soils that possess some stickiness.  The soils which do not possess stickiness e.g. sands, augers are not able to create a hole.  AUGER BORING IS THUS MOST EFFECTIVE IN CLAYS, SILTY CLAYES, CLAYEY SILTS etc.  HOLLOW STEM AUGERS are sometimes are used for NON STICKY soils.

PERCUSSION DRILLING  ROPE HUNG BAILERS are dropped from a certain height to create hole in the soil and filling it with some soils from its bottom end.  It can be used manually as well as by machine operated depending upon the depth of exploration.

JET AND WASH DRILLING  A bore hole is advanced into the soil using a high pressure water jet to cut the soil and flush the cuttings out of the hole.  Because the water jet tends to disturb the soil below the bottom of the hole, JET DRILLING IS NOT USED where undisturbed sample is required.  In wash drilling, the soil is cut by UP/ DOWN action of chopping bit, ROTARY action of bit, ROTARY ACTION ON CUTTING PIPE.  When undisturbed sample are required, rotary boring is preferred since they do not disturb soil below the bottom of the hole as much as the up/down action of chopping bit.

HIGH SPEED ROTARY DRILLING  For drilling in ROCK, the preceding techniques do not work and we have to resort to high speed drilling in which a core cutter with its leading end fitted with diamond drill bit is simultaneously rotated and pressed down.  When the core cutter fills up, it is lifted to the ground surface and the rock core is carefully removed.  During the drilling process, drilling fluid circulates around the bit to reduce the temperature produced due to drilling and to take out slurry of rock dust from the bottom.