Birla Vishvakarma Mahavidyalaya Gujarat Technological University Subject: SOIL MECHANICS (2150609) Prepared by: Name Enrollment number KACHCHHI JATEENKUMAR M. 140073106010 KOTWAL KRUNALKUMAR H. 140073106011 Guided By: Prof. B. R. DALWADI

SOIL INVESTIGATION

BROAD OBJECTIVES Subsurface conditions Subsurface soil profile To get specific, reliable & adequate information about:- Subsurface conditions Subsurface soil profile Ground water (hydro-static/hydro-dynamic) conditions Geological information Past history To assess feasibility and suitability of type of foundation (shallow/deep) To generate adequate and reliable information regarding soil profile and soil parameters for design and execution purpose To evaluate parameters for constrains in activities, considering safety and security

SOIL INVESTIGATION To recognize, to be familiar of the site PHASES OF SOIL EXPLORATION: RECONNAISSANCE SURVEY: To recognize, to be familiar of the site To collect general details regarding site from published literatures such as journals, reports, geological maps, soil survey maps etc. To visit the site for getting idea about the terrain and its geological features. To talk with local people, to study existing structures with similar site conditions etc. (sites with BC soil)

Few samples can be collected for laboratory testing. 2. PRELIMINARY EXPLORATION: Few bore holes may be drilled to observe the soil types and their depths. Few samples can be collected for laboratory testing. It depends on nature of structure and site.(Narmada dam site) 3. DETAILED EXPLORATION: Drilling large no. of bore holes, collection of disturbed and undisturbed samples for lab. Testing. It depends on nature of structure and site. SUMMARY: Purpose of soil exploration:- To find the sequence, extent and location of the subsurface strata. To determine engineering properties of the strata. To determine ground water conditions.

TYPES OF SOIL SAMPLES little or no disturbance to the soil structure UNDISTURBED SAMPLES:- little or no disturbance to the soil structure natural structure and properties will be preserved useful for important laboratory tests like shear test, consolidation test etc. DISTURBED SAMPLES:- NON-REPRESENTATIVE SAMPLES: mixture of soils from different layers/levels complete disturbance to soil structure and properties can not be used for any test 2 REPRESENTATIVE SAMPLES: disturbance to soil structure water content may or may not be changed no change in mineral constituents suitable for classification and identification tests

FIELD METHODS OF EXPLORATION 1. OPEN EXCAVATIONS: to prepare trial pits, trenches upto required depth ADVANTAGES:- -simple method, involves manual operations -direct examination of soil strata -easy collection of disturbed and undisturbed samples -useful for preliminary exploration for shallow foundations only. DISADVANTAGES:-economical for shallow footings only. -upto about 3.0m depth otherwise cost increases with depth

details along vertical / horizontal / inclined line 2. BORING / DRILLING METHODS: drilling of bore holes details along vertical / horizontal / inclined line different boring methods based on soil types samples can be collected from greater depths e.g. 30m / 40m depths useful for both preliminary and detailed exploration time consuming and costly

(1) AUGER BORING: bore hole is drilled / advanced by pushing and twisting / rotating an auger post hole type auger / helical auger may be manually operated ( upto 12-15m) or power driven auger (upto 15-30m) rate of progress according slow / fast extensively used for subsurface exploration of highways, airfields, railways simple, light and inexpensive equipment disturbed bur representative samples, for collecting undisturbed sample the bottom of the BH should be cleaned carefully generally useful for cohesive soils, for cohesionless soils, bailer (a heavy metallic cylinder with flap valve at bottom) is used GWT can be determined Casing pipes generally not required i.e. uncased BH (2) WASH BORING: Boring / drilling is advanced (i) partly by chopping and twisting of a light drill bit and (ii) partly by jetting with water which is pumped through a hollow drill bit and drill rod Casing pipes are required Samples :highly disturbed and non representative Before collection of UDS, careful cleaning of BHY is required Suitable for all common soils which do not contain stones and boulders Not suitable for very hard and cemented soils or rocks

Auger boring Power drills Boring tools Auger boring Power drills

Wash Boring

(3) PERCUSSION DRILLING: Boring is advanced by alternatively raising and dropping a heavy drill bit (also called as a churn bit)- churning action Small quantity of water is added during boring After sufficient churning, bit is lifted and slurry removed by using bailer or sand pump Samples :highly disturbed and non representative Casing is generally required except rock Oldest method Applicable to all soils and rock Best suited for coarse gravel deposits, boulderly soils and very hard soils (4) ROTARY DRILLING: BH is advanced by rapid rotation of the drilling bit which cuts, chips and grinds the material into small particles Water or drilling mud is pumped through drilling rods and bit Light, portable or heavy drilling rig required. Very fast method in all soils and rocks, Suitable for all soils and rocks Not well suited for deposits with very coarse gravels, numerous stones and boulders and badly fissured rocks Samples :highly disturbed and non representative Except soft soils, BH is uncased

To measure resistance to penetration of a rod, cone or sampler etc. 3. SUBSURFACE SOUNDINGS / PROBING METHODS : Can be considered as soil exploration methods as well as field tests (why?) To measure resistance to penetration of a rod, cone or sampler etc. Empirical correlations between soil properties ( E, Poisson’s ratio, bearing capacity, settlement etc.) and resistance offered gives idea about soil type, extent etc. Direct observation of soil type & collection of sample may or may not be. e.g. SPT, DCPT, SCPT

SPT

(i) electrical receptivity methods 4. GEOPHYSICAL METHODS: based on the measurement of change in the physical characteristics of mineral and fluids e.g. resistance to electrical current, magnetic fields, elastic waves, density etc. give idea about soil strata Previously developed and extensively used for finding oil and minerals by companies like ONGC, useful upto greater depths. (i) electrical receptivity methods (ii) seismic refraction/reflection methods

[A] ELECTRICAL RESISTIVITY METHODS Wenner’s Method :

[A] ELECTRICAL RESISTIVITY METHODS: Wenner’s Method : (i) ELECTRICAL PROFILING : idea parallel to the ground i.e. in linear / longitudinal direction keep electrodes at constant spacing and move along a line change in curve indicates change in soil profile Distance ‘a’ ρ Depth ‘a’ (ii) ELECTRICAL SOUNDING : idea in vertical direction i.e. wrt the depth, spacing ‘a’ should be successively increased

ADVANTAGES of GEOPHYSICAL METHODS : compared to borings, large area or projects of great linear extent can be explored more rapidly and economically e.g. sites for dams and reservoirs, large group of buildings, factory site, tunnels, highways, airfields, etc. subsurface irregularities can be detected easily which can be missed by drilling ( because these methods cover areas, zones) simple, quick, economic covering large area and great depth well suited for reconnaissance survey DISADVANTAGES: no collection of samples and hence no exact ideas about soil properties materials can not be identified definitely

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