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Geo techincal investigation for foundation designing

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Geo techincal investigation for foundation designing

  1. 1. Haider Ali Jafferi Civil Engineer Hyderabad, Sindh
  2. 2. Introduction: Geotechnical investigations are performed to obtain information on the physical properties of soil and rock underlying the site to design earthworks and foundations for proposed structures, and for repair of damages to earthworks and structures ,caused by subsurface conditions
  3. 3. Site Plan
  4. 4.  In-situ Soil Density by Core Cutter Method  Atterberg Limits  Sieve Analysis  Soil Classification by USCS  Permeability of soil by Constant Head Method
  5. 5.  Apparatus Used:  Standard: ASTM D2937  Significance:  Field Work:  Soil excavated up to a depth of 3 ft.  The core cutter is driven inside the soil with the help of hammer.  Soil is trimmed around the core cutter and core cutter is removed.
  6. 6.  Lab Observations: Internal dia of core cutter = 4 in Height of core cutter = 5 in Core cutter cross sectional area =πd2/4 = 12.56 in2 Mass of empty core cutter = 1383.8 g = 3.044 lbs Mass of core cutter + soil = 3017.7 g = 6.639 lbs Mass of soil =6.639 – 3.044 = 3.595 lbs Volume of core cutter = 62.8 in3 Bulk density = ρb= M2 –M1/V = 1588.1907 kg/m3 Dry density = ρd= ρb/1 + m.c = 1489.5202 kg/m3
  7. 7.  Apparatus Used:  Standard Reference: ASTM D-422  Significance:  Field Work:  Bore holes are drilled with the help of earth augers.  Holes were drilled at 3 ft interval up to 12 ft and disturbed samples of the soil were collected.  Soil samples were collected in the bags and were transported to the lab for laboratory tests and observations.
  8. 8.  LABORATORY OBSERVATIONS:  Sieves were arranged in the order and were tightly held on the sieve shaker.  About 500 g of soil disturbed soil sample of depth 3 ft was placed on the top sieve (sieve no 4).  Sieve shaker was then turned on and sieves were shaken for 5 minutes
  9. 9. Gradation Test Results:  Sample # 1 (3 ft.) Cu=4.8 Cc=1.5 So soil is Poorly Graded (SP)  Sample # 2 (6 ft.) Cu=3.28 Cc=1.2 So soil is Poorly Graded (SP)
  10. 10.  Sample # 3 (9 ft.) Cu=2.9 Cc=1.0 So soil is Poorly Graded (SP)  Sample # 4 (12 ft.) Cu=2.65 Cc=1.1 So soil is Poorly Graded (SP)
  11. 11.  Standard Reference: ASTM D431  Significance:  Liquid Limit:  Apparatus Used:  Lab Work:  Soil sample was passed through sieve no. 40.  Water was added to the taken soil sample gradually in order to make a paste.  The soil paste was filled in the Cassagrande apparatus, and blows were applied.  No of blows were counted and a graph was made to determine the intermediate value of m.c at standard 25 blows.
  12. 12.  Lab Observations:  Sample # 1 (3 ft.) Trial A: No of blows = 31 M.C = 29.5 % Trial B: No of blows = 23 M.C = 33.5%  Sample # 2(6 ft.) Trial A: No of blows = 23 M.C = 32.8 % Trial B: No of blows = 30 M.C = 33.5%
  13. 13.  Sample # 3(9 ft.) Trial A: No of blows = 27 M.C = 26.7 % Trial B: No of blows = 21 M.C = 29.6%  Sample # 4(12 ft.) Trial A: No of blows = 22 M.C = 29.9 % Trial B: No of blows = 30 M.C = 27.2%
  14. 14.  Sample # 1 (3 ft.) Trial A: M.C = 21.3 % Trial B: M.C = 23.1%  Sample # 2 (6 ft.) Trial A: M.C = 12.5% Trial B: M.C =17.6 %  Sample # 3 (9 ft.) Trial A: M.C = 19.3 % Trial B: M.C = 16.7%  Sample # 4 (12 ft.) Trial A: M.C = 17.7 % Trial B: M.C = 19.3%
  15. 15.  Apparatus Used:  Significance:  Lab Work:  Soil was passed through sieve # 200.  Soil sample was filled in Permeameter in three fills and were properly tampered.  Time period was noted for the water to discharge, in order to carry out important calculations.
  16. 16.  Laboratory Observations: h = 41.5 in L = 7.5 in Q = 20 ml = 0.02 L t = 2:30 hr = 9000 sec A = 75.42 cm2 = 11.69 in2 K = Q L/A h t K = 5.325 x 10-9 cm/sec
  17. 17.  In-situ Field Density:  Bulk Density= 1588.19 kg/m3  Dry Density = 1491.01 kg/m3 For well graded soil, Cu >6 1 < Cc <3 The results of experiment shown that the soil type was “poorly graded sandy soil” and its symbol is “SP”. For permeability, if Vale of K is less than 0.0001, than the soil will be clayey other wise will be sandy. Our result of experiment was 5.325 x 10^-9, and soil type came out to be clayey.
  18. 18.  The foundation designing mainly depends upon the bearing capacity of soil.  During the test, no water table was intercepted during the bore holes.  The previous geotechnical studies shown that the bearing capacity of the soil in this vicinity is about 1 ton per square feet.

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