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Geotechnical Investigation For Foundation Designing
Haider Ali JafferiCivil Engineer
Hyderabad, Sindh
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
Geotechnical Investigations
Site Details
Site Plan
In-situ Soil Density by Core Cutter MethodAtterberg LimitsSieve AnalysisSoil Classification by USCSPermeability of soil by Constant Head Method
Test Performed
Apparatus Used:Standard: ASTM D2937Significance: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.
Core Cutter Method
Lab Observations:Internal dia of core cutter =
4 inHeight of core cutter = 5 inCore cutter cross sectional area =πd2/4 = 12.56 in2
Mass of empty core cutter = 1383.8 g = 3.044 lbsMass of core cutter + soil = 3017.7 g = 6.639 lbsMass of soil =6.639 – 3.044 = 3.595 lbsVolume 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
Core Cutter Cont……..
Apparatus Used:Standard Reference: ASTM D-422Significance: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.
SIEVE ANALYSIS
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
SIEVE ANALYSIS Cont…
Gradation Test Results: Sample # 1 (3 ft.)Cu=4.8Cc=1.5So soil is Poorly Graded (SP) Sample # 2 (6 ft.)Cu=3.28Cc=1.2So soil is Poorly Graded (SP)
Soil Classification By USCS
Sample # 3 (9 ft.)Cu=2.9Cc=1.0So soil is Poorly Graded (SP) Sample # 4 (12 ft.)Cu=2.65Cc=1.1So soil is Poorly Graded (SP)
SIEVE ANALYSIS Cont…
Standard Reference: ASTM D431Significance: 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.
ATTERBERG LIMITS:
LIQUID LIMITS Cont…Lab Observations:Sample # 1 (3 ft.)Trial A:No of blows = 31M.C = 29.5 %Trial B:No of blows = 23M.C = 33.5%
Sample # 2(6 ft.)Trial A:No of blows = 23M.C = 32.8 %Trial B:No of blows = 30M.C = 33.5%
LIQUID LIMITS Cont…Sample # 3(9 ft.)Trial A:No of blows = 27M.C = 26.7 %Trial B:No of blows = 21M.C = 29.6%
Sample # 4(12 ft.)Trial A:No of blows = 22M.C = 29.9 %Trial B:No of blows = 30M.C = 27.2%
PLASTIC LIMITSample # 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%
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.
PERMEABILITY OF SOIL
Laboratory Observations:h = 41.5 inL = 7.5 inQ = 20 ml = 0.02 L
t = 2:30 hr = 9000 secA = 75.42 cm2 = 11.69 in2
K = Q L/A h t K = 5.325 x 10-9 cm/sec
PERMEABILITY OF SOIL Cont…
In-situ Field Density:Bulk Density= 1588.19 kg/m3Dry 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.
Summary Of Results
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.
Conclusional Recommendations