REVIEW OF LITERATURE AND SCOPE OF PRESENT STUDY
3.3 PLANNING OF EXPERIMENTS
The cylindrical encasement sleeve was formed by overlapping the geomesh to required diameter over 10mm wide section and then stitching over it. The number of stitches and the thread used was kept same for all the tests. The strength of the seam was tested through wide width tensile test (ASTM D 4884), with the specimens having the horizontal seam at mid depth. The load deformation response is shown in Fig. 3.28. The seam strength is found to be 2.45 kN/m.
0 5 10 15 20 25 30 35
Axial strain (%) 0
1 2 3
Tensile load (kN/m)
Fig.3.28: Tensile load-strain behaviour of the geomesh seam
of that particular parameter on the overall behaviour. The geometry of the composite foundation system and the parameters considered in the test programme are illustrated in Figs. 3.29, 3.30 and 3.31. Diameter of geocell (dgc) is taken as the equivalent diameter of the geocell pocket opening shown through hatch mark in Fig.3.31. As per the findings of Dash et. al. (2001a), in all tests, the geocell mattress was kept at a depth (u) of 0.1D from the base of the footing to get maximum performance improvement.
Fig. 3.29: Geometry of stone column-clay bed-geocell mattress foundation system (sectional view)
Stone column Clay
L
Sand Geocell layer h
u DT5 DT1
DT3 DT4
DT6 DT2
DT7
DT8
LOAD Footing
D D
D
Fig. 3.30: Layout of stone column (plan view)
Fig. 3.31: Plan view of a typical geocell layer in chevron pattern.
d
−x/D +x/D
(0,0)
transverse member diagonal member footing
bodkin joint
b b
footing
0.876 S
S dsc
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In total 25 series of model load tests were conducted to establish the influence of the different parameters pertaining to the stone column-clay-geocell mattress, foundation system. The details of these test series are presented in Table 3.1. Tests in series 1 were performed on unreinforced soft clay bed. In series 2 and 3, tests were performed on stone column reinforced clay beds. In these tests the length (L) and spacing (S) of the stone columns were varied.
Under series 4-8 tests were carried out on geocell-sand mattress overlying clay bed.
The parameters studied in these tests include the height of the geocell mattress, pocket size and the relative density of infill sand. Based on the results from these tests, optimum dimensions of the geocell mattress giving maximum performance improvement are determined.
The tests in series 9-12 were carried out on the composite foundation system comprising of geocell-sand mattress overlying stone column reinforced soft clay bed.
In these tests, length of the stone column was varied for different height of the geocell mattress. In test series 13-16, tests were performed on composite foundation system by varying the spacing of the stone column for different height of geocell mattress.
Under series 17-18, tests were conducted to study the influence of the pocket size of geocells on the overall performance of the composite foundation system (i.e., clay bed-stone column-geocell mattress). Tests in series 19 and 20 were conducted on composite foundation bed by varying the relative density of sand in the geocell sand mattress.
Table 3.1 Details of laboratory model tests Test
Series
Type of reinforcement
Details of parameters investigated
1 Clay Bed Constant parameter: cu = 5kPa
2 Clay + SC Constant parameter : cu = 5kPa, S/dsc = 2.5 Variable parameter: L/dsc =1,3,5,7
3 Clay + SC Constant parameter: cu = 5kPa , L/dsc = 5 Variable parameter: S/dsc = 1.5, 2.5, 3.5
4 Clay + GC Constant parameter: cu = 5kPa, u/D = 0.1, dgc/D = 0.8, b/D = 6, ID = 80%
Variable parameter: h/D = 0.53, 0.9, 1.1, 1.6
5 Clay + GC Constant parameter: cu = 5kPa, dgc/D = 0.8, h/D = 0.53, b/D = 6, u/D=0.1
Variable parameter: ID = 35%, 50%, 80 %
6 Clay + GC Constant parameter: cu = 5kPa, dgc/D = 0.8, h/D = 0.9, b/D = 6, u/D = 0.1
Variable parameter: ID = 35%, 50%, 80 %
7 Clay + GC Constant parameter: cu = 5kPa, ID = 80 %, h/D = 0.53, b/D = 6, u/D = 0.1
Variable parameter: dgc/D = 0.8, 1.1,1.33
8 Clay + GC Constant parameter: cu = 5kPa, ID = 80 %, h/D = 0.9, b/D = 6, u/D = 0.1
Variable parameter: dgc/D = 0.8, 1.1, 1.33
9 Clay + GC + SC Constant parameter: cu = 5kPa, h/D = 0.53, b/D = 6, dgc/D = 0.8, S/dsc = 2.5, ID = 80 % Variable parameter: L/dsc = 1, 3, 5, 7
10 Clay + GC + SC Constant parameter: cu = 5kPa, h/D = 0.9, dgc/D = 0.8, b/D = 6, S/dsc = 2.5, ID = 80 % Variable parameter: L/dsc = 1, 3, 5, 7
11 Clay + GC + SC Constant parameter: cu = 5kPa, h/D = 1.1, b/D = 6, dgc/D
= 0.8, S/dsc = 2.5, ID = 80 % Variable parameter: L/dsc = 1, 3, 5, 7
12 Clay + GC + SC Constant parameter: cu = 5kPa, h/D = 1.6, dgc/D = 0.8, b/D = 6, S/dsc =2.5, ID = 80 % Variable parameter : L/dsc = 1, 3, 5, 7
13 Clay + GC + SC Constant parameter: cu = 5 kPa, L/dsc = 5, h/D = 0.53, b/D = 6, dgc/D = 0.8, ID = 80%
Variable parameter : S/dsc = 1.5, 2.5, 3.5
Cont…
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14 Clay + GC + SC Constant parameter: cu = 5 kPa, L/dsc = 5 , h/D = 0.9, dgc/D = 0.8, b/D = 6, ID = 80%
Variable parameter : S/dsc = 1.5, 2.5, 3.5
15 Clay + GC + SC Constant parameter: cu = 5 kPa, L/dsc = 5 , h/D = 1.1, b/D = 6, dgc/D = 0.8, ID = 80%
Variable parameter : S/dsc = 1.5, 2.5, 3.5
16 Clay + GC + SC Constant parameter: cu = 5 kPa, L/dsc = 5 , h/D = 1.6, b/D = 6, dgc/D = 0.8, ID = 80%
Variable parameter : S/dsc = 1.5, 2.5, 3.5
17 Clay + GC + SC Constant parameter: cu = 5kPa, L/dsc = 5, S/dsc = 2.5, b/D = 6, h/D = 0.53, ID = 80%
Variable parameter: dgc/D = 0.8, 1.1,1.33
18 Clay + GC + SC Constant parameter: cu = 5kPa, L/dsc = 5, S/dsc = 2.5, b/D = 6, h/D = 0.9, ID = 80%
Variable parameter: dgc/D = 0.8, 1.1, 1.33
19 Clay + GC + SC Constant parameter: cu = 5kPa, L/dsc = 5,S/dsc = 2.5, b/D = 6, h/D = 0.53, dgc/D = 0.8 Variable parameter: ID = 35%, 50%, 80%
20 Clay + GC + SC Constant parameter: cu = 5kPa, L/dsc = 5, S/dsc = 2.5, b/D = 6, h/D = 0.9,dgc/D = 0.8 Variable parameter: ID = 35%, 50%, 80%
21 Clay + GC + BG +SC Constant parameter: cu = 5kPa, L/dsc = 5, S/dsc = 2.5, u/D = 0.1, dgc/D = 0.8 , ID = 80%, Variable parameter: h/D = 0.53, 0.9
22 Clay + ESC Constant parameter: cu = 5kPa, L/ds c = 5, S/ds c = 2.5 Variable parameter: Lesc/dsc = 1, 3, 5
23 Clay + GC + ESC Constant parameter: cu = 5kPa, L/dsc = 5, S/dsc = 2.5, b/D = 6, dgc/D = 0.8 , ID = 80%, h/D = 0.53
Variable parameter: Lesc/dsc = 1, 3, 5
24 Clay + GC + ESC Constant parameter: cu = 5kPa, L/dsc = 5, S/dsc = 2.5, b/D = 6, dgc/D = 0.8 , ID = 80%, h/D = 0.9
Variable parameter: Lesc/dsc = 1, 3, 5
25 Clay + GC + BG + ESC Constant parameter: cu = 5kPa, L/dsc = 5, S/dsc = 2.5, Lesc/dsc = 3, b/D = 6, dgc/D = 0.8, ID = 80%
Variable parameter: h/D = 0.53, 0.9
Note. GC: Geocell, SC: Stone column, BG: Base geogrid, ESC: Encased stone column
The influence of a layer of geogrid at the base of the geocell mattress, on the overall performance of composite foundation system was studied under test series 21.
Performance of clay bed with encased stone columns was investigated under series 22. Tests under series 23 and 24 were carried out with encased stone columns in the clay bed, underlying geocell mattress.
To understand the combined influence of geocell mattress, base geogrid and encased stone columns, tests in series 25 were carried out, by using all these reinforcements together i.e. geocell-sand mattress, base geogrid, encased stone columns.
3.4 TEST DESCRIPTION