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Fig.6c. Settlement Reduction Factor (B) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ in Case-IV

Figure 6 c. Settlement Reduction Factor (B) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ in Case-IV

Related Figures (29)

Fig.1. Plate load test arrangement for load on column & load on tributary soil in the five different cases (After Parakash et al, 2005) C.G. of plate coincided with C.G. of the group (shown in Fig.1 below). To quantify the degree of improvement, load tests on plates of same size and directly resting on sub-base were conducted prior to column installation. Further, it is reported that the tests were conducted upto a loading intensity equal to twice the design loading intensity for working columns.
Fig.1. Plate load test arrangement for load on column & load on tributary soil in the five different cases (After Parakash et al, 2005) C.G. of plate coincided with C.G. of the group (shown in Fig.1 below). To quantify the degree of improvement, load tests on plates of same size and directly resting on sub-base were conducted prior to column installation. Further, it is reported that the tests were conducted upto a loading intensity equal to twice the design loading intensity for working columns.
Fig.3a. Field Dynamic Cone Penetration Test Ratio of reinforced to virgin ground in Case-I & II (After Parakash et al, 2005) Fig.3b. Field Dynamic Cone Penetration Test Ratio of reinforced to virgin ground in Case-III (After Parakash et al, 2005)
Fig.3a. Field Dynamic Cone Penetration Test Ratio of reinforced to virgin ground in Case-I & II (After Parakash et al, 2005) Fig.3b. Field Dynamic Cone Penetration Test Ratio of reinforced to virgin ground in Case-III (After Parakash et al, 2005)
Fig.3c. Field Dynamic Cone Penetration Test Ratio of reinforced to virgin ground in Case-IV (After Parakash et al, 2005)
Fig.3c. Field Dynamic Cone Penetration Test Ratio of reinforced to virgin ground in Case-IV (After Parakash et al, 2005)
3.1 Standard Penetration Tests
3.1 Standard Penetration Tests
Fig.3d. Field Dynamic Cone Penetration Test Ratio of reinforced to virgin ground in Case-V (After Parakash et al, 2005)
Fig.3d. Field Dynamic Cone Penetration Test Ratio of reinforced to virgin ground in Case-V (After Parakash et al, 2005)
3.2 Dynamic Cone Penetration Tests
3.2 Dynamic Cone Penetration Tests
The field test data of Prakash et al (2005) together with some reasonably assumed subsoil parameters and stone column design parameters, the settlement reduction factor (B) has been calculated for all the five cases for design loading intensity (DLI) as well as twice the design loading intensity (2DLI). The dilation percentage of column head for which the result matches with the field results of Prakash et al (2005) are noted and presented in Table-1.
The field test data of Prakash et al (2005) together with some reasonably assumed subsoil parameters and stone column design parameters, the settlement reduction factor (B) has been calculated for all the five cases for design loading intensity (DLI) as well as twice the design loading intensity (2DLI). The dilation percentage of column head for which the result matches with the field results of Prakash et al (2005) are noted and presented in Table-1.
Fig.4. The mechanistic model of ‘unit-cell’ encapsulating a stone column (Saha, 2005a) and a typical field load-settlement data (Prakash et al, 2005) The cylindrical unit is being loaded vertically at the top (i.e., upper boundary) by a uniform rigid load of intensity p, per unit area. On sustained loading, a vertical settlement 5, of the cylindrical unit occurs. This result in a bulge at the column head extending up to critical column depth H,, with the consequent sharing of the applied vertical stress p, by soil (o’,,) and column (o',.). The compressive vertical stress at cell top induces in the perpendicular direction an expansive horizontal stress o',, at column head and equal and opposite horizontal stress o'y; in ambient subsoil around column head. This induced horizontal stress around column top in turn results in a total amount of horizontal deformation of 25, of column head within critical depth. The behavior of the stone column would depend on the states of stress and strain developed in the components of the unit-cell. Expressions for the induced stresses and strains and some useful dimensionless design parameters, for some possible states of stress and strain in the stone column and ambient soil, have been derived (Saha; 2005a, 2007). The general assumptions & boundary conditions are that the cylindrical unit-cell surface is frictionless, the end bearing of stone column is rigid and non- deformable, the ambient sub-soil is elastic, the friction between
Fig.4. The mechanistic model of ‘unit-cell’ encapsulating a stone column (Saha, 2005a) and a typical field load-settlement data (Prakash et al, 2005) The cylindrical unit is being loaded vertically at the top (i.e., upper boundary) by a uniform rigid load of intensity p, per unit area. On sustained loading, a vertical settlement 5, of the cylindrical unit occurs. This result in a bulge at the column head extending up to critical column depth H,, with the consequent sharing of the applied vertical stress p, by soil (o’,,) and column (o',.). The compressive vertical stress at cell top induces in the perpendicular direction an expansive horizontal stress o',, at column head and equal and opposite horizontal stress o'y; in ambient subsoil around column head. This induced horizontal stress around column top in turn results in a total amount of horizontal deformation of 25, of column head within critical depth. The behavior of the stone column would depend on the states of stress and strain developed in the components of the unit-cell. Expressions for the induced stresses and strains and some useful dimensionless design parameters, for some possible states of stress and strain in the stone column and ambient soil, have been derived (Saha; 2005a, 2007). The general assumptions & boundary conditions are that the cylindrical unit-cell surface is frictionless, the end bearing of stone column is rigid and non- deformable, the ambient sub-soil is elastic, the friction between
the installed stone column and host soil as well as the self weights of stone column and in-situ soil are neglected. Within the framework of above assumptions and boundary conditions, and also assuming that the column has dilated by a very small magnitude, w fraction of the initial volume along its critical depth, with consequent lateral compression of soil along critical depth, the expression for SRF (=f) is given below.
the installed stone column and host soil as well as the self weights of stone column and in-situ soil are neglected. Within the framework of above assumptions and boundary conditions, and also assuming that the column has dilated by a very small magnitude, w fraction of the initial volume along its critical depth, with consequent lateral compression of soil along critical depth, the expression for SRF (=f) is given below.
Fig.5b. Settlement Reduction Factor (B) Vs. Upper Boundary Strain Level (p,/E;) for load on column ‘unit’ in Case- III
Fig.5b. Settlement Reduction Factor (B) Vs. Upper Boundary Strain Level (p,/E;) for load on column ‘unit’ in Case- III
Fig.5a. Settlement Reduction Factor (6) Vs. Upper Boundary Strain (p,/Es) for load on column ‘unit’ in Case-I & II
Fig.5a. Settlement Reduction Factor (6) Vs. Upper Boundary Strain (p,/Es) for load on column ‘unit’ in Case-I & II
Fig.5d. Settlement Reduction Factor (6) Vs. Upper Boundary Strain Level (p,/E;) for load on column ‘unit’ in Case-V Fig.5c. Settlement Reduction Factor (6) Vs. Upper Boundary Strain Level (p,/E;) for load on column ‘unit’ in Case-IV
Fig.5d. Settlement Reduction Factor (6) Vs. Upper Boundary Strain Level (p,/E;) for load on column ‘unit’ in Case-V Fig.5c. Settlement Reduction Factor (6) Vs. Upper Boundary Strain Level (p,/E;) for load on column ‘unit’ in Case-IV
Fig.6a. Settlement Reduction Factor (8) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ in Case-I & II
Fig.6a. Settlement Reduction Factor (8) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ in Case-I & II
Fig.6b. Settlement Reduction Factor (8) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ in Case-III
Fig.6b. Settlement Reduction Factor (8) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ in Case-III
Stone Column Reinforced Ground : LOAD TEST ON TRIBUTARY SOIL
Stone Column Reinforced Ground : LOAD TEST ON TRIBUTARY SOIL
Fig.7b. Settlement Reduction Factor (8) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ at different spacing in Case-II
Fig.7b. Settlement Reduction Factor (8) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ at different spacing in Case-II
Fig.7d. Settlement Reduction Factor (6) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ at different spacing in Case-IV
Fig.7d. Settlement Reduction Factor (6) Vs. Upper Boundary Strain Level (p,/E,) for load on soil ‘unit’ at different spacing in Case-IV
Fig.9. Settlement Reduction Factor (8) Vs. Area Ratio at different loading intensities in alluvial soil Fig.10. The Domain of Settlement Reduction Factor (B) Vs. Area Ratio in alluvial soil
Fig.9. Settlement Reduction Factor (8) Vs. Area Ratio at different loading intensities in alluvial soil Fig.10. The Domain of Settlement Reduction Factor (B) Vs. Area Ratio in alluvial soil
Fig.8. Design Settlement Reduction Factor (8) against Upper Boundary Strain Level (p,/E,) in Alluvial Soil
Fig.8. Design Settlement Reduction Factor (8) against Upper Boundary Strain Level (p,/E,) in Alluvial Soil
Fig.12. Settlement Reduction Factor (8) Vs. Upper Boundary Strain Level (p,/E,) at different column spacing in Alluvial Soil
Fig.12. Settlement Reduction Factor (8) Vs. Upper Boundary Strain Level (p,/E,) at different column spacing in Alluvial Soil
Fig.13. Upper Boundary Strain Level Vs. Soil-Column Vertical Strain Ratio when each ‘unit’ of ‘Unit-Cell’ is separately loaded in Alluvial Soil
Fig.13. Upper Boundary Strain Level Vs. Soil-Column Vertical Strain Ratio when each ‘unit’ of ‘Unit-Cell’ is separately loaded in Alluvial Soil
The negative sign indicates that the degree of dilation decreases with increasing area-ratios (or decreasing column spacings). Fig.11. Field dilation of stone column head in alluvial soil
The negative sign indicates that the degree of dilation decreases with increasing area-ratios (or decreasing column spacings). Fig.11. Field dilation of stone column head in alluvial soil
Fig.14. Area-Ratio Versus Soil-Column Vertical Strain Ratio for different upper boundary strain levels when each ‘unit’ of ‘Unit-Cell’ is separately loaded in Alluvial Soil Fig.l5 shows the upper boundary strain Level versus soll- column vertical strain ratio when each ‘unit’ of ‘Unit-Cell’ is separately loaded. Again, a definite trend of variation of upper boundary strain against soil-column vertical strain ratio could be observed for specific values of area-ratio. As area-ratio increases from A,=0.057 (that is, a column spacing of 4d) to A=0.124 (a column spacing of 2.71d), the soil-stone column vertical strain ratio increases, the increase being higher at low loads and decreases gradually at higher loads. It is also noticed that as area-ratio is further increased to A,=0.129 (a column spacing of 2.65d), soil-stone column vertical strain ratio decreases, signifying that optimum economic improvement due to this ground improvement technology has been achieved somewhere between these spacings of 2.65d (A,=0.129) and 2.71d (A,=0.124). Hence, at or near a spacing of 2.70d, optimization is achieved.
Fig.14. Area-Ratio Versus Soil-Column Vertical Strain Ratio for different upper boundary strain levels when each ‘unit’ of ‘Unit-Cell’ is separately loaded in Alluvial Soil Fig.l5 shows the upper boundary strain Level versus soll- column vertical strain ratio when each ‘unit’ of ‘Unit-Cell’ is separately loaded. Again, a definite trend of variation of upper boundary strain against soil-column vertical strain ratio could be observed for specific values of area-ratio. As area-ratio increases from A,=0.057 (that is, a column spacing of 4d) to A=0.124 (a column spacing of 2.71d), the soil-stone column vertical strain ratio increases, the increase being higher at low loads and decreases gradually at higher loads. It is also noticed that as area-ratio is further increased to A,=0.129 (a column spacing of 2.65d), soil-stone column vertical strain ratio decreases, signifying that optimum economic improvement due to this ground improvement technology has been achieved somewhere between these spacings of 2.65d (A,=0.129) and 2.71d (A,=0.124). Hence, at or near a spacing of 2.70d, optimization is achieved.
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