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Figure 11. Variation of mobilized shear stress versus horizontal deflection (o,= 36 kPa) at in-situ dry density (ya ot A A Po ON bs Ate cg Ah cee ee Tee eT ae ake Pendle ae ot ne Figure 11. Variation of mobilized shear stress versus horizontal deflection (o,= 36 kPa) at in-situ dry density (ya

Figure 11 Variation of mobilized shear stress versus horizontal deflection (o,= 36 kPa) at in-situ dry density (ya ot A A Po ON bs Ate cg Ah cee ee Tee eT ae ake Pendle ae ot ne Figure 11. Variation of mobilized shear stress versus horizontal deflection (o,= 36 kPa) at in-situ dry density (ya

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Figure 1. Location map of the Simbal Landslide, along the M2 Motorway in Salt Range Pakistan A major landslide occurred on 10th August, 2005 near the village Simbal along the Lahore-Islamabad Motorway (M-2) in the Salt Range area, after a period of intense Monsoon rainfall (Figure 1). As a result of that event approximately 91,500 m? colluvium and 41,000m? of limestone and shale boulders translated down slope and blocked one lane of the motorway (Ahmed et al., 2012).
Figure 1. Location map of the Simbal Landslide, along the M2 Motorway in Salt Range Pakistan A major landslide occurred on 10th August, 2005 near the village Simbal along the Lahore-Islamabad Motorway (M-2) in the Salt Range area, after a period of intense Monsoon rainfall (Figure 1). As a result of that event approximately 91,500 m? colluvium and 41,000m? of limestone and shale boulders translated down slope and blocked one lane of the motorway (Ahmed et al., 2012).
Figure 2. A) Upper part of the landslide failure surface, red squares showing the sample location on the slip surface, B) Toe of the landslide, stabilized with a retaining/gabion wall structure after failure (photographs, 2009) The Simbal Landslide occurred in the Precambrian Salt Range Formation, along the leading edge of an emergent thrust sheet (Wynne, 1878; Yeasts et al., 1984; Lillie et al., 1987). The landslide activated from an area along the flank of Skaser Hill, underlain by limestone of early Eocene age (See Figure 2 A&B). The maximum thickness of the Eocene limestone in this area is about 70m (Gee 1935; Fermor 1935). There were also a number of large size boulders (> 2m) present in the landslide material, which were brought down by the landslide. Some of these boulders were observed to be embedded in the day-lighted failure surface. The landslide was approximately 75m long, 90m wide and 50m high. The pre-failure slope was inclined between 42° and 45° as observed in the field.
Figure 2. A) Upper part of the landslide failure surface, red squares showing the sample location on the slip surface, B) Toe of the landslide, stabilized with a retaining/gabion wall structure after failure (photographs, 2009) The Simbal Landslide occurred in the Precambrian Salt Range Formation, along the leading edge of an emergent thrust sheet (Wynne, 1878; Yeasts et al., 1984; Lillie et al., 1987). The landslide activated from an area along the flank of Skaser Hill, underlain by limestone of early Eocene age (See Figure 2 A&B). The maximum thickness of the Eocene limestone in this area is about 70m (Gee 1935; Fermor 1935). There were also a number of large size boulders (> 2m) present in the landslide material, which were brought down by the landslide. Some of these boulders were observed to be embedded in the day-lighted failure surface. The landslide was approximately 75m long, 90m wide and 50m high. The pre-failure slope was inclined between 42° and 45° as observed in the field.
Figure 3. A & B) Soil sampling by Shelby Tube sampler, C & D) In-situ density determination by Core Cutter Method (IS- 27270, Part 29) matrix soil was determined (Figure 3). The average dry density of the landslide soil was found to be ~14.2 kN/m’.
Figure 3. A & B) Soil sampling by Shelby Tube sampler, C & D) In-situ density determination by Core Cutter Method (IS- 27270, Part 29) matrix soil was determined (Figure 3). The average dry density of the landslide soil was found to be ~14.2 kN/m’.
Figure 4. Gradation curve obtained from sieve analysis and hydrometer results of the soil matrix representing the Simbal landslide slip surface The average specific gravity of the landslide matrix was determined as 2.67, using “Standard Test method of Specific Gravity of Soil” (ASTM D854-97). This specific gravity value was used to calculate the void ratio and porosity of the soil samples and further to calculate the degree of saturation at different dry densities. The results of the Atterburg Limits tests (ASTM D4318) revealed that the liquid limit of the soil samples was 31%, the plastic limit 22%, and hence, Plasticity Index of 9, which is quite low. On the basis of the test results, the soil was classified as A-2-4(AASHTO) or GC (USCS) Silty Clayey Gravel.
Figure 4. Gradation curve obtained from sieve analysis and hydrometer results of the soil matrix representing the Simbal landslide slip surface The average specific gravity of the landslide matrix was determined as 2.67, using “Standard Test method of Specific Gravity of Soil” (ASTM D854-97). This specific gravity value was used to calculate the void ratio and porosity of the soil samples and further to calculate the degree of saturation at different dry densities. The results of the Atterburg Limits tests (ASTM D4318) revealed that the liquid limit of the soil samples was 31%, the plastic limit 22%, and hence, Plasticity Index of 9, which is quite low. On the basis of the test results, the soil was classified as A-2-4(AASHTO) or GC (USCS) Silty Clayey Gravel.
Table 1. Summary of dry density test results
Table 1. Summary of dry density test results
Figure 5. Soil moisture-density relationships from Standard Proctor and Modified Proctor tests The influence of dry bulk density of the soil matrix material was examined by compacting remolded samples using both the Standard Proctor method (ASTM D698-07) of 600 kN-m/m’ and the Modified Proctor method (ASTM D1557-97) of 2,700 kN-m/m’. These tests were performed on specimens of the landslide soil matrix to obtain the optimum moisture content and maximum dry unit weight in order to conduct a series of shear strength tests at various densities. The results of soil matrix moisture-density tests (Figure 5) showed that the maximum dry densities were 16.3kKN/m? for the Standard Proctor and 18.5kN/m* Modified Proctor test, respectively. Increasing compaction density effect reduces the void sizes in the soil sample (Figure 5 and Table 1).
Figure 5. Soil moisture-density relationships from Standard Proctor and Modified Proctor tests The influence of dry bulk density of the soil matrix material was examined by compacting remolded samples using both the Standard Proctor method (ASTM D698-07) of 600 kN-m/m’ and the Modified Proctor method (ASTM D1557-97) of 2,700 kN-m/m’. These tests were performed on specimens of the landslide soil matrix to obtain the optimum moisture content and maximum dry unit weight in order to conduct a series of shear strength tests at various densities. The results of soil matrix moisture-density tests (Figure 5) showed that the maximum dry densities were 16.3kKN/m? for the Standard Proctor and 18.5kN/m* Modified Proctor test, respectively. Increasing compaction density effect reduces the void sizes in the soil sample (Figure 5 and Table 1).
Figure 6. Variation in the coefficient of permeability with dry density of the soil matrix material The Falling Head Permeameter test (ASTM D2434) was used to evaluate hydraulic conductivity of the landslide soil matrix. This was felt to be more appropriate procedure for coarse-grained soils as well as fine-grained soils. A goal of this test was to evaluate the change in hydraulic conductivity with in-situ dry density. The purpose of this was to investigate the effect of soil densification on permeability of the soil, and later, to verify how the degree of saturation varies with soil densification.
Figure 6. Variation in the coefficient of permeability with dry density of the soil matrix material The Falling Head Permeameter test (ASTM D2434) was used to evaluate hydraulic conductivity of the landslide soil matrix. This was felt to be more appropriate procedure for coarse-grained soils as well as fine-grained soils. A goal of this test was to evaluate the change in hydraulic conductivity with in-situ dry density. The purpose of this was to investigate the effect of soil densification on permeability of the soil, and later, to verify how the degree of saturation varies with soil densification.
Figure 7. Stress - Strain curve to find the maximum unconfined compressive strength (UCS) of test samples
Figure 7. Stress - Strain curve to find the maximum unconfined compressive strength (UCS) of test samples
Table 2. UU triaxial test results, comparison of cohesion and friction angle with the varying degrees of saturation
Table 2. UU triaxial test results, comparison of cohesion and friction angle with the varying degrees of saturation
Figure 8. Relationships between deviator stress and axial strain at varying degrees of saturation on samples remolded to the in-situ field density 2 presents a summary of the triaxial test results. The specimen cohesion intercept decreased from 42.4 kPa (at 40% saturation) to 5.5 kPa (at 88% saturation); while the angle of internal friction decreased from 35.4° (at 30% saturation) to just 4° (at 88% saturation). Figures 10 present the variation of cohesion and friction with percent saturation. Note that the cohesion rises markedly from 20 to 40% partial saturation, and then decreases linearly with increasing levels of partial saturations; the Figure 10 further illustrates how the inter-particle friction decreases almost linearly with increasing moisture content.
Figure 8. Relationships between deviator stress and axial strain at varying degrees of saturation on samples remolded to the in-situ field density 2 presents a summary of the triaxial test results. The specimen cohesion intercept decreased from 42.4 kPa (at 40% saturation) to 5.5 kPa (at 88% saturation); while the angle of internal friction decreased from 35.4° (at 30% saturation) to just 4° (at 88% saturation). Figures 10 present the variation of cohesion and friction with percent saturation. Note that the cohesion rises markedly from 20 to 40% partial saturation, and then decreases linearly with increasing levels of partial saturations; the Figure 10 further illustrates how the inter-particle friction decreases almost linearly with increasing moisture content.
Figure 9. Failure envelopes for Simbal landslide matrix for different normal stresses with a remolded dry density of 14.2kN/m?
Figure 9. Failure envelopes for Simbal landslide matrix for different normal stresses with a remolded dry density of 14.2kN/m?
Figure 12. Observed relationship between shear and normal stress at the in-situ (natural) dry density (yq =14.2 kN/m*)
Figure 12. Observed relationship between shear and normal stress at the in-situ (natural) dry density (yq =14.2 kN/m*)
Figure 13. Results of direct shear tests, between shear stress and horizontal deformation (6, = 36 kPa) at Standard Proctor dry densities (vq =16.3 kN/m’)
Figure 13. Results of direct shear tests, between shear stress and horizontal deformation (6, = 36 kPa) at Standard Proctor dry densities (vq =16.3 kN/m’)
Figure 14. Plots of shear versus normal stress in the direct shear tests, illustrating fairly linear relationships at Standard Proctor dry densities (yy =16.3 kN/m°)
Figure 14. Plots of shear versus normal stress in the direct shear tests, illustrating fairly linear relationships at Standard Proctor dry densities (yy =16.3 kN/m°)
Figure 15. Plots of the shear stress versus shear displacement (at 6,= 36 kPa) for varying degrees of saturation and constant rate of shearing at Modified Proctor densities (yg =18.5 kN/m*)
Figure 15. Plots of the shear stress versus shear displacement (at 6,= 36 kPa) for varying degrees of saturation and constant rate of shearing at Modified Proctor densities (yg =18.5 kN/m*)
Figure 16. Relationship between shear stress and normal stress at Modified Proctor dry densities (vq =18.5 kN/m°)
Figure 16. Relationship between shear stress and normal stress at Modified Proctor dry densities (vq =18.5 kN/m°)
Figure 17. Variation in apparent cohesion of the soil matrix at different dry densities at varying degrees of saturation
Figure 17. Variation in apparent cohesion of the soil matrix at different dry densities at varying degrees of saturation
Figure 18. Variation of friction angle of the soil matrix at different dry densities at varying degrees of saturation
Figure 18. Variation of friction angle of the soil matrix at different dry densities at varying degrees of saturation
Related topics:
GeologyGeotechnical EngineeringDegree of saturationDry Density
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