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Geomechanics and Engineering Volume 30, Number 3, August10 2022 , pages 219-231 DOI: https://doi.org/10.12989/gae.2022.30.3.219 |
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Effect of degree of compaction & confining stress on instability behavior of unsaturated soil |
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Ali Murtaza Rasool
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| Abstract | ||
| Geotechnical materials such as silt, fine sand, or coarse granular soils may be unstable under undrained shearing or during rainfall infiltration starting an unsaturated state. Some researches are available describing the instability of coarse granular soils in drained or undrained conditions. However, there is a need to investigate the instability mechanism of unsaturated silty soil considering the effect of degree of compaction and net confining stress under partially and fully drained conditions. The specimens in the current study are compacted at 65%, 75%, & 85% degree of compaction, confined at pressures of 60, 80 & 120 kPa, and tested in partially and fully drained conditions. The tests have been performed in two steps. In Step-I, the specimens were sheared in constant water content conditions (a type of partially drained test) to the maximum shear stress. In Step-II, shearing was carried in constant suction conditions (a type of fully undrained test) by keeping shear stress constant. At the start of Step-II, PWP was increased in steps to decrease matric suction (which was then kept constant) and start water infiltration. The test results showed that soil instability is affected much by variation in the degree of compaction and confining stresses. It is also observed that loose and medium dense soils are vulnerable to pre-failure instability i.e., instability occurs before reaching the failure state, whereas, instability in dense soils instigates together with the failure i.e., failure line (FL) and instability line (IL) are found to be unique. | ||
| Key Words | ||
| constant shear stress; degree of compaction; failure line; instability; water infiltration | ||
| Address | ||
| Ali Murtaza Rasool: National Engineering Services Pakistan (NESPAK), Lahore, Pakistan; University of Central Punjab (UCP), Lahore, Pakistan; National College of Arts (NCA), Lahore, Pakistan 4Department of Civil & Environmental Engineering, Saitama University, Japan | ||