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The mechanical behavior of sandy ground during shallow circular tunneling is explored for various overburden heights H (=0.5D, 1.0D, 1.5D and 2.0D; D is the diameter of the tunnel) and various dilatancy coefficients (ψ/ϕ = 0, 1/3, 1/2, and 1; ϕ and ψ are the internal friction angle and dilation angle, respectively) through finite difference analyses. The ground is modeled as a linear elastic-perfectly plastic material that employs the Mohr–Coulomb yield criterion and obeys the non-associated flow rule. The ground reaction curve is applied in conjunction with the stress path as a conceptual tool for interpreting the mechanical response of the ground to tunneling. It is revealed that, at a certain relaxation value, a yield zone develops during tunneling and extends to the surface. This relaxation value increases with increases in the overburden and ψ/ϕ values for the cases of less shallow tunnels (i.e., H = 1.0D, 1.5D and 2.0D), while for the shallowest case (H = 0.5D), the extent of the yield zone to the ground surface is not sensitive to the ψ/ϕ value. The shear strain due to tunneling also increases with an increase in the ψ/ϕ value. Moreover, the ψ/ϕ value affects the radial displacement and the surface settlement due to tunneling. The magnitudes of the surface settlement and the radial displacement at the tunnel crown both decrease with an increase in the ψ/ϕ value. The relative difference in the displacement at the tunnel crown between the upper bound and lower bound values, ψ/ϕ (at the last computed stage), increases with an increase in the overburden height. It is recommended, therefore, that careful consideration be given to the dilatancy angle in the case of relatively less shallow tunnels. Keywords: Shallow tunnels, Dilatancy, Overburden, Ground reaction curve, Stress path

Much of the seismic activity of northern Sweden consists of micro-earthquakes occurring near postglacial faults. However, larger magnitude earthquakes do occur in Sweden, and earthquake statistics indicate that a magnitude 5 event is likely to occur once every century. This paper presents dynamic analyses of the effects of larger earthquakes on an upstream tailings dam at the Aitik copper mine in northern Sweden. The analyses were performed to evaluate the potential for liquefaction and to assess stability of the dam under two specific earthquakes: a commonly occurring magnitude 3.6 event and a more extreme earthquake of magnitude 5.8. The dynamic analyses were carried out with the finite element program PLAXIS using a recently implemented constitutive model called UBCSAND. The results indicate that the magnitude 5.8 earthquake would likely induce liquefaction in a limited zone located below the ground surface near the embankment dikes. It is interpreted that stability of the dam may not be affected due to the limited extent of the liquefied zone. Both types of earthquakes are predicted to induce tolerable magnitudes of displacements. The results of the postseismic slope stability analysis, performed for a state after a seismic event, suggest that the dam is stable during both the earthquakes.

Shallow and deep seated landslides in natural slopes are often induced by rainfall. The cause of the failure is usually considered to be due to the decrease in effective confining stress due to a suction loss by water infiltration. However, rainwater infiltrates into the slope surface resulting in a reduction of shear strength of soil and deformation and failure may occur even without significant change in effective stress. It is thus essential to examine the deformation and failure characteristics of the soil induced by wetting. This study investigates on the wetting-induced deformations under isotropic compression condition and triaxial shearing condition using a triaxial test apparatus for unsaturated soils. Two soil samples collected from the active landslide sites from Pakistan were used to examine both the shear strength and deformation behavior during water infiltration at different levels of deviatoric stress by keeping the deviatoric stress constant during the water infiltration stage. The test results showed that, even though the deviatoric stress is kept constant during water permeation at different stress levels, the distortional deformation was exhibited due to wetting by a significant amount for both samples. The effect of water infiltration on the deformation behavior of unsaturated soil regarding the change in the degree of saturation and void ratio was also observed. There was a decrease in the void ratio for both specimens during increasing the degree of saturation at different level of deviatoric stress ratio. Under higher deviator stress, more decrease in void ratio and an increase of the degree of saturation were observed. Therefore, it can be said that deformation of soil due to water infiltration is a critical phenomenon and it should be considered while analyzing the soil behavior due to water infiltration by rainfall or rise in groundwater level, even if the slope is not failed, significant deformations may hinder the performance of natural slopes. [ABSTRACT FROM AUTHOR]

The territory of Azad Jammu and Kashmir (AJK) is vulnerable to different natural hazards because of its proximity to a geo-dynamically active zone and its tropical and monsoonal climatic pattern. Both factors operate in various combinations and result in the occurrence of disasters generated by natural hazards like floods, earthquakes, and landslides at different intervals. There are numerous landslides in the study area, out of which the Donga Kass landslide has been selected for study due to its ongoing activity which poses a significant risk to the nearby community and infrastructure. Therefore, assessment of two possible triggering factors (i.e., earthquake and rainfall) for this landslide was conducted through the laboratory testing using the DPRI-5 Ring shear simulator. Undrained cyclic loading tests were performed to simulate the dynamic loading and earthquake-induced landslides, while pore pressure control tests simulated the rise of groundwater level during rainfall for rainfall-induced landslides. Based on the laboratory test results, a critical seismic acceleration and a critical pore pressure ratio are suggested for Donga Kass landslide. Using these values and combining with rainfall data and monitored pore water pressure in bore holes, early warning system can be activated to reduce any potential landslide risk in the future. [ABSTRACT FROM AUTHOR]