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Finite element methods
Published in John C. Small, Geomechanics, 2018
The effective stress within a soil will increase with depth due to the overburden pressure. The lateral stress is related to the vertical stress by the earth pressure coefficient K′0. This effective stress variation with depth is shown in Figure 3.17, where the vertical effective stress and the lateral effective stress are seen to increase with depth. At any point in the soil, we therefore have () p′=σ′v+2K′0σ′v3=(1+2K′0)σ′v3q′=σ′v−K′0σ′v=(1−K′0)σ′v
Simple Equations for Estimating Bearing Capacity of Liquefiable Soils Underneath Shallow Foundations
Published in Journal of Earthquake Engineering, 2022
Arman Kazemi, Hadi Shahir, Peyman Ayoubi
Effect of overburden pressure () due to foundation embedment on the liquefied bearing capacity is presented in Fig. 6 for a square foundation of 10-m width. In order to study the effect of overburden pressure on both mechanisms of failure, 10 and 15 m have been considered as liquefaction thicknesses and the related graphs are presented in Fig. 6(a,b). In Fig. 6(a) in which the liquefaction thickness is equal to foundation width and lateral failure mechanism is dominant, increasing the foundation embedment depth leads to greater bearing capacity. In Fig. 6(b) in which the liquefaction thickness is greater than the foundation width, punching failure mechanism is dominant for soil 1 while lateral failure mechanism is observed for soil 3. In the case of soil 2, however, punching failure mechanism is dominant for pressures less than 20 kPa, and lateral failure is observed for values greater than 20 kPa. This could be attributed to tendency of foundation soil to punching failure in lower overburden pressure due to embedment and to the lateral failure in higher values of overburden pressures. Likewise, the lateral failure mechanism, in the punching failure mechanism also, as foundation depth increases, the bearing capacity in liquefaction condition gets greater. As observed in Fig. 6(b), the gradient of line for soil 1 is greater than soil 3, meaning that the effect of surcharge on bearing capacity of punching failure is greater than lateral failure.
Three dimensional undrained bearing capacity analysis of laterally loaded pile in heterogeneous marine deposits
Published in Marine Georesources & Geotechnology, 2022
Ardavan Izadi, Reza Jamshidi Chenari
Three different idealized types of undrained shear strength profile for natural marine clay deposits were observed by Davis and Booker (1973). Recent marine deposits without surface strength exhibit undrained shear strength increasing linearly with depth (λ) as demonstrated in Figure 1a. The aged marine deposits, as demonstrated in Figure 1b, bear a surface shear strength of Cu0 increasing through depth with a trend similar to recent marine deposits. For a firm to stiff normally and lightly over-consolidated clays illustrated in Figure 1c, a constant range of undrained shear strength was observed up to the transformation depth (Zt) as elaborated by Jamshidi Chenari and Karimian (2011). At further depth, the soil strength increases with depth and effective overburden pressure. Based on the mineralogy of marine clay deposits, a range of 0.6–3 kPa/m for λ was reported in the literature (Davis and Booker 1973; Tani and Craig 1995).
Seismic response evaluation of structures on improved liquefiable soil
Published in European Journal of Environmental and Civil Engineering, 2021
Ayman Abd-Elhamed, Sayed Mahmoud
When a saturated cohesionless soil is subjected to ground shaking during an earthquake, it tends to densify. The volume reduction due to the rapid loading condition occurs over a very short period of time and causes the generation of excess pore water pressure in an undrained condition. With continuing vibration, the pore water pressure builds up and causes a decrease in the effective stress. At the point where the excess pore pressure equals the total overburden pressure (i.e., the state of zero effective stress), the soil completely loses its strength and behaves as a viscous liquid as opposed to soil (see Figure 4). As shown in Figure 4a, the particles distribution indicate that the ground is stable where the ground particles are interlocked with each other. However, the occurrence of an earthquake causes repeated shearing stresses, and thus the ground particles are separated from each other due to the loss of the effective stress as shown in Figure 4b. At this stage, the ground turns into a liquid state, and the particles continue to decrease with increases in the water level (see Figure 4c).