International Journal of Civil Engineering
Volume:19 Issue: 2, Feb 2021

The determination of the stress distribution around driven piles in soft clays constitutes a complex problem. The stress distribution is affected by a range of factors such as soil permeability, soil strength, sensitivity, remoulding, distance from adjacent piles and number of piles. The mechanisms of pile installation and subsequent consolidation are investigated by considering that pile installation may be represented by the expansion of a long vertical cylindrical cavity. The stress paths followed by typical soil elements at the soil–pile interface are analyzed by means of the theoretical relationships obtained during the undrained expansion of a cylindrical cavity in soft cohesive soils and modified to take into account the severe remoulding caused by pile installation. It is shown that the shaft resistance of driven piles may be calculated by considering either a drained stress path or an effective stress path during undrained loading. It is also shown that soft clay remoulding caused by pile driving is a major factor that must be taken into account for a reasonable estimation of the limiting skin friction.

Baffle array is generally embedded ahead of the protecting site for reducing rock avalanche’s flow energy. This study explored the arc-shape baffles in comparison with common baffles (cylindrical and square baffles) according to the application of science in practice. The comparing process of three categories of baffles was delved into experimentally, primarily highlighting the disaster reduction effectivity. The comparison of disaster reduction effective between these three categories of baffles is analyzed by three elements, which are deposition, VRR (velocity decrease rate), and U* (dimensionless velocity). Based on the rock avalanche final deposition, the optimal configuration for arc shape, square, and cylindrical baffles satisfy Sr = 4.5 and Sc = 3.5, Sr = 4.5 and Sc = 4.5, and Sr = 4.5 and Sc = 2.5, separately. As suggested from the results, the arc-shape baffle is the optimal case among those three categories of baffle. Shape alteration (cylindrical to arc-shape) can elevate the fragment block degree; the succeeding avalanches can occur around the avalanche deposits, causing kinetic energy to dissipate significantly. Besides, based on the contrast of VRR, U*, and deposition, arc-shape baffle mechanism was reported significantly superior to block. The energy dissipation system of the arc-shape baffle is primarily explained as: (1) the friction of rock fragment will be generated in the movement around the arc surface, thereby causing additional loss of kinetic; (2) a natural cushion is formed when rock fragment accumulated between the arc-shape baffle, being critical to energy dissipation for subsequent rock avalanches.

The paper aims to analyse the influence of slenderness on the ultimate behaviour of piles with a very small diameter (less than 10 cm) that are often employed in soil reinforcement and for which the slenderness can significatively influence the failure behaviour, reducing the ultimate load. The aim is reached by means of numerical analyses on small-diameter piles of different geometries, embedded in clayey soil. The critical load is evaluated numerically in undrained conditions and then compared to the bearing capacity estimated by the classical approaches based on limit equilibrium method. The numerical model is first calibrated on the basis of the results of experimental laboratory tests on bored piles of a small diameter in a cohesive soft soil (average undrained shear strength cu = 15 kPa). The comparison between the critical load and the bearing capacity shows that their ratio becomes less than 1 for critical slenderness LCR that decreases, nonlinearly, with the decreasing of the pile diameter. The results of the analysis show that varying the diameter of the pile from 0.06 to 0.18 m, LCR varies from 65 to 200. The aforementioned evidence suggests that the evaluation of the ultimate load of piles of very small diameter has to follow the considerations on the critical load of the pile, especially if it is embedded in soft soil; on the contrary for piles of greater diameters (bigger than 20 cm) the buckling is not meaningful because LCR is so big that the common slenderness does not exceed it.

In this research, a numerical algorithm was proposed for evaluating the bearing capacity of rough strip footing rested on horizontal half-plane using the stress characteristics method. The bearing capacity coefficients, the layout of stress characteristic lines as well as the geometric specifications of the plastic and non-plastic regions beneath the footing for different values of internal friction angles have been calculated. The obtained results were in good agreement with those reported in the literature for φ≤25∘. The results revealed that by increasing the internal friction angle, the bearing capacity coefficients, as well as the depth of the plastic domain beneath the footing increase and the emergence point of the non-plastic curved wedge moves toward the footing edges. It was also shown that the roughness only affects the bearing capacity factor due to the unit weight and the maximum depth affected by the stress characteristic lines beneath the rough footing was almost 0.62 times the footing's width which corresponds to φ=25∘.

The present study evaluates the effect of stress history and loading conditions on dynamic behavior and failure characteristics of low plasticity cohesive soil. A series of two-way strain controlled cyclic triaxial tests were performed on soil samples collected from seismically active region of Gujarat (India). The effect of stress history and loading conditions on low plasticity soil was evaluated for OCR values of 1–4 and cyclic axial strain amplitude (εa) variation of 0.5%, 1%, 1.5%, and 2%, respectively. The low plasticity soil was observed to undergo liquefaction even at lower amplitude and higher OCR. Liquefaction resistance of soil was observed to increase with the increasing OCR (1–4) and decrease with the increment in cyclic strain amplitude (0.5%—2.0%). The rate of stiffness degradation exhibited bilinear response when pore pressure ratio (ru) was observed to be 0.85. This indicated the generation of cyclic instability prior to flow liquefaction in low plasticity cohesive soil. Two-staged failure response was observed due to the subsequent transition from cyclic instability behavior to flow liquefaction. The low plasticity cohesive soil was found to experience first ‘clay-like behaviour’ due to commencement of cyclic instability and then ‘sand-like behaviour’ due to initiation of flow liquefaction. The low plasticity cohesive soil was observed to experience cyclic instability between 0.85 < ru < 0.95, and then, flow liquefaction at ru > 0.95.

Sabkha (salt-encrusted flat) soils are problematic because they lose strength due to wetting, and they have liquefaction potential. These soils are spread in North Africa, Australia, and most of the Eastern Province of Saudi Arabia. Owing to a lack of experimental studies, the cyclic behavior of sabkha soils is relatively unknown. The monotonic and cyclic behaviors of sabkha soil were studied based on effective stress (50, 100, and 150 kPa) and cyclic stress ratio (CSR) (0.15, 0.35, and 0.65) using cyclic triaxial and bender element tests. Results indicate that the sabkha exhibits ductile behavior with the cohesion value of 9.33 kPa and a friction angle of 33°. The maximum shear moduli are 18,900, 49,500, and 63,500 kPa for effective confining pressures of 50, 100, and 150 kPa, respectively. Furthermore, the shear modulus tended to decrease with shear strain for different cyclic stress ratios. On the other hand, the damping ratio depends on the level of the cyclic stress ratio. At a cyclic stress ratio of 0.15, the damping ratios remained constant with shear strain. For a cyclic stress ratio of 0.65, the damping ratios decreased with shear strain. However, at a cyclic stress ratio of 0.35, the damping ratio varied with shear strain depending on effective stress.

Explosions release energy and generate shock waves. Analysis of how shock waves damage transmission media is crucial in protection engineering. Soil liquefaction due to explosions occurs in a highly nonlinear manner. The time point at which soil receives stress waves has yet to be determined. Therefore, this study analyzed the dynamic reaction and liquefaction phenomenon that protects soil after it has received a shock wave. A numerical analysis model was developed and verified through on-site explosion experiments for measuring ground acceleration and excess water pressure. Finite element analysis was employed to establish a numerical analysis model based on experimental site conditions. The LS-DYNA finite element program was used for numerical simulations. The analysis model had a three-dimensional structure with fluid–solid coupling and consisted of eight-node elements. To analyze the dynamic reaction and liquefaction phenomenon that occurs after soil has received a shock wave, a multimaterial arbitrary Lagrangian–Eulerian calculation model was combined with an element erosion algorithm. Meshes were overlapped to achieve fluid–solid coupling for subsequent analysis. The nonlinear dynamic reaction in soil triggered by shock wave transmission and the liquefaction of the material due to excess water pressure were analyzed. The research results showed that the relative errors between numerical analysis and experimental results were within 10%, verifying that the fluid–solid coupling numerical model developed in this study can effectively be used to analyze the dynamic reactions of materials receiving shock waves. Shock waves from both multisite time-delayed explosions and from continual explosions at a single nearby site lead to soil liquefaction. Compared with single-site explosions, multisite time-delayed explosions more easily trigger liquefaction in saturated sandy soil. Analysis of shock wave transmission characteristics and ground shock effects revealed that at a distance of 600 cm from the explosion center, the shock wave was substantially attenuated. The results of shear strain failure analysis indicated that soil liquefaction had an approximate area of scale distance Z = 30.81–64.89 cm/g1/3 and approximate depth of Z = 17.62 cm/g1/3. The results verify the validity of the numerical model and algorithm developed in this study, which can describe the liquefaction process of saturated soil under explosion loading.

Joint board cable foundation is a kind of foundation form proposed by the author which is applied to transmission lines. In the study of pullout resistance of a joint board cable foundation, the most important factor is the critical depth of the anchor plate. Theoretical analyses, numerical simulations, and field tests were carried out to study the impact of the critical burial depth on the uplift capacity. Test results were corrected by the back-stepping cohesive force method. The theoretical analyses, numerical simulations, and field test results are consistent. It is found that the development of the plastic failure zone in the foundation is directly controlled by the shear strain. Through the field test, the pullout resistance of the anchor plate is studied, and it is found that the depth ratio has the most influence on the pullout capacity of the anchor plate. The field tests also provide valuable data for theoretical calculation, numerical simulation, and design of joint board cable foundations. The field test data analysis and numerical simulation results show that the optimal burial depth ratio of the joint board cable foundation is about 2.5–3.0. Therefore, in the design of the joint board cable foundation, 2.5 can be adopted as the critical depth ratio of the joint board cable.