International Journal of Civil Engineering
Volume:18 Issue: 2, Feb 2020

The presented geotechnical random field (GRF) algorithm is utilized to realize the soil inherent variability based on in situ site investigation results. This paper aims at investigating the effect of cone penetration test (CPT) borehole arrangements in horizontal plane on slope stability reliability analysis considering stochastic fields of soil design parameters via the conventional stationary along with the non-stationary random field adopted in the GRF approach. An advantage of the GRF algorithm is that it yields conservative results in comparison to the conventional stationary random field theory; therefore, using non-stationary random field underestimates slope stability reliability. The current study tried to highlight the importance of the availability of in situ profiles of soil strength parameters when stability analysis of geotechnical structures is concerned. Slope stability was chosen to interpret the role of the CPT profiles in the adjacent site in determining the factor of safety of the slope against shear failure. Furthermore, the results of the case under study showed that when the geometric dimensions of the slope are too small compared to the horizontal correlation length, more CPT borehole data availability leads only to very slightly conservative results in comparison to the case with single available CPT profile.

The paper focuses on the geotechnical experiments and numerical simulation of 2D consolidation analysis for the cohesive soils fully saturated by solutions of four salt concentrations, i.e. 0.0, 9.9, 19.8, and 33.0 g/L. The experiments were carried out on undisturbed soil samples taken from the boreholes in Hanoi area where the subsoil has not been affected by saline intrusion yet. The composition and properties of the cohesive soil in salt-affected conditions were investigated with transmission electron microscopic method and other geotechnical experiments. Consolidation analysis with finite element method was applied to an assumed embankment on saline subsoil. The analytical results showed that swelling mineral of montlorillonite is present in the Hanoi cohesive soils. The water content of the studied soils decreases as the salt concentration increases. Meanwhile, the bulk density unclearly changes in the same testing conditions. The coefficient of consolidation reduces, respectively, with the salinities, from 22 to 50% as salinities rise up to 33.0 g/L. Compressibility index increases linearly and proportionally with the salinities. In 2D analytical model, the settlement or vertical displacement of the subsoil in HD1 site reaches 14.8% and that of GL2 site is 18.7% at saline solution of 33.0 g/L. The horizontal displacement of the subsoil reaches 13.90% in HD1 site and 17.55% in GL2 site from the baseline. The time at primary consolidation completion is longer as saturated solution is saltier. The prolongation of primary consolidation time gets over 30% if the subsoil is at the most salty. These changes illustrate the degradation of soils in the saline media.

Design and analysis of geosynthetic-reinforced soil structures subjected to repeated loading (e.g. compaction, traffic and earthquake loads) require a proper understanding of the cyclic soil–geosynthetic interface behaviour. This research is undertaken to study the interface properties between sand-expanded polystyrene (EPS) mixtures and geogrid reinforcement under cyclic loading. A series of cyclic tests is performed and the influences of normal stresses, cyclic shear amplitudes and number of cycles are studied. The experiments are conducted using a large-scale direct shear test device allowing to perform displacement-controlled cyclic tests. Accordingly, the influence of the aforementioned parameters on interface shear stiffness and damping ratio is discussed. The results of the experiments showed that adding 0.9% EPS beads to the sand bed leads to the decrease in interface shear stiffness by 30% to 63%, depending on the shear displacement amplitude. In contrast, for the same EPS content ratio, the interface damping increases roughly twice, irrespective of the applied shear displacement amplitude. The value of hardening factor was also found to increase with cycle number under different normal stress levels.

In this paper, a theoretical approach is established to determine the active wedge angle of unsaturated soils, based on the limit equilibrium method, while matric suction varies linearly with respect to depth. In the previous researches, constant suction distribution profile within the soil has been pointed out, however, generally linear and nonlinear suction profiles develop above the ground water table. The range of suction value covers transition zone and residual zone of unsaturation. Sensitivity of the proposed model, with respect to different parameters, shows that the value of active wedge angle is more dependent on the internal friction angle, in comparison to other properties. Therefore, instead of a complex relation, simple equation can be used. The results show that the active wedge angle for unsaturated soils is equal to π6+78ϕ. Comparisons between the presented model and experimental data show that, for some values of internal friction angle, the active wedge angle in unsaturated state is close to saturated state.

Previous studies regarding geosynthetic-reinforced pile-supported (GRPS) embankments over soft soils have mainly focused on load transfer mechanisms and design approaches. However, little attention was given to the lateral performance of rigid piles in GRPS embankment systems. This paper presents the results of 3D finite element analyses to examine and compare the lateral response and failure mechanisms of floating and end-bearing piles in soft soils under geosynthetic reinforced embankments. The effects of geosynthetic reinforcement and pile length on the stability of the embankments are also investigated. The results indicate that the induced lateral responses in the piles are distinctly different for floating and end-bearing piles. Failure of the floating pile is primarily caused by the inclination of the pile. However, for end-bearing piles, bending failure is clearly established as the principal mode of failure. The benefit of the geosynthetic layers in improving the stability of piled embankments is not particularly apparent. Moreover, the increase in pile length is significant in enhancing the stability of GRPS embankments. Specifically, when the normalized pile length varies from 0.75 to 1.15, the critical height of embankment increases from 6.2 to 11.8 m. However, the effect of pile length becomes negligible when the normalized pile length exceeds 1.15. The lateral movement and failure modes of GRPS embankments are strongly dependent on pile length. Therefore, it is essential to consider this aspect when analyzing the stability of the GRPS embankment.

This study was aimed to determine the influence of temperature within the landfill on the shear strength of the MSW samples through the shearing procedure. Different waste samples, i.e., the fresh (C1), 2 years old (C1-2Y) and lab oratory prepared (C2) MSW samples, were heated up, prepared, and placed in the shearing box with the designated temperatures of about 25, 45, and 65 °C (i.e., the range of an anaerobic landfill). The Mohr–Coulomb strength parameters for the warmed-up and room-temperature specimens were separately calculated and compared. The temperature decreases the friction angle from 21 to 17° for T > 45 °C. The cohesion was also decreased by temperature from 19.9 to 13.1 kPa. In addition, two nonlinear envelopes were developed for the specimens tested at room and simulated temperature within the landfill. The test results show a reduction of about 20% for friction angle and shear strength at the temperatures between 45 and 65 °C. Although the warmed-up specimens of fresh MSW were denser under certain normal stress, heating the MSW specimens to temperatures of 45 and 65 °C resulted in loss of the shear strength. Results further indicated that the temperature of the wastes plays an important role when the shear stress is conducted on the MSW specimens. It can be then concluded that temperature of the landfill should be considered as a factor influencing the shear strength of MSW. Considering temperature for site investigation of the shear strength and the correlation of the results with the laboratory tests is important, too.

Stabilizing micropile groups is a light retaining structure constructed quickly and safely for slope reinforcement in practice. To carry out engineering design of any structure, a simplified analytical procedure for a micropile group with consideration of stability of the piled slope is presented. According to the upper bound theorem of kinematical limit analysis, an analytical method is proposed to evaluate the net thrust force on a micropile group with 3 × 3 layout of piles and the slip surface of the piled slope for a specified factor of safety. Then, internal forces of the micropile group can be computed using plane rigid frame model for the part of the structure above the slip surface under the net thrust force and beam-on-elastic-foundation model for the rest part. A laboratory model test and corresponding 3D-numerical simulation are conducted to verify the proposed method. Moreover, analysis of a practical slope shows that flexural rigidity of a micropile and micropile numbers of a group have a great effect on internal forces of micropiles. In particular, the internal forces are relatively sensitive to pile numbers in a group. However, micropile length and spacing in plane in a group have little effect on the internal forces, which is rather different from traditional stabilizing piles with a large cross section.

This paper presents both experimental and numerical study on a slope made up of c-ϕ soil. The effect of different reinforcements such as geotextile and geogrid are also studied in both cases. Small shaking table tests are conducted on the model slope to evaluate the different parameters like acceleration amplifications and horizontal deformation at different levels of the slope. In addition to the variation of the c-ϕ nature of the soil, the variation of water content is also done for the model soil slope. The effect of variation of frequency level, base shaking and a number of reinforcement layers are also studied. Using PLAXIS, numerical models are developed for both unreinforced and reinforced soil slope made up of c-ϕ soil. Comparison of the results as obtained from the experimental study is done with those of the numerical models. Results presented either in tabular form or graphically and from the results acceptability of the models is also discussed.

In this paper, the interaction phenomenon of two closely spaced symmetrical circular plate anchors buried at shallow depth in homogenous and layered sand strata was carefully observed from a series of large-scale model tests. A numerical model is further proposed by validating the experimental data. The motivation for the present investigation actually arrived from the fact that the uplift capacity of anchors is often analyzed as a single entity, whereas the anchors are actually placed in group. The present experimental observations revealed that the interacting anchors experience higher displacement along with the significant reduction in the uplift capacity at the closer spacing. Similar to the single anchors, the uplift capacity of interacting anchors increases with the embedment depth. The size effect of the anchor plate is found to be a significant parameter in pronouncing the interaction effect. However, the rate of reduction in the uplift capacity mainly depends on the embedment depth and the relative density of soil. Unlike the homogenous sand bed, the shear mobilization is not uniform in a layered sand bed although the rupture surface is progressive from the edge of the anchor plate to the ground surface in both the cases. The proposed numerical model performs well in capturing the interaction of circular plate anchors in homogenous and layered sand bed as well. The quality of the results is assured by comparing with the similar works available in the literature.

Results of several cyclic triaxial and resonant column experiments on calcareous sand were presented by the authors in a preceding paper to obtain the shear modulus and damping ratio of the sand under various effective confining pressures and relative densities. The calcareous sand was taken from Bushehr, one of the most strategic ports of Iran in the Persian Gulf. This technical note compares dynamic properties of this coastal sand with a comprehensive database compiled from the experiments on various siliceous sands. The discrepancy observed between the experimental results of the calcareous sand and those of the siliceous sands is demonstrated. These differences can be attributed to the grains’ shape, mineralogy, and texture of the calcareous and siliceous sands. The comparative study provides useful insights into the dynamic properties of the studied calcareous sand.