Search

The utilization of a mechanically stabilized earth wall (MSE wall) is prevalent due to its stability and cost-effectiveness compared to conventional earthwork construction methods. In addition, the railway transportation infrastructure has played a vital role in connecting Thailand's numerous regions. The behavior of a 6-m-high MSE wall constructed on a hard ground foundation, which was reinforced with high-density polyethylene on one side and a metallic strip on the other side, was studied in this research. The purpose of this MSE wall is to support the railway structure under dynamic train loads at 100, 150, and 200 km/h. The three-dimensional finite-element method was used to simulate and investigate the behavior of the MSE wall in terms of lateral displacement, settlement, and strain of reinforcement materials. The findings of the study demonstrate that there is a positive correlation between train speed and both lateral displacement and settlement. This relationship is most pronounced at the top of the MSE wall, which is primarily attributable to the influence of surface waves. The MSE wall's behavior under the influence of dynamic train loads was most prominently displayed by the surface waves, which were a curved wavefront at 150 km/h and a Mach cone at 200 km/h. The settlement profile increased when the speed of dynamic train loads increased. The impact of velocity fluctuations on the strain of the reinforcement material was insignificant. Due to the hard ground foundation, the behavior of the MSE wall on both types of reinforcement materials exhibited similar tendencies. Moreover, it was observed that the maximum tension lines closely follow the bilinear coherent gravity method with a standard distance of 0.3H from the facing, where H represents the equivalent height of the MSE wall. [ABSTRACT FROM AUTHOR]

The development of underground spaces generates large amounts of construction wastes, which are generally disposed for the landfill outside of the city in China. This study briefly reviewed a landslide tragedy of a CSW landfill in China; Lessons learned from the failure of risk assessment and preventions were discussed, which showed that two challenging strategies are significant for the risk identification and mitigation. One is the effective early warning system based on field large-deformation measurement; the other is the efficient risk assessment with internal deformation data. To this end, a new sensing method is developed for the large-deformation measurement inside CSW landfills. The proposed fibre-optic based transducer can measure large deformation of up to 1200 mm with a high accuracy. Finally, the risk assessment of CSW landfill was proposed with the combined use of field monitoring data and risk evaluation model. The theoretical equations for stability analysis and potential application framework for the application of this technique in the risk assessment of CSW landfill landslide are presented. This approach possesses the advantages of capturing excessive and irregular deformation of solid waste landfills and of efficient response for the risk mitigation with the help of early warning system.

The bentonite is commonly used mixed with soils for groundwater retention and waste contaminant facilities. The incorporation of bentonite could significantly reduce hydraulic conductivity. In this study, the effects of bentonite content, hydration time and effective confining pressure on the static properties of a sand–bentonite mixture were studied using experimental and numerical methods. Firstly, a large number of drainage static triaxial tests on the sand–bentonite mixture with various bentonite contents were conducted. The test results show that the increase in bentonite content and hydration time leads to a slight decrease in shear strength and initial tangent modulus of the sand–bentonite mixture. The presence of bentonite reduces the shear shrinkage and dilatancy trend of the mixture. The cohesion of the mixture increases with the increase in bentonite content and hydration time, but the internal friction angle decreases correspondingly. The hydration of bentonite on the surface of sand particles changes the contact form between particles. The bentonite slurry between pores of the sand skeleton also affects the mechanical behavior of the sand–bentonite mixture. Then, a series of 3D discrete element models were established for numerical simulations of drainage static triaxial tests. The numerical model parameters were calibrated by experimental results. The meso-mechanism of bentonite content affecting the mechanical behavior was revealed according to the contact force distribution between particles. The research results are helpful to understand further the mechanism of bentonite on the mechanical properties of the sand–bentonite mixture.

In recent times, large-scale infrastructural projects are being constructed on varieties of soil, especially in highly compressible marine clays and soft soil. The coefficient of consolidation (cv) is one of the most important technical parameters used to estimate the consolidation characteristics of the soil. The experimental laboratory techniques used to obtain cv are time-consuming and possess different practical limitations. In this study, a reliable method for predicting cv is presented based on machine learning (ML). The study considered 11 inherent soil variables, among which the least significant variables are discarded using univariate feature selection technique. Different ML models were developed like the random forest, artificial neural network, and support vector machine for nonlinear mapping of the cv using dimensionally reduced independent variables. Verification against experimental data demonstrates that the Random Forest model accurately predicts the cv (with MAE = 0.0231, MSE= 0.00148, and RMSE = 0.03854). Further, a comparative study of the proposed model is presented with available empirical equations and numerically simulated data. Moreover, the strengths and shortcomings of different ML algorithms are also discussed in detail. [ABSTRACT FROM AUTHOR]

This paper proposes a novel optical fiber sensor-based nondestructive method, namely, the long-gauge fiber Bragg grating (LGFBG) method, for integrity assessment of cement-grouted soil nails. This LGFBG sensor was developed by encapsulating a number of straight, bare FBG sensors inside an aluminum tube, and then mounting them on a steel bar surface for monitoring average strain distributions of soil nails subjected to tension force. Measured strain distributions of LGFBG sensors were finally used for the prediction of effective elastic modulus (EEM) distributions along the soil nails and the assessment of soil nail integrity in terms of the predicted EEM. A number of pullout tests of soil nails with different defects in the laboratory were performed to verify the feasibility of this proposed method. Pullout test results indicate that the elongation contributions of defective soil nail sections are 1.5 to 3 times the intact soil nail sections, whereas the related EEM values of the two defective soil nail sections are around 0.3 to 0.5 times that of intact soil nail sections. The statistical hypothesis Student’s t-test was used to determine the magnitude ranges of the modulus ratio leading to a rejection of the null hypothesis for a prespecified level of significance. In this study, a significance level of 0.01% is suggested for the integrity evaluation of cement-grouted soil nails. [ABSTRACT FROM AUTHOR]

The utilization of fly ash (FA) produced from various thermal power plants and other industrial sources is a big challenge and an opportunity for material and civil engineers. This study aims to utilize FA for improving the engineering characteristics of Montmorillonitic Indian clay (BC) soil. A rigorous testing plan is designed and performed using different proportions of FA (5, 15, 25, and 35 %) to investigate the time-dependent deformation behavior of expansive BC soil and also to examine the influence of the wetting-drying cycle on the time-dependent swelling behavior of reconstituted soils in Oedometric free swell condition. It is proposed to evaluate the time-dependent parameters of the FA-BC matrix under wetting-drying cycles using the elastoviscoplastic considering swelling (EVPS) model. The mineralogical characteristics of both natural and reconstituted samples were investigated using the scanning electron microscope and X-ray diffraction. From the experimental result, it is observed that the time-dependent swelling coefficient decreases with the percentage of FA content increase. The FA used in the study results in decreasing not only the swelling potential of BC soil samples but also the swelling-shrinkage behavior of the soil. It is observed that the reconstituted soils are influenced by both the degree of FA content and the wetting-drying cycles. The swelling strain limit decreases exponentially with the increase of the FA content. The EVPS model works very well in predicting the long-term consolidation and swelling behavior of the FA-BC matrix under different stress states. [ABSTRACT FROM AUTHOR]