Clayey sand soils require improvement in civil engineering projects due to their low density, high porosity, and inadequate shear behavior. On the other hand, the extensive use of cement in soil stabilization is associated with environmental concerns such as high COQ emissions. In this study, the effect of partial replacement of cement with zeolite (up to 50 %) and the addition of polyvinyl alcohol (PVA) fibers (up to 0.8 wt%) on improving the mechanical, microstructural and environmental properties of clayey sand soil was investigated. Samples were prepared with different cement contents (3 and 6 %) and, after 7 and 28 days of curing, were subjected to compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), scanning electron microscope (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and toxicity characteristic leaching procedure (TCLP) tests. The compaction test results showed that maximum dry density (MDD) decreases and optimum moisture content (OMC) increases with increasing zeolite content. The performance of different mixtures showed that the optimum mixture consisted of 6 % cement, 20 % zeolite, and 0.8 % fibers, which increased UCS, ITS, and UPV by 320 %, 194 %, and 35 %, respectively, compared to unstabilized soil. Micro-structural analyses showed the formation of CSH and CAH gels and improved interfacial transition zone bonds. Also, TCLP results showed that zeolite reduced heavy metal leaching. This study, with an innovative approach, investigated the simultaneous effectiveness of zeolite, cement, and fibers and introduced the potential of the UPV method as a non-destructive method for evaluating the mechanical performance of stabilized soil.

This research evaluated the effects of various percentages of crumb rubber, tire scrap fibers, palm fibers, polymer bags fibers, palm ash, and polypropylene fibers on the compaction and compression behavior of clayey sand stabilized with cement. The results of compaction tests showed the maximum dry density decreased as the proportions of these waste materials and cement increased. The most suitable moisture content of soil decreased by increasing the percentages of crumb rubber, tire scrap fibers, and polymer bag fibers, but increased by increasing the percentages of palm fibers, palm ash, polypropylene fibers, and cement. Compared to other wastes, palm fibers had a more substantial effect on the compaction and strength properties of the stabilized soil due to its uniform distribution in the soil and stronger bonding between the soil particles. Moreover, the specimens stabilized with 1% polypropylene fibers and 6% cement showed the best ductility behavior.

Soil liquefaction poses a significant risk to both human lives and property security. Recent in-situ cases have shown that clayey sand can experience multiple liquefaction events during mainshock-aftershock sequences, known as repeated liquefaction. While existing studies have focused on the cyclic behavior of initial liquefaction events, there is a lack of research on the mechanisms and cyclic response of repeated liquefaction in clayey sand. The factors that control repeated liquefaction in clayey sand are still not fully understood. In this study, a series of cyclic triaxial tests were conducted on sand with varying clay content (0 %, 5 %, 10 %, 15 %, and 20 %) under earthquake sequences. The test results showed that the liquefaction resistance initially decreased significantly and then increased with the number of liquefaction events. Sands with higher clay content exhibited earlier recovery of resistance during continuous liquefaction events. The analysis of the test results revealed that the repeated liquefaction resistance of clayey sand was quite intricate. Sands with a relative density (after reconsolidation) below 80 % were primarily influenced by the degree of stress-induced anisotropy, while sands with a relative density above 80 % were mainly affected by relative density.

The liquefaction and weakening of saturated sands under cyclic stress loading is a major concern in earthquake engineering. This study proposes a model based on initial cyclic shear strain (gamma c,i) to predict the excess pore pressure generation in undrained saturated sands. Here, gamma c,i is defined as the average cyclic shear strain prior to the significant accumulation of excess pore pressure. To calibrate and validate the model, a series of undrained stress-controlled cyclic triaxial (CTX) tests were conducted on Fujian sand with 10 % Kaolin clay (FS-10) and Silica sand no.7 with 5 % Kaolin clay (SS7-5). The FS-10 and SS7-5 specimens displayed typical flow liquefaction and cyclic mobility as they approached initial liquefaction. A critical excess pore pressure ratio (ru,c) is introduced to characterize the effects of liquefaction failure modes on excess pore pressure generation. The model also incorporates reduction factors related to small-strain secant shear modulus and reference shear strain to account for variations in calculating gamma c,i. Ultimately, the initial cyclic shear strain-based model exhibited a strong correlation with experimental data under different confining pressures and loading cycles. In addition, it provides a critical initial cyclic shear strain for assessing soil liquefaction in engineering practices, particularly for improved ground with complex stress states.

Seismic loading has been widely recognized as a critical factor contributing to soil liquefaction. This paper introduces centrifuge tests conducted to characterize the seismic response of clayey sand foundations under surcharge induced by upper structures such as dams, with a focus on examining the effectiveness of different liquefaction mitigation measures. Three models with a surcharged block above are considered: one with soil untreated, one improved with stone columns, and the other enhanced by closed diaphragm walls. In addition, a free ground model is tested to examine the dynamic characteristics of the tested soil. Results show that the soil used is prone to liquefaction, but this trend can be somewhat suppressed by the presence of the surcharge. However, the excess pore pressure within the shallow layer keeps rising after shaking, posing the surcharged structure to instability. With the inclusion of stone columns, seepage can be effectively facilitated, thus eliminate the large pore pressure concentration. The construction of closed diaphragm walls effectively reduces the surface settlement by providing lateral restraint of the soil core. This investigation sheds light on the liquefaction mitigation mechanisms of different measures for clayey sand subjected to large overburden and provides references for improving the seismic design.

The study of dredged fill in Guangdong (GD), China, is of great significance for reclamation projects. Currently, there are relatively few studies on dredged fill in Guangdong, and there are many differences in the engineering characteristics of dredged fill foundations formed through land reclamation and natural foundations. In order to have a more comprehensive understanding of the physico-mechanical properties of blowing fill in the coastal area of GD and to understand the effect of its long-term creep row on the long-term settlement and deformation of buildings, the material properties, microstructure, elemental composition, triaxial shear properties, and triaxial creep properties of dredged fill in Guangdong were studied and analyzed through indoor geotechnical tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), and conventional triaxial shear tests and triaxial creep tests. The test results showed that the Guangdong dredged fill is characterized by a high water content, high pore ratio, and high-liquid-limit clayey sand, and the mineral composition is dominated by quartz and whitmoreite. The scanning electron microscopy results showed that the particles of the dredged fill showed an agglomerated morphology, and the surface of the test soil samples had scaly fine flakes and a fragmented structure. In the triaxial shear test, the GD dredged fill showed strain hardening characteristics, and the effective stress path showed continuous loading characteristics; the consolidated undrained shear test showed that the GD dredged fill had shear expansion characteristics under low-perimeter-pressure conditions. It was found that, with an increase in bias stress, the axial strain in the consolidated undrained triaxial creep test under the same perimeter pressure conditions gradually exceeded the axial strain in the consolidated drained triaxial creep test. The results of this study are of theoretical and practical significance for further understanding the mechanical properties of silty soils in the region and for the rational selection of soil strength parameters in practical engineering design.

Based on the actual situation of the project on the Weihai-Yanhai Expressway of Rongwu Expressway, the effects of water content change and the dry-wet cycle on the mechanical behavior of unsaturated clayey sandy soil were analyzed in this study. In this study, ventilated undrained triaxial shear tests were carried out on unsaturated clayey sandy soils with different water contents (6%, 8%, 10%, 12%, 14% and 16%). Concurrently, the soil samples were subjected to three distinct wet and dry cycle pathways (2 similar to 22%, 2 similar to 12%, and 12 similar to 22%) to gain an understanding of how the mechanical features of the soil changed under the different conditions. The test findings demonstrate that when the water content increases, the unsaturated clayey sandy soil's cohesiveness and shear strength diminish. The strength of shear decline exhibits a pattern of first being quick, followed by sluggish. The strength of shear and cohesiveness of clayey sandy soil declined under the influence of the dry and wet cycles, with the first cycle primarily affecting variations in cohesiveness and strength of shear. Furthermore, the strength of shear and cohesiveness of clayey sandy soil diminish more with increasing wet and dry cycle amplitude and upper water content limits. Lastly, the drying shrinkage and hygroscopic expansion of clay particles in clayey sandy soils during wet and dry cycles are not significant, resulting in less structural damage and deterioration of the mechanical properties of the soils. The study's findings have a significant impact on the durability of roadbeds made of unsaturated clayey sandy soil in both wet and dry situations.

Oil pollutants affect the mechanical properties of soils differently. The effect of the kind of oil pollutants on the geotechnical characteristics of a type of soil is an interesting subject that has been examined less in previous studies. The results of this research can be used in designing structures built on soils that are likely to be contaminated with oil pollutants. This study comprehensively investigated the effect of the type of pollutants on the mechanical properties of sandy clay soil to provide the necessary parameters in the remediation plan for soils contaminated with various oil pollutants. A series of laboratory tests, including pH, standard compaction, one-dimensional consolidation, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), falling head permeability, and direct shear, was conducted on the clean and polluted samples. Scanning electron microscopy (SEM) micrographs confirmed that oil pollutants change the soil structure into a flocculated but dispersed one. In addition to the low dielectric constant of oil pollutants, their high viscosity played an important role in altering the geotechnical parameters of clayey sand. The higher the viscosity of the oil pollutant, the higher the maximum dry density (MDD), cohesion coefficient, compression index (Cc), swelling index (Cs), and permeability coefficient of oil-polluted soil. The samples polluted with used motor oil and crude oil, due to their high viscosity, had the greatest drop in compressive strength and shear strength, respectively; whereas the kerosene-polluted sample, due to its low viscosity compared to other oil pollutants, had the greatest rise in compressibility. Thus, in geotechnical plans, special attention should be paid to the bearing capacity and settlement of clayey sand contaminated with crude oil and kerosene, respectively. Oil pollution alters the mechanical properties of soil and poses hazards to the environment.The low dielectric constant and high viscosity of oil pollutants play important roles in changing the properties of soils.Used motor oil greatly reduces the compressive strength of clayey sand, while crude oil and kerosene make the shear stress and settlement of clayey sand more critical, respectively.

Soil deposits containing some amounts of plastic fines (i.e., clay) with different saturation conditions can behave differently under seismic loading, which needs to be considered properly in the design practice. The energybased method (EBM) has been consistently employed as an alternative means to evaluate the liquefaction resistance of soils. Therefore, an experimental study was undertaken to characterize the coupled effects of clay inclusion and saturation degree on the liquefaction resistance and cyclic response of Toyoura sand, using the energy concept. The experimental results showed that the addition of clay and saturation degree significantly affected not only the liquefaction resistance and capacity energy to liquefaction but also the failure mechanism of the Toyoura sand. It was also found that the evolutions of excess pore water pressure, double amplitude axial strain, and stiffness degradation with dissipated energy were greatly influenced by adding clay and change in saturation degree. A novel energy-based model was developed that uniquely correlates the capacity energy to cyclic resistance for all fully and partially saturated clean/clayey sands. For the first time, a unique model was established that directly links the state parameter, under the critical state soil mechanics (CSSM) framework, to capacity energy, EBM, in saturated clean/clayey sands.