This article evaluates the long-term wet-dry durability of lime, fly ash, and lime-fly ash slurry injection stabilization of expansive soil in the desiccated state. To achieve this objective, the expansive soil was compacted in large cylindrical test moulds and desiccated after making a central hole for slurry injection. Subsequently, the lime slurry/ fly ash slurry/ lime-fly ash slurry, prepared with the predetermined water-binder ratio, was injected into the desiccated expansive soil and cured for 28 days. The test results of lime and lime-fly ash slurry injected soils showed that there is improvement during the first wetting. However, at the end of four wet-dry cycles, the volumetric deformations of lime- and lime-fly ash slurry-treated soils increased to 10.6% and 13.6%, respectively, which are much lower than the volumetric deformation of untreated soil (30.7%). Additional analyses were also conducted to trace the growth of desiccation cracks of both untreated and treated soils. At the end of the third drying cycle, the total percentage of the cracks (surface cracks + annular gap) in lime slurry- and lime-fly ash slurry-treated soils reduced to 1.18% and 5.37% from the untreated soil value of 31.9%. The findings of the present study underline the positive impact of using lime, and lime in conjunction with fly ash for controlling the volume change behaviour of expansive soils. Furthermore, combination of lime and fly ash significantly reduces the consumption of lime, leading to sustainability in geotechnical practices.

Improper anti-drainage treatment of weakly expansive soil subgrades can lead to significant post-construction deformation and uneven settlement, which severely affect the operational safety and service life of engineering projects. To comprehensively analyze the evolution of soil volume and strength under different hydraulic coupling paths during wetting-drying (W-D) cycles, a loaded W-D cycle testing device was developed. Soil volume was measured during the W-D cycles, and the shear strength and soil-water characteristic curves were analyzed after different cycles. The results indicate that during the W-D cycles, changes in soil volume and strength exhibited distinct stages with similar evolution characteristics. Under the investigated loading conditions, the soil demonstrated significant collapsibility during the wetting process, which gradually diminished as the number of cycles increased. Eventually, the W-D cycles caused the soil to reach an equilibrium state, where its swelling and shrinkage behavior became nearly elastic. At equilibrium state, there is a corresponding void ratio for any moisture content, which is the elastic void ratio (e0el). The e0el is irrespective of the number of cycles and initial dry density. Conversely, higher load and larger amplitude in W-D cycles tend to decrease the e0el. Furthermore, by correlating the unsaturated soil matric suction, secant modulus, and stress path, the volume evolution mechanism of the soil was analyzed based on the soil effective stress theory and pore evolution. The results of this study can serve as a crucial reference point for revealing the deformation mechanism of weakly expansive soil subgrades and selecting appropriate road settlement control methods.

Understanding the volume change behavior of deep-water sediments is essential for the safety design of deep-water engineering structures. In this study, the volume change behaviors of marine sediments from the South China Sea were studied through oedometer and isotropic compression tests. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests have been conducted to investigate the microstructure evolution of two types of sediments under loads. The experimental results showed that the structural anisotropy of intact specimens is more pronounced in oedometer tests with the increase of stress, however, depolarization occurs in the isotropic consolidation test. The volume change after yield in the oedometer and isotropic consolidation tests comes from inter-aggregate pore variations associated with the adjustment of the soil fabric. The reconstituted specimen presents a more uniform distribution of pores than that of the intact specimen, and the macropores are more easily compressed for the reconstituted specimen than those of the intact specimen. With increasing stress, the oedometer compression and isotropic consolidation curves of intact specimens gradually approach those of the reconstituted specimen. The deformation mechanism under high stresses is that soil particles are reoriented and the variation of micropores.

Conventional triaxial apparatus has limited capabilities for advanced testing of frozen soils, such as loading under controlled temperature and volume change measurements. To bridge this gap, in this paper, we presented a novel ultrasound-integrated double-wall triaxial cell designed specifically for stress and strain-controlled, as well as temperature-controlled testing of frozen soils. Monitoring pore ice content during triaxial tests in frozen soils poses a significant challenge. To overcome this hurdle, we developed an in-cell ultrasonic P wave measurement setup, which was integrated into the triaxial device to monitor freeze advancement at any stage of the test. We proposed a three-phase poromechanics-based approach to estimate the pore ice content of frozen soil samples based on the P-wave velocity. A series of creep tests under different freezing temperatures have been undertaken for frozen soil samples to investigate the effect of ice content and temperature on the volumetric deformations of frozen soils during creep tests. Our study demonstrates the potential of the proposed ultrasound-integrated double-wall triaxial apparatus for creep tests of frozen soils.

Industrial wastes cause damage to the environment and pose a threat to public health. The utilization of industrial wastes is inevitable if a circular economy needs to be achieved. Cement kiln dust (CKD) is a potential engineering material that can be used in many civil engineering works. The volume change behavior of a CKD is reported here. One-dimensional swelling and compression tests were carried out on CKD specimens to derive the compressibility parameters and coefficient of permeability. A cyclic wet-freeze-thaw-dry test was carried out to study the volume change of the material upon exposure to various seasonal climatic processes under a low surcharge pressure. The experimental results show that CKD can exhibit swelling under light loads. The correlations between plasticity properties and compressibility parameters that are applicable to fine-grained soils were found to overestimate the parameters of the CKD. The magnitudes of frost heave and thaw settlement were found to be significant, with an uprising type of movement accompanied by strain accumulation when the material was taken through several wet-freeze-thaw-dry cycles.

A series of dynamic centrifuge modeling tests were conducted to evaluate the volumetric threshold shear strain of loose gravel-sand mixtures composed of various ratios of gravel and sand by weight. The maximum and minimum void ratios of the mixtures were evaluated, and the optimum packing condition was determined when the mixture contained approximately 60-70 % gravel by weight. A total of six centrifuge modeling tests were performed at 50-g centrifuge gravitational acceleration. Each centrifuge model was subjected to six shaking events consisting of uniform sinusoidal motions with various amplitudes and numbers of cycles. During the entire duration of the test, the development of excess pore water pressure and settlement was monitored. Empirical relationships of pore water pressure ratio and shear strains were developed for these mixtures. The development of excess pore water pressure in the mixtures with greater than 60 % gravel exhibits transient behavior, while residual excess pore water pressure was observed in the mixtures with less than 60 % gravel. Based on the results, the volumetric threshold strain evaluated from the generation of pore water pressure and volume change during shaking is similar. The values were found to be in a range of 0.03-0.10 % and are influenced by soil composition. The threshold strain increases as the amount of gravel in the soil mixture increases.

The stability of the slopes is critical for ensuring the safety and longevity of soil structures including, embankments, stockpiles, and retaining walls. Many of these soil structures remain in partially saturated conditions throughout their design life. In such cases, the matric suction (i4.'m) becomes a key parameter influencing the stability of the soil. However, i4.'m in soil varies during the water infiltration, leading to potential instability and collapse. To better understand this behaviour, constant shear drained (CSD) tests, which replicate the stress path experienced by the soil during water infiltration were conducted. A series of CSD experiments on silty sand in the partially saturated state was performed to examine the effects of i4.'m on the onset of instability. The results show that the onset of instability in silty sand increases with i4.'m. The volume change behaviour for partially saturated silty sand exhibits dilative behaviour compared to the fully saturated condition for the density considered in this study. Moreover, the methodology for the onset of instability for fully saturated soils was extended to analyse the onset of instability in partially saturated soil. A unique onset of instability was obtained for partially saturated soil using various methods considered for this study.

The volumetric instability of expansive soils caused by moisture variations often leads to catastrophic consequences, including geohazards, structural damage, and high repair costs. The situation becomes more intricate when expansive soils are subjected to the chemical composition present in the fluid. This study investigates the chemical effects on the swelling and mechanical properties of expansive soil through comprehensive experiments. The results indicate that chemical effects inhibit swelling deformation and pressure, while saline solutions enhance effective stress and shear strength, evidenced by upward shifts in the strength envelope. Notably, the chemical influence on bentonite exhibits a threshold around 0.5 mol/L NaCl solution; below this threshold, soil properties change significantly with increasing solution concentration, whereas beyond it, the impact diminishes. Additionally, this study considers the effects of infiltration methods, initial moisture content, and shearing rate on shear strength. Different infiltration methods result in similar maximum volume variation and swelling pressure despite varied duration curves, with double infiltration reacting the fastest, top infiltration reacting slower, and bottom infiltration reacting the slowest. For soil samples with identical solutions, low initial moisture content causes notable strain softening and peak shear strength, while higher moisture reduces strain softening and peak strength. Under the same conditions, rapid shearing leads to higher shear strength.

This paper presents a simple thermo-elasto-plastic constitutive model for saturated fine-grained soils, addressing thermal volume change, excess pore pressure, and shear strength. The model incorporates a novel temperature-dependent plastic modulus formulation that attributes the thermoplastic strain to an internal state variable representing the thermal stabilization of soils due to cyclic thermal loading. It can capture the accumulative volume expansion of highly overconsolidated (OC) soils, and the accumulative contraction of normally consolidated (NC) and slight OC soils after several heating-cooling cycles. A thermally induced pore pressure formula is derived with consideration of thermo-elastic expansion of pore water and soil particles, thermo-plasticity of soil skeleton as well as the elastic unloading due to the decrease of effective stress under undrained heating. The effect of temperature on the shear strength was emphasized. An insight into the evolution of shear strength with temperature is provided. The consolidated stress history and stress path play a vital role in the thermal effect on the shear strength. The proposed model comprises nine parameters, which can be easily calibrated by element tests (triaxial tests and oedometer tests). The adequacy of the proposed model has been verified with experimental results from fine-grained soils documented in the literature.

Organic soil is usually required to be improved/treated before engineering construction, especially in cold regions due to deterioration introduced by freeze-thaw cycle. In this study, cement-and-fly ash is adopted as agents to stabilise the organic soil. A photogrammetric method is proposed to accurately reconstruct the surface of these cement-and-fly ash-treated organic soils and measure the volume before and after freeze-thaw cycles (F-T-C). Meantime, unconfined compression (U-C) test was performed to evaluate the performance of these specimens after different numbers of F-T-C, and the influence of organic content on soil behaviour was also investigated. These results indicated that an increase in the cement content enhanced the resistance of the organic soils against volume change before and after F-T-C. A proper adoption of cement-and-fly ash significantly improves the unconfined compression strength (UCS) of organic soils subjected to different numbers of F-T-C. The strength of treated organic soil continuously decreased with increasing content of organic. A model was also established to predict soil stress-strain curves with consideration of the number of F-T-C and volumetric changes after the F-T-C.