This paper aims to investigate the effects of zeolite and palm fiber on the strength and durability of cement soil. Based on the findings of previous research, optimal proportions of zeolite, palm fiber, and cement, as well as the appropriate curing age, were determined. Subsequently, unconfined compressive strength tests, dry-wet cycle tests, and freeze-thaw tests were conducted, utilizing NaCl and Na2SO4 solutions over the specified curing period. The strength and durability characteristics of the samples were evaluated by assessing mass and strength loss, taking into account the combined effects of NaCl and Na2SO4 solution erosion. The test data also provide a fitting relationship between strength and the number of cycles under the influence of different solutions, thereby offering a basis for theoretical predictions without the need for additional experiments. Finally, the microscopic mechanisms were analyzed using scanning electron microscopy (SEM). The results indicate that the cement soil composite of zeolite and palm fiber, when combined in optimal proportions, exhibits the best durability and minimal loss of strength and mass, irrespective of whether exposed to clean water or salt erosion, as well as during dry-wet or freeze-thaw cycles.

The evolution of loess microstructure exerts a direct impact on its collapse evolution during dry and wet (DW) cycles. In this study, a hydro-mechanical coupling numerical model considering DW cycles and mechanical loading was established by extending the Barcelona Basic model, meanwhile combining with the test results to reveal the effect of DW cycling on the collapse deformation and strength response of loess. Additionally, the microscopic mechanism of loess collapse evolution was revealed through microscopic tests. Results indicated DW cycles caused the net compaction of loess, with the first DW cycle exerting the most significant effect on its deformation, consequently deteriorating the loess. Wetting under constant loading leads to a collapse of macrostructures formed by aggregates. Moreover, DW cycles transformed the structural units from line and surface contact to point. The basic structural units exhibited obvious grade properties, in which DW cycles trigger the collapse of compound aggregates, with the number of relatively stable mononuclear aggregates and intergranular pores increasing. DW cycles in an open environment induced the loss of cementing materials such as soluble salts and reduced the bonding strength among basic structural units. This subsequently tended to weaken the structural properties of loess and decreased the mechanical properties.

To prevent the cracking of silty clay under cyclic wet-dry cycling (W-D), which leads to the increase of deformation and strength attenuation of silty clay, microencapsulated phase change material (mPCM) was used to improve it. The deformation and strength characteristics of silt with different dosages (1 %, 2 % and 4 %) of mPCM and their changing patterns were analyzed and studied by indoor compaction test, crack observation test, consolidation test and straight shear test, and compared with silt without modifier. The results showed that with the increase of mPCM dosage, the optimum water content of silt and the maximum dry density decreased. A 2 % dosage of mPCM inhibited the development of silty clay cracks, reduced crack width and deformation, and increased the compression modulus of the soil samples by nearly 2.3 times. Under dry and wet cycling conditions, the cohesion decay of silty clay is greater than the angle of internal friction. The addition of 2 % mPCM significantly increased the shear strength of silty clay, cohesion by nearly 2.1 times, and internal friction angle by 1.4 times. The mPCM inhibits crack development mainly by regulating the internal temperature field of soil samples, thus improving soil strength. This study provides a reference for inhibiting soil cracking from a new temperature perspective.

In practical engineering applications, cured lightweight soils are commonly used as roadbed fillers and subjected to intermittent and discontinuous traffic loads. However, previous studies primarily focused on the effects of continuous loading on the mechanical properties of cured soils. To address this knowledge gap, this study investigated the deformation characteristics of fiber-reinforced cured lightweight soils under dry and wet cycles and intermittent loading. Dynamic triaxial tests with varying intermittent ratios and numbers of dry and wet cycles were conducted to assess the influence of these factors on the accumulated plastic strain of fiber-reinforced cured lightweight soils. Based on the test results, a prediction model was developed to estimate the accumulated plastic strain of the cured soils under intermittent loading. The findings indicated that the interval length has a dampening effect on the accumulated plastic deformation of the soil, thereby improving its ability to resist deformation. Additionally, the accumulation of plastic deformation gradually increased with the number of wet and dry cycles but eventually stabilized. In multistage loading, the accumulated plastic strain displayed a rapid increase and stabilization trend similar to that in observed the first loading stage. However, the magnitude of the cyclic dynamic stress ratio determines the deformation at later loading stages. Finally, an improved exponential model was used to establish and validate a prediction model for the cumulative plastic strain of the fiber-reinforced cured lightweight soil under intermittent loading (single and multistage). This prediction model provides important guidance for the practical application of fiber-reinforced cured lightweight soils in engineering projects.