This study investigates the stabilization of lateritic soil through partial replacement of cement with flue gas desulfurization (FGD) gypsum, aiming to enhance its engineering properties for pavement subgrade applications. Lateritic soils are known for their high plasticity and low strength, which limit their utility in infrastructure. To address these challenges, soil specimens were treated with varying cement contents (3%, 6%, 9%) and FGD gypsum additions (1%-6%). Laboratory tests were conducted to evaluate plasticity, compaction, permeability, unconfined compressive strength (UCS), California Bearing Ratio (CBR), and fatigue behaviour. The optimal mix 6% cement with 3% FGD gypsum demonstrated significant improvements: UCS increased by over 110% after 28 days, permeability reduced by 26%, and soaked CBR improved by 56% compared to untreated soil. Additionally, fatigue life showed remarkable enhancement under cyclic loading, indicating increased durability for high-traffic applications. To support predictive insights, machine learning models including Decision Tree, Random Forest, and Multi-Layer Perceptron (MLP) were trained on 168 data samples. The MLP and Random Forest models achieved high prediction accuracy (R2 approximate to 0.98), effectively capturing the non-linear interactions between mix proportions and UCS. SHAP (SHapley Additive exPlanations) analysis identified curing duration as the most influential factor affecting strength development. This integrated experimental-computational approach not only validates the feasibility of using FGD gypsum in sustainable soil stabilization but also demonstrates the effectiveness of machine learning in predicting key geotechnical parameters, reducing reliance on extensive laboratory testing and promoting data-driven pavement design.

Modifying lateritic soils, which are widely distributed in humid and rainy regions around the world, for embankment construction is a practical necessity for highway and railway projects. These embankments are susceptible to infiltration of rainfall, wetting and vibration from earthquakes and traffic. Further study is required to investigate the dynamic response characteristics of these embankments under combined action of wetting and vibration. Two scaled-down physical models of embankments were built: one with unmodified lateritic soils, which are typical soils with high liquid limit in central-southern China, and the other with lateritic soils modified with lime at a content of 8%. A self-designed model test system was used to conduct model tests of both embankments under combined action of wetting and vibration. White noise excitation was employed to quantitatively compare the two types of embankments in terms of variations of dynamic properties, such as natural frequency and damping ratio, with wetting degrees. Three types of seismic waves-Chi_Chi, NCALIF and SFERN-were used to quantitatively compare the two types of embankments in terms of variations of dynamic response parameters, including PGA amplification effect, pore water pressure and earth pressure, with wetting degrees and acceleration amplitudes. The test results reveal significant differences in dynamic properties and responses of the two types of embankments. Compared to the unmodified embankment, the damping ratio and PGA amplification factor of the modified embankment are reduced by up to 53.5% and 37.5%, respectively, resulting in an effective mitigation of the combined action of wetting and vibration. Test values of natural frequency, damping ratio, PGA amplification factor, dynamic pore water pressure and dynamic earth pressure of both types of embankments are presented. The research findings provide a theoretical basis for highway and railway construction and for revision of technical specifications in regions with widespread lateritic soils.

Elastic shear moduli of soil at various temperatures and suctions are important for analysing the serviceability limit state of energy piles and many other structures. Up to now, however, the coupled effects of temperature and suction on elastic shear modulus and the stiffness anisotropy, have not been well understood. This experimental study investigated the anisotropic elastic shear modulus of a compacted lateritic clay. A temperature and suction-controlled triaxial apparatus equipped with bender element probes and local strain measurements was used. Soil suctions from 0 to 300 kPa, and a temperature range of 5-40 degrees C were applied. The results at saturated and unsaturated conditions consistently reveal that the shear modulus is smaller after heating at a given stress and suction. Several mechanisms may contribute to this thermal-induced reduction in shear modulus, such as the heating-induced reduction of interparticle force and air-water surface tension. Moreover, the reduction in shear modulus upon heating depends on the shear plane and the degree of anisotropy changes.

This study evaluates styrene butadiene rubber (SBR) and styrene acrylic latex (SA) as modifiers in cement-treated subbase materials (CTSB) to enhance mechanical properties and reduce cement usage sustainably. Optimal ratios for stabilizing sub-standard lateritic soils were identified, reducing water demand and increasing mechanical strength in polymer-modified cement pastes. A 10 % SA and a 15 % SBR as cement replacement by mass significantly improved bearing strength and strain capacities in CTSB, signifying enhanced flexibility and elasticity. Despite slight changes in compaction characteristics, the study identified 1.6 % SA and 2.4 % SBR as optimal binder (i.e., polymer-cement mixture) contents, compared to 3.3 % cement for conventional CTSB with similar unconfined compressive strength standards. SBR-enriched CTSB exhibited superior resilient modulus, indicating stronger inter-particle bonding. The integration of SA and SBR reduced capillary rise and enhanced moisture stability. This sustainable approach enhances pavement durability and reduces CO2 emissions by minimizing cement use. The findings emphasize the potential of polymer-modified CTSB for cost-effective and environmentally friendly road construction, offering significant implications for advancing pavement engineering materials and promoting eco-friendly practices within the industry.

Introduction The engineering geological characteristics of Yunnan's lateritic soil are quite unique, making it prone to shallow group landslides under rainfall conditions. This study focused on an old lateritic soil landslide as a case study.Methods Soil column ponding infiltration experiment was conducted to investigate the infiltration behavior of the lateritic soil. Numerical simulation software was employed to analyze the rainfall-induced seepage characteristics of the landslide, and a comprehensive assessment of the failure mechanisms of the lateritic soil landslide was conducted.Results The study findings are as follows: (1) During water infiltration, the infiltration time curve of the lateritic soil column showed a parabolic growth trend. The migration rate of the wetting front rapidly decreased from 0.15 to 0.2 cm/min to 0.1 cm/min and then stabilized at approximately 0.04 cm/min. (2) Long-term heavy rainfall is the condition for the formation of this old lateritic soil landslide. By coupling the seepage process, the stability coefficient of the lateritic soil slope was calculated, revealing that the instability rainfall threshold of the slope under prolonged rainfall conditions is generally 120 mm/d. (3) The main changes in the seepage field occurred in the shallow soil layer. In the later stages of rainfall, the infiltration rate of the slope was controlled by the permeability coefficient of the lateritic soil. As the rainfall intensity increased, the depth of rainfall impact increased, and the pore water pressure in the shallow soil layer tended to gradually increase and then stabilize under different rainfall intensities. (4) Under long-term rainfall conditions, the volumetric water content of the soil at the toe of the lateritic soil slope first peaked. After the rainfall ended, moisture in the slope continued to migrate to the toe, keeping the soil at the toe in a saturated state. (5) The formation and evolution of this lateritic soil landslide could be divided into five stages: initial natural stage, rainfall infiltration-crack expansion, shallow creep-progressive collapse of the front edge, sliding surface penetration-overall instability, and landslide braking accumulation.Conclusion The research results provide significant theoretical guidance and practical implications for understanding the causes and prevention of lateritic soil landslides in similar areas.

Lateritic clay has distinct properties from other clays due to its high sesquioxide content. Its stiffness characteristics have not been well understood, especially when the soil is unsaturated and anisotropic. This study investigated the stiffness characteristics of compacted lateritic clay through suction -controlled triaxial compression tests equipped with local strain measurements. Both vertically and horizontally cut specimens were tested to determine the evolution of stiffness anisotropy during shearing. Three suctions (0, 10, and 150 kPa) and two confining pressures (50 and 200 kPa) were considered. When strains are relatively small (e.g., less than 0.2%), the secant Young's modulus E sec of vertical specimens is consistently higher than that of horizontal specimens at all suctions and stresses due to the inherent anisotropic structure. The degree of anisotropy increases with increasing suction since suction enhances the stiffness more significantly in vertical specimens than in horizontal specimens. This behaviour may be due to an enhanced force chain in the vertical direction during shearing. As strains increase, the degradation of E sec normalized by the maximum Young's modulus E 0 is almost independent of suction and anisotropy. Lateritic clay has a higher degradation rate than other clays with a similar plasticity index because of its aggregated microstructure.

In tropical regions, heavy rainfall induces erosion and shallow landslides on road embankments. Cement-based stabilization methods, common in these regions, contribute to climate change due to their high carbon footprint. This study explored the potential application of coir fiber-reinforced laterite soil-bottom ash mixtures as embankment materials in the tropics. The objective is to enhance engineered embankment slopes' erosion resistance and stability while offering reuse options for industrial byproducts. This study examined various mix designs for unconfined compressive strength (UCS) and permeability, utilizing 30% bottom ash (BA) and 1% coir fiber (CF) with varying sizes ranging from 10 to 40 mm, 6% lime, and laterite soil (LS), followed by microstructural analyses. The results demonstrate that the compressive strength increases as the CF length increases to 25 mm. In contrast, permeability increases continuously with increasing CF length. Lime-treated mixtures exhibit superior short- and long-term strength and reduce permeability owing to the formation of cementitious materials, as confirmed by microstructural analyses. A lab-scale slope box was constructed to evaluate the surface erosion of the stabilized laterite soil embankment. Based on the rainfall simulation results, the LS-BA-CF mixtures show better resistance to erosion and deformation compared to untreated LS, especially when lime is added to the top layer. This study provides insights into a sustainable and cost-effective approach for slope stabilization using BA and CF, offering a promising solution for tropical regions susceptible to surface erosion and landslides.

To foster the sustainability of green construction materials utilized in transport infrastructure and generally in soil stabilization for the same purpose, there have been continued efforts towards innovative results for consistent improvement of the mechanical properties of soils. Metakaolin (MK) has been in use as a supplementary material due to its pozzolanic properties. However, it has always produced a limit beyond which there is recorded decline in its ability to cement and strengthen soils in a stabilization protocol. In this research work, a new innovative cementitious material made from 1:1 NaCl + NaOH blend activator mixed with sawdust ash called Ashcrete (A) has been introduced. It is blended with MK in the lateritic soil stabilization procedure. Preliminary results showed that the lateritic soil (LS) has weak consistency with plasticity index above 17%, maximum dry density (MDD) of 1.77 g/cm3 and classified as A-7 soil on American Association State Highway and Transportation Officials (AASHTO) method. The MK and the Ashcrete (A) showed high compositions of aluminosilicates qualifying them as supplementary cements. The MK was used at the rate of 3, 6, and 9%, while the Ashcrete (A) was incorporated at the rate of 2, 4, 6, 8, and 10%. The results of the stabilization exercise showed that the California bearing ratio (CBR) and unconfined compressive strength (UCS) consistently increased with the addition of MK + A blend. This outcome was a shift from the previous work, which had used only MK and recorded 6% addition at which the MK-treated lateritic soil recorded its highest strength, and beyond this mark, there was a decline. The highest strength in this research work was recorded with the stabilization pattern of LS + 9%MK + 10A, which translates to that for a 200 g LS to be treated, 18 g of MK, and 20 g of A are needed to achieve the highest CBR and UCS recorded in this research paper. Finally, the recorded CBR (7-day soaked and unsoaked) and the UCS (7, 21, and 28 days) of the MK + A-treated LS fulfilled the requirements for the construction of a subgrade and subbase.

A very common hazard in Rwanda is represented by the instability of steep road cut slopes in lateritic soil. In its natural state, this material appears as a fine-grained weak and altered rock, generally in unsaturated conditions. Steep cut slopes made by this material could remain stable for a long time unless weathering weakens its mechanical behavior and heavy rainfall provokes a rapid landslide. This paper presents the results of an experimental investigation on the microstructural, petrophysical, and geotechnical properties of lateritic soil from a road cut slope located in Kabaya (Ngororero District-Rwanda), which was recently subjected to a landslide. The mechanical properties of the material are strictly related to the geological origin and history of the deposits, their formation environment, and weathering processes. These characteristics were revealed by peculiar microstructural features (micro-texture, porosity, and degree of alteration of original mineral paragenesis). The experimental investigations included identification and classification tests, direct shear tests on saturated samples, and swelling tests. This multidisciplinary approach provided insights into the relationship between geotechnical properties and the microstructural, petrophysical, and chemical characteristics of the altered rocks. This study showed how different levels of chemical alteration operated by weathering processes, in conjunction with brittle deformation related to the tectonic history, formed in the same site two shallow rock layers with similar macro-scale features and mechanical behaviors but markedly different microstructural and chemical properties. The innovative aspect of this research suggests an integrated multidisciplinary approach to considering microstructural aspects in addition to mechanical behavior in the slope stability analyses in lateritic soil. In particular, this study demonstrates the importance of such an approach since the failure mechanism is better explained if it is based on microstructural observations instead of considering the soil shear strength parameters only. This research helped to explain the formation of the landslide failure mechanism in a specific road cut slope, which could be assumed as representative of many other similar slopes subjected to landslides in Rwanda.

This paper aims at investigating the combined effects of wetting and traffic loading on the dynamic response of lateritic soil subgrade in the southern region of China. Vehicle tests involving four axle loads of trucks travelling at four speeds and vibration tests involving six repetitive vibration loadings were carried out in a test of the Nanning-Zhanjiang expressway under three types of wetting conditions. The effects of wetting, vehicle speed, moving load, repeated loading, and loading numbers on the dynamic stress, dynamic acceleration, dynamic displacement, and accumulative deformation of the subgrade are investigated. The results show that under the effect of wetting, the dynamic response generated by the moving load on the subgrade increases, and excessive moving loads increase the dynamic response of the subgrade. The dynamic response of the subgrade exhibited exponential attenuation along the depth direction and transverse direction, and the influence depths were 2.3 m and 3.3 m for axle loads of 7 t and 30 t, respectively. At a depth of 0.3 m from the subgrade surface, the time-domain curves of the dynamic stresses are a double hump. The accumulative deformation rapidly increased and then gradually stabilized. When the loading was 3 million cycles, the accumulative deformation at the wetted twice stage was 16.8 % and 35.2 % greater than that at the wetted once and unwetted stages, respectively. The research results provide a reference for the structural design and safe operation of expressway subgrades in lateritic soil areas.