Sodium hydroxide (NaOH)-sodium silicate-GGBS (ground granulated blast furnace slag) effectively stabilises sulfate-bearing soils by controlling swelling and enhancing strength. However, its dynamic behaviour under cyclic loading remains poorly understood. This study employed GGBS activated by sodium silicate and sodium hydroxide to stabilise sulfate-bearing soils. The dynamic mechanical properties, mineralogy, and microstructure were investigated. The results showed that the permanent strain (epsilon(p)) of sodium hydroxide-sodium silicate-GGBS-stabilised soil, with a ratio of sodium silicate to GGBS ranging from 1:9 to 3:7 after soaking (0.74%-1.3%), was lower than that of soil stabilised with cement after soaking (2.06%). The resilient modulus (E-d) and energy dissipation (W) of sodium hydroxide-sodium silicate-GGBS-stabilised soil did not change as the ratio of sodium silicate to GGBS increased. Compared to cement (E-d = 2.58 MPa, W = 19.96 kJ/m(3)), sulfate-bearing soil stabilised with sodium hydroxide-sodium silicate-GGBS exhibited better E-d (4.84 MPa) and lower W (15.93 kJ/m(3)) at a ratio of sodium silicate to GGBS of 2:8. Ettringite was absent in sodium hydroxide-sodium silicate-GGBS-stabilised soils but dominated pore spaces in cement-stabilised soil after soaking. Microscopic defects caused by soil swelling were observed through microscopic analysis, which had a significant negative impact on the dynamic mechanical properties of sulfate-bearing soils. This affected the application of sulfate-bearing soil in geotechnical engineering.

Controlled low-strength material (CLSM) is a flowable, self-leveling backfill material used as an alternative to compacted soil for backfilling trenches, retaining walls, underground cavities, and in pavement construction. This study aims to investigate the permanent deformation of CLSM reinforced with basalt fibers. Basalt fibers with lengths of 6 and 24 mm are incorporated into CLSM mixtures to assess their impact on flowability, setting times, and mechanical properties. Mechanical testing indicates that longer fibers improve tensile strength through a bridging effect. Repeated load triaxial tests are conducted to evaluate the permanent strain behavior under repeated loading. The results show that permanent strain increases with the deviator stress and number of loading cycles. A regression model accounting for the number of loading cycles and deviator stress provides accurate permanent-strain predictions, and the permanent strain behaviors are classified based on the refined shakedown theory. Therefore, the basalt-fiber-reinforced CLSM suggested in this study may be suitable for pavement base material due to its relatively low permanent strain under typical stress conditions.

Stabilizing and improving weak and poorly graded soils in road construction projects is a widely used and highly interesting technology. This research study utilizes paper sludge ash (PSA) residues as a geopolymer waste material to stabilize loose and poorly graded sands (SP), improve mechanical properties, and support sustainable pavement development. Geotechnical tests using the unconfined compressive strength test (UCS), Young's modulus (Es), California bearing ratio (CBR), and a direct shear test (DST) assessed the performance and strength development of geopolymer-stabilized soil. The stabilized soil's microstructure and chemical mineralogy were also examined using SEM and XRD. Additionally, a laboratory testing apparatus was designed and developed to assess the permanent strain behavior of subgrade soil and geopolymer-stabilized soil layers under cyclic loading. The research analysed variables including curing duration (1, 3, and 7 days), PSA concentration (5, 10, and 15%), and the type and concentration of alkaline activators (NaOH or Na2SiO3). Soil samples treated with PSA and Na2SiO3 geopolymers showed higher UCS, Es, and CBR values, leading to improved strength from increased N-A-S-H and C-A-S-H gel formation among sand soil particles. On the contrary, the NaOH solution enhanced the strength parameter of geopolymer-stabilized soil samples. The results showed that geopolymer-stabilized soil significantly improved its resistance to permanent deformation after applying loads. The mineralogical examination also shows a high concentration of lime and cubic aluminate, which may be active cementitious pozzolanic material. This research reflects that PSA has promising potential to stabilize sandy soil and improve the design and maintenance of roads and infrastructure in areas with weak soils.

Traffic-induced cyclic stresses in the subsoil are three-dimensional, and it is important to acknowledge that cyclic major, intermediate, and minor principal stresses have obvious impacts on the permanent strain of the subsoil. Therefore, a series of cyclic true triaxial tests were performed on intact marine clay to investigate the evolution of permanent major principal strain (epsilon(p)(1)) under long-term true triaxial cyclic loads in this study, considering the effects of the amplitudes of cyclic deviator stress (q(ampl)), coefficient of the cyclic intermediate principal stress (b(cyc)), and the slope of the stress path (eta). The test results indicated that epsilon(p)(1) exhibits an increasing trend with increasing CSR, but decreases nonlinearly with an increase in b(cyc)and eta. This implies that the increasing amplitude of cyclic deviator stress promotes the development of epsilon(p)(1), and the accumulation of epsilon(p)(1) is limited by the growing amplitudes of the cyclic mean principal stress and cyclic intermediate principal stress. Considering the effects of CSR, b(cyc), and eta on epsilon(p)(1), a five-parameter empirical model is established to describe the accumulation of epsilon(p)(1) under true triaxial cyclic loads. In addition, the proposed model is verified by the permanent deformation data in this study and previous studies.

In this paper, a comprehensive series of dynamic triaxial tests were conducted to delve into the influence of temperature and moisture content on the behavior of frozen silty clay. Upon scrutinizing the experimental outcomes under prolonged reciprocal cyclic loading, insights were gained into how varying temperatures and moisture contents impact the cumulative permanent strain (CPS) and critical dynamic stress (CDS) of frozen clay. The results show that the variation curves of CPS with the number of cyclic loadings show significant changes at different temperatures and moisture contents. Additionally, based on the assessment of vertical CPS recorded at the 100th and 1000th loading iterations, criteria for assessing the plastic stability and plastic creep threshold of frozen silty clay were devised. Consequently, an analysis was conducted to delineate the correlation between the variation in vertical cumulative strains and the dynamic stresses applied within the frozen clay, resulting in the formulation of a series of correlation curves. The relationship between the changes in CDS affected by different temperatures and water contents were analyzed. The CDS under the plastic stability and plastic creep limits showed a slowly increasing trend with decreasing temperatures and a slowly decreasing trend with increasing water contents.

To satisfy the economic requirements and reduce the impact to the surrounding buildings and underground structures, the dynamic compaction (heavy tamping) and static compaction are combined used in the soil filling for airport subgrade. Despite compaction the subgrades in the same degree of compaction, the subgrades filled by dynamic and static compaction method show different increase potential in the permanent strain under cyclic loading, which then further result in the differential settlement and safety problems. This study firstly investigated the compaction characteristics under static compaction and different dynamic compaction scheme, during which the static and dynamic compaction strain and stress evolutions were monitored. The cyclic triaxial tests were then performed to investigate the sample preparation method derived difference in permanent strain under cyclic loading. Furthermore, to provide a microscopic interpretation to this difference, the pore size distributions of the silt samples based on mercury intrusion porosimetry (MIP) test and the internal particle contact stresses from discrete element method (DEM) simulation were respectively explored. The main conclusions are as follows: (1) The dynamic compaction processes can be divided into rapid and slow compaction strain stages determined by strain growth rate and compaction numbers, which further influences the homogeneity of soil samples; (2) The statically compacted samples have more significant permanent strain than the dynamic ones due to the localized stress concentration and different pore microstructures; the permanent strain increases with dynamic compaction energy until a stable stage is reached. (3) The MIP results show that the dynamic compaction transforms the macropores into mesopores; the higher compaction energy enhances this transforming effect but results in a decrease in the overall homogeneity.

This paper aimed to investigate the feasibility of partially or completely replacing natural aggregates with recycled aggregates from construction and demolition wastes for low-carbon-emission use as coarse-grained embankment fill materials. The laboratory specimens were prepared by blending natural and recycled aggregates at varying proportions, and a series of laboratory repeated load triaxial compression tests were carried out to study the effects of material index properties and dynamic stress states on the resilient modulus and permanent strain characteristics. Based on the experimental results and by considering the main influencing parameters of the resilient modulus and permanent deformation, an artificial neural network (ANN) prediction model with optimal architecture was developed and optimized by the particle swarm optimization (PSO) algorithm, and its performance and accuracy were verified by supplementary analyses. A shakedown state classification method was proposed based on the unsupervised clustering algorithm, and a prediction model of critical dynamic stress was established based on the machine learning (ML) method and the shakedown state classification results. The research results indicate that the stress state has a greater influence on the resilient modulus and permanent deformation characteristics than other factors, and the shear stress ratio has a significant effect on the shakedown state. The resilient modulus and critical dynamic stress of such specimens vary linearly with confining pressure. The improved PSO-ANN prediction model exhibits high prediction accuracy and robustness, superior to several other commonly used ML regression prediction algorithms. The resilient modulus and critical dynamic stress prediction methods based on ML algorithms can provide technical guidance and theoretical basis for the design and in-service maintenance of similar unbound granular materials.

The stable and safe operation of highway/railway lines is largely dependent on the dynamic behavior of subgrade fillings. Clay soils are widely used in subgrade construction and are compacted at different remolding water contents and compaction degrees, depending on the field conditions. As a result, their dynamic behaviors may vary, which have not been fully investigated until now. To clarify this aspect, a series of cyclic triaxial tests were carried out in this study with three typical remolding water contents (w = 19%, 24%, and 29%), corresponding to the optimum water content as well as its dry and wet sides, and two compaction degrees (Dc = 0.8 and 0.9), which were selected according to the field-testing data. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were also conducted on typical samples to investigate the corresponding soil fabric variations. The findings indicate the following: (a) The soil fabric at the optimum remolding water content and its dry side was characterized by a clay aggregate assembly with a bimodal pore size distribution. In contrast, the soil fabric on the wet side of the optimum water content consisted of dispersed clay particles with a unimodal pore size distribution. (b) As the compaction degree increased, to ensure the optimum water content and its dry side, large pores were compressed to make them smaller, while small pores remained unchanged. Comparatively, all the pores on the wet side were compressed to make them smaller. (c) For each compaction degree, as the remolding water content increased, a non-monotonic changing pattern was identified for both the permanent strain and resilient modulus; the permanent strain first decreased and then increased, while, for the resilient modulus, an initial increasing trend and then a decreasing trend were identified. In addition, a larger changing rate of the permanent strain (resilient modulus) was observed on the dry side, indicating a larger effect of the remolding water content. (d) For each remolding water content, as the compaction degree increased, the permanent strain exhibited a decreasing trend, but an increasing trend was identified for the resilient modulus. Moreover, the rate of change in the permanent strain (resilient modulus) on the dry side of the optimum water content was larger than that on the wet side. In contrast, the minimum rate of change was identified at the optimum water content. The obtained results allowed for the effects of the remolding water content and compaction degree on the dynamic behavior to be analyzed, and they helped guide the construction and maintenance of the subgrade.

Mine haul roads are the unpaved roads that are constructed from the overburden materials obtained from the mining operations and are used for the movement of heavily loaded dumpers and trucks. The haul roads constructed from this overburden material shows continuous distress in the form of over ruts, potholes, and shear failures, creating major issues in the movement of dumpers. In the present research study, an experimental investigation was conducted based on mechanistic empirical design to evaluate the strength-deformation characteristics, durability, and environmental emissions of cement stabilized overburden soil of a local mine. The unconfined compression tests were conducted at cement dosages varying from 1 to 6% of dry soil mass and increase in the unconfined compressive strength were examined at different intervals of time until 28 days of the curing period. In the case of static triaxial tests, the enhancement in undrained shear strength and elastic modulus of stabilized specimens was determined in comparison to the untreated specimens, whereas in cyclic triaxial tests, the reduction in permanent deformations and increase in resilient modulus were evaluated under different confining pressures and cyclic deviatoric stresses. An empirical model has been proposed to predict the long-term rutting of overburden under repeated loading. The proposed model is based on the behaviour of various parameters, such as applied cyclic deviatoric stress, number of load repetitions, loading frequencies, and on the permanent deformation characteristic of mine overburden soil. In addition, durability and environmental sustainability aspects of the treatment has also been studied to determine the optimal dose of cement.

To properly model the subgrade soil responses under dynamic loads, permanent deformation and damping characteristics must be studied in addition to the subgrade resilient modulus. Soils having relatively high resilient modulus may or may not have small permanent strains (epsilon(p)) and low damping characteristics (xi). Therefore, in addition to the resilient modulus (M-R), permanent deformation and damping characteristics also need to be studied for undisturbed subgrade soils to replicate field conditions under cyclic loading properly. This study correlates permanent strain and damping information with resilient modulus testing for undisturbed subgrade soils. For this study, 76 Shelby tube samples of subgrade soils were collected from existing pavements in three different regions: SC-93 in Pickens County (Upstate Area), US-521 in Georgetown County (Coastal Plain), and US-321 in Orangeburg County (Coastal Plain, near the fall line). Statistical models were developed to correlate resilient modulus (k(1), k(2), k(3)), permanent strain (alpha(1), alpha(2), alpha(3), alpha(4)), and damping model parameters (beta(1), beta(2), beta(3)) with soil index properties for undisturbed soils. Models were also developed to correlate epsilon(p) and xi with subgrade soils M-R.