Field investigations and laboratory tests were performed to determine the cause of engineering distress due to the swelling of lime-stabilized and phosphogypsum-stabilized soil and subsequent cracks on a roadway in China. An exploratory pit was excavated to inspect the damage state. The thickness and water content of the subbase before and after failure were compared. Laboratory compaction and expansion tests were performed to investigate the swelling behavior and the expansion potential of both the mixture from the in-situ subbase and the newly made mixture in the laboratory. It was found that the main reason for heaving in the roadway was due to the overuse of phosphogypsum in mixture of the subbase. In addition, continuous heavy rainfalls were the triggering factor for a series of chemical reactions that occurred among the mixtures in the water-rich surroundings. These combined factors resulted in the failure of the roadway subbase. This work reveals that the dosage of phosphogypsum must be controlled in a reasonable range when it is used in roadway engineering.

Yunnan Province, China, has complex topography and geomorphology, many ravines and valleys, and frequent landslide geological disasters and is of great significance in the assessment of regional landslide geological disasters in Yunnan Province for disaster prevention and mitigation. In this study, Yunnan Province was selected as the research area, and the average annual deformation rate of radar line-of-sight in Yunnan Province over four years from 2018 to 2021 was obtained with SBAS-InSAR technology, which was used as one of the index factors for the susceptibility evaluation of Yunnan Province. The deformation rate reflects the slow movement of the land surface. In addition, elevation, slope, aspect, lithological classification, geological structure, rainfall, distance from roads, distance from rivers, topographic undulation, and NDVI were selected as evaluation index factors and combined with the annual mean deformation rate. A random forest model was used to evaluate and accurately analyze landslide geological disasters in Yunnan Province. The results showed that as an important index factor, the annual mean deformation rate of Yunnan Province can be added to the random forest model to improve the prediction accuracy. The area with high susceptibility accounted for 10% of the entire province, and the number of landslides in the region accounted for 68% of the province. Additionally, the results for prone zoning were highly correlated with the landslide distribution. The accuracy of the random forest model prediction was 0.80, and the AUC value was 0.87, indicating that the random forest model was a highly accurate and reliable evaluation method for studying landslide geological disasters. It is very suitable for the evaluation of landslide susceptibility in Yunnan Province.

In this study, superabsorbent polymers (SAP) were introduced as an admixture in subgrade soils for the potential of improving their moisture susceptibility under moisture variation conditions. A series of experiments was performed on the soil samples to investigate the feasibility and influences of SAP on their fundamental physical properties and mechanical performance. In addition, wetting-drying (W-D) cyclic tests were conducted on the samples to simulate the moisture varying conditions that subgrade soils could experience in service. Compaction tests showed that SAP decreased the maximum dry density, but had no effect on the optimum moisture content. Soil amended by SAP exhibited superior uniformities in moisture distribution and grain size distribution. SAP helped enhance the direct shear behaviors of subgrade soils and increased the cohesive strengths and internal friction angles. The W-D cycles obviously degraded the mechanical properties. During the W-D cycles, SAP could also remarkably improve shear strength and the larger the SAP content, the better the shear performance. Results proved that a proper content of SAP ($\le 0.75\%$ ) added in the subgrade soils had no apparent impact on the volume stability, however a high content of SAP could significantly increase the volume by as much as 12.35%. Based on the test results, an optimal SAP content of no more than 0.75% is recommended.

The load transfer mechanism of a geosynthetic-reinforced and pile-supported embankmentis is influenced by the interactions among embankment fill, bridging layer, piles and foundation soil. In this paper, an integrated method for calculating the loads carried by the pile and subsoil is developed based on the displacement compatibility principle, which takes the soil arching effect, tensioned membrane effect and pile-soil interaction into account. In the presented method, the magnitude of shear stress due to the arching action depends on the relative displacement within the embankment fill and the elastic-perfectly plastic stress-displacement response is considered, the tension and strain in the geosynthetic are obtained using the parabolic method, and the hyperbolic model is adopted to relate the negative and positive skin friction with differential settlement between pile and surrounding soil. The proposed method of determining the stress on the pile and subsoil provides a better agreement with the field measurement comparing to the existing analytical methods. In addition, a parametric study is conducted to evaluate the effects of several factors on the load transfer behavior, such as the mobilization coefficient of shear strength, cohesion and internal friction angle of embankment fill, pile spacing, and compressive modulus of subsoil. The results indict that the cohesion plays a more important role in transferring of load from soft subsoil to rigid piles than the internal friction angle of embankment fill. Additionally, different optimal pile spacings which lead to the maximum stress concentration ratio are found for different embankment heights.

A complete case record of a deep foundation pit with pile-anchor retaining structure excavated in red sandstone stratum is presented in this study. The horizontal displacement of pile top, the horizontal displacement at various depths, the axial force of anchor cable, and ground settlement during construction are measured. A three-dimensional numerical model is established to analyze the additional stress and deformation induced by the excavation and the accuracy of the FEM model is verified by comparing with field measured results. Both the measured and numerical simulation results show that the deformation of the pile-anchor supported deep excavation is significantly affected by the spatial effect. The results show that the deformation in the middle of the foundation pit is greater than the pit angle and that the deformation of the long side is greater than that of the short side and gradually decreases from the middle to the pit angle. The deformation and stress in the middle of the long side of the foundation pit are the largest, which is the most unfavorable part. With the increase of vertical excavation depth, the spatial effects tend to increase, and the influence scope of spatial effects is about five times the vertical excavation depth in the red sandstone stratum. The ground settlement outside the pit is mainly distributed in a groove shape, and the maximum settlement occurs about 8.5 m away from the pit edge. Finally, parametric studies of reinforcement parameters indicated that 1.5–2.0 times the initial elastic modulus and cohesive force of soil should be used for reinforcement. It is recommended that the ranges for pile diameter, pile spacing, anchor cable prestressing and inclination angle should be selected as 0.8–1.2 m, 1.4–2.0 m, 100–150 kN, and 10°–20°, respectively.

An engineering failure with serious cracks and heaving in the roadway subbase because of the overuse of phosphogypsum was investigated, and an effective stabilization solution was implemented. For this purpose, mix-proportion design, compaction, expansion, and shrinkage tests were performed on the treated mixture to investigate the engineering properties. Based on the laboratory results, in situ tests were conducted to verify the engineering behaviors of the recycled subbase, which included the static plate load test (SPLT), dynamic cone penetrometer test (DCP), Benkleman beam method test (BBM), and portable falling-weight deflectometer test (PFWD). The test results show that the swelling problem can be controlled by adding lime and fly ash to the problematic mixture at a reasonable proportion. The in situ tests show that the average resilience modulus of the SPLT was 191.5 MPa, which is approximately four times the value before the treatment. The dynamic modulus of the DCP test and PFWD test also indicate an increase of approximately $4–5\text{times}$ , and the deflection value of the BBM test was only 37.2 mm after the treatment. The in situ test results show that the recycled subbase can satisfy the roadway requirements and present a good performance. The proposed mix proportion of $6.5\%\mathrm{L}+20\%\mathrm{F}+73.5\%\mathrm{H}$ was applied in this problematic subbase. The construction control requirements are outlined in this paper. The treated roadway subbase has worked well for nearly 9 years, which indicates a successful application of in situ stabilization.