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Xanthan gum biopolymers have gained increasing attention in geotechnical engineering due to the effectiveness and environmental-friendliness, and are proposed as a potential alternative to conventional materials for soil stabilization. Cyclic wetting and drying are the crucial factors that affect the behavior of surface soil, which are also a major challenge for biopolymer applications. This study aims to investigate the strength durability of xanthan gum-treated soil during wetting–drying cycles. The soil was treated with different contents of xanthan gum (0, 0.5, 1.5% by the mass of dry soil) and a total of 12 wetting–drying cycles were applied. Unconfined compression tests were performed to evaluate the changes in soil mechanical properties. The changes in microstructure were observed using nuclear magnetic resonance technology and scanning electrical microscopy. The results showed that soil mechanical properties decreased significantly in the first four cycles, and then tended to equilibrium. The compressive strength of soil treated with 1.5% xanthan gum could be approximately twice than that of non-treated soil after 12 cycles, and its strength reduction caused by wetting–drying cycling is about 20% less than that of the latter. When increasing the water content at drying stage, specimens subjected to wetting–drying cycles with less moisture change presented higher compressive strength, in which case the effectiveness of biopolymer treatment can be maximally retained. Xanthan gum treatment conferred great resistance to wetting–drying cycling due to its cementation and aggregation effects. The presence of xanthan gum leads to more inter-aggregate pores with a radius of about 0.1–1 μm and limits the development of macropores. The strengthening effect of xanthan gum depends on direct clay particle–biopolymer interactions and inter-particle connection formed by xanthan gum matrix. From the results, xanthan gum biopolymers can significantly improve the mechanical properties of soil at shallow depth even after wetting–drying cycles. [ABSTRACT FROM AUTHOR]

Freeze–thaw cycle is one of the primary rock physical weathering agents which causes the deterioration and softening of rocks in cold regions. The frost-weathered rocks are prone to damage and destruction under loading. Determining the deterioration and stress–strain behavior of rocks following cyclic freezing and thawing is of crucial importance for evaluating the stability of rock excavation engineering in cold regions. A long-term artificial freeze–thaw cycles test on fresh sandstone samples was designed in this paper. The saturated condition was selected to accelerate the effect of freeze–thaw weathering. The mechanical behavior of the specimens undergoing different freeze–thaw cycles was further investigated through the uniaxial compression test. Experimental results indicate that the cycling of freezing and thawing causes a gradual decline in uniaxial compression strength followed by a rapid fall. An obvious beginning compaction stage can be observed in the stress–strain curve and the strain of the compaction stage increases during the freezing and thawing process. The deterioration of the sandstone was expressed by uniaxial compression strength, elastic modulus, and frost resistance coefficient in a piecewise decay model. A damage critical point can be distinguished in the model. Then, piecewise damage strain equations under the combination of freeze–thaw action and loading were derived by introducing the damage mechanics theory. The presented model was validated by the test results in this paper and a published article. It demonstrates that the simulated data agree well with the test results, indicating the effectiveness of the presented model in describing the stress–strain behavior of sandstone suffering long-term freeze–thaw weathering. [ABSTRACT FROM AUTHOR]

The studied slope is located in the middle reach of the Yalong River in the eastern margin of Qinghai-Tibet Plateau in Southwest China. A large hydropower station is planning to be built near the slope. Understanding the stability mechanism of the slope is important for dam site design. Under a combination of tectonic activity, unloading and weathering, the bedrock mass was fractured. On the basis of field investigation, the GSI classification system and Barton criterion were introduced to determine the strength of the rock mass. The kinematic, limit equilibrium and discontinuum modeling methods were carried out to comprehensively understand the stability of the slope. The kinematic analyses show that only wedge mode is possible for large rock mass failure. However, limit equilibrium analyses show that both wedge failure and circular slip are not expected for rock mass. The slope rock mass is now in the surface rebalance stage. The potentially unstable part is the covering deposit. The 40 million m3 surface deposit is now nearly in a limit equilibrium state. The possibility of failure reaches 41%. Mitigation measures must be put into effect on the deposit to assure the stability of the slope. The results indicated that the failure mechanism of the slope was not controlled by the discontinuities in the rock mass at present but depended on the stability of the surface deposit. [ABSTRACT FROM AUTHOR]

A considerable number of engineering hazards are caused by loose internal structure of sands. Thus, many researchers have explored a variety of reinforcement methods. A new reinforcement technique was experimentally evaluated in this study. In particular, a hybrid method with a combination of fiber and polymer was studied. Three different types of fibers (sisal, polypropylene, and palm) in combination with varying concentrations of polymers were experimented to improve the internal structure and strength of sand samples reconstituted at different densities. Through a series of laboratory tests, the compressive and tensile strength variations of different combinations were obtained, and the interaction between fibers and polymer inside the sand was evaluated by scanning electron microscopy (SEM). The experimental results show that the tensile and compressive strength of the reinforced sand increases with the increase of the polymer concentration, sample density, and different fiber combinations. This provides some references for future practical engineering applications. [ABSTRACT FROM AUTHOR]

Vegetation has good application in slope stabilization, but its beneficial effects on reinforcing topsoil are generally limited by the soil properties it was cultivated in. This study aims at evaluating the strength improvements of sand-root composite by treating with polyurethane polymer and hence investigating the mechanism of polymer-root-soil interactions. Vegetation roots were selected and mixed with dry sand and polymer solution to prepare remolded specimens. A series of experimental tests were then performed at different percentages of root content (0, 0.4, 0.8, 1.2, and 1.6 % by weight of dry sand) and polymer content (1, 2, and 4% by weight of dry sand) to evaluate the shear parameters and unconfined compressive strength (UCS). The combined mechanism was studied by scanning electron microscopy (SEM) images. The results showed that the strengthening effect has greater efficiency with higher polymer content. Through varying contents of vegetation root, it was found that low root content induced an undesirable weakening effect on the strength of the treated soil. However, this situation was somewhat improved with the increase in root content. The good flexibility of polymers not only promote the capacity of soil to energy absorption, but also impart good ductility to soil. The presence of polymers greatly strengthens soil stability due to its special network structure, by which the improved shear resistance at the root-soil interface provides sufficient anchorage effect for the tensile strength of roots to be fully mobilized. Overall, the synergistic effect of root reinforcement and polymer treatment has the potential for its use in soil stabilization. [ABSTRACT FROM AUTHOR]

Detailed engineering geological studies and stability assessments were carried out on Xiari rock slope in southwestern China. Geomorphic analysis of digital elevation models, detailed structural field mapping and boreholes data indicate that the slope has a poor rock mass quality and complex deformation mechanism. The necessary rock mass parameters were determined by means of slope mass rating (SMR), geomechanic classification system ( Q) and geological strength index (GSI). Slope stability analyses were performed by means of kinematic, limit equilibrium and numerical modeling techniques. Analyses results indicate that slope stability is mainly controlled by the discontinuities. The combination of discontinuities and topography makes the slope susceptible for a large landslide. The major potential mode of slope failure is planar failure. Planar failure has a higher probability in comparison to wedge failure, while wedge failure contributes towards a more severe hazard, like the landslide in part A of the study area. Numerical analysis results indicate a catastrophic landslide in the future, with a volume estimated to be more than 2.5 × 10 m. [ABSTRACT FROM AUTHOR]