Experimental Investigation On Wetting Deformation And Strength Characteristics Of Unsaturated Compacted Loess

With the implementation of China's western development strategy and the "Belt and Road" construction,an increasing number of the construction of the tunnel project has to cross the yellow soil layer.This paper relies on the construction project of the "Mengxi-Huazhong" railway construction project of the central energy channel in China.That is to say,groundwater is encountered during tunnel excavation construction,which causes the collapse and deformation of loess.The deformation and cracking of the initial branch of the tunnel and collapse of the face of the tunnel seriously affects the construction safety of the loess tunnel.In this paper,in order to solve the problem of wetting deformation and the strength weakening of loess,pressure plate instrument,steam balance method and GDS-HKUST type unsaturated soil triaxial apparatus are adopted.After the compaction and remolding of loess samples from the engineering site,the related experimental research was carried out and some innovative results were obtained the following aspects:(1)Studies on the full suction range of SWCC of the compacted loess were carried out.Initial water content and dry density of the soil sample were controlled and pressure plate was used to measure the SWCC of the compacted loess in the middle and low suction range.Determined the high suction section of SWCC by using the saturated salt solution method.Considering the possible volume shrinkage behavior of compacted loess in the process of water loss shrinkage,the shrinkage test of compacted loess in the drying path was carried out in parallel,and the influence degree of considering the shrinkage behavior of loess on the soil-water characteristic curve was compared and analyzed.The test results show that the data points measured by the pressure plate meter and the saturated salt solution method have a good consistency.As the dry density increases,the corresponding saturation is higher under the same suction conditions.The water SWCC of compacted loess between dry density are obviously different.The soil sample with higher dry density has stronger water holding capacity.The corrected by considering the effect of shrinkage deformation is saturated under the same suction.The shrinkage deformation has a more significant impact on the soil water characteristic curve.(2)The experimental study on the humidification deformation of compacted loess under different stress conditions was carried out systematically.The initial moisture content and dry density of soil samples were controlled.Based on the triaxial apparatus of unsaturated soil,the humidification tests of loess samples with different dry densities under different stress conditions were carried out under the condition of isotropic compression.The volume deformation of samples during the humidification process was obtained and the effects of stress state and dry density on the humidification deformation were analyzed.The test results show that under different stress states,the maximum humidifying body strain is positively correlated with the confining pressure.Under the same dry density condition,the higher the confining pressure is,the greater the humidifying body strain is.The higher the dry density is,the less the void pores in the soil and the less the maximum wet strain.Under different stress ratios,two kinds of tests,"load-humidification" and "unload-humidification",were carried out to analyze the influence of stress ratio,confining pressure and water-force path on the humidification deformation.Under different stress ratios,two kinds of tests,"load-humidification" and"unload-humidification",were carried out to analyze the influence of stress ratio,confining pressure and water-force path on the humidification deformation.The test results show that the stress ratio has a restraining effect on the volume behavior of the soil sample.Under the small stress ratio condition,the soil sample may expand in volume.Under the condition of larger stress ratio,when the confining pressure is greater than the yield stress,the soil sample will shrink by volume due to humidification.The wetting shear strain rate of samples with loading path in the early stage was lower than that of samples with unloading path in the early stage.After the samples were humidified,the variation trend of pore ratio tended to be consistent with the increase of stress ratio.(3)A practical formula for predicting the shear strength of different moisture content of compacted loess is established,which provides a reference for numerical calculation in the case of sampling difficulties.