Water Movement And Wetting-induced Deformation Characteristics Of Remolded Lanzhou Loess Under One-dimensional Loading-wetting Condition

With the implementation of the western development and the national initiative of "The Belt and Road",there are more engineering projects in the Loess Plateau area,such as the "cutting of mountains to make cities" in Lanzhou and Yan’an.As we all know,the strength and deformation modulus of unsaturated loess are closely related to the water content.In the past,the loess specification calculated the wet deformation assuming that the loess layers were fully saturated.Although the current specification considers the wetted chances coefficient for loess layers at different depths,the value of these coefficients is still lack of sufficient scientific basis.Moreover,it still does not give incremental collapse deformation calculation method during wetting.It has been pointed out that the development rate of wetting deformation will have different hazards to the upper structures.Therefore,the establishment of a hydraulic coupling model of loess considering the mutual influence of wetting deformation and water infiltration can provide a scientific basis for the reasonable evaluation of the influence of loess foundation’s humidification on the engineering structures.In this paper,the infiltration model and the wetting-induced deformation model of the remodeled loess in Lanzhou under the condition of load and water infiltration were proposed,and the method to obtain the parameters of the model was given.One-dimentional infiltration tests under different vertical pressure were carried out using a self-made soil column device,and the numerical simulation of water movement and development of collapse deformation in soil column was carried out by COMSOL,and the reasonableness of the infiltration model and the hygroscopic deformation model of the remodeled Lanzhou loess under load and water immersion conditions was studied.The main results are as follows.(1)Based on the Green-Ampt infiltration model and the improved Green-Ampt infiltration model proposed by Wang Wenyan et al.for loess,an infiltration model and a wetting-induced deformation model were proposed for the loess under one-dimensional load-infiltration conditions.The model can consider the influence of moisture infiltration by wetting deformation,and calculate the wetting deformation based on the moisture profile obtained from the infiltration model.In addition,the model was reliable because it would automatically convert to the Green-Ampt model when there was no collapse deformation.(2)The data of suction and water content of remodeled loess in Lanzhou with different void ratios were obtained by indoor element tests with self-made and modified instruments,and the water retention curve model considering the deformation effect was fitted.The fitting result showed the model could better show the effect of the deformation on the water retention curve.Furtherly,the unsaturated hydraulic conductivity function considering the deformation effect was obtained based on the saturation hydraulic conductivity of specimens with different pore ratios and the relative unsaturated hydraulic conductivity obtained by indirect method.Using the water retention curve model and the unsaturated hydraulic conductivity function considering the deformation effect,the parameters of saturated water content,initial water content,saturated hydraulic conductivity of the equivalent saturated body and frontal suction in the proposed water infiltration model were calculated.(3)Based on the one-dimensional constant water content compression test of different water content specimens,the double-line method was applied to obtain the compression curve of loess under different pressure,and the relationship between suction and collapse coefficient,and the saturation zone collapse coefficient and transition zone collapse coefficient in the proposed wetting induced deformation model were calculated by combining with the water retention curve model considering the deformation effect.(4)The soil column experiment of the remolded and compacted Lanzhou loess considering the load and immersing water condition was carried by utilizing the self-made one-dimensional soil column load and immersing water test device.At the same time,we predicted the moisture infiltration and wetting-induced deformation in the soil column by using the established moisture infiltration model and wetting-induced deformation model based on the model parameters determined by the indoor element test.Based on the comparison between the experimental results and the predicted results,it showed that the model could better simulate the development process of moisture infiltration and collapse deformation with the change of load pressure.(5)Based on the infiltration and deformation parameters determined by the indoor unit tests,the parameters in the built-in Richards equation of COMSOL Multiphysics software were modified to numerically simulate the one-dimensional soil column load infiltration test,and the simulated changes of moisture profile and pore ratio profile were obtained.The relationship between the depth of wetting front and the time as well as the relationship between the collapse deformation and the time were respectively close to those predicted by the established infiltration model and the wetting-induced deformation model,which showed that the proposed model was reasonable.