| As a populous province in China,Shandong Province is short of land resources for transportation infrastructure construction.In order to maximize the protection of the red line of cultivated land,low subgrade is widely used in highway construction in this area.Due to the high ground moisture level and significant seasonal freezing and thawing factors in the region,the moisture content of low subgrade during the operation period has increased year by year.The wetting and softening phenomenon of low subgrade is very common and prone to engineering disasters such as strength damage,structural instability,and local collapse.How to quickly and effectively regulate the excess moisture inside the low subgrade and ensure that the low subgrade remains in a reasonable humidity state during the operation period is one of the urgent problems to be solved in the research direction of service performance of low subgrade.Therefore,this paper aims at the strength retention performance of low subgrade,with the goal of actively controlling the internal moisture content of low subgrade.Through the development of a new composite named RMG,and the use of model tests,numerical simulations,and other means to carry out a series of studies on moisture migration.It provides a new technology for the engineering practice of controlling the moisture content of low subgrade in seasonally frozen areas,and provides a scientific and theoretical basis for the promotion of this technology.This paper is based on the National Natural Science Foundation of China(52178429)and the Shandong Provincial Natural Science Foundation of China(ZR201911100218),and the main research contents and achievements are as follows:(1)Based on the composite processing technology of geosynthetics,a new material RMG with both moisture absorption and moisture control function was developed.RMG consists of a layer of super absorbent polymer between a moisture proof geotextile and a high suction permeable geotextile.During the preparation process,the design of proportion,the cutting and composite of relevant raw materials were carried out,and the relevant parameters of RMG were determined,providing basic data for subsequent model tests.Based on the active regulation mechanism of RMG,performance analysis was conducted on moisture absorption,high and low temperature resistance,and self-healing ability.The laying position of RMG in low subgrade is preliminarily determined,and it is pointed out that RMG has good feasibility and universality in guiding the construction of relevant subgrade projects.(2)An indoor model test device was developed to conduct model tests on moisture migration under freezing and thawing using an indoor soil column model.Taking into account complex conditions such as underground moisture replenishment and overlying loads in the natural environment,comparative tests were conducted under four different working conditions:pure soil samples,laying moisture proof geotextile samples,laying RMG samples,and laying RMG samples after gravel replacement using controlled variables.With the help of temperature and humidity sensors and cloud platform management systems,real-time monitoring of temperature and moisture content changes in soil column models under various operating conditions is carried out.After the test,the data of temperature and moisture content were collated and compared,and the corresponding temperature change rules and moisture migration characteristics were summarized.The research shows that the temperature change of the soil column sample paved with RMG has a certain degree of hysteresis compared to other samples,indicating that RMG has a certain degree of thermal insulation effect on the interior of the subgrade.The variation rule of the moisture content field shows that RMG can dynamically absorb excess pore moisture at a certain depth in the subgrade.It can maintain dynamic stability of the volumetric moisture content of the subgrade and control the subgrade to always be in the optimal moisture holding state.Then,the low subgrade can have good long-term serviceability.(3)COMSOL Multiphysics finite element software is used to conduct numerical simulation calculation of moisture transfer model.Design a true and reliable mathematical model,establish and couple the differential equations of the temperature and moisture content field.Convert them into partial differential equations and input them into the calculation software.Then,according to the actual conditions,the simulation calculation is carried out through the input of relevant parameters and the setting of model boundary conditions.After the calculation is completed,the calculation results are compared with the indoor model test data to study the variation rules of the moisture content and temperature field in the subgrade with RMG paving.The good similarity between the COMSOL Multiphysics numerical simulation results and the indoor test results is verified.(4)A full section all-weather comprehensive test system for subgrade is assembled and built,and all-weather full section scale model tests for low subgrade is conducted by this.In order to evaluate the application effect of RMG in physical engineering,six freeze-thaw cycles of three sets of scale models under different operating conditions were designed and conducted simultaneously.Through periodic moisture content testing,the engineering application characteristics of RMG are summarized.The design and application methods of RMG are proposed. |
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