Salinization Accumulation Mechanism Of Aeolian Sand Subgrade In Desert Area

Aimed In this paper,the pavement salinization disease of a highway in the desert area of Western Inner Mongolia was investigated systematically.The groundwater level along the pavement was far from the surface(>50m),the climate was dry,the soil moisture content was very low,and the capillary channel of aeolian sand subgrade was cut off,which still caused the salinization disease.Highway disease is particularly evident in areas with large temperature difference.Even if the roadbed filling is replaced at the disease site,the corresponding disease site will continue to be destroyed.Salinization of roadbed soils often leads to pavement diseases and reduces the quality of pavement.However,there are still no effective measures to control and prevent salinization,and there is no definite conclusion as to when to reach the time effect of salinization.Therefore,on the basis of field investigation,indoor soil column test and multi-field coupled finite element software simulation,this paper studies the law of salt migration and accumulation in Aeolian Sand Roadbed in the desert area of Western Inner Mongolia,and prevents the occurrence of roadbed salinization and road diseases caused by roadbed salinization in the non-saline soil area of this area in an effective time,which is helpful for optimizing roadbed disposal measures.This paper draws the following conclusions through research:1.Through the investigation and analysis of the climate environment in the diseased section and the field sampling and analysis of the chemical composition of the soil samples at the depth of 30 cm,50 cm and 80 cm of the diseased section,the results show that the samples in the non-diseased section have low salinity and non-saline soil,and the salt components in the diseased section are soluble sodium sulfate,sodium sulfate and alkali.Potassium salt is predominant.The total amount of soluble salt in most of the base samples is more than 0.5%,and the degree of salinization is medium and strong.The salt content of the samples in the diseased section is generally higher than 0.3%.There is obvious salinization phenomenon in the base and roadbed of the diseased section,which is typical sulfate saline soil.Sodium sulfate saline material mainly comes from the marine sedimentary stratum environment;when the temperature of the roadbed soil decreases,sodium sulfate crystallizes and precipitates.Accumulative swelling is one of the important causes of Pavement Transverse uplift in desert areas of Western Inner Mongolia.2.According to the results of indoor water vapor test and indoor and outdoor water and salt migration test of aeolian sand roadbed,it is traditionally considered that compacted aeolian sand has the effect of preventing salt and salt,which does not fully consider the effect of salinization time.Compacted aeolian sand only prevents capillary water from carrying salt and wind migration,but does not consider the water carrying in the roadbed under desert climate conditions.Salt mainly migrates in the form of vapor water and film water,so the use of aeolian sand to fill subgrade in desert areas can not prevent subgrade salinization.3.The results of indoor and outdoor water and salt migration experiments show that the accumulation of salt in shallow layer of Aeolian Sand Subgrade in desert area,film water and vapor water in soil layer affected by temperature exist simultaneously and provide a carrier for salt migration.Due to the change of ambient temperature,the change range of internal temperature of compacted aeolian sand subgrade tends to be gentle with the increase of burial depth,which can be divided into two parts: the severely affected area(0~50 cm)and the weakly affected area(50~120 cm).The peak temperature of each layer has a lagging effect.Salt migration in the deep area of compacted aeolian sand subgrade is the concentration of salt content in the underlying surface and the initial aeolian sand layer of sodium sulfate subgrade.The gradient provides the original power for it.4.On this basis,through field and laboratory tests,the temporal and spatial distribution law and theoretical analysis of water,heat and salt transport in Aeolian Sand Subgrade in desert area are studied,and the transport equation of water,heat and salt is constructed.Salt transport in the process of salinization of Aeolian Sand Subgrade in desert oasis area is studied by indoor soil column test and COMSOL Multiphysics multi-field coupled numerical simulation software.The regression formulas of salinization time in non-saline Aeolian Sand Roadbed in desert oasis region with initial moisture content and initial salinity are established.The time nodes of aeolian sand roadbed salinization(salinity exceeding 0.3%,which is the critical criterion)are predicted.5.According to the mechanism of soil salinization of aeolian sand subgrade,the barrier technology of preventing soil salinization of Aeolian Sand Subgrade in the desert area of Western Inner Mongolia is put forward to prevent salt from migrating into the subgrade from the source,and the prevention and control measures of laying gravel cushion on the underlying surface of new highway subgrade are put forward:mainly laying on the surface of the subgrade to prevent the formation of water vapor and the fragmentation of salt transport conditions carried by film water.Stone barrier faults,rather than capillary water barrier faults,prevent salt from migrating into the roadbed in the marine sedimentary foundation environment.