Experimental Study On Mechanical Properties Of Subgrade Soil Under Freeze-Thaw Cycles Coupled With Dynamic Loads

After decades of rapid development,China's expressways have played a decisive role in promoting the growth of the national economy.As the main load-bearing structure of road engineering,the stability of roadbed performance is particularly important to ensure the safe operation of road traffic.The factors affecting the performance of roadbed are complex and varied,among which the complex external environment in seasonal frozen soil area seriously affects the engineering properties of roadbed.At present,the research on the mechanical properties of roadbed in seasonal frozen soil region after freeze-thaw cycles is relatively scarce,especially in the dynamic characteristics of roadbed soil under the coupling effect of freeze-thaw and dynamic loads,which needs further analysis.In this paper,relying on the road construction project in Songhua River Basin of Northeast China,taking the silty clay with low liquid limit from Songhua River Basin as the research object,the dynamic characteristics of subgrade compacted soil under the coupling action of freeze-thaw cycle and dynamic load are studied.The freeze-thaw cycle test equipment developed independently is adopted to carry out freeze-thaw test under the condition of water replenishment and no water replenishment,and the samples after freeze-thaw are tested.Laboratory dynamic tests were carried out.The main influencing factors of freeze-thaw process and dynamic triaxial process are analyzed,and regression analysis is made with experimental data.Finally,the cumulative deformation prediction model and the design method of dynamic resilience modulus in seasonal freezing zone are established.Specific research contents are as follows:1.Experiments on frost heave and thaw settlement of subgrade soils were carried out.Through the indoor frost heave and thaw settlement test,the evolution law of frost heave and frost heave rate of subgrade soil under the condition of supplementary and non-supplementary water freeze-thaw is analyzed.Secondly,the law of water migration after the soil undergoes freeze-thaw cycle is studied.Combined with factor sensitivity analysis method,the degree of influence of main factors on frost heave rate of soil is systematically analyzed.The results show that the number of freeze-thaw cycles has the greatest influence on the frost heaving rate,followed by the initial compaction degree and the initial moisture content.2.Experiments on modulus of resilience of subgrade soil under the coupling action of dynamic load and freeze-thaw cycle are carried out.According to the service characteristics of Subgrade in seasonal frozen zone,a coupling test scheme of dynamic load and freeze-thaw cycles is designed.The dynamic triaxial tests of subgrade soil after different freeze-thaw cycles are carried out systematically.Considering the effects of freeze-thaw cycles,dynamic stress amplitude,confining pressure,initial moisture content,initial compaction degree and loading frequency,the dynamic resilience modulus of soil after freeze-thaw cycles is studied.Based on the evolution characteristics,the recommended values of dynamic resilience modulus of subgrade soil in seasonal frozen zone are given.3.The cumulative plastic strain test of subgrade soil under the coupling action of dynamic load and freeze-thaw cycle is carried out.In order to obtain the evolution law of cumulative plastic strain of subgrade soil under the coupling action of dynamic load and freeze-thaw cycle,a coupling test scheme of dynamic load and freeze-thaw cycle was designed.The effects of freeze-thaw cycle number,dynamic stress amplitude,confining pressure,initial moisture content,initial compaction degree and loading frequency were analyzed.The influence of various factors on the cumulative plastic strain of subgrade soil is qualitatively analyzed by single factor method,and the contribution rate of each factor to the cumulative plastic strain of subgrade soil is quantitatively analyzed by factor sensitivity analysis method.Based on a large number of experimental data,a prediction model of cumulative plastic strain is established by using multivariate regression method,and the theoretical calculation value is compared with the measured value,which shows that the model is reliable enough.It provides an important reference for roadbed design,construction and disaster prevention under the coupling action of dynamic load and freeze-thaw cycle.