含水率变化下压实路基土动态回弹模量试验研究与预估模型

路基土动态回弹模量MR是路面设计和使用性能评价采用的关键参数,运营期间受含水率变化影响显著。以压实红黏土为研究对象,制备了6个不同含水率和3种不同压实度的试样,采用滤纸法测试了不同状态下的基质吸力,并通过动三轴试验研究了含水率、压实度、动偏应力和围压对动态回弹模量的影响。试验结果表明:MR随压实度、围压的增大而增大,随动偏应力增大呈非线性减小;MR随含水率增大急剧降低,从最佳含水率增加4.5%时,不同压实度下MR均降低约50%,动偏应力和压实度对MR的影响随含水率增大逐渐减弱;MR随含水率和饱和度的变化规律与土性显著相关,而不同土样的MR随基质吸力变化趋势基本一致。进而引入基质吸力,建立了综合考虑含水率和应力水平影响的压实路基土MR预估模型,通过本文和文献试验数据证实了该模型的适用性,并基于13种土样的试验结果建立了模型参数与物性指标之间的经验关系。

Experimental study and prediction model of dynamic resilient modulus of compacted subgrade soils subjected to moisture variation

The dynamic resilient modulus (M_R) of subgrade soils is the key parameter used in pavement design and performance evaluation, and is significantly affected by variation of moisture content during operation. The compacted lateritic soil is used, and the test specimens are prepared using six different moisture contents and three degrees of compaction. The repeated loading triaxial tests are conducted to investigate the effects of moisture content, degree of compaction, dynamic deviator stress and confining pressure on dynamic resilient modulus, and the soil suctions of different specimens are measured using the contact filter paper method right after cyclic loading tests. The test results indicate that M_R increases with the increasing confining pressure and degree of compaction, and decreases nonlinearly with the increasing dynamic deviator stress. The values of M_R decrease greatly with the increasing moisture content, as moisture content increases by 4.5% from the optimum moisture content, they decrease to about 50% of the initial values, and the influences of dynamic deviator stress and compactness on M_R decrease with the increasing moisture content. In addition, the relationships for both M_R - moisture content and M_R - degree of saturation are highly soil type-dependent, while the variation of M_R with soil suction is similar for different soils. Thus by incorporating the soil suction into confining stress, a new prediction model for the resilient modulus taking into account both the stress state and the moisture content is proposed. The suitability of the proposed model is validated through the experimental data from this study and the existing literatures. Then the empirical relationships between model parameters and physical properties of soils are developed based on the statistical regression analysis performed on 13 different soils, and a good agreement between the measured and predicted values of M_R obtained using the regression model parameters is found. This study may provide a simple and reliable method for