膨胀土填料改进CBR试验方法的提出与验证

Suggestion and verification on modified CBR test method for expansive soils fill

针对膨胀土的本质特征及其CBR强度往往达不到现行路基设计规范要求(≥3%)的现象,从制件时的浸水方式、上覆压力以及制样含水率三方面着手,全面分析了标准CBR试验方法用于评价膨胀土填料强度特性的不合理性。依据封闭包盖法成功修建填芯路堤实体工程中膨胀土的实际工况,提出一套评价膨胀土这类特殊土真实强度的改进CBR试验方法:采用重型击实标准、湿法最佳含水率制件,改试件浸泡顶部浸水为侧向浸水并增大上覆压力。通过对比分析两种土类(膨胀土和非膨胀土)六个土样的标准试验方法与改进试验方法的CBR测试结果,验证了改进试验方法的合理性和可行性,为膨胀土地区的路堤修建直接采用不同胀缩等级的膨胀土填筑下路堤提供了依据。

In view of the characteristics of expansive soils and the situation that CBR （California Bearing Ratio） of expansive soils seldom satisfied the requirements of current specifications for the design of highway subgrades （CBR〉3%）, from three aspects, i. e., soaking method of prepared samples, surcharge during soaking period and moisture content of prepared samples, the irrationality of using standard CBR test to estimate the bearing capability of expansive soils was extensively analyzed. According to the actual condition that the envelope and water barrier method was used to successfully build test embankments with core filled with expansive soils, a modified CBR test method to evaluate the real bearing capability of this kind of special soils was suggested and studied. The method included preparing samples with heavy compaction standard and the optimum moisture content in light of wet compaction test, changing the water soaking method from the top to the lateral of samples, meanwhile, increasing the load on the samples during the soaking period. The rationality and feasibility of the modified method were verified by comparing the test results of routine and modified CBR tests on six samples including expansive soils and nonexpansive soils. The evidence was provided for the construction of embankments in areas of expansive soils where the expansive soils with different swelling potentials could be directly used to fill the lower part of the embankments.