考虑吸附结合水影响的高液限土路基压实度控制标准

Control Standards for Degree of Compaction of High Liquid Limit Soil Subgrade Considering Effects of Adsorbed Bound Water

为了确定用高液限土直接填筑高速公路下路堤时压实度控制的下限值,选取海南高液限土,并以长沙黏土质砂为对比样,开展基本物理性质、电镜扫描、重型湿法击实、浸水CBR和非饱和固结试验;利用容量瓶法测定土样的吸附结合水含量;分析吸附结合水对高液限土击实特性、强度、水稳性和压缩性的影响;将吸附结合水视为土中固相的一部分,提出并论证高液限土压实度控制下限值计算式。研究结果表明:海南高液限土含有大量微孔隙和叠片状结构的黏土矿物,吸附结合水的能力远强于黏土质砂;吸附结合水含量与塑限密切相关,约为塑限的85.3%;吸附结合水作用使高液限土相对黏土质砂而言最佳含水率偏高,最大干密度偏低;当初始含水率低于吸附结合水含量时,高液限土CBR试件浸水后的膨胀量显著增大;吸附结合水对高液限土在高含水率状态下仍能保持一定CBR强度和低压缩性起到了积极作用,并可在路基运营期内始终保持稳定;采用高含水率的高液限土填筑下路堤时,其压实度控制下限值并非定值,而是与其吸附结合水含量和最佳含水率相关,前者越大于后者,压实度控制下限值越低。研究成果可为高液限土路基设计与施工及相关技术标准的制修订提供参考。

To determine the lower bound of the degree of compaction of high liquid limit soil used directly to fill the lower part of an expressway embankment,several soil samples from Hainan as well as a clayey sand sample from Changsha were studied.Various tests,including scanning electron microscopy,heavy wet compaction,soaked California Bearing Ratio(CBR),and unsaturated consolidation tests were conducted on the soil samples.Adsorbed bound water content(ABWC)was measured using a volumetric flask method to evaluate its influence on the compaction properties as well as the strength,water stability,and compressibility of high liquid limit soil.An equation for estimating the lower bound of the degree of compaction of high liquid limit soil was proposed and validated by considering the ABWC as a part of the solid phase.The test results show that the ability to absorb bound water of the high liquid limit soil is much stronger than that of clayey sand because of the presence of numerous micropores and laminated structures contained in the high liquid limit soil.The ABWC is closely related to(approximately 0.853 times)the plastic limit.This can be attributed to the influence of ABWC that the optimum water content(OMC)is higher but the maximum dry density is lower in high liquid limit soil than in clayey sand.The swelling ratio of CBR specimens of high liquid limit soils increases significantly after inundation when the initial water content is lower than the ABWC.The ABWC has an active effect in maintaining the high strength and low compressibility of high liquid limit soil with high water content and can remain stable during the operation period of the embankment.When using the high liquid limit soil with high water content to fill the embankment,the lower bound of the degree of compaction is not a fixed value but is depended on the ABWC and OMC.The lower bound decreases further when the ABWC exceeds OMC.The results of this study can assist in designing and constructing high liquid limit soil subgrade and in revising the related technical standards with references.