考虑持水能力的黄泛区高液限黏土路用压实标准

Subgrade Compaction Control Standard of High Liquid Limit Clay in Shandong Yellow River Flood Area Considering Its Water Retaining Characteristics

黄河下游冲淤积在山东省形成了大量特殊的高液限黏土,由于沿线平原区路基填料极度匮乏,若弃之不用将造成极大损失.本文从施工期和运营期2个阶段对土体的强度和模量进行了试验探讨.黄泛区高液限黏土主要由高含量的磨圆粉粒及黏粒组成,高于最优含水率压实时,土体表现出空气体积率低、饱和度高的特点.基于滤纸试验,发现高进气值导致土体具有很强的持水性.基于不排水、不排气的三轴试验,获得了不同压实状态下土体归一化静强度和抗剪强度指标与饱和度、空气体积率的相关关系.该类土存在的最优饱和度为79%(相应空气体积率为8%).相较于土体的强度特征,黄泛区高液限黏土回弹模量受含水率的影响更敏感,含水率由20%增加至23%时,尽管路基依然保持稳定,但回弹模量的大幅衰减导致路基压缩应变增加近200%.结合我国和日本的路基压实控制标准,提出黄泛区高液限黏土的填筑含水率不应高于23%,空气体积率不高于8%(即压实度控制在90%及以上),以保证土体强度和模量的长期稳定性.

Large area of special high liquid limit clay was formed due to the depositing in the downstream of Yellow River at Shandong province.Without the use of such clay in those plain areas in lack of filling materials,great resource waste would be caused.This paper experimentally examined the soil strength and modulus in both construction and operation periods.The high liquid limit clay in Yellow River flood area consisted of higher rounded silt particle and clay particle,which presented low volume ratio of air and high saturation degree when compacted above the optimum moisture content.Based on the filter paper tests,it was indicated that high air intake value resulted in strong water retention capacity.Through the unventilated-undrained triaxial test,the relationships between the normalized static strength,shear strength and saturation degree/volume ration of air were obtained at different compaction states.It was found that the soil had an optimum saturation ratio at 79%(volume ratio of air=8%).The soil resilient modulus was more sensitive to the moisture contents.Although the subgrade remained safe when moisture contents increased from 20%to 23%,the compression strain increased by almost 200% due to the sharp decrease in the resilient modulus.Considering the subgrade compaction standard specified in China and Japan,the high liquid limit clay in Yellow River flood area should be compacted lower than 23%moisture content and 8% volume ratio of air,i.e.,no less than 90%compaction degree,to ensure the long-term stability of soil strength and modulus.