地铁荷载下宁波软黏土冻融水泥土动力学特性研究

Study on Dynamic Characteristics of Cement Soil of Ningbo Soft Clay in Freeze-Thawing Cycles under the Load of Metro

在复杂软弱地层条件下,为有效抑制人工冻结冻胀融沉,可采用水泥土改良后人工冻结二次加固,水泥土冻融后的动力学特性,对地铁隧道长期运营至关重要。运用GDS动三轴仪研究水泥掺入比、振动频率及振次对冻融水泥土动应变、动弹性模量及动阻尼的影响。结果表明:冻融水泥土水泥掺入比越大,滞回圈面积越小,呈现先快后慢发展的趋势,其累积塑性应变最大减小50%;在其它条件相同情况下,动弹模随振动次数的增加而非线性减小,随振动频率升高、水泥掺入比的增大而线性增大;动阻尼比随振动次数的增加而非线性增加,随振动频率升高、水泥掺入比的增大而线性减小,并存在变化临界值;软土水泥土冻融前后的动力学特性有一定差异,一次冻融后的强度较冻融前减小6%;工程中联络通道周围产生非均质冻融水泥土水泥掺量应大于5%;地铁长期循环荷载的后期作用对软土水泥土加固冻融后的动力学特性影响很小,工程中可以不予考虑。

In some special weak stratum conditions,to effectively restrain artificial freezing frost heave and thaw settlement,an improved cement soil can be used after artificial freezing second-reinforcement. The kinetic characteristics of cement soil after freeze thawing is essential to the long-term operation of the subway tunnel. In this paper,the GDS dynamic triaxial apparatus was used to study the influence of cement mixing ratio,vibration frequency and vibration time on the dynamic strain,dynamic elastic modulus and dynamic damping of cement soil subjected to freeze thawing. The results show that the greater the cement mixture ratio,the smaller the hysteresis loop area is,and the trend is initially fast and then slows down. The cumulated plastic strain decreased by 50% at maximum. Subject to the same conditions,the dynamic elastic modulus decreases non-linearly with the increase of the number of vibration,and it increases linearly with the increase of vibration frequency and the cement mixing ratio. The dynamic damping ratio increases non-linearly with the increase of vibration frequency,and decreases non-linearly with the increase of vibration frequency and the cement mixing ratio,and there is a critical value. The dynamic characteristics of the soil before and after freezing and thawing are different. The soil strength after freezing and thawing reduces by 6%. The content of freeze thawing heterogeneous cement should be greater than 5% around the communication channel in engineering practices. The later effect of long-term cyclic loading of the subway on the dynamic behavior of cement stabilized soft soil after freeze consolidation is little and can be neglected.