Tunnel excavation, pile driving and pipe cutting will cause different degrees of disturbance to the surrounding soil, which brings great potential risks to the safe operation of the project. In this study, the influence law of thixotropy on the compression characteristics, stress-strain relationship and shear strength index of soft clay in the Binhai area of Tianjin is investigated by using one-dimensional compression and triaxial tests, combined with two factors, which are the degree of initial perturbation and the resting time. The study shows that the mechanical properties of the soil will be greatly improved after 1d of resting, while the enhancement effect will be weakened in the later stage. The larger the initial disturbance degree, the worse the mechanical properties of the soil. Finally, based on the data analysis, the prediction models of soft clay shear strength index c and & phi; value are established respectively.

软黏土的触变性对于实际工程设计和施工具有重要意义.为了分析天津地区软黏土触变性,本文基于正交试验研究了含水率、矿粉含量和pH值对其十字板强度和触变强度比率等指标的影响.试验结果表明:影响天津软黏土触变强度比率的主次因素依次为含水率、矿粉含量、pH值;软黏土的触变强度比率随含水率的增大而呈指数增大;随矿粉含量增大而呈接近线性减小;随pH值的增大而增大,但其增加幅度逐渐降低,且碱性比酸性环境更有利于软黏土强度的恢复;通过回归分析,建立了包含含水率、矿粉含量、pH值3个因素的天津软黏土触变强度比率预测公式,据此预测触变强度,预测结果较好.研究成果能够为工程实践提供理论参考.

城市污泥固化土用作路基填料,对于节约工程成本、保护环境等具有重要意义.本文以城市污泥固化土为研究对象,利用DDS动三轴仪,从干湿循环次数、初始静偏应力、动应力3个方面研究其对累积塑性应变及动强度特性的影响.试验结果表明:在干湿循环单独作用下,土体累积塑性应变随干湿循环次数的增加先增大后趋于稳定,但与初始静偏应力耦合作用下对土体累积塑性应变的影响不太显著.动应力对其影响较大,且存在临界值:当动应力小于临界值时,累积塑性应变呈现出先增大后逐渐稳定的趋势;当动应力大于临界值时,累积塑性应变在达到某一振次后快速增大,土体迅速产生变形破坏.干湿循环与初始静偏应力都会降低土体的动强度,但干湿循环在达到10次后,动强度将趋于平稳,不再受其影响.通过回归分析,建立了考虑干湿循环次数、初始静偏应力及动应力等因素影响的城市污泥固化土稳定型累积塑性应变模型,并验证了其可行性.

污泥具有高含水率、力学性质差和污染物含量高等特点,可以通过固化技术将其转化为固化土,达到城市污泥安全处理与合理利用的目的.为了得到在多变的自然气候环境影响下固化土的动力特性,以城市污泥固化土为研究对象,在不同冻融温度和不同冻融循环次数条件下,通过动三轴试验仪对城市污泥固化土进行多振次循环动荷载试验,探讨其在经历不同冻融温度和不同冻融循环次数后的长期动力力学指标变化规律.试验结果表明,污泥固化土破坏形式呈现脆性破坏的特征,并具有明显的剪切面;在低温冻结和多次冻融循环耦合作用下,随着冻融温度降低和冻融循环次数的增加,污泥固化土的轴向应变增速和最终值会随之增大,动强度亦随之降低;对不同时刻动应力-应变曲线进行分析,得到不同冻融温度循环条件下城市污泥固化土动强度与冻融循环次数的关系式,为城市污泥固化土动强度计算提供理论依据.污泥固化土静、动长期强度随冻融次数的变化规律基本一致,在其他条件相同的情况下,污泥固化土静长期强度明显大于其动长期强度.

The rational and effective disposal of sludge has always been a key topic of interest. Freeze—thaw cycles can change the mechanical properties and structural characteristics of soils, leading to a range of engineering geological problems. The sludge curing technology can be used to transform municipal sludge into a new type of sludge-cured lightweight soil. The effects of the number of freeze-thaw cycles and freezing temperature on the unconfined compressive strength and compression modulus of the improved sludge-solidified lightweight soil were investigated by unconfined compressive strength and one-dimensional compression tests. A structural quantitative parameter that considers the freeze-thaw cycles, i.e., the freeze-thaw structural potential, is proposed. The variation pattern of the freeze-thaw structural potential under the influence of different factors was analysed. The test results show that the strength and compression modulus initially rapidly decreased, and then tended to be stable with the increase in the number of freeze-thaw cycles. A lower freezing temperature led to smaller strength and compression modulus. The first two freeze-thaw cycles had a greater influence on the freeze-thaw structure potential. The influence of freezing temperature on the freeze-thaw structural potential is significant when the pressure and number of freeze-thaw cycles are small, and diminishes as the pressure and number of freeze-thaw cycles increase. It was found that there was a good non-linear relationship between the freeze-thaw structural potential and both the unconfined compressive strength and compressive modulus. On this basis, models for the freeze-thaw structural potential as a function of the unconfined compressive strength and compression modulus, taking into account the effects of freezing temperature and the number of freeze-thaw cycles, are proposed respectively, and the accuracy of the models is further verified. The results can provide a reference for the applications of solidified light soil in various fields including engineering fillings in seasonally frozen areas.

当透水性较差的饱和软黏土处于施工速度快(加荷速率快)的实际工况时,往往夹杂着应力松弛现象,给工程实践的安全运营带来巨大隐患.以天津滨海吹填软土为研究对象,采用WF应力路径三轴仪,通过不固结不排水(UU)三轴剪切试验,分析了不同初始应变、围压、剪切速率、取样深度和结构性等因素对其应力松弛特性的影响规律.试验结果表明:不同试验条件下,天津滨海吹填软土的应力松弛过程都可分为快速、慢速和稳定3个阶段;应力松弛速率随初始应变和取样深度的增大而增大,而围压和剪切速率对其影响不太显著,土的结构性增强会明显增大应力松弛速率,从而加剧应力松弛现象的产生;通过对比分析,确定幂函数模型更适合描述不同试验条件下吹填软土的应力松弛变化规律.研究结果对天津滨海吹填软土场地安全施工与运营具有重要的现实意义.

It is of great significance for engineering construction and environmental protection to improve saline soil by curing technology to make it an excellent roadbed filler. In this paper, taking light solidified saline soil as the research object, laboratory tests were carried out by using true triaxial apparatus. The effects of the ratio of intermediate principal stress, salt content and confining pressure on the stress-strain relationship, failure strength and shear strength index were analyzed. The strength failure mode of light solidified saline soil was revealed and the calculation method of strength index was established. The test results showed that the slope of the stress-strain curve increases with the increase in the ratio of the intermediate principal stress and the confining pressure, but the salt content has little effect on it. The salt content has a significant effect on the failure stress. When the salt content is at 4%, the failure stress reaches the maximum. Under different conditions, the light solidified saline soil could produce different strength failure modes of lateral expansion, taper, oblique crack, and diagonal. Through analysis and calculation, the prediction formula of failure strength and shear strength index of light solidified saline soil considering the ratio of intermediate principal stress and salt content was established. The comparison showed that the Mohr-Columb strength criterion is conservative in describing the strength of light solidified saline soil and it tends to underestimate the actual strength of the soil. The research results can provide references for engineering practice.