黄土卸荷蠕变特性与典型开挖型黄土滑坡机理研究

STUDY ON THE UNLOADING CREEP CHARACTERISTICS OF LOESS AND THE MECHANISM OF TYPICAL EXCAVATED LOESS LANDSLIDE

开挖卸荷是黄土滑坡的主要诱发因素之一,为深入研究黄土的卸荷蠕变特性与开挖型黄土滑坡的机理,本文选择典型开挖型黄土滑坡——榆林市上庄滑坡黄土作为研究对象,进行了一系列三轴卸荷蠕变试验,分析了卸荷对黄土蠕变特性的影响,并结合试验成果和数值模拟方法对开挖型黄土滑坡机理进行了揭示。三轴卸荷蠕变试验结果表明在卸荷条件下,卸荷应力水平越大,试样蠕变变形越大且达到稳定蠕变状态所需的时间就越长。初始固结应力越大,试样蠕变破坏所需卸荷值占围压的比例越小。利用等时曲线法求取了试样长期强度并计算出研究区黄土的长期黏聚力与长期内摩擦角值,引入长期强度折损率,并对瞬时强度与长期强度的规律进行了对比分析。数值模拟计算结果显示在坡脚开挖处形成了应变集中区,坡面由上至下的位移逐渐增大。相较于未开挖情况下,开挖后土体中卸荷应力明显增大,导致坡体蠕变变形增大,最终造成了坡体滑移。研究成果可为此类滑坡防治提供理论借鉴。

Excavation unloading is one of the main inducing factors of loess landslides.In order to deeply study the unloading creep characteristics of loess and the mechanism of excavated loess landslides,we selected the typical excavation loess landslide—the loess of Shangzhuang landslide in Yulin City as the research object and carried out a series of triaxial unloading creep tests of loess.We analyzed the influence of unloading on the creep characteristics of loess and revealed the mechanism of excavation-type loess landslide based on the experimental results and numerical simulation methods.The greater the unloading stress level of the sample,the greater the creep deformation of the sample and the longer it takes for the sample to reach a stable creep state.The larger the initial consolidation stress is,the smaller the proportion of the unloading value of the specimen's creep failure to the confining pressure is.We obtained the long-term strength of the sample by the isochronous curve method and calculated the long-term cohesion and long-term internal friction angle of the loess in the study area.In addition,we introduced the long-term strength loss rate and analyzed the law of instantaneous strength and long-term strength.Numerical simulation results show that a strain concentration area is formed at the toe of the excavation slope.The displacement of the slope gradually increases from top to bottom.Compared with the unexcavated condition,the unloading stress in the soil after excavation increases significantly,which leads to the increase of the creep deformation of the slope body,and finally causes the slope body to slip.The research results can provide theoretical support for landslide prevention.