降雨边坡模型试验监测技术分析

针对降雨边坡模型试验中监测技术相对滞后这一问题,基于边坡降雨模型试验,分析了目前边坡降雨模型试验中监测技术的监测原理、监测方法及监测技术,探讨了目前室内边坡降雨模型试验中监测设备的优点及其存在的不足,最后,提出了室内边坡降雨模型试验监测技术的发展方向。研究结果对室内边坡降雨模型试验监测技术的完善具有一定的参考价值。

热带不同植被边坡水文效应室内模型试验

结合海南地区台风强降雨规律,对3种植被条件的粉土边坡模型进行了人工降雨试验,为热带生态护坡的植被选择提供依据。通过测量两次降雨过程中的总降雨量、地表径流量、雨水渗出量、坡体储水量及相应时间,对3种植被条件边坡的水文效应开展了分析。相较于裸土边坡,细叶结缕草(Zoysia japonica)边坡和肾蕨[Nephrolepis auriculate(L.)]边坡均具有较好的抗雨水冲刷能力,肾蕨边坡更占优势。降雨前后,裸土边坡渗透性大幅降低;细叶结缕草边坡渗透性有所下降,但不明显;肾蕨边坡渗透性则显著提高。肾蕨边坡良好的储水持水能力在一般情况下是有利于边坡稳定的,但在长期干旱后遭遇强降雨时,也有可能因其储水能力太强而给边坡稳定带来不利影响。相比之下,裸土边坡和细叶结缕草边坡的储水和持水能力均较差。综合比较来看,一般情况下,肾蕨的水文效应对于保持边坡的稳定性是最有利的。

西宁寒旱黄土区植物边坡水文效应室内模型试验研究

为寻求一种西宁寒旱黄土区防治浅层滑坡的护坡草本植物,本研究对3种植物条件的黄土边坡进行人工降雨试验,通过采集降雨过程中素土边坡模型、耐寒型麦冬草边坡模型和高羊茅边坡模型的土壤体积含水量数据,分析总降雨量、土壤体积含水量与对应时间的关系。试验结果表明,在两次人工降雨过程中,高羊茅边坡模型的土壤体积含水量达到稳定状态所需时间最长,耐寒型麦冬草边坡模型次之,素土边坡模型的土壤体积含水量达到稳定状态所需时间最短,高羊茅对坡体的渗透性影响最大。因此,相比纯素土和种植耐寒型麦冬草,西宁寒旱黄土区种植高羊茅能更好地固土护坡。

基于弹性波波速的降雨型滑坡预警系统

降雨是诱发滑坡最主要的因素。为减少滑坡灾害造成的人员伤亡和经济损失,滑坡早期预警系统成为了最佳选择之一。根据弹性波传播的基本原理和基于降雨型滑坡变形破坏的特点,提出利用弹性波波速来反映边坡表面土体含水率和位移的变化。开发研制了一套三轴渗流-弹性波测试三轴仪和相关系统。该装置能让水从底部渗入土体,模拟降雨入渗土体的过程,同时能测试弹性波波速。试验过程中同步测试含水率、变形和弹性波波速的变化。还进行了降雨滑坡模型试验。利用三轴弯曲元注水试验和降雨滑坡模型试验,深入分析和研究降雨引起的土体滑坡过程与弹性波波速演化规律,揭示波速与含水率和变形的耦合关系。研究结果表明,弹性波波速随着含水率的增大而缓慢减小,随着变形的增大而急剧减小,临近失稳时,波速骤然减小。根据试验结果对含水率和变形导致弹性波波速减小可能的机制进行了解释,提出弹性波在波速骤然减小时发出滑坡预警。研究结果为滑坡防灾减灾和预测预报提供新的方法和可靠的依据。

Centrifuge modeling of dynamic behavior of pile-reinforced slopes during earthquakes

A series of centrifuge model tests of sandy slopes were conducted to study the dynamic behavior of pile-reinforced slopes subjected to various motions.Time histories of accelerations,bending moments and pile earth pressures were obtained during excitation of the adjusted El Centro earthquake and a cyclic motion.Under a realistic earthquake,the overall response of the pile-reinforced slope is lower than that of the non-reinforced slope.The histories of bending moments and dynamic earth pressures reach their maximums soon after shaking started and then remain roughly stable until the end of shaking.Maximum moments occur at the height of 3.5 m,which is the deeper section of the pile,indicating the interface between the active loading and passive resistance regions.The dynamic earth pressures above the slope base steadily increase with the increase of height of pile.For the model under cyclic input motion,response amplitudes at different locations in the slope are almost the same,indicating no significant response amplification.Both the bending moment and earth pressure increase gradually over a long period.

Experimental study of motion characteristics of rock slopes with weak intercalation under seismic excitation

In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation.The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads.

A new method for the stability analysis of geosynthetic-reinforced slopes

This paper is concerned with the stability analysis of reinforced slopes.A new approach based on the limit equilibrium principle is proposed to evaluate the stability of the reinforced slopes.The effect of reinforcement is modeled as an equivalent restoring force acting the bottom of the slice and added into the general limit equilibrium(GLE) method.The equations of force and moment equilibrium of the slice are derived and corresponding iterative solution methods are provided.The new method can satisfy both the force and the moment equilibrium and be applicable to the critical failure surface of arbitrary form.Furthermore,the results predicted by the proposed method are compared with the calculation examples of other researchers and the centrifuge model test results to validate its correctness and effectiveness.

Comparisons between centrifuge and numerical modeling results for slope toppling failure

This paper presents series studies on the toppling mechanism by centrifuge tests and numerical simulations. Two different discrete element methods, i.e., the continuum-based discrete element method(CDEM) and the discontinuous deformation analysis(DDA), are adopted. The modeling results show that both the methods can accurately capture the failure modes of the centrifuge tests, including three distinct zones and two failure surfaces. Comparisons are made between the physical test and numerical simulation results. The critical inclination angle of the tilting table where the slope models are fixed on can be moderately predicted by the two methods, with different degrees of precision. The error between the test results and the simulated results is within 1% for the slope models without rock-bridges by both CDEM and DDA. However, it is amplified for the staggered-joint models that simulate the rock-bridges. With DDA, the average error is about 5%, and the maximum error is up to 17%. While with CDEM, the errors for the aligned-joint models are ranged from 1% to 6%, and it is from 10% to 29% for the staggered-joint models. The two numerical methods show the capability in simulating toppling failure of blocky rock mass with and without rock-bridges. The model with rock-bridges which provides a certain bending resistance is more stable than the one without any rock-bridge. In addition, the two failure surfaces were observed, which is different from the common understanding that only one failure surface appears.