【作者】 汪斌；

【导师】 唐辉明；

【作者基本信息】 中国地质大学 ， 地质工程， 2007， 博士

【摘要】 三峡库区是滑坡等地质灾害多发地带。自2003年135m蓄水伊始，到2006年156m蓄水位以来，绝大多数滑坡经受到了库水位作用的考验没有复活。但库水位波动对滑坡的稳定性和变形破坏失稳的影响机制仍为迫切需要解决的重要应用课题之一。论文选取三峡库区三大滑坡之一的巴东县黄土坡滑坡前缘临江崩滑堆积体及深部滑带土作为研究对象。在流变试验的基础上，对滑带土的流变特性和长期强度进行了研究，建立了应力—应变—时间三者关系的蠕变方程，为滑坡的建模和稳定数值计算奠定力学基础；另外，将前缘崩滑堆积体作为渗流场以及其与应力场耦合分析的工程实例，建立了三峡库区典型的地质—渗流场—应力场三位一体的耦合计算的概化模型，对不同工况下的滑坡的流固耦合作用进行了理论上和数值模拟分析。总之，滑坡滑带土的流变性以及滑坡渗流场与应力场耦合作用的研究是当前岩土工程和工程地质界研究的热点。本文正是建立在这一内在因素和外在因素分析基础之上，进行了以下主要内容的研究：1．滑坡区的工程地质特征是研究滑坡的形成、变形、破坏机制的基础，也是建立地质—渗流场—应力场三位一体的耦合计算的概化模型的基本前提。重点研究了黄土坡滑坡区的工程地质条件，以及前缘临江崩滑堆积体的空间组成结构、软弱层的物质成分及物理力学性质等。2．三峡库区一些滑坡的变形与复活的控制因素在于滑带土的力学特性强度损伤积累和时间效应，这一内在的地质力学机理与外在的地面变形演化过程彼此呼应。因此，影响滑坡稳定性的一个重要因素在于滑动带土的长期蠕变效应。对滑坡滑带土的蠕变特性进行研究并建立适合该滑坡蠕变特性的应力、应变和时间三者关系的方程就显得十分必要。研究了黄土坡滑坡1#崩滑体TP3平硐处的深部滑带土的长期蠕变特性，建立适合该滑坡的蠕变特性的Buger’s方程，并对参数进行了无约束非线性回归辨识。基于滑带土的常规试验和蠕变试验研究，得到了瞬时强度与残余强度破坏包络线，滑带土的峰值强度包线与长期强度包线。3．推导了多孔介质饱和．非饱和、稳定-非稳定渗流问题的微分方程以及方程的有限元格式，用有限元分析程序对库水位变化下引起含泥化夹层(软弱带)的斜坡的饱和—非饱和渗流场进行了全面的分析，包括水位波动的动态自由面的变化特征和坡体内孔隙水压力(基质吸力)、体积含水量、稳定性系数等的变化规律，最后应用到黄土坡滑坡前缘的非饱和渗流场的研究中。主要成果有：①库水位上升或是下降，不同水力特征的层状岸坡内在开始前几个时步内总形成一个楔形的非饱和区(位于相对弱透水层与坡面相交部位)和两个渗流自由面。这与Rulon和Freeze(1985)用类似结构砂坡来研究降雨入渗时在坡体内形成的双自由面相似。②岩土体的饱和渗透系数、土水-特征函数以及坡体的结构特征等共同决定了水位升降过程中岸坡内孔隙水压力和浸润线的分布。模拟结果可作为对库岸尤其对于含弱透水层边坡的稳定性评价及岸坡的排水加固提供参考依据。4．根据库水位波动对滑坡产生的力学作用，总结出库水位下降引起的三种类型孔隙水压力。据不同的水文地质条件，归纳并分析了地下水对斜坡稳定性影响的力学机制的三种模式：潜水含水层模式、纯承压含水层模式和承压水与潜水含水层的混合模式。阐述了非饱和土力学理论，将其应用于滑坡的稳定分析中。对传统极限平衡分析方法进行延拓，将考虑基质吸力对抗剪强度贡献的Morgenstern-Price条分法应用到岸坡的稳定性计算中。结果表明：在库水位下降过程中，稳定性系数总体变化趋势是先减然后递增，然后趋于达到一个稳定的常数；总存在一个最小的稳定性系数，它对应一个最危险水位，一般发生在库水位开始下降后10-15米左右。通过比较考虑基质吸力与不考虑基质吸力对滑动面的抗剪贡献所计算的稳定性系数，前者计算的稳定性系数稍大，一般要大0.5％左右。5．阐述并严格地推导了Terzaghi准三维固结和Biot三维固结微分方程，并对其进行比较分析。对基于虚功原理的渗流场和应力场的微分方程进行空间域及时间域离散，充分考虑双场耦合作用，推导出以位移增量和孔隙水压力增量为方程域变量的饱和—非饱和岩土体耦合固结控制方程。6．基于滑坡区的工程地质特征，考虑不同岩性物理特性及水力学参数在空间上的差异性，建立了三峡库区典型的地质—渗流场—应力场的耦合计算概化模型。通过对五种典型工况下的黄土坡滑坡1#崩滑堆积体的应力场与渗流场耦合的FEM模拟分析，得出以下几点结论：①蓄水前，仅在前缘浅层极小区域出现塑性区，说明总体上，浅层与深层滑坡均稳定。在库水位蓄水过程中，前缘的最大剪应力随库水位上升而变大，方向几乎与滑动面倾向一致，而且剪应力集中带有向浅层滑坡体后缘扩展的趋势。位移场及变形集中分布在高应变梯度带的滑动面上，且呈前缘位移大的牵引式变形，塑性区有沿浅层滑带向后缘扩展趋势。当库水位175m时，模拟成果表明，塑性区有向后缘纵深处发展贯通趋势，已对深部滑体的稳定性产生了影响；②由于耦合计算充分考虑了库水位作用下的应力边界和水头边界的变化，坡体内的渗透的体积力以及坡外的库水压力，在快速蓄水和泄水工程中，模拟结果表现出不同于单场计算的孔压场，具有明显的Cryer效应；③通过工况五的的数值模拟以及基于极限平衡法的稳定性计算，得出的滑坡的位移场、塑性区扩展趋势以及稳定性变化趋势。得出影响滑坡稳定性变化趋势的主要力学机制：库水位下降前期，作用在滑带上的有效应力的增加以及基质吸力对抗剪强度增加对滑坡稳定性的有利影响小于渗透力和超孔压力对滑坡的不利影响，而后期(本例中t≥6d)前者对滑坡稳定性的有利影响大于后者对滑坡的不利影响。这正是影响滑坡稳定性变化趋势的主要力学机制。更多还原

【Abstract】 The Three Gorges area is a region prone to geological hazards such as landslides. Thestability is controlled under the interior and exterior factors. Over the period of 2003 and 2006,the reservoir water level has risen from initial 135m to 156m, and the majority of landslides haveexperienced the challenge without failures and reactivation. However, it is still urgent to researchon the failure and reactivation mechanism of landslide induced by the reservoir water fluctuation.This paper takes the front collapsed debris of Huangtupo landslide, which is one of the greatestlandslides in There Gorges area, and the deep slip bands as the major study objects. On one hand,based on the creep test of the slip band soil, which mostly control the stability of the landslide,the research focus on the attributes of rheology and long-term strength. The proper creepconstitutive creep equations are established which set up mechanics base for further geologicalmodel and numerical simulations. On the other hand, taking the front debris of Huangtupolandslides as the numerical simulation engineering background, the research on the coupledhydraulic and mechanics actions are conducted in theory and in numerical simulations under 5different typical engineering cases.Moreover, the research on the rheology attributes of slip band and the coupled hydraulicand mechanical action are the popular and challenging problems currently in the field ofgeotechnical engineering and engineering geology. The following major problems are researchedwith respect to the interior and exterior factors:1. The characteristics of the engineering geological conditions of Huangtupo landslide areanalyzed, and the emphasis is put on the research of the front debris slipped body. The spatialdistribution, composition and the physical characteristic of the weak layer (slip band) are studiedin details, which are the preconditions for establishment of simulation model.2. As matter of results, large-scale landslide’s deformations and revival controlling factorsin Three Gorges reservoir lie in the mechanics characteristic of slip band’s strength damageaccumulation and its time-depended effects. This interior geological mechanics conforms withthe exterior deformation evolvement. So the major factor influencing the landslide stability liesin slip band’s long-term strength effects. It is very necessary to research on the mechanicsattributes of slip band soil and urgent to establish the proper stress-strain-time constitutive of it. In this chapter, the long-term rheology behavior of slip band soil, which is sampled from theexplorative cave TP3 in Huangtupo landslide, is studied. The Burger’s creep model andparameter’s non-restrain regressions are conducted, which can properly represent thestress-strain-time creep attributes. Based on the creep test, the envelope equations of transientstrength and residual strength, and the envelope equations of peak strength and long-termstrength are established.3. The differential equations and FEM equations for saturated-unsaturated, steady-unsteadyseepage in porous medium are deduced. Aimed to the type of slope containing marl interlayer,applied the FEM program to saturated-unsaturated, steady-unsteady seepage numerical analysis,the dynamic changes of free surface, the distributions of pore water pressure including thenegative suctions, volumetric water content and the variation law of FOS of slope are discussedand researched systematically. Finally, the results and conclusions are applied to the fronts ofHuangtupo landslide’s unsaturated seepage research. The main conclusions are following:①whenever impounding or sluicing of the reservoir, in the seepage numerical simulationcalculations, the interlayer (containing different layer of hydraulic conductivity) type of slopetakes on the wedge-shaped unsaturated zone and a double flee surface during the front time steps,which conforms the facts that the same conclusions were obtained using such experimentsotherwise under the conditions of rainfall infiltration conducted by Rulon and Freeze in 1985.②The saturated hydraulic conductivity, the characteristic curve of soil-water, and the characteristicof slop structural combination together determine the free surface and pore water pressuredistributions. Hence, the modeling results can provide evidences for the evaluating of slopestability and the design of water chaining and enforcement measurement for such type slope.4. According to the mechanical actions under the condition of reservoir water fluctuations,three typical pore water pressures are concluded. And in light of different hydrologicalgeological conditions, three mechanics patterns influencing the FOS for the ground water inslope are summed up as: preatic aquifer model, confined aquifer model, preatic and confinedcombined aquifer model. Introduced unsaturated soil mechanics theory into slope stabilityanalysis, the traditional limit equilibrium analysis is extended to consider thesaturated-unsaturated soil mechanics. The Morgenstem-Price stability method, which fullyallows for the contribution to anti-strength from suction, is applied to ideal reservoir slopestability evaluation. The results shows that during the water drawdown, there exists a minimumFOS and its general variation trend is firstly decrease rapidly then increase to a constantgradually. The FOS reflects the most dangerous water level, generally equal to a less 10-15mcontrasted with initial level. By contrast the FOS calculated via considering the slice bottom’ssuctions contributions and not involved it, it shows that the former is normally greater 0.5％thanthe latter.5. The Terzaghi qusi-3D consolidation theory and Biot true 3D consolidation differentialequations are rigidly deduced and demonstrated. The difference between them are compared andanalyzed. Based on the virtual work principles, the discretizations of FEM equations in timedomain and spatial domain of seepage and stress field are conducted. And considering the double field interactions effects, the saturated-unsaturated FEM formations and the coupled hydraulicand mechanics field FEM formations are deduced in the form of displacement incrementalvariable and pore water pressure incremental variable.6. The last not the least, based on the fully insight into the engineering geological andhydro-geological conditions present in the second chapter in details, considering the differentstrength characteristic of the lithology and variations of hydraulic conductivity of landslides, thetypical geology-seepage-stress combined coupled simulation model are established. Via of 5typical engineering cases, the FEM coupled simulation analysis is carried on the fronts ofHuangtupo landslide in Three Gorges region. The conclusions are reached as following:①Before reservoir impounding, the yield zone just exists in front shallow section in very smallscale, which shows the shallow and deep landslides are stable as a whole. However, with thewater level rising, the maximum shear stress in front are increasing with time, and its principaldirections are almost parallel with the slip bands, and the stress centralized zones extendsbackwards to the landslide. The displacements and strains concentrates on the highstrain-gradients slip band zones, which show the deformation belongs to the front traction type.When water level rise to 175m, the simulation results show that yield zone extends backwardsand run-through the deep slip band, which can account for the influence on the deep wholelandslide’s stability.②Due to the coupled simulation calculations allowing for the variation ofhead boundary and stress boundary under the level drawdown, during the process of impoundingand sluicing, the modeling pore water pressure results different from the single field calculationresults, and it takes on the Cryer’s effects, that is excess pore water pressure occurs on thebottom near the slip band.③Though the simulation and the calculations in engineering case 5, itshows that the trends of extend, the deformation field and the FOS calculated based on the limitequilibrium are well conformed. And we can reach the following conclusion: During theprophase in case 5, the positive contributions coming from the increment of effective stress andunsaturated seep suctions are less then the negative contributions coming from the hydraulicpressure and excess pore water pressure, and subsequently, vice versa, which is the realmechanism of the FOS of landslide influenced by the water level.更多还原