【作者】 刘珣；

【导师】 项伟；

【作者基本信息】 中国地质大学 ， 岩土工程， 2010， 博士

【摘要】 极端冰雪灾害条件下,反复冻融作用使岩体及支护结构内部应力平衡状态发生改变,严重威胁地质灾害体防治工程结构体系的正常运行,使支护结构体系失效随之产生滑坡、崩塌等地质灾害,造成人民生命财产的重大损失。2008年初,一场大范围持续性的极端冰雪灾害席卷我国中部及南方大部分地区,给国民经济造成了巨大损失,也随之引发了一系列次生地质灾害。多年来,国内外关于极端低温条件下的研究多集中于寒区深层岩土体冻融问题,对于表层岩体(地面以下20cm以内)的冻融研究少有涉及,因此,亟待开展极端冰雪灾害对我国中、南部地区表层岩体与支护结构安全性影响研究。本文依托“十一五”国家科技支撑计划重点项目“极端冰雪灾害条件下岩土体与支护工程一体化安全性研究”(编号2008BAC47BOX),在充分调研2008年极端冰雪灾害气候、岩土工程实例和系统研究国内外相关文献资料的基础上,以我国中、南部地区极端冰雪灾害条件下的边坡岩体及支护工程为背景,基于试验力学、低温学、冻土学、冻岩力学、岩土工程学及损伤力学等理论,围绕受低温冻结、融化影响显著的岩体及支护结构,开展了一系列物理、力学试验研究,包括岩石声波试验、X-射线衍射试验、封闭／开放式冻融试验、常规物理试验、冻融前后岩石及胶结面单轴压缩试验、三轴压缩试验、直剪试验、砼抗压试验、SEM微观试验及岩体与支护结构相互作用中型物理模型试验,并进行了深入分析。文中首先阐述了自主研制能模拟极端冰雪灾害气候条件、并可配合MTS大型岩石伺服机使用的环境控制系统的全过程。然后,以受灾较重的湖北地区灰色砂岩及常用挡土墙、喷锚支护结构为例,系统研究了极端冰雪灾害条件下,在温度、含水量、冻融方式等多因素作用下,岩石、岩体与挡土墙支护结构相互作用及岩体与喷锚支护结构相互作用的变形规律、强度特性及破坏屈服准则。其次基于三轴压缩试验成果,通过引入统计损伤理论,建立了冻融前后岩石、岩石与喷射砼相互作用的冻融损伤软化统计本构模型。在此基础上,开展了极端冰雪灾害条件下岩体与支护结构相互作用中型物理模型试验,并提出了适合极端冰雪灾害条件下岩体与支护结构相互作用物理模型试验研究的方法和建议。取得的主要研究成果如下：(1)自主研制了箱体内胆尺寸为1000×1000×1000mm的专用环境控制系统,该系统具有内部空间大、模型进出便利、连续冻融稳定性高、冻融速度快、温度可程控及具有专用加载配套设施等特性,不但能进行常规岩土体冻融试验,同时具备配合大型MTS800电液伺服加载系统对中型岩土体与支护结构相互作用物理模型进行冻融循环条件下各种力学试验的能力,该系统在箱内净容积、高低温控制性能、岩土体吊装及加载便利性等方面达到国内先进水平。(2)首先对取自2008年冰雪灾害重灾区的灰色砂岩进行了声波、物理指标测试,分别开展了10℃--20℃封闭式冻融循环及20℃--20℃开放式冻融循环试验,然后研究了常温、不同含水量(干燥和饱和)以及经历不同冻融循环次数的砂岩尺寸、质量变化规律。其次对冻融前后砂岩分别进行了单轴、三轴压缩力学试验,分析得出其破坏形态、应力-应变曲线特征、强度屈服准则及强度指标,最后对冻融前后砂岩进行了SEM微观扫描分析研究。试验结果表明,砂岩饱水或经历开放式冻融循环后,单轴抗压强度、弹性模量及变形模量显著下降；而在经历封闭式冻融循环后,上述指标呈现截然相反的变化趋势。说明含水量是砂岩冻融损伤的决定因素,据此提出砂岩在分别遭受封闭/开放式冻融循环时的两种损伤破坏模式：内部微损伤模式和沿层理面弱化模式。砂岩经历封闭/开放式冻融循环后的单轴破坏形式不同,但本质都是剪切破坏,开放式冻融循环后砂岩单轴强度显著降低、应变增大,在卸荷阶段表现出明显的流变性。低围压下,干燥和饱和砂岩均呈现典型的对角剪切破坏,应力-应变曲线明显存在脆性→延性的转化过程并在卸载过程中发生应力跌落。随着含水量的增大,砂岩粘聚力、摩擦角降低,抗剪强度降低。微观分析表明,由于冻融循环作用,砂岩内部孔隙和颗粒间空隙增大,颗粒之间出现挤压和相对错动导致水分逐渐侵入岩石内部造成破坏。(3)选取岩体与挡土墙支护结构相互作用体为研究对象,制作灰色砂岩与常用C20普通浇筑砼相互作用试样,研究了常温以及经历不同冻融循环次数后胶结面试样尺寸、质量变化规律。然后对开放式冻融前后试样进行了胶结面直剪试验,得到其剪切破坏强度准则及其影响因素。试验结果表明,随冻融次数的增加,胶结面试样高度及质量均呈增大趋势,砂岩和砼部分直径也分别增大,5-10次循环后即丧失强度导致胶结面脱落。随着轴压增大,胶结面剪切应力增大。随着冻融循环次数的增加,水平应力峰值明显降低,冻融前后胶结面剪切屈服后均出现不同程度的剪切流变现象,多个试样出现间歇性应力跌落。冻融循环3次后,胶结面处粘聚力有所降低,而摩擦角却增大。(4)选取岩体与喷锚支护结构相互作用体为研究对象,制作砂岩与C20喷射砼相互作用试样,研究了常温以及经历不同冻融循环次数后胶结面试样尺寸、质量变化规律。然后对开放式冻融前后胶结面试样进行了单轴压缩试验、中/低不同围压条件下三轴压缩试验及中/低不同轴压条件下胶结面剪切试验,分析得出其破坏形态、应力-应变曲线特征、强度屈服准则及强度指标。最后对冻融前后胶结面试样进行了SEM微观扫描分析研究。试验结果表明,常温及经历冻融后,胶结面试样在单轴压缩试验中破坏形式均为沿轴向拉伸劈裂,并无从胶结面处发生剪切滑移的趋势。随着含水量增加,胶结面试样强度明显降低。随着冻融次数增加,弹性模量、变形模量线性降低。低围压下,常温干燥/饱和胶结面试样破坏多数表现为对角向裂缝,随着含水量增大,峰值强度降低,粘聚力、摩擦角也降低；中等围压下,经历3次开放式冻融循环后试样三轴破坏形式为砼部分压碎,岩石部分轻微开裂,整体表现出明显的延性,砼的脆性破坏限制了整体强度的提高。粘聚力较低围压下冻融前变化不明显,摩擦角则大幅降低；随着冻融次数增加,剪切应力峰值平均值明显降低,且卸荷阶段出现明显的蠕变现象。随着轴向应力的增大,剪切应力峰值增大。在低轴压下,冻融循环次数的增加导致胶结面处粘聚力明显降低,摩擦角却反而略有提高,而高轴压下,胶结面处粘聚力及摩擦角均明显降低。微观分析表明,经历开放式冻融循环后,砂岩表面颗粒变得零碎,胶结弱化,砼表面颗粒之间的胶结弱化,且相互间发生错动和位移；而造成破坏的根本原因则是胶结物与两种材质之间的缝隙宽度经冻融后增大。(5)根据中、低围压下三轴压缩试验成果，引入基于Weibull分布统计规律及微元强度概念的统计损伤力学理论,建立了常温下不同含水量(干燥及饱和)砂岩及其与喷射砼相互作用两种损伤软化统计三维本构模型,并通过对峰值应力、应变与围压的关系拟合,将其推广至任意围压下的损伤软化统计本构模型。随后还建立了经历3次开放式冻融循环后的砂岩与喷射砼相互作用损伤软化统计一维本构模型。最后根据上述本构模型绘制出常温及冻融损伤后的应力-应变曲线,并与试验曲线进行了对比,结果表明,所建立的损伤软化统计本构模型可靠。(6)采用常用C20喷射砼与砂岩制作岩体与喷锚支护结构相互作用物理模型,并模拟极端冰雪灾害气候条件对模型进行了周期性补水条件下的冻融循环试验。试验过程中,采用电测法和光纤光栅测量法对物理模型岩石、砼、岩石与砼胶结面表面、岩石与砼胶结面内部受温度变化引起的应变进行了测量,系统研究了模型表面主应变、主应力、最大剪切力、主应力方向角及模型内部应变形成及变化规律。试验结果表明,冰雪覆盖条件下的岩石表面支护工程在经历一定次数冻融循环后,由于岩石远无法达到饱和含水率,加之砼凝固后吸水性很差,实际情况并不会发生理想化的冻胀融沉,而是呈现出局部冻胀融沉、局部热胀冷缩的中间状态。当冻融循环周期为24小时时,模型表面逐步由弹性变形阶段进入塑性变形阶段。而当冻融循环周期增大为48小时后,由于温度对模型内部及表面作用更充分,模型重新呈现弹性变形特性。鉴于此,为模拟实际温度变化且充分考虑塑性变形累积对实际工程的不利影响,建议实验技术规范中岩石与支护结构相互作用模型试验冻融周期每次不大于24小时。冻融过程中,岩石与砼胶结面平面内对降温过程更敏感,压应力、压应变及最大剪切力增长显著,而垂直于岩石与砼胶结面平面方向(含表面)变形对升温过程更敏感,拉应力及拉应变增长显著；当温度上升时,模型表面最大剪切力减小；当温度下降时,最大剪切力增大；无论是在岩石、砼还是岩石与砼胶结面侧表面,主应力方向角波动幅度基本均集中在一个90°的象限内。即使是在胶结面侧表面上不远的两点,其主应力方向仍有不同,但其变化范围有部分重合；模型内部平行于岩石与砼胶结面平面方向上,受温度变化影响时拉应变增长更显著,且波动最小,呈明显的冻胀融沉性质。垂直于岩石与砼胶结面平面方向上材料应变受温度变化影响最剧烈,且波动最大；岩石与砼胶结面平面内受温度变化影响时压应变增长更显著,且波动较大。本文的创新点主要表现在：(1)自主研制了能配合MTS大型岩石伺服机使用的专用环境控制系统,该系统具有内部空间大、模型进出便利、连续冻融稳定性高、冻融速度快、温度可程控及具有专用加载配套设施等特性,在箱内净容积、高低温控制性能、岩土体吊装及加载便利性等方面达到国内先进水平。(2)研究得出极端冰雪灾害条件下,在温度、含水量、冻融方式等多因素条件下,岩石、岩体与挡土墙支护结构相互作用、岩体与喷锚支护结构相互作用三种情况的破坏形态、应力-应变曲线特征、强度屈服准则及强度指标,并据此建立了常温下砂岩、砂岩与喷射砼相互作用损伤软化统计三维本构模型及冻融循环后砂岩与喷射砼相互作用损伤软化统计一维本构模型。结果表明,所建立的损伤软化统计本构模型可靠。(3)开展了极端冰雪灾害条件下,岩体与支护结构相互作用中型物理模型试验,深入研究并得出两种材料相互作用的动态响应规律及破坏机理,提出了适合极端冰雪灾害条件下岩体与喷锚支护结构相互作用物理模型试验研究的方法和建议。更多还原

【Abstract】 Under extreme ice and snow disaster condition, repeated freezing and thawing change the internal stress balance status of rock mass and supporting structure, the structure of geohazard prevention will under a serious threat. The supporting system failure will lead to landslides, collapses and other geological disasters, resulting in great loss of lives and property. In early 2008, a persistent large-scale extreme ice and snow disaster swept most areas of central and southern of China, the disaster caused enormous losses to the Chinese economy, and also a series of secondary geological disasters are developed. Over the years, the research at home and abroad about extreme low temperatures almost focused on the freeze-thaw questions of rock and soil mass of great depth in cold region, the surface rock mass(less than 20cm below the surface) was rarely involved in freeze-thaw studies. Therefore, it is urgent to carry out the research on the safety influence of extreme ice and snow disaster for the surface rock mass and supporting structure in central and southern regions of China.This dissertation relies on the key projects of "Eleventh Five-Year" National Science and Technology Support Plan "Safety Research on Integration of Rock and Soil Mass and Supporting Engineering under the Conditions of Extreme Snow and Ice Disasters" (No.2008BAC47B0X). On the basis of extreme climatic of ice and snow disaster, geotechnical engineering examples and relevant literature of home and abroad, the dissertation is set in the rock slope and supporting engineering in central and southern regions of China under extreme ice and snow disaster condition, and based on the theory of test mechanics, cryogenics, frozen earth mechanics, frozen rock mechanics, geotechnical engineering and damage mechanics. In this dissertation, the author carried out a series of physical, mechanical experimental research including rock acoustic tests, X-ray diffraction experiment, closed/open freeze-thaw tests, routine physical tests, before and after freeze-thaw rock and cement surface uniaxial compression test, triaxial compression test, direct shear test, concrete compression testing, SEM micro-scanning test and medium physical model test of interaction between rock mass and supporting structure, according to the rock mass and supporting structure affected by freezing and thawing. Firstly, the dissertation describes the whole independent research process of the environmental control systems that not only can simulate the extreme ice and snow disaster climatic conditions, but also can work in conjunction with large-scale rock MTS. Then, the dissertation takes the gray sandstone and common retaining walls, spray-anchor structure from the heavily-disaster area of Hubei province for instance, and the interaction between rock mass and retaining walls supporting structure, the interaction between rock mass and spray-anchor structure under extreme ice and snow disaster condition, this dissertation researched systematically on the deformation law, strength properties and failure yield criterion under the action of multiple factors such as temperature, moisture, freeze-thaw method etc. Secondly, based on triaxial compression test results, and through the introduction of statistical damage theory, the freeze-thaw damage softening statistical constitutive model for the rock, the interaction between rock and shot-crete before and after freeze-thaw are presented in this paper. Based on above results, a medium physical model test of interaction between rock mass and supporting structure under extreme ice and snow disaster condition is provided. In addition, the dissertation proposed some research methods and recommendations suitable for the physical model test of interaction between rock mass and supporting structure under extreme ice and snow disaster condition. The major conclusions got in this dissertation are as follows:(1) A set of dedicated environmental control systems of cabinet liner size 1000×1000×1000mm has been developed independently. The system has the characteristics of a large interior space, convenience for circling, a continuous freeze-thaw stable, freeze-thaw speed, the temperature can be programmed and has a dedicated loading facilities, etc. and the system can not only regular freeze-thaw test of rock and soil mass, but also can carry out a variety of mechanical tests of a medium physical model of interaction between rock mass and supporting structure under freeze-thaw condition with cooperating large-scale rock MTS. The system reach the domestic advanced level in the fields of the net volume inside, high and low temperature control performance, rock and soil mass lifting and loading convenience and so on.(2) Firstly, author carried out the acoustic and physical indicators test of gray sandstone from the 2008 disaster hit area, and carried out closed freeze-thaw cycles test in 10℃～-20℃and open freeze-thaw cycles test respectively. Then the propeties of gray sandstone’s size and quality variation at ordinary temperatures of different water content (dry and saturated) and after different freeze-thaw cycles are provided. Secondly, author carried out the uniaxial, triaxial compression mechanical tests of the sandstone before and after freeze-thaw, and analysis in arriving at its damage pattern, stress-strain curves, strength yield criteria and strength indexes. Finally, the sandstone before and after freeze-thaw was analyzed by SEM micro-scanning. Experimental results shows, after the sandstone is saturated or open-freeze-thaw cycles, its uniaxial compressive strength, elastic modulus and deformation modulus decrease significantly. after closed-freeze-thaw cycles, the indicators shows that the opposite trend of changes, the data indicate that sandstone’s water content is the decisive factor of freeze-thaw damage. Accordingly, two kinds of failure modes of damage after sandstone was subjected to closed/open freeze-thaw cycles are proposed:internal micro-damage mode and weakening pattern along the bedding plane. After closed/open freeze-thaw cycles, the uniaxial failure modes of sandstone are different, but they are the essence of shear failure. After open freeze-thaw cycles, the uniaxial compression strength of sandstone decreases significantly, the strain increases and it shows significant rheological behavior in unloading stage. Under low confining pressure, dry or saturated sandstone shows a typical diagonal shear failure, the stress-strain curve evident that a transformation process of brittle to ductile, and appears a stress drop during the unloading process. With water content increases, the cohesion, internal friction angle and shear strength of sandstone will reduce. SEM micro-scanning analysis shows that, because of the freeze-thaw cycles, the pores within sandstone and the voids between particles increase, the squeeze between the particles and the relative dislocation lead to gradual intrusion of water and damage inside the rock.(3) Choosing the interaction between rock mass and retaining wall supporting structure as research object, the interaction sample made up of gray sandstone and C20 normal pouring concrete, the cement plane sample’s size and quality variation at ordinary temperatures and after different freeze-thaw cycles is produced. Secondly, the direct shear test of cement plane samples before and after open freeze-thaw cycles was carried out, and the sample’s shear failure strength criterion and influencing factors is provided. Experimental results shows, with freeze-thaw cycles increases, the height and quality of samples are increasing, the diameter of sandstone and concrete part are also increasing, and with the loss of strength, cement planes breaks off after 5-10 cycles. With axial pressure increases, the shear stress of cement plane increases. In addition, as freeze-thaw cycles increases, the peak value of horizontal stress drops significantly, the phenomenon of different levels of shear rheology appears after cement plane shear yield and some samples appears the phenomenon of intermittent stress falling. After 3 cycles, the cohesion of cement planes will reduce and its friction angle will increase.(4) Choosing the interaction body between rock mass and anchor-shotcrete supporting structure as research object, the interaction sample made up of gray sandstone and C20 shotcrete, and the cement plane sample’s size and quality variation at ordinary temperatures and after different freeze-thaw cycles are produced. Secondly, author carried out the uniaxial compression test, triaxial compression test under medium/low levels of confining pressure, direct shear test under medium/low levels of axial pressure of cement plane samples before and after open freeze-thaw cycles, and analysis for its damage pattern, stress-strain curves, strength yield criteria and strength indexes. Finally, the cement plane samples before and after freeze-thaw was analyzed by SEM micro-scanning. Experimental results shows, in ordinary temperature or after freeze-thaw cycles, all of the failure modes of the cement plane samples are split along the axial tensile in uniaxial compression test, and does not occur the sliding trend of shear from the cementation surface. As water content increases, cement plane’s strength decrease significantly. With freeze-thaw cycles increases, elastic modulus and deformation modulus decreases linearly. Under low confining pressure, most of dry or saturated samples show a right angle to the crack failure, and as water content increases, cohesion, friction angle and peak value of strength will reduce. Under moderate confining pressure, after 3 open freeze-thaw cycles, samples’ damage in the form of part of the crushed concrete in triaxial compression test, some minor cracking of the rock shows significant ductility. Author believes that the overall increase in intensity is limited by the concrete’s brittle failure. In addition, the cohesion of samples does not change significantly than that of low confining pressure and before freeze-thaw, but the friction angle reduces substantially. With freeze-thaw cycles increases, the average peak value of shear stress drops significantly, and the creep phenomenon obviously appears in the unloading stage. With axial stress increases, the peak value of shear stress increases. Under low axial pressure, an increase in the number of freeze-thaw cycles leads to the cohesion of cement plane decreases significantly, but the friction angle increases slightly. Under high axial pressure, both of the cohesion and the friction angle of cement plane decrease significantly. SEM micro-scanning analysis shows that, after the open freeze-thaw cycles, the particles of sandstone surface become fragmented, and the cement among particles of concrete surface become weaker, and dislocation and displacement occurs in the particles. But the fundamental reason of cement plane damage is that the width of the gap between cement and the two kinds of material increases after freeze-thaw cycles.(5) According to the triaxial compression test results under middle and low confining pressure, the dissertation introduced the statistical damage mechanics theory based on Weibull distribution statistical law and the concept of micro-element strength firstly. Secondly, author built up two kind of three-dimensional damage softening statistical constitutive model for sandstone and the interaction between sandstone and shotcrete of different water content (dry and saturated) in ordinary temperatures. In addition, through the fitting of the relationship among peak stress, peak strain and confining pressure, the dissertation extended it to the damage softening statistical constitutive model suitable for arbitrary confining pressure. Then, the one-dimensional damage softening statistical constitutive model for interaction between sandstone and shotcrete afer 3 open freeze-thaw cycles are provided. Finally, according to the above constitutive model, a comparison was carried out between the stress-strain curves based on model calculations and based on experimentations. The result shows that the damage softening statistical constitutive models are reliable.(6) Choosing C20 shotcrete and gray sandstone, the physical model of interaction between rock mass sandstone and shotcrete supporting structure is produced, and the freeze-thaw cycles test with periodic water-supplied under the conditions of extreme snow and ice disasters are presented. During the experiment, for the strain caused by surface temperature change of rock, concrete, surface and inside of the cement plane between rock and concrete, measured by electrical measuring method and measurement of fiber gratings, the dissertation researched systematically on the principal strain, principal stress, maximum shear stress, principal stress direction angle on model surface, and the formation and the variation of strain within the model. Experimental result shows, because the rock can not be reached saturation water content and the poor absorption of concrete after solidification, there will not be idealized frost heave and thawing settlement in the supporting engineering under ice and snow after many freeze-thaw cycles, in fact, the supporting engineering will show the intermediate state between the state of frost heave and thawing settlement and the state of expanding with heat and contracting with cold. When the freeze-thaw cycle is 24 hours, elastic deformation stage is gradually into the plastic deformation stage on the model surface. But after the freeze-thaw cycle changes to 48 hours, temperature operates more fully to surface and inside of the model, the model shows elastic deformation properties again. In view of that, to simulate the actual temperature change and take full account of the negative impact by cumulative plastic deformation, the freeze-thaw cycle of physical model test should not more than 24 hours in experimental technique specifications. During the freeze-thaw cycles, deformation is sensitive to the cooling process in the cement plane, and compressive stress, compressive strain and maximum shear stress increase significantly. In contrast, deformation is more sensitive to the heating process in the perpendicular direction to the plane (including the surface), and tensile stress and tensile strain increase significantly. When temperature rises, the maximum shear force on model surface reduces, and when temperature drops, the maximum shear force increases. In addition, whether on the surfaces of rock, concrete or lateral surface of the cement plane, principal stress direction angles are concentrated in a 90 degree of the quadrant. Even to the two-point very near on the lateral surface of the cement plane, the principal stress directions of them are still different, but their ranges have some overlap. In the horizontal direction to the cement plane of internal model, during temperature changes, more pronounced increase in tensile strain and the change fluctuation of tensile strain is the smallest, the phenomenon of frost heave and thawing settlement appears. In the perpendicular direction to the cement plane, the strain of materials is affected most dramatic by temperature change and the change fluctuation of is the largest strain. In the cement plane, the compressive strain increases more significantly and the change fluctuation of strain is large during temperature changes.The innovation points are as follows:(1) A set of dedicated environmental control systems with cooperating large-scale rock MTS has been developed independently. The system has the characteristics of a large interior space, convenience for cycling, a continuous freeze-thaw stable, freeze-thaw speed, the temperature can be programmed and has a dedicated loading facilities, etc. The system reach the domestic advanced level in the fields of the net volume inside, high and low temperature control performance, rock and soil mass lifting and loading convenience and so on.(2) The damage pattern, stress-strain curves, strength yield criteria and strength indexes of rock, interaction body made up of rock mass and retaining wall supporting structure and interaction body made up of rock mass and anchor-shotcrete supporting structure under the action of multiple factors such as temperature, moisture, freeze-thaw method etc are presented under extreme ice and snow disaster condition. Based on the above results, two kind of three-dimensional damage softening statistical constitutive model for sandstone and interaction between sandstone and shotcrete in ordinary temperatures are provided. In addition, the one-dimensional damage softening statistical constitutive model for interaction between sandstone and shotcrete after 3 open freeze-thaw cycles has been built up at the same time. The result shows that the damage softening statistical constitutive models are reliable. (3) A medium physical model test of interaction between rock mass and supporting structure under extreme ice and snow disaster condition was presented. This dissertation researches and works out the dynamic response law and failure mechanism of interaction between two kinds of material. In addition, the dissertation proposed some researches on methods and recommendations useable for the physical model test of interaction between rock mass and supporting structure under extreme ice and snow disaster condition.更多还原