【作者】 吴银亮；

【导师】 余宏明；

【作者基本信息】 中国地质大学 ， 地质工程， 2013， 博士

【摘要】 在我国,从古生代的寒武纪一直到新生代的第三纪,几乎每个时代都有石膏或者硬石膏的沉积。这些石膏或者硬石膏往往与其他碳酸盐岩沉积共生,形成含有石膏或者硬石膏的岩类,在本文中将这类岩石称为石膏质岩。在自然状况下,这类石膏质岩往往具有一定的强度,表面上具有较好的工程性质,但遇水之后石膏质岩中的石膏和硬石膏容易溶解,产生硫酸根离子,侵蚀混凝土,硬石膏遇水水化成石膏,产生体积膨胀,而且这类岩石受水影响之后强度性质变差。正是由于石膏质岩这些特殊的工程性质,当建设中的隧道通过赋存有该类岩石地层的时候,如果缺乏对石膏质岩性质的了解,往往会疏忽其对隧道工程可能产生的病害,给隧道建设和运营带来隐患。因此,本文对宜巴高速路凉水井隧道建设中遇到的该类石膏质岩进行了详细的工程性质研究,以加深对该类岩石性质的了解,指导工程实践活动,具有一定的工程意义。本文在收集研究区地层沉积资料、石膏质岩隧道病害特征等工作的基础上,通过X射线-衍射矿物鉴定试验、离子色谱分析试验、电镜扫描试验、岩石重塑样膨胀试验、溶蚀及溶出特性试验、单轴压缩试验、三轴压缩试验、硫酸盐对混凝土侵蚀试验等试验手段研究石膏质岩的矿物组成成分、石膏质岩的微观结构、硬石膏的水化膨胀性质、石膏质岩的溶蚀及溶出特性、溶出的硫酸根离子浓度、石膏质岩不同含水状态及干湿循环后强度性质等,定性的分析这些性质对隧道工程的危害。并在所得到的溶出试验数据的基础上,通过硫酸盐外部及内部侵蚀混凝土试验,模拟石膏质岩对隧道混凝土结构侵蚀劣化情况。通过以上的关于石膏质岩工程性质的研究,取得了以下成果：(1)通过对区域地质资料的分析及现场工程地质调查,掌握了研究区石膏质岩的成因环境及层位分布特征,了解了研究区石膏质岩的赋存状态。利用X-矿物衍射试验、化学全分析试验,并结合石膏质岩水化程度分析试验,掌握了研究区石膏质岩化学及矿物成分,并有效的鉴定了研究区石膏质岩中包含的矿物成份及石膏和硬石膏在石膏质岩中各自所占的比例。(2)通过对石膏质岩粉末重塑样进行的膨胀性试验,研究了石膏质岩的膨胀性质,得出了石膏质岩重塑样遇水产生一定的膨胀变形及膨胀力。试验中测定的膨胀率能达到6%,并且膨胀率的大小与重塑样的初始于密度有关。膨胀力能够达到572kPa～824kPa的级别,并且膨胀力的大小随着重塑样的初始干密度的增大而增大、随着吸水率的增大而增大。结合其他资料及石膏质岩的性质,总结了石膏质岩的膨胀受环境湿度、围岩的应力状态、石膏质岩中硬石膏的含量及结构特征等几个方面因素的影响。石膏质岩吸水膨胀,将产生侧向变形,对隧道混凝土衬砌结构产生的挤压作用增强,导致混凝土结构局部应力集中,会产生结构破坏,影响混凝土结构的耐久性,对隧道产生一定的工程危害。(3)石膏质岩溶蚀及溶出试验表明,石膏质岩在静水环境中机械潜蚀与化学溶解作用同时存在,但是起主要作用的是化学溶解,静态溶蚀存在溶解平衡,溶蚀量先增加后稳定。在动水环境中起主要作用的是机械溶蚀,溶蚀后试样质量会持续降低,最终破坏了石膏质岩的整体结构。对动态溶蚀而言,对溶蚀速度起控制性作用的就是溶蚀时间长短、石膏质岩与水接触面积大小及水流的流速。不同酸碱条件及离子成分的溶液环境,也影响石膏质岩的溶蚀作用,偏酸性环境下石膏质岩溶蚀作用将会更大。温度会影响石膏质岩在溶液中的溶解度,从而影响石膏质岩的溶蚀量及溶蚀速率。石膏质岩溶蚀后溶出大量的硫酸根离子,溶蚀90天后离子浓度可达到1530mg/L,具有中等腐蚀性。通过扫描电镜观察石膏质岩溶蚀前后微观结构,可见溶蚀前石膏质岩的微观晶面完整、纹路良好、晶面之间联系紧密,溶蚀后晶格之间的物质被溶解掉,晶面间空隙增大,晶体边缘也变成了毛边状、刀削状,节理面不再明显。自然环境中石膏质岩与水接触可能发生静态溶蚀,也可能发生动态溶蚀,但是无论哪种溶蚀,石膏质岩都会溶出大量的硫酸根离子于水溶液中,使地下水具有腐蚀性,随着渗流运动,会长期接触隧道衬砌结构,对混凝土及支护结构中某些钢构件产生腐蚀,造成工程病害。同时由于溶蚀作用,石膏质岩被水流冲蚀带走,会对隧道围岩产生一定的掏空作用,将会对隧道路面基础及支护结构产生危害。(4)通过强度试验表明石膏质岩强度较低,属于软岩,强度指标随含水率变化十分敏感,遇水软化显著。石膏质岩单轴抗压强度各项指标随含水率变化十分敏感,抗压强度、弹性模量、变形模量都随着含水率的增高,都呈现下降的趋势。泊松比则随着含水率的增大而近似呈现增大的趋势。干湿循环作用对石膏质岩力学性质劣化明显。石膏质岩试样的抗压强度、弹性模量及变形模量随着干湿循环次数的增加而不断降低,泊松比随着干湿循环次数的增加而整体增大。石膏质岩的三轴压缩试验结果曲线表明,石膏质岩存在压硬性,岩样的弹性模量和屈服强度随着围压的增大而增大。随着围压的增大,石膏质岩变形特性由低围压下的脆性向高围压下的延性转变,饱和状态下这种延性的主应力及围压转化节点为18MPa和8MPa,相比于干燥状况下的59MPa及15MPa有很大程度的降低。通过对比石膏质岩饱水前后的强度指标,发现在饱水后内摩擦角的大小被削弱了42.6%,粘聚力的大小被削弱了53.97%,这是因为水不仅降低了石膏质岩分子间的吸引力,同时也降低了石膏质岩颗粒间的嵌入及联锁作用造成的。石膏质岩的泊松比和弹性模量都随着围压的增大而增大。但在同一级围压下,饱水状态下石膏质岩的泊松比比干燥状态的大,弹性模量比干燥状态的要小。通过对石膏质岩强度性质的试验研究,认为该类岩石遇水后软化显著,变形增大、强度降低,并且含水率越高,浸水软化的影响愈严重,从而影响隧道围岩的稳定性,对隧道建设不利,工程开挖中应结合工程特点和要求,采取加强支护和及时衬砌等工程措施。(5)通过室内硫酸盐侵蚀混凝土试验,模拟了石膏质岩对隧道混凝土的劣化作用。无论是石膏质岩溶出的硫酸根离子对混凝土的外部腐蚀、还是石膏质岩误作为混凝土骨料对混凝土的内部腐蚀,石膏成分都会与混凝土材料发生一系列的物理化学反应,最终使混凝土结构膨胀、强度降低、性能劣化。在分析试验数据的基础上,完成了防止硫酸盐侵蚀的高性能混凝土配合比设计工作。外部硫酸盐侵蚀混凝土试验：以石膏质岩饱和溶液、Na2SO4溶液、酸性环境的Na2SO4溶液作为侵蚀溶液,研究砂浆和混凝土试样在上述溶液作用下的强度与质量变化规律,结果表明混凝土试块在后两种溶液中发生侵蚀破坏,浸泡在饱和石膏质岩水溶液中试块的强度变化不大,说明在静止溶液中饱和石膏水的侵蚀能力有限,需要较长时间才能出现侵蚀危害。但在复杂的现场环境下,这种侵蚀可能会加速。内部硫酸盐侵蚀混凝土试验：通过水泥净浆、水泥砂浆、碎石混凝土试验表明石膏质岩无论作为块体埋入水泥砂浆石块中,还是作为混凝土粗、细集料掺入水泥砂浆及碎石混凝土中都使试块产生膨胀破坏,破坏程度都随着掺量的增加而增大,石膏质岩作为细集料对混凝土的膨胀率和强度的影响更大。无论以上哪种侵蚀,石膏成分都会与混凝土结构成分发生物理化学反应,电镜可见砂浆、混凝土试块内部生成钙矾石的状况,尤其是在石膏质岩作为集料时,其表面的钙矾石生成量很大,直接对骨料接触面造成破坏,对混凝土强度造成不良影响。根据硫酸盐侵蚀混凝土试验结果,提出了防止硫酸盐侵蚀的高性能混凝土配比方案,研究了隧道二次衬砌防水混凝土的原材料品种、配合比设计方案及配制技术要求,并应采用加强混凝土强度等级、提高其防裂、抗渗与抗硫酸盐侵蚀性能的材料措施。(6)根据现场调查及试验研究,总结石膏质岩对隧道工程建设可能产生的危害如下：石膏质岩水化膨胀危害,石膏质岩遇水体积膨胀,产生侧向膨胀力,对隧道混凝土衬砌结构挤压作用增强,导致混凝土结构局部应力集中,会导致结构破坏,影响混凝土结构的耐久性。石膏质岩遇水软化危害,石膏质岩遇水后软化特征显著,强度降低,变形增大,在地应力作用下塑性变形将会更加明显,从而对隧道围岩稳定性产生很大的影响。石膏质岩溶蚀及溶出危害,石膏质岩易溶蚀,加之隧道拱部及边墙常常成为地下水流经廊道,石膏质岩体受水流机械潜蚀作用,易被掏空,所以隧道顶部衬砌支护将会产生滴水、漏水现象,同时由于石膏质岩被溶蚀后,围岩体结构遭到破坏,强度降低,导致隧道围岩稳定性降低。石膏质岩溶蚀后溶出大量的酸根离子于地下水中,对隧道混凝土具有中等腐蚀性,长期腐蚀隧道混凝土支护结构,会导致初期支护的混凝土强度逐渐劣化,并最终失去承载能力,造成病害。石膏质岩误作为混凝土骨料危害,采用石膏质岩或者含石膏质岩的骨料,配制混凝土或混凝土接触到它们时,骨料表面的石膏矿物将参与水泥的水化反应,与水泥中的铝酸钙、铁铝酸钙矿物反应或与水化形成的的水化铝酸钙或单硫型的水化硫铝酸钙(AFm)继续反应,生成膨胀性物质三硫型水化硫铝酸钙(AFt),当骨料—浆体界面的膨胀应力达到一定程度时会使混凝土开裂,因此降低了混凝土强度,造成病害,这是石膏质岩作为混凝土骨料产生的一种硫酸盐侵蚀危害。(7)隧道穿越石膏质地层时,将产生诸多病害。鉴于石膏质岩对隧道工程产生病害原因的复杂性、复合性,文章最后从隧道的勘察、设计施工以及隧道的后期运营维护三个方面对此类隧道建设提出一些意见与建议,以指导工程实践。更多还原

【Abstract】 Gypsum or anhydrite, as a common sedimentary composition in China, almost exists in every age from the Cambrian period of Paleozoic to the Tertiary of Neozoic. And it is often consist in sedimentary rock in the form of its intergrowth with other carbonate sediment. In this paper, this sedimentary rock is called gypsum rock. In the natural conditions, the engineering properties of gypsum rock are apparently well and its strength is high. However, after contacted with water, its strength properties will be worse due to the solution of gypsum or anhydrite in the gypsum rock which generates sulfate ion erosive for concrete. Moreover, volume expansion will be aroused by the hydration of anhydrite. In that case, if tunnel construction through these kind sediments, the lack of knowledge in properties often causes tunnel disaster. Therefore, research on the engineering properties of gypsum rock of Yi-ba highway is conducted in this paper to deepen the understanding of the nature of this rock and this research is engineering guidance, which has a certain engineering significance.Based on the collection of strata material in the study area and the disaster characteristics in gypsum rock tunnel, a series of laboratory experiments including X-ray diffraction mineral appraisal test, ion chromatography test, scanning electron microscope test, remodeling sample expansion test, corrosion experiment and the leaching characteristic experiment, uniaxial compression test, triaxial compression test, sulfate erosion test on concrete and others are conducted to study the mineral composition and microstructure of gypsum rock, the concentration of dissolving sulfate ion, the corrosion and leaching characteristic, the hydration expansion of anhydrite and its strength properties under different moisture contents and times of drying and wetting cycles. Based on the datas of test, the internal and external sulfate erosion test were conducted to simulate erosion degradation of gypsum rock to the concrete structure. Through the above research on the engineering properties of gypsum rock, the main results are presented as follows.(1)Based on the analysis of the regional geological data and engineering geological investigation, we realize the formation environment and distribution characteristics of gypsum rock in the research area. We also know the existence forms of gypsum rock. The mineral and chemical composition of gypsum rock and the respective proportions of gypsum and anhydrite in gypsum rock were effectively identified by X-ray diffraction mineral appraisal test, chemical overall analysis test and hydration degree analysis test.(2) The expansion test of remodeling samples of gypsum rock was conducted to discuss the expansion properties of gypsum rock. We can conclude that the remodeling samples of gypsum rock cause certain expansion deformation and expansion force when in water. According to the expansion analysis of remodeling samples, the expansion rate of samples can reach6%and the size of expansion rate changes with the initial dry density of remodeling samples. The expansibility of gypsum rock is in the range from572kPa to824kPa. Moreover, its expansibility will increase with the increase of the initial dry density and water absorption. Then, the influence factors on the expansion of gypsum rock such as environmental humidity, the stress state of surrounding rock, the anhydrite content and the structural characteristics of gypsum rock are summarized with the properties of gypsum rock and other references. The expansion of gypsum rock will cause the lateral deformation of tunnel engineering concrete structure, which results in local stress concentration of concrete structure, and the structural failure. All these can influence the durability of concrete structures, which may take certain hazards to the tunnel engineering.(3)The corrosion experiment and the leaching characteristic experiment of gypsum rock indicate that there are both mechanical corrosion and chemical solution effect when the gypsum rock in static water environment. But the chemical solution plays the leading role. There is a dissolving balance in static corrosion, in the process of which the corrosion quality increases at first and reaches to a balance point at last. When the gypsum rock is in dynamic water environment, the mechanical dissolution plays a principal role. The corrosion quality continues to reduce and the structure of gypsum rock mass is destroyed ultimately. For the dynamic corrosion, corrosion speed is controlled by the length of corrosion time, the area of gypsum rock contacting with water and flow velocity. The corrosion effect of gypsum rock is affected by the solution with different ph conditions and ion components. The solubility of gypsum rock is affected by temperature, thus the gypsum rock corrosion quantity and rate are affected by it too. When gypsum rock is in corrosional condition, it can dissolve out a mass of sulfate ion which is highly corrosive for the tunnel reinforced concrete lining structure. The maximum concentration of sulfate-ion was1530mg/L. At the same time, by observing the microstructure photographs through scanning electron microscope (SEM) before or after the corrosion of gypsum rock and then comparing them, we notice that before the corrosion crystal plane of gypsum rock is intact, ridge is fine, the contact between crystal planes is close. But after, it is that some substances between the lattice is dissolved obviously. The distance of crystal planes of gypsum rock is enlarged, the edge of the crystal becomes to be shaped, joint plane is no longer apparent. In natural environment, there is static corrosion or dynamic corrosion when gypsum rock meets with water. But no matter which corrosion gypsum rock will dissolve out a mass of sulfate ion into the solution, which will contact the tunnel lining structure in a long-term. The sulfate ion can cause corrosion to lining concrete structure and some steel members of the supporting structure. At the same time due to the corrosion effect, gypsum rock is carried away by water, which will cause certain adverse effect and damage to tunnel pavement foundation and supporting structure.(4) The strength test research results indicate that the gypsum rock whose changes of strength and deformation index with moisture content are very sensitive, is soft rock with low compressive strength and its softening characteristics is obvious in water. The values of physical mechanics parameters of samples reduce with the increase of moisture contents in rock, including uniaxial compressive strength, elastic modulus, deformation modulus and poisson’s ratio. Poisson’s ratio increases with the increase of moisture contents. The drying and wetting cycles have a obvious effect on the strength reducing of gypsum rock.The values of physical mechanics parameters of samples reduce with the increased times of drying and wetting cycles to the rock, including uniaxial compressive strength elastic modulus, deformation modulus and poisson’s ratio. Poisson’s ratio increases with the increased times of drying and wetting cycles in a low level. Gypsum rock of triaxial compression test results’s curves show that gypsum rock are hard pressed, the elastic modulus of the rock and the yield strength with the confining pressure increases. And with the increase of confining pressure, gypsum rock’s deformation characteristics are transfer brittleness to ductility from low pressure to high pressure. And the critical point of the change are deeply reduced,which in saturated is18MPa and8MPa,but in natural is59MPa and15MPa.By contrasting values of internal friction angle and cohesive strength before and after saturated gypsum rock, it is found that the value of internal friction angle has been weaken approximately by42.6%and cohesive strength by53.97%. So we can conclude that the effect of water to gypsum rock is mainly reflected in the intercalative and interlocking binding between the particles of gypsum rock, as same as the attractive influence between the molecules of gypsum rock. Whether dry or saturation state, the poisson ratio of gypsum rock and elastic modulus are increasing with pressure.But in the same level of confining pressure, the poisson of the saturated state is smaller than the natural state, and the elastic modulus is bigger than the natural state. Through the strength properties test research, we realize that the softening property of gypsum rock is observably when in water with its deformation increasing and intensity decreasing at the same time, which makes a great impact on the stability of tunnel surrounding rock and the tunnel construction. Strengthen support and timely lining engineering measures should be taken in tunnel construction combined with engineering characteristics and requirements.(5) The indoor sulfate erosion to the concrete test was conducted to simulate the degradation effect of gypsum rock to tunnel concrete structure. According to the test results we can realize that whether the external corrosion of sulfate ion leaching from gypsum rock to concrete structure or the internal corrosion of gypsum rock to concrete structure when is used as concrete aggregate, a series of physical and chemical reactions between gypsum rock composition and concrete materials occur, which eventually make concrete structure intumescent, strength reduced, structure damaged, performance degenerated. Based on the test data, the work of high performance concrete designing was completed to prevent sulfate erosion of gypsum rock. External sulfate erosion concrete test, the long-term strength and quality changes of the mortar and concrete blocks were measured in saturated solution with Na2SO4erosion solution, acid environment Na2SO4solution in as erosion solution. The results show that the concrete blocks in the two kinds of solution both occur erosion damage. The strength change of concrete block soaked in saturated gypsum rock solution is not big, which shows that the erosion ability of static saturated gypsum rack solution is limited. It will take a long time to appear the erosion hazard. In internal sulfate erosion to the concrete test, by cement net pulp test, cement mortar test, crushed stone concrete test,it shows that blocks occur expansion damage when the gypsum rock whether is used as a block embedded into cement mortar stone, or as concrete coarse and fine aggregate mixed into cement mortar and concrete rubble into concrete. The damage degree increases with the dosage. Using the gypsum rock as fine aggregate into concrete can make great affect on expansion rate and strength of concrete blocks. No matter what kind of erosion above, a series of physical and chemical reactions between gypsum rock composition and concrete materials will occur. By electron microscope, the ettringite could be seen visibly in mortar or concrete block, especially the gypsum rock is used as aggregate, the ettringite of contact surface is very big, which directly destroys the contact surface in result of the adverse impact on concrete body. According to the test results, we put forward the scheme ratio of high performance concrete to prevent sulfate erosion and study the raw material variety, mix design scheme and configuration of the tunnel secondary lining waterproof concrete. Technical measures should be taken to strengthen the concrete strength grade, improve its crack resistance, permeability and resistance to sulfate erosion performance.(6)According to the field investigation and indoor test research, we summary the harms of gypsum surrounding rock to tunnel construction as follows. The expansion harm of gypsum rock and volume expansion appear when the gypsum mass rock meet with water, which cause lateral expansion force and the extrusion effects to tunnel concrete lining structure. All these result in the local stress concentration in concrete structure and leading to structural damage, which can influence the durability of the concrete structure. The softening harm of gypsum rock. The softening characteristics of gypsum rock is significant when in water with its deformation increasing, strength decreasing. The plastic deformation will be more obvious under the action of stress, which makes a influence on the stability of tunnel surrounding rock. Leaching harm of gypsum rock. The erosion can easily appear when gypsum rock with water. A drip phenomenon on tunnel top could occur when the gypsum rock is hollowed out by water, which has a mechanical dissolution effect on gypsum rock. At the same time if gypsum mass rock is corroded, the surround rock mass structure will destroy with its strength and the stability of surrounding rock tunnel reduced. When gypsum rock is in corrosional condition, it will dissolve out a mass of sulfate ion which is highly corrosive for the tunnel reinforced concrete lining structure. In this case, the concrete strength of tunnel support structure gradually decreases and eventually loses its bearing capacity. The harm of gypsum rock used as concrete aggregate. The gypsum mineral of aggregate surface participated in hydration reaction of cement when the gypsum rock is used as aggregate concrete or the concrete contacts to gypsum rock, which will react with calcium aluminate, iron calcium aluminate minerals of cement and hydrated calcium aluminate or sulphoaluminate (AFm) of single sulfur type to generate a swelling material called hydrated sulphoaluminate (AFt) of three sulfur type. When expansion stress of the aggregate-slurry interface reaches a certain degree, the concrete will craze with the result of reducing its strength. This is a kind of sulfate erosion (internal erosion) hazard of gypsum rock used as concrete aggregate.(7) It will cause many diseases when the gypsum rock exposed in tunnel surrounding rock. In view of complex, compound diseases of gypsum rock, some opinions and suggestions are put forward from the tunnel survey, design and construction of the tunnel and the later operation maintenance to the tunnel in the article.更多还原