【作者】 张宇；

【导师】 孔宪京；

【作者基本信息】 大连理工大学 ， 水工结构工程， 2017， 博士

【摘要】 混凝土面板堆石坝(简称面板坝)是上世纪80年代发展起来的一种新坝型,由于其具有断面小、透水性好、施工进度快和适应性良好等特点,深受坝工界的青睐,经常成为首选坝型。经过40多年的发展,以分层填筑、薄层振动碾压技术为标志的现代混凝土面板堆石坝日渐成熟,我国相继建造了一批坝高大于150m的高面板坝。随着筑坝建设经验的积累以及设计水平的提高,面板坝的高度还在不断增加,一批250m级高面板坝也在规划或可研中,有多座高面板坝位于西部高地震烈度区,这些高坝大库—旦因地震发生溃坝等严重灾害,其后果将是灾难性的。面板坝的最主要防渗结构是上游坝面的混凝土面板(简称面板),其安全性和完整性是保证整个大坝正常运行的首要条件。强震作用下,面板的主要破坏形式是竖缝间面板的挤压破坏、以及上部面板沿坝轴向的水平结构性裂缝,这两种破坏形态均与面板的应力和变形特性紧密相关。因此,准确把握和预测面板地震响应特性,探明面板地震破损机理并开展抗震对策研究,是实现强震区高面板坝的建设由200m级向250m以上级跨越的重要前提。数值模拟分析技术是研究面板坝地震响应规律、揭示防渗结构破损机理、评价大坝抗震性能及论证抗震措施有效性的重要手段之一。目前对面板抗震性能的数值研究主要存在两个方面的局限:(1)以往研究工作主要针对单一面板坝工程,很难综合考虑河谷地形条件、坝体几何形状、地震动输入特性等多种因素对大坝地震响应的影响,难以得到具有普遍适用性的面板薄弱区域分布规律。(2)工程中仍普遍采用混凝土单轴强度准则来评价面板安全性及破损形态,利用线弹性模型来模拟面板混凝土本构关系,该方法具有明显的局限性。一方面,混凝土单轴强度准则无法反映多轴受力状态下混凝土真实的强度特性,难以对面板的动力破损进行准确评价,无法从受力特性角度探明面板动力破损产生机理。另一方面,线弹性模型虽然具有计算高效、易于程序实现、可以较好地反映面板应力分布基本规律等优点,但该模型不能模拟准脆性及韧性面板材料开裂后非线性应力应变关系,难以满足面板动力开裂、渐进破损过程的非线性分析要求。基于此,本文首先采用三维有限元数值分析方法,对面板地震响应特性开展了系统研究,确定了面板高应力区范围,指明了面板抗震薄弱部位。引入混凝土多轴强度准则,改进了面板抗震安全评价标准及评价方法。采用基于堆石体和接触面的广义塑性模型的弹塑性分析方法,从面板受力状态角度对面板动力破损形态、破损机理开展了系统研究。在此基础上,引入混凝土弥散裂缝模型,对面板动力开裂、渐进破坏过程进行了模拟,阐明了面板动力开裂破坏特性。在上述研究成果基础上,分别从结构设计的改进和材料性能的提高两个方面,提出了能够大幅度提高面板抗震性能的工程对策,并利用数值分析方法定量评价了抗震措施的有效性。本论文的主要研究内容可概括为:(1)通过对面板堆石坝进行大量、系统的三维有限元数值计算,探明了面板的高应力区分布规律,揭示了面板抗震薄弱区域。通过对近百个设计工况的计算结果进行总结归纳,阐明了坝高、岸坡坡比、地震动输入特性等因素对面板高应力分布区域的影响。研究结果表明:地震作用下,面板在距坝底0.6H～0.8(H为坝高)、沿坝轴向0.4L～0.6i(L为坝轴长)的范围内将产生顺坡向高动拉应力(超过3MPa),在抗震设计时应重点关注该区域面板的抗震安全。(2)首次提出了一种通过设置永久水平抗震缝来有效降低面板动拉应力的工程措施,并通过数值分析方法定量评价了该工程措施的有效性,成果已被猴子岩面板堆石坝(Ⅷ度地震烈度区建最高面板坝)采用。通过对近百个设计工况的三维有限元数值模拟结果进行总结归纳,明确了水平抗震缝设置位置(高程和长度)对面板动拉应力分布的影响,据此建议了设置水平抗震缝的合理区域,以便为工程抗震设计提供使用依据。研究结果表明:当水平缝被设置于面板最大顺坡向动拉应力发生高程(H0)时,动拉应力的降幅可达40%以上,且当水平缝设置高程位于H0±0.05H范围内时,动拉应力的降低幅值可达20%以上。为得到理想的动拉应力降低效果,建议将水平缝沿高度方向设置于0.7H～0.9H、沿水平向设置于0.35L-0.65L范围内。(3)引入混凝土 Ottosen多轴强度准则作为面板安全评价标准,发展了考虑混凝土多轴受力特性的面板安全评价方法,对运行期内面板的安全性进行了评价。研究结果表明:无论在震前满蓄期还是地震作用下,面板均表现出明显多轴受力特性。利用多轴强度准则更能反映实际面板破损情况,单轴强度准则会高估中下部面板发生挤压破坏,低估地震作用下中上部面板发生拉裂和挤压破坏。(4)基于混凝土多轴强度准则,从面板受力特性角度阐明了面板地震破损机理。研究结果指出,拉-压组合应力状态是面板发生动力破损时主要的应力状态之一,由于拉压共同作用造成的拉断和片状劈裂破坏是面板主要的动力破损形态。研究从面板多轴受力特性角度阐明了面板动力破损机理,即坝顶堆石体顺河向甩动导致的面板动拉应力、堆石体指向河谷的坝轴向残余变形引起的面板挤压应力与震前面板应力的耦合作用,是面板发生拉裂或挤压破损的主要原因。此外,研究结果还指出水平抗震缝的设置可以显著改善面板拉-压不利应力状态,降低面板发生挤压破损的可能性。(5)联合混凝土共轴旋转裂缝模型、堆石料及接触面的广义塑性模型,建立了高面板坝静、动统一的弹塑性分析方法,针对200m级面板坝开展了二维非线性有限元分析,模拟了地震过程中面板动力开裂、渐进破坏的发展过程。研究结果表明,地震作用下面板薄弱区域内可能产生贯穿性有害裂缝(宽度大于0.1mm),面板表现出明显的脆性破坏特性(开裂破坏发生在0.2s内)。研究结果还表明,地震作用下堆石坝体产生顺河向的甩动变形,此时垫层料相对于面板沿坝坡方向的相对变形会通过接触面传递给面板摩擦力作用,该摩擦作用是导致面板内产生过高动拉应力进而引起开裂破坏的主要原因。(6)从材料改性的设计思路出发,针对面板的抗震薄弱部位提出了一种UHTCC-钢筋-混凝土新型面板结构(新型面板)。通过引入UHTCC受拉应变硬化本构关系,实现了 UHTCC-钢筋-混凝土面板堆石坝弹塑性静、动统一分析方法,定量评价了新型面板的抗震性能。研究结果表明,强震作用下新型面板表现出延性破坏以及无贯穿性裂缝的特点,具有良好的抗震控裂性能。通过对不同截面形式的新型面板动力控裂性能进行对比,指出在面板上游侧0.6H～0.9H范围粘贴3cm厚UHTCC的形式为最优截面形式。(7)以古水面板坝(245m)面板为研究对象,从实际工程角度验证了水平抗震缝和UHTCC-钢筋-混凝土新型面板这两项抗震对策的有效性。研究结果表明,与不设缝面板相比,设置水平抗震缝后面板内动拉应力幅值降低约50%,出现开裂破损的面板面积降低约38%,面板的抗震安全性显著提高。另一方面,与普通钢筋-混凝土面板(简称普通面板)发生贯穿性有害裂缝的开裂特点不同,UHTCC-钢筋-混凝土新型面板内无贯通性裂缝产生,UHTCC层有效地阻止了混凝土层中裂缝向上游的扩展,新型面板的抗震控裂性能明显优于普通面板。更多还原

【Abstract】 Concrete faced rockfill dam(short for CFRD)is a new type of dam developed in the late 1980s.Because of the characteristics of small cross-section,water permeability,convenient construction and excellent adaptability in practice,CFRD is often the preferred type of dam.After 40 years of development,the modern CFRD becomes mature with the symbol of layered filling and thin-layer vibrated rolling technology.In China,a number of CFRDs higher than 150m have been built.With the accumulation of dam construcntion experience and the improvement of dam design level,the height of CFRD is still increasing.A number of CFRDs higher 250 are in plan.China has built and proposed a number of high CFRDs located in the western high seismic intensity area.Once these high dams damaged owing to seismic shaking,the consequences will be disastrous.As the main anti-seepage structure of CFRD,the safety and integrity of face slab are important foundations to ensure the effective operation of the dam.Under strong seismic shaking,the main failure modes of the face slab are crushing damage along the vertical joint of face slab,and the horizontal structural cracks.These damage modes are closely related to the stress and deformation characteristics of face slab.Therefore,it is very important to realize the seismic response characteristics of face slab,reveal the seismic damage mechanism,and propose the effective anti-seismic countermeasures.Numerical analysis is one of the important methods to study the dynamic response of the face dam,reproduce the catastrophic process,reveal the failure mechanism,evaluate the seismic performance of the dam and demonstrate the effectiveness of the seismic measures.In the past,there are some limitations in the research work.1)Research are mainly focused on single dam project owing to various dam material,site conditions,dam geometries,input motion characteristics and other factors.Therefore,the characteristics of dynamic stress distribution in face slab can not be drawn.2)Although the study of constitutive model of rockfill in recent years has gradually developed to the elasto-plastic model,the research of slab nonlinear analysis method is still lagging behind.The linear elastic model is still used to simulate the slab concrete,and the evaluation of slab safety and failure is still based on the concrete uniaxial strength criterion.On the one hand,the method of seismic safety evaluation of slab based on concrete uniaxial strength criterion can not reflect the true strength characteristics of concrete under multi-axis stress,and it is difficult to evaluate the dynamic damage of the slab and failure mechanism accurately.On the other hand,although the linear elastic model has the advantages of computational efficiency and easy realization of the program,the model can not reflect the nonlinear stress-strain relationship after cracking of quasi-brittle and ductile materials.On the basis,a series of three-dimensional finite element numerical analysis was performed to investigate the dynamic response characteristics of face slab during the operation period.The distribution law and range of the high stress area of the slab were delineated,and the weak area of the slab was clarified.The elasto-plastic analysis method of the progressive failure of the slab was established combining the generalized plastic model of rockfill and contact surface.The criterion and evaluation method of slab seismic safety were improved by introducing the multi-axial strength criterion of concrete.The dynamic damage mechanism of slab was expounded from aspect of the stress state in slab.Furthermore,the co-axial rotating cracking model was introduced in the elastic-plastic analysis method.The progressive cracking progress of face slab during earthquake was modeled,and mechanism of the dynamic cracking failure was expounded from the aspect of the dam deformations.The main contents of the paper include the following aspects:(1)Through the large-scale and systematic three-dimensional finite element calculation of the concrete faced rockfill dam,the distribution law of the high stress zone of the slab was proved,and the weak area of the slab was clear.The influences of the dam geometries and ground motion input characteristics on the high stress distribution area of the slab were clarified through the calculation of nearly a hundred design conditions.The results showed that the dynamic tensile overstress within slab(more than 3MPa)distributed in the area ranging from 0.6/H～0.8H(His dam height)in vertical direction,and 0.4Z～0.6L(L is dam axis length)in the dam-axis direction.And this vulnerable area in face slab was recommended as the key area in anti-seismic design for CFRDs.(2)An anti-seismic engineering measure was proposed to reduce the dynamic tensile stress in slab by setting the permanent horizontal seismic joint in the high tensile stress area in face slab.The validity of the measure was quantitatively evaluated by numerical analysis.The measure was adopted by the Houziyan CFRD(223m)design.A series of three-dimensional finite element calculation were carried out to clarify the influence of the position of horizontal seismic joints on the dynamic stress distribution of the slab.It was suggested the reasonable area of horizontal seismic joints should be set up for the seismic design of the project.The results showed that the horizontal tensile strength could be effectively reduced with the magnitude more than 40%,in the case that set the joint in the range of 0.75H-0.9H along the dam.(3)Introducing the Ottosen multi-axis strength criterion,safety evaluation method of slab was developed.The results showed that the force of the slab exhibited obvious multi-axial force characteristics both before and after the earthquake.The traditional evaluation method based on the uniaxial strength criterion would overestimate extrusion damage of lower slab,and underestimate the occurrence of cracking and extrusion damage of the upper slab under the earthquake.(4)Based on the multi-axial strength criterion of concrete,the extrusion failure mode and damage evolution process of the slab were elucidated from aspect of stress state in face slab.The results showed that the pull-compressive stress state is one of the main stress states when the slab was subjected to seismic extrusion damage.Furthermore,the effectiveness of horizontal anti-seismic joint on mitigating the extrusion damage was evaluated.The results indicated that the setting of the horizontal joint not only could significantly reduce the seismic stress of the slab,but also can significantly improve the slab pull-pressure adverse stress state,and reduce the possibility of slab extrusion damage.(5)The co-axial rotating cracking model was introduced in the elastic-plastic analysis method.The two-dimensional finite element asymptotic cracking failure calculation of the 200m-level face dam was carried out under the seismic loading.The development of cracks in the middle slab and the evolution of stress were investigated.The results showed that the macroscopic cracks were likely to occur in the vulnerable area of the slab,and the slab exhibited obvious brittle fracture characteristics during earthquake.The deformation of embankment moving towards downstream would generate frictional force in the interface between the face slab and cushion.The research results indicated that the friction force was the main reason for the cracking failure of the slab.(6)Based on the design idea of material modification,a UHTCC-reinforced concrete slab structure(new type slab)was proposed.By introducing the strain hardening constitutive relation of UHTCC,the nonlinear static and dynamic analysis method of UHTCC-reinforced concrete face rockfill dam was realized for the first time,and the seismic resistance of new slab was evaluated quantitatively.The results showed the new type face slab exhibited ductile failure characteristics with non-penetrating cracks during earthquake.(7)Using Gushui CFRD(245m)as a benchmark,the anti-seismic effectiveness of the horizontal joint and the UHTCC-reinforced concrete face slab was verified from the practical engineering point of view.Compared with the seismic performance of face slab without joint,the maximum tensile stress and the cracking area in slab with joint at EL.223 5m approximately reduced 50%and 38%respectively.Distinguished from penetrating cracking characteristics of traditional reinforced concrete face slab,the UHTCC-reinforced concrete face slab effectively prevented the cracks in concrete substrate penetrating towards upstream.The abovementioned results indicated that the two types of anti-seismic measures effectively improved the seismic performance of face slab,and it was suggested to consider the use of anti-seismic joints and UHTCC-reinforced concrete face slab,in the case of building high CFRD in the high seismic intensity area.更多还原