Seepage simulation of high concrete-faced rockfill dams based on generalized equivalent continuum model

This research focused on the three-dimensional(3 D) seepage field simulation of a high concrete-faced rockfill dam(CFRD) under complex hydraulic conditions. A generalized equivalent continuum model of fractured rock mass was used for equivalent continuous seepage field analysis based on the improved node virtual flow method. Using a high CFRD as an example, the generalized equivalent continuum range was determined, and a finite element model was established based on the terrain and geological conditions, as well as structural face characteristics of the dam area. The equivalent seepage coefficients of different material zones or positions in the dam foundation were calculated with the Snow model or inverse analysis. Then, the 3 D seepage field in the dam area was calculated under the normal water storage conditions, and the corresponding water head distribution, seepage flow, seepage gradient, and seepage characteristics in the dam area were analyzed. The results show that the generalized equivalent continuum model can effectively simulate overall seepage patterns of the CFRD under complex hydraulic conditions and provide a reference for seepage analysis of similar CFRDs.

A simplified physically-based breach model for a high concrete-faced rockfill dam:A case study

A simplified physically-based model was developed to simulate the breaching process of the Gouhou concrete-faced rockfill dam （CFRD）, which is the only breach case of a high CFRD in the world. Considering the dam height, a hydraulic method was chosen to simulate the initial scour position on the downstream slope, with the steepening of the downstream slope taken into account; a headcut erosion formula was adopted to simulate the backward erosion as well. The moment equilibrium method was utilized to calculate the ultimate length of a concrete slab under its self-weight and water loads. The calculated results of the Gouhou CFRD breach case show that the proposed model provides reasonable peak breach flow, final breach width, and failure time, with relative errors less than 15% as compared with the measured data. Sensitivity studies show that the outputs of the proposed model are more or less sensitive to different parameters. Three typical parametric models were compared with the proposed model, and the comparison demonstrates that the proposed physically-based breach model performs better and provides more detailed results than the parametric models.

Reservoir water effects on earthquake performance evaluation of Torul Concrete-Faced Rockfill Dam

This study presents earthquake performance analysis of the Torul Concrete-Faced Rockfill （CFR） Dam with two-dimensional dam-soil and dam-soil-reservoir finite element models. The Lagrangian approach was used with fluid elements to model impounded water. The interface elements were used to simulate the slippage between the concrete face slab and the rockfill. The horizontal component of the 1992 Erzincan earthquake, with a peak ground acceleration of 0.515g, was considered in time-history analysis. The Drucker-Prager model was preferred in nonlinear analysis of the concrete slab, rockfill and foundation soil. The maximum principal stresses and the maximum displacements in two opposite directions were compared by the height of the concrete slab according to linear time-history analysis to reveal the effect of reservoir water. The changes of critical displacements and principal stresses with time are also shown in this paper. According to linear and nonlinear time-history analysis, the effect of the reservoir water on the earthquake performance of the Torul CFR Dam was investigated and the possible damage situation was examined. The results show that the hydrodynamic pressure of reservoir water leads to an increase in the maximum displacements and principal stresses of the dam and reduces the earthquake performance of the dam. Although the linear time-history analysis demonstrates that the earthquake causes a momentous damage to the concrete slab of the Torul CFR Dam, the nonlinear time-history analysis shows that no evident damage occurs in either reservoir case.

Seismic responses of high concrete face rockfill dams:A case study

Seismic responses of the Zipingpu concrete face rockfill dam were analyzed using the finite element method. The dynamic behavior of rockfill materials was modeled with a viscoelastic model and an empirical permanent strain model. The relevant parameters were obtained either by back analysis using the field observations or by reference to parameters of similar rockfill materials. The acceleration responses of the dam,the distribution of earthquake-induced settlement, and the gap propagation under the concrete slabs caused by the settlement of the dam were analyzed and compared with site investigations or relevant studies. The mechanism of failure of horizontal construction joints was also analyzed based on numerical results and site observations. Numerical results show that the input accelerations were considerably amplified near the top of the dam, and the strong shaking resulted in considerable settlement of the rockfill materials, with a maximum value exceeding 90 cm at the crest.As a result of the settlement of rockfill materials, the third-stage concrete slabs were separated from the cushion layer. The rotation of the cantilever slabs about the contacting regions, under the combined action of gravity and seismic inertial forces, led to the failure of the construction joints and tensile cracks appeared above the construction joints. The effectiveness and limitations of the so-called equivalent linear method are also discussed.

Three-dimensional seismic response analysis of a concrete-faced rockfill dam on overburden layers

Reasonable seismic response analysis of a high rockfill dam is of great engineering significance in guiding its design and ensuring its seismic safety during operation,especially of a concrete-faced rockfill dam(CFRD)on overburden layers.The three-dimensional seismic behavior of the Miaojiaba CFRD is simulated and analyzed by the finite element method(FEM).The results indicate that:1)the amplification coefficient along the dam axis gradually increases with the altitude,and reaches maximum at the dam crest;2)the vertical residual deformation mainly exhibits downwards and reaches maximum near the dam crest;3)the earthquake significantly aggravates the deformation of peripheral joints;4)the impounding condition and overburden characteristics have great effects on the dam's seismic response.

汶川地震紫坪铺面板堆石坝地震波输入研究

对国家强震动台网中心紫坪铺面板堆石坝区域台站实测主震记录以及大坝台网实测余震记录进行分析,研究主震与强余震地震动的基本特征。分别选取茂县地办、郫县走石山、成都中和这3组基岩台站实测主震地震动,紫坪铺台站2008年11月6日实测余震地震动以及按水工抗震规范人工生成地震动作为数值计算的地震动输入,对紫坪铺大坝进行三维动力有限元分析,并与实测结果进行对比。研究表明,郫县走石山与成都中和2个远场台站位于断层下盘,其实测地震动的加速度反应谱长周期(0.65 s以后)分量过于丰富,不宜作为断裂带附近紫坪铺大坝的地震动输入;紫坪铺大坝台站实测的余震地震动1 Hz附近(大坝基频)的频率成分相对较少,且持续时间较短,以至于难以激发大坝响应;对比坝顶实测地震动加速度反应谱和数值计算反应谱,建议汶川地震中紫坪铺大坝动力计算时可采用茂县地办台站实测地震动或按抗震设计规范反应谱人工生成地震动。

紫坪铺混凝土面板堆石坝应力-应变分析

利用考虑剪胀性和应变软化性的K-G模型和目前应用较广泛的E-μ模型,对紫坪铺混凝土面板坝进行了二维有限元应力-应变对比计算分析,同时将分析结果与采用双屈服面弹塑性模型三维有限元计算结果以及已建其他工程观测资料比较,得到了坝体应力-应变规律,表明这种K-G模型计算所得的沉降和水平位移在正常范围内,尤其是水平位移的计算明显比邓肯-张E-μ模型计算结果合理,初步验证所建议模型的合理性。

紫坪铺高面板坝“5.12”震害调查与安全状态评价

紫坪铺高混凝土面板堆石坝经受了汶川大地震超抗震设计标准的考验,现场监测与调查结果表明:强震导致大坝出现较大震陷和水平变形,面板发生挤压破坏、脱空、错台等震害现象。从目前大坝总体渗流量、泄洪设施运用情况、高边坡稳定性,以及施工质量控制等方面综合评价认为,震害具有可修复性,震后的防渗系统仍然有效,大坝整体结构稳定安全。

基于土石坝动力特性的坝料动力参数反演

采用现行的室内外试验方法确定的土石料动力参数与实际坝料的动力参数有何差异是人们关心的问题之一。提出了基于土石坝动力特性的坝料动力参数反演方法,并使用该方法反演了一个假想混凝土面板堆石坝的坝料动力参数,证明该方法是可行的,计算精度基本满足实际工程要求。利用紫坪铺面板堆石坝在汶川地震中的余震加速度响应信息,反演了坝料的最大动剪切模量系数K和指数n。结果表明,由室内动三轴试验得到的坝料最大动剪切模量系数K值偏小,建议进一步研究予以修正。

紫坪铺“5.12”震害对面板堆石坝抗震措施的若干启示

结合面板堆石坝设计规范的修编工作,总结分析了"5.12"汶川地震中紫坪铺面板堆石坝的震害特征,获得了关于面板堆石坝抗震措施的若干启示,包括坝顶及其附近坝坡的防护、面板垂直缝的抗挤压措施和水平施工缝的抗震设计、面板堆石坝的地震变形控制及基于抗震计算和工程经验确定抗震措施的重要性等,对做好面板堆石坝抗震措施具有重要意义。

紫坪铺面板堆石坝汶川地震永久变形实测结果分析

分析了汶川大地震紫坪铺面板堆石坝永久变形实测结果。研究表明,大坝顶部区产生的永久沉降最大,而且在永久沉降变形构成中占主要的部分。地震后紫坪铺大坝外形轮廓均在地震前外形轮廓之内,坝坡地震永久变形矢量均指向坝内,表明大坝地震后整体是收缩的,有利于大坝的整体稳定。建议了土石坝地震分区震陷率的概念与方法,论证了坝顶加固的土石坝抗震加固技术的科学性与合理性。

汶川地震中紫坪铺面板堆石坝永久应变反演分析

紫坪铺大坝是世界上第一个遭受强震的百米以上面板堆石坝,在"5.12"汶川地震中有明显的局部损伤。采用有限元数据平滑方法,对大坝位移监测数据进行处理,得到了坝体典型剖面的永久应变。分析了大坝在地震中沉降和堆石料剪胀变形发生的部位和原因,表明坝体最大震陷率发生在2/3坝高附近;大坝发生剪胀的范围为坝顶区域和从坝顶往下25～30 m的上下游坝坡附近;永久剪应变过大是造成面板水平施工缝错台的直接原因。

紫坪铺面板堆石坝关键技术问题的处理

紫坪铺工程面板堆石坝于2003年3月开始填筑,2005年6月填筑完成,历时27个月,总填筑量为1 177万m3,面板分三期施工,大坝监测数据表明大坝填筑质量优良。截止到2005年9月9日,最大实测沉降值为88.8 cm,为本阶段最大坝高的0.57%。大坝安全是枢纽安全的最重要保证,对关键技术问题的处理又将直接决定大坝的长期运行安全性,处于特殊复杂地质区域的紫坪铺大坝尤其如此。重点阐述了紫坪铺面板堆石坝几个较关键技术问题的处理措施。

基于变形控制标准的高土石坝地震可靠度分析

基于可靠度分析的设计方法是科学定量地研究和保证岩土工程安全性的重要手段之一。通过定量考察土石坝工程中的不确定性因素,综合评估地震失效概率,可为高土石坝抗震设计和风险评估提供参考。以坝顶震陷率作为地震安全控制指标,提出了同时考虑地震和筑坝料参数不确定性的高土石坝地震可靠度分析方法。首先,采用地震烈度作为地震危险性的宏观衡量尺度,通过引入地震烈度概率模型,将基于概率烈度的地震动峰值作为地震强度因子,调整规范谱人工地震波的幅值进行动力有限元计算。然后,采用适用于处理小样本和非线性问题的高斯过程响应面法,建立筑坝料参数与坝顶震陷率之间的非线性映射关系,结合蒙特卡罗法计算高土石坝地震失效概率。最后,以紫坪铺面板堆石坝为例,应用该方法考察了设计基准期内的地震失效概率。

Investigation of the 5.12 Wenchuan Earthquake damages to the Zipingpu Water Control Project and an assessment of its safety state

On May 12, 2008, a major earthquake measured 8 on the Richter scale jolted Wenchuan County in Si- chuan Province, China with the epicentral intensity of XI degrees. Zipingpu Dam is located 17.17 km from the epicenter and the influence intensity at the damsite reached IX―X degrees. It is the first time in the world for such a high concrete-faced rockfill dam (CFRD) in China to experience such a strong earthquake occurring in such a short distance. Due to its location of special importance to the down- stream areas, the safety state and damaging condition of the Zipingpu Dam has attracted great atten- tions from various circles. Based on site investigation of the damages to the Zipingpu Dam and com- parison analysis of the observation data obtained before and after the earthquake, the paper makes a comprehensive assessment of the key technical issues relevant to this high CFRD, including its safety state and the high slope stability after the earthquake.

紫坪铺混凝土堆石坝抗震风险分析

结合"5·12"汶川强震考验的紫坪铺混凝土面板堆石坝工程的震损情况,利用高土石坝抗震风险分析模型,针对坝坡失稳和坝体永久变形两种常见的破坏模式应用可靠性理论与静、动力有限元计算等方法展开深入研究,利用蒙特卡罗随机抽样方法计算大坝失事概率,最后结合震损统计结果和高土石坝抗震风险评价矩阵等级表,对紫坪铺大坝进行抗震风险等级评定,结果表明紫坪铺大坝在地震后具有高风险,需要及时进行抗震加固。

Strengthening of the concrete face slabs of dams using sprayable strain-hardening fiber-reinforced cementitious composites

In this study,sprayable strain-hardening fiber-reinforced cementitious composites(FRCC)were applied to strengthen the concrete slabs in a concrete-face rockfill dam(CFRD)for the first time.Experimental,numerical,and analytical investigations were carried out to understand the flexural properties of FRCC-layered concrete slabs.It was found that the FRCC layer improved the flexural performance of concrete slabs significantly.The cracking and ultimate loads of a concrete slab with an 80 mm FRCC layer were 132%and 69%higher than those of the unstrengthened concrete slab,respectively.At the maximum crack width of 0.2 mm,the deflection of the 80-mm FRCC strengthened concrete slab was 144%higher than that of the unstrengthened concrete slab.In addition,a FE model and a simplified analytical method were developed for the design and analysis of FRCC-layered concrete slabs.Finally,the test result of FRCC leaching solution indicated that the quality of the water surrounding FRCC satisfied the standard for drinking water.The findings of this study indicate that the sprayable strain-hardening FRCC has a good potential for strengthening hydraulic structures such as CFRDs.

考虑前期震动影响的紫坪铺面板坝震后抗震安全评价

围绕经受了"5.12"汶川大地震的紫坪铺大坝的震后加固,根据地震后最新核定的地震动参数,采用三维真非线性动力反应分析方法,进行了紫坪铺大坝震后抗震安全评价。紫坪铺大坝是经历了汶川大地震强震的,在进行震后的抗震计算和抗震安全性评价时,应当考虑前期震动的影响。采用试验研究和计算分析,研究了前期震动对大坝地震反应的影响,进行了设计地震下的大坝动力分析,从稳定、变形、面板防渗体系安全等多角度,对震后大坝的抗震安全性进行了评价,分析了抗震薄弱环节,对抗震加固措施提出了建议。所提出的抗震安全性评价方法以及有关规律和结论,可为工程设计和建设提供技术依据。