水位升降作用下大坝防渗数值模拟研究

为研究水位波动下大坝内力及变形规律,基于数值模拟法分析了防渗墙在水位上升和下降工况下防渗墙的变形规律,结果表明：蓄水前后防渗墙的水平位移变化趋势相同,其中蓄水前后墙顶的最大位移分别为110 mm和220 mm。此外,蓄水对墙体的垂直变形影响不大;防渗墙上游面和下游面最大主应力随高程的增大而先增大后减小,不同工况下墙体的最大应力小于混凝土的容许强度;随弹性模量的增大,墙体变形随混凝土弹性模量的增大而减小,墙体主应力随混凝土弹性模量增大而增大。关于防渗墙的选取要综合考虑工程地质条件及坝体形式等因素,合适的混凝土弹性模量可以降低墙体的最大应力。     

源口水库大坝除险加固设计

源口水库大坝除险加固采用坝坡填筑料置换,解决上游坝坡在水位骤降期的坝坡稳定问题;在粘土心墙中设置混凝土防渗墙,提高坝体的渗透可靠性,为降低坝内混凝土防渗墙的拉应力,墙体采用低弹模混凝土;大坝除险加固施工期水库仍能蓄水发挥效益.介绍了该大坝除险加固设计中的技术处理与经验总结.     

塑性混凝土心墙坝应力变形特性研究

为研究塑性混凝土心墙坝的应力变形特性,通过选取合适的本构模型、接触单元、施工过程和蓄水过程模拟方法等,结合工程实际,运用三维非线性有限元法对大坝应力变形进行计算分析。研究结果表明:在竣工期和蓄水期,坝体的水平位移及垂直位移的分布特征与一般均质土坝一致;大坝的大主应力均为压应力,从坝面向坝内应力逐渐增大,且最大值发生在坝体底部心墙附近;小主应力除局部存在较小的拉应力外,其余均为压应力。     

防渗墙弹性模量及坝高对墙体力学特征影响分析

为了研究混凝土防渗墙在正常蓄水及校核水位工况下,混凝土弹性模量对防渗墙的内力和变形影响规律,基于数值模拟软件进行相关计算,结果表明：(1)墙体的水平位移受混凝土弹性模量的影响非常小。不同弹性模量下墙体的变形基本相同,最大变形为墙体15m位置的5.7mm。(2)混凝土弹性模量5GPa时属于临界值。当小于该临界值时,防渗墙的应力状态变化不显著;当大于该临界值时,防渗墙的应力状态显著发生改变。实际工程中,混凝土刚度过大,可以提高防渗墙墙体强度,但也会导致局部出现受拉区。(3)坝体越高,应选择弹性模量较小的混凝土;坝体越低,可选择弹性模量较大的混凝土。当大坝高度小于20m时,混凝土弹性模量可选用小于6GPa;当大坝高度大于50m时,混凝土弹性模量应尽量小于5GPa。     

碾压式沥青混凝土心墙坝三维静动力数值模拟研究

为研究碾压式沥青混凝土心墙坝施工及运行期的受力特性,以新疆某水利枢纽工程为例,采用非线性邓肯-张E-B模型进行大坝三维有限元静力计算,采用等效线性粘弹性模型进行大坝三维有限元动力计算,采用三维等价结点力法研究坝体地震永久变形,主要研究坝体在静动力条件下坝体和防渗体的应力、变形以及基座与心墙的相对位移。结果表明,静力条件下,坝体最大沉降约占坝高的0. 27%,蓄水后心墙最大压应力较竣工期减少约14. 2%,蓄水后心墙顺河向最大位移较竣工期增大约2. 6倍、沿坝轴线方向减小约13. 3%;动力条件下,坝体地震沉降约占坝高的0. 09%,地震发生时坝体最大横断面心墙出现拉应力,其值约为最大压应力的9. 5%,地震结束后心墙最大压应力减小约16. 7%,未出现拉应力,地震后坝体顺河向发生永久位移,心墙最大压应力较地震前增大1. 9%,心墙顺河向最大位移较地震前增大约15. 4%、沿坝轴线方向减小约11. 5%。     

张峰水库左坝肩防渗墙应力分析

山西张峰水利工程大坝左坝肩低液限粘土坝基上设有混凝土防渗墙,墙身深入坝体心墙内,该墙是坝体防渗的关键部位。通过非线性数值分析方法,对采用不同材料和施工工艺情况下,防渗墙的应力进行了分析,得出:采用塑性混凝土可以减小墙体应力,提高墙体的抗裂性能;在坝体不高的情况下,调整施工工艺,将先打防渗墙后筑坝改为先填筑坝体再进行防渗墙施工的工艺,更将大幅度减少墙体应力,提高防渗墙的抗裂性能,从而将提高大坝的防渗性能。     

土石坝超深混凝土防渗墙变形与受力分析

我国病险土石坝已开始应用超过60 m的超深混凝土防渗墙进行加固。受库水变化和帮坡加载等作用、基岩嵌固条件及墙体材料性能等影响,防渗墙受力复杂多变。结合花凉亭水库大坝除险加固工程,采用Biot固结理论和南水双屈服面弹塑性模型,对混凝土防渗墙在坝体内的变形与受力情况进行三维仿真分析。成果表明:坝体混凝土防渗墙受老坝帮坡加固和库水上升的影响较小;超深混凝土防渗墙建议适当提高抗压强度、降低弹性模量,以满足其受力和耐久性要求;对于非直线型大坝拐弯处的混凝土防渗墙,底部墙体应力会增大,可考虑增设钢筋等措施。研究成果可为超深混凝土防渗墙的设计提供借鉴。     

土工膜防渗石渣坝应力变形有限元分析

某水库大坝为土工膜防渗石渣坝,坝面利用复合土工膜作为面板进行防渗。对该水库大坝建立三维非线性有限元模型,模拟大坝填筑施工、复合土工膜铺设及水库蓄水过程,分析了竣工期和蓄水期下坝体和复合土工膜的应力变形情况,论证了该土工膜防渗石渣坝结构设计的合理性。计算结果表明,蓄水前后坝体的位移和应力分布符合一般规律,且蓄水对坝体安全有利,坝体不会出现剪切破坏;复合土工膜在坝面下半部分由于受边界约束出现拉应变,产生拉应力,但计算得到的横向和纵向安全系数均满足规范要求,土工膜安全可以得到保证。     

砂土ＵＨ模型在土石坝有限元分析中的应用

利用砂土ＵＨ模型对两岔河水库工程心墙堆石坝进行了应力变形三维有限元计算,分析了坝体在竣工期和满蓄期的应力变形特性。结果显示:坝体在竣工期和满蓄期的最大沉降分别为７３．８ｃｍ和７７．７ｃｍ;坝体在竣工期和满蓄期的大主应力、小主应力均存在拱效应,大主应力的拱效应更显著,心墙内小主应力均为正,未出现拉应力;竣工期和满蓄期防渗墙左右两侧小主应力出现了拉应力区,防渗墙最大拉应力和压应力均在混凝土强度容许范围内。大坝应力变形的计算结果符合心墙堆石坝应力变形一般规律。有限元计算结果均在合理范围内,表明砂土ＵＨ模型在土石坝工程中有较好的适用性。     

小浪底水库斜墙堆石坝有效应力应变分析

本文用Duncan非线性模型和笔者建议的双屈服面弹塑性模型(简称南水模型),分析了黄河小浪底水库大坝设计断面住施工和蓄水过程中的有效应力和变形状态。按Duncan模型计算的竣工期变位,显著大于按弹塑性模型的计算结果,但所计算的孔隙压力却较低。此外,Duncan模型计算的施工期斜墙的水平位移很大,这是上游坝体在雨水浸透情况下稳定性不够的反映。两种模型的最大差别反映在蓄水期计算结果上。按Duncan模型,蓄水将使坝顶显著地向下游水平位移,且有相当大的上抬;按弹塑性模型,坝顶向上游移动,其垂直变位为下沉。两种模型的计算结果均表明,防渗墙顶部及附近土体中无水力劈裂的迹象,但水库运行初期淤积体内有相当高的超静孔隙压力,50年后则大部分消散。计算的施工期防渗墙垂直应力不大,但水库蓄水后有显著增加。     

饱和软粘土的塑性指数对其压缩变形参数的影响

本文对粘性土的塑性和塑性指数的物理意义及其对饱和软粘土力学性状的影响进行了深入研究，归纳了国内外关于这一领域的一些研究成果，结合笔者的试验研究分析了饱和软粘土的塑性指数对若干变形参数影响的定量关系。这些参数包括压缩指数、回弹指数、次固结系数、初始再固结体积压缩系数等。上述关系有较好的相关性，可用于工程计算。     

复杂围岩的应力与位移计算方法研究

岩体具有流变性能 ,围岩开挖后 ,视之为粘弹性体与粘塑性体的组合体比较恰当 ;在围岩的粘弹性区采用中村模型 ,用数学的方法 ,求出粘弹性区、粘塑性区的应力和位移表达式     

Contrasting shell/tissue characteristics of Dreissena polymorpha and Dreissena bugensis in relation to environmental heterogeneity in the St. Lawrence River

The zebra mussel, Dreissena polymorpha, is widespread in the St. Lawrence River while the conspecific quagga mussel, Dreissena bugensis, is found only in the Lake Ontario outflow region of the river. This situation provided an opportunity to evaluate in situ environmental and interspecific heterogeneity in shell and tissue growth. Shell dry weight, carbon content, and shell strength of D. polymorpha from the four spatially discrete water masses differed significantly. For instance, D. polymorpha total and tissue mass increased over the summer in the shallow fluvial Lac Saint-Pierre but decreased in the upstream and downstream water masses. Standardized shell mass and strength of D. polymorpha was lowest where the mussels experienced salinity or low calcium. Although the response pattern of mass and glycogen content for D. polymorpha was spatially complex, mussels from the stressful oligohaline estuary population had the weakest shells and lowest glycogen content, even though their standardized tissue mass was the heaviest. This disparity in shell and tissue response suggests that some aspect of shell physiology alone may be limiting these mussels in estuarine environments. Tissue characteristics of D. polymorpha and D. bugensis were similar at the site where both were present, but the shell strength of D. bugensis was only equivalent to the weakest of D. polymorpha. We also conclude that lighter shells might make D. bugensis more susceptible to predation or mechanical damage but may also offer a bioenergetic advantage that is contributing to its rapid displacement of D. polymorpha where the two species co-occur.     

Retention of morphological and ecological traits of Lake Superior cisco Coregonus artedi after translocation into inland lakes

Introductions of Coregonus artedi from Lake Superior into several inland lakes in Minnesota in the 1920s and 1930s constituted a natural experiment of how phenotypic plasticity and adaptation can shape cisco diversity. Genetic data were consistent with a Lake Superior origin for the introduced populations, which resembled contemporary Lake Superior cisco in possessing large, elongated bodies and short fins, and in maturing at older ages. Native inland cisco had smaller, deeper bodies, longer fins, and matured at younger ages. Introduced populations also retained the Lake Superior characteristic of inhabiting the upper portion of the water column and showed a high degree of planktivory. However, introduced cisco exhibited small but measurable shifts in body shape and fin lengths toward native inland forms. These morphological shifts were possibly associated with greater benthivory after translocation. Assuming that native inland populations were well adapted to inland lakes and that selective pressures on native and introduced populations were similar, these results indicated that substantial further phenotypic, behavioral, and life history change is required before the introduced populations become similarly adapted to their new environments. The findings suggest that anthropogenic environmental alterations such as climate change and eutrophication might occur at a faster pace than adaptive evolutionary responses. In addition, translocated Great Lakes coregonines could possibly maintain traits exhibited in their source lake, and may not fully restore ecological functions of extirpated populations.     

First report of extraordinary corkscrew gastropods of the genus Bulinus in Lake Malawi

Open-coiled shells are rarely observed in gastropods, but they may occur at a relative frequency ranging from a small percentage of specimens in a population up to being specific to populations or even species. The origin of such corkscrew-like shells are poorly understood, but may include developmental anomalies, ecophenotypic plasticity or genetic inheritance. Here, we report the first case of gastropods from Lake Malawi with corkscrew-like shells, and we use comparative molecular studies with two mitochondrial gene fragments (COI and 16S rRNA) to examine its origin. The specimens belong to the genus Bulinus, more specifically to one of five clades of Bulinus recovered from the Malawi Basin. Beyond being seemingly specific to one of these Bulinus clades, network analyses indicate low genetic differentiation from the other, regularly shaped specimens in this clade. Although our results do not fully discard the possibility of corkscrew-like shells being genetically inherited or being caused by growth disturbance, their restrictive occurrence in a few geographically isolated populations in sympatry with specimens displaying a regular shell shape supports the hypothesis that the corkscrew-like shell shape in Bulinus is caused by ecophenotypic plasticity. For now, it is unclear whether aspects of the physical environment, or biotic interactions, such as a release from predation, caused the corkscrew-like morphotype. The phenomenon may have been caused by the multiple environmental changes that Lake Malawi has been undergoing over recent decades.     

堆石料广义塑性模型对不同应力路径适应性研究

针对同一系列某花岗岩堆石料不同应力路径加载试验,进行了修正广义塑性模型与修正南水模型的应力路径适应性对比研究。研究结果表明:两类模型均可以很好地预测常规三轴加载试验结果;对于等p加载应力路径试验,二者可以很好地预测强度特征,但是预测的体变偏差较大,两类模型均低估了等p试验下堆石料的体缩特性;对于等应力比加载试验,南水模型预测结果优于广义塑性模型,对剪胀(缩)规律预测较好。广义塑性模型预测结果与试验值相差较大, 主要原因在于常规三轴试验下的剪胀方程并不适用于等应力比试验,采用本文建议的修正剪胀方程后,广义塑性模型对等应力比路径试验预测精度明显提高。     

弹塑性损伤蠕变模型的有限元数值实施

利用有限元软件ＡＢＡＱＵＳ为平台,采用隐式应力积分回映算法编制了ＵＭＡＴ子程序。对不同围压下的三轴压缩试验和蠕变试验进行有限元数值模拟,并与试验结果进行对比分析,结果表明所编写的本构模型数值模拟结果与试验结果非常接近,可以有效反映软岩的力学特性,丰富了ＡＢＡＱＵＳ的材料库。采用该模型对地下开挖进行数值计算,得到了岩体表面的位移关系和洞口顶部的下沉随时间的变化规律,结果表明该子程序是正确和可信的,可以为地下工程分析提供合理的建议。     

应力洛德角变化影响的研究

本文提出的土体弹塑性应力 应变关系的完全应力增量表述，可把应力洛德角变化对土体应力 应变关系的影响归因于应力增量中广义剪分量引起的剪切屈服与剪胀。同时也给出了纯应力洛德角变化引起的土体塑性变形(排水)与孔压生成(不排水)的计算式。具体算例与有关实验定性一致。     

混凝土准脆性界面裂纹本构模型比较

以混凝土界面断裂分析为目的,选取若干典型的层间界面准脆性断裂的本构模型进行分析和数值模拟对比研究。在局部本构水平上,采用这些界面裂纹本构模型,对各种载荷工况下材料的准脆性断裂行为进行数值模拟。在对选择的典型黏性界面裂纹进行定性分析比较时着重考虑以下两点:①采用选择的模型对I型裂纹和II型裂纹的断裂行为进行数值计算;②对混合型断裂载荷作用下模型的扩容行为特性进行数值分析。通过对数值结果的分析比较得出结论:库仑型裂纹模型比较适合模拟复杂载荷下的界面断裂行为,但是其扩容特性仍有待改善。     

粘性土的抗剪强度特性试验研究

利用环剪仪针对塑性指数不同的三种粘性土，在不同的固结状态下进行了较系统的试验研究，探讨了大变形粘土的抗剪强度变化规律，分析了残余强度的影响因素。试验结果表明：(1)本试验所采用的环剪仪无论对于粉质粘土还是粘土均具有良好的稳定性，测试精度高，因此能够保证试验结果的准确性；(2)对于塑性指数不大的粉质粘土，应力历史对其抗剪强度的影响并不显著；(3)对于塑性指数较大的粘土，应力历史对残余强度没有影响，而峰值强度随着超固结比的增大而增大，最终接近粉质粘土的峰值强度；(4)塑性指数是影响残余强度非常重要的因素，随着塑性指数的增大，残余强度显著降低；(5)粘性土剪切沉降曲线的类型与塑性指数和超固结比有关。