保德县汾家沟骨干坝除险加固

以保德县汾家沟骨干淤地坝除险加固工程为实例,介绍了在特定的施工环境下的一些除险加固工程的施工布置,方案及方法,质量控制方面的一些技术措施。     

Numerical simulation of two-phase flow in deformable porous media: Application to carbon dioxide storage in the subsurface

In this paper, conceptual modeling as well as numerical simulation of two-phase flow in deep, deformable geological formations induced by CO₂ injection are presented. The conceptual approach is based on balance equations for mass, momentum and energy completed by appropriate constitutive relations for the fluid phases as well as the solid matrix. Within the context of the primary effects under consideration, the fluid motion will be expressed by the extended Darcy's law for two phase flow. Additionally, constraint conditions for the partial saturations and the pressure fractions of carbon dioxide and brine are defined. To characterize the stress state in the solid matrix, the effective stress principle is applied. Furthermore, the interaction of fluid and solid phases is illustrated by constitutive models for capillary pressure, porosity and permeability as functions of saturation. Based on this conceptual model, a coupled system of nonlinear differential equations for two-phase flow in a deformable porous matrix (H²M model) is formulated. As the displacement vector acts as primary variable for the solid matrix, multiphase flow is simulated using both pressure/pressure or pressure/saturation formulations. An object-oriented finite element method is used to solve the multi-field problem numerically. The capabilities of the model and the numerical tools to treat complex processes during CO₂ sequestration are demonstrated on three benchmark examples: (1) a 1-D case to investigate the influence of variable fluid properties, (2) 2-D vertical axi-symmetric cross-section to study the interaction between hydraulic and deformation processes, and (3) 3-D to test the stability and computational costs of the H²M model for real applications.     

吹填土真空预压过程中夹砂层的作用机理

采用有限差分软件FLAC3D对吹填土中设置夹砂层进行数值模拟,研究了夹砂层对吹填土固结沉降的作用机理,结果表明夹砂层在吹填土中形成了水平向排水通道,可以提高吹填土在真空预压时的固结速度,增加固结沉降量,同时提出在夹砂层上下表面设置土工布的处理方法,有助于夹砂层在吹填土中的稳定成形,并起到限制吹填土不均匀沉降的作用。     

滨海吹填土固结蠕变特性试验研究

围海造陆形成的吹填土地基与天然形成地基的工程特性存在诸多差异,为了保证吹填土地基的长期稳定性和安全性,有必要揭示吹填土与天然土工程特性的差异。利用单向固结仪,开展了不同加荷方式下滨海典型软土和围海造陆吹填土的蠕变特性试验对比研究,得到了不同试验条件下土体的应变、应力和时间的关系,对比分析两种软弱土蠕变性状的差异和影响因素,同时给出次固结系数的变化规律。试验结果表明,分级加载下两种滨海软土均具有明显的非线性蠕变特性,高应力水平下经排水加固的吹填土最终变形量明显低于软黏土,而次固结变形较大;吹填土的一维固结蠕变特性受加荷比和试样高度影响,加荷比越大、高度越高土样最终蠕变量越大;次固结系数与加荷比和荷载等级有关,表现为次固结系数随荷载增大先增大后减小,峰值随加荷比增大而减小。     

One-dimensional consolidation of double-layered soil with non-Darcian flow described by exponent and threshold gradient

Based on non-Darcian flow law described by exponent and threshold gradient within a double-layered soil, the classic theory of one-dimensional consolidation of double-layered soil was modified to consider the change of vertical total stress with depth and time together. Because of the complexity of governing equations, the numerical solutions were obtained in detail by finite difference method. Then, the numerical solutions were compared with the analytical solutions in condition that non-Darcian flow law was degenerated to Dary’s law, and the comparison results show that numerical solutions are reliable. Finally, consolidation behavior of double-layered soil with different parameters was analyzed, and the results show that the consolidation rate of double-layered soil decreases with increasing the value of exponent and threshold of non-Darcian flow, and the exponent and threshold gradient of the first soil layer greatly influence the consolidation rate of double-layered soil. The larger the ratio of the equivalent water head of external load to the total thickness of double-layered soil, the larger the rate of the consolidation, and the similitude relationship in classical consolidation theory of double-layered soil is not satisfied. The other consolidation behavior of double-layered soil with non-Darcian flow is the same as that with Darcy’s law.     

强夯模型试验及其研究进展

简要分析了强夯模型试验设计的理论依据,讨论了强夯模型试验的相似条件,并对强夯相似准则进行了推导,提出了相似强夯模型试验和非相似强夯模型试验的概念。深入分析了强夯模型试验中严重制约强夯机理研究及工程应用的模型箱尺寸和相似比例系数选取、仪器精度及数据处理等问题,提出在模型试验中提高数据采集仪器的灵敏性和精度、建立灰色系统模型提高数据处理的精确性等建议。     

某路基堆载预压处理的有限元数值模拟

针对软弱黏土路基易发生失稳及工后沉降大的缺点,采用塑料排水板堆载预压对路基进行处理。采用等效砂墙方法及剑桥模型,建立了台州湾围海工程路基堆载预压处理的平面有限元模型。分析不同堆载高度下塑料排水板间距和长度对加载速度、预压时间和沉降值的影响。分析结果表明,预压时间受排水板长度影响明显; 预压期结束后,路面沉降均匀,可以保证路面施工质量。     

不同含水率下非饱和黄土K0固结特性试验

针对非饱和原状黄土进行了不同含水率下的恒荷重K0固结试验研究,分析了含水率对割线模量,应力应变特性及侧压力系数的影响。试验表明,在其他条件相同的情况下,割线模量随着荷载的施加逐渐减小,最终趋于稳定,达到稳定值时的割线模量随着含水率的增大而减小,且与含水率线性相关;含水率越大,静止侧压力系数K0增长速率越快,至土结构完全破坏,K0趋于稳定;不同含水率的K0值最终趋于稳定,且稳定值差异性较小;提出了考虑含水率因素的连续加载条件下K0固结过程的变形模型,为研究黄土地区K0固结过程中土体变形特性及路堤沉降提供参考。     

武汉原状粉质黏土与其重塑土的试验对比研究（I）：试验结果描述

以武汉沙湖粉质黏土为研究对象,首先借助于高压固结仪,对重塑土和原状土进行了室内侧限的固结试验;其次利用改进的应力控制式常规三轴仪,在不同的加荷路径和排水条件下,对重塑土和原状土分别进行了常规三轴试验研究,并对试验资料进行了较为系统的分析．结果表明：1）原状土的侧压力系数约为0．56,超固结比约等于1．2,为弱超固结土体,其结构屈服压力稍大于其前期固结压力;2）原状土初始的切线模量及其抗剪强度均高于重塑土相应的值;3）在固结排水条件下的三轴剪切试验,原状土的剪胀量要小于重塑土的剪胀量,但在固结不排水条件下,原状土体的剪胀趋势却明显要高于重塑土的剪胀趋势．