Numerical stress-deformation analysis of cut-off wall in clay-core rockfill dam on thick overburden

The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden layer, the frictional force induced by the differential settlement between the cut-off wall and surrounding soils, and the water pressure. Thus, reduction of the stress of the cut-off wall has become one of the main problems for consideration in engineering design. In this paper, numerical analysis of a core rockfill dam built on a thick overburden layer was conducted and some factors influencing the stress-strain behaviors of the cut-off wall were investigated. The factors include the improvement of the overburden layer, the modeling approach for interfacial contact between the cut-off wall and surrounding soils, the modulus of the cut-off wall concrete, and the connected pattern between the cut-off wall and the clay core. The result shows that improving the overburden layer,selecting plastic concrete with a low modulus and high strength, and optimizing the connection between the cut-off wall and the clay core of the dam are effective measures of reducing the deformations and compressive stresses of the cut-off wall. In addition, both the Goodman element and the mud-layer element are suitable for simulating the interfacial contact between the cut-off wall and surrounding soils.

Active earth pressure for subgrade retaining walls in cohesive backfills with tensile strength cut-off subjected to seepage effects

The commonly used Mohr-Coulomb(M-C) failure condition has a limitation that it overestimates the tensile strength of cohesive soils. To overcome this limitation, the tensile strength cut-off was applied where the predicted tensile strength is reduced or eliminated. This work then presented a kinematical approach to evaluate the active earth pressure on subgrade retaining walls in cohesive backfills with saturated seepage effects. An effective rotational failure mechanism was constructed assuming an associative flow rule. The impact of seepage forces, whose distribution is described by a closed-form solution, was incorporated into the analysis. The thrust of active earth pressure was derived from the energy conservation equation, and an optimization program was then coded to obtain the most critical solution. Several sets of charts were produced to perform a parameter analysis. The results show that taking soil cohesion into account has a distinct beneficial influence on the stability of retaining walls, while seepage forces have an adverse effect. The active earth pressure increases when tensile strength cut-off is considered, and this increment is more noticeable under larger cohesion.

Application of High-Density Seismic Image in Nondestructive Exploration of Cut-off Cement-Soil Wall in Earth Dam

In order to quickly explore the quality of cut-off wall in dams, a new method of high-density seismic image was adopted and estimated by model and in-situ wall tests.The vibration exciter was employed and several parameters such as hypocentral distance, length of signal record and sampling space in signal collection were determined, which are 8 m, 0.25 ms and 128 ms respectively. Through time and frequency field signal analyses, it is concluded that, the smaller arrival times of reflected longitudinal and surface waves, and the higher their main frequencies, the higher the strength of the wall, vice versa. Accordingly the construction quality of the wall can be evaluated quickly by high-density seismic image.

含漂砂卵砾石深厚覆盖层复合地基处理施工关键技术的研究与应用

以硬梁包水电站为依托,针对深厚覆盖层地质条件复杂多变且含巨漂砂卵砾石地层条件,阐述了通过对防渗墙及地下连续墙采用精准施工技术、发泡泥浆护壁工艺、超常规振冲碎石桩填料自动化精确测量、反滤层精准布设施工工艺、振冲桩承载力快速简便检测方法、超深防渗墙防渗单元质量智能融合与辨识关键技术、智能化精确计量超常规振冲碎石桩填料等基础加固和防渗处理方法开展的研究与应用,有效地解决了泥浆漏失和护壁稳定性问题以及超常规碎石桩施工中遇到的技术难题,实现了对超深防渗墙质量的分析和定量评价,降低了防渗体出现隐患的风险,可对差异沉降进行有效管控,对项目施工进度和质量起到了促进作用,所取得的经验可供类似工程参考。

砂卵石地层超深防渗墙工艺试验研究

针对襄阳市东西轴线东汊干坞超深防渗墙地质环境及施工工艺要求,进行了原位工艺试验,验证了砂卵石地层超深防渗墙成槽可行性。结合工艺试验,总结出了在砂卵石易透水、易塌孔地层中进行超深防渗墙施工工艺的要点,比选确定了防渗墙墙体材料,为防渗墙施工提供了试验数据及理论支撑。

某水库超深混凝土防渗墙应力应变监测分析

对某水库超深混凝土防渗墙内埋设应变计和土压力计的现场实测方法进行了说明,对观测到的140 000组数据进行了系统分析,得出了超深混凝土防渗墙的受力状态,对类似工程具有借鉴意义。

深厚覆盖层上超深防渗墙细部设计问题探讨

超深防渗墙细部设计是深厚覆盖层上修建土石坝防渗处理的关键性问题。为此,在归纳总结国内外已建工程中超深覆盖层上防渗墙设计和建设经验的基础上,提出坝基防渗墙的设计中几点需要关注的问题,包括采用刚性墙还是塑性墙问题、防渗墙上下游侧的处理问题、封闭式防渗墙入岩深度问题、防渗墙顶部是否布设钢筋问题。针对这些问题在设计中需要注意以下几方面:(1)应根据数值计算的应力和变形指标确定钢塑性选择标准,加大研究塑性混凝土墙并推广应用;(2)结合有限元数值计算,分析防渗墙顶部一定范围内与两侧覆盖层之间的应力状况,评价防渗墙的上下游设置固结灌浆的必要性;(3)入岩深度的确定要结合岩石的坚硬完整性或岩石的破碎程度考虑;(4)防渗墙应力指标作为防渗墙顶部墙内特定范围内是否设置钢筋笼的标准。

超深基坑止水帷幕TRD与防渗墙工法对比分析

重点从成本、工效、抗渗质量、环保、耗材等方面对TRD工法墙和成槽机施工的防渗墙做了详细的对比分析论证,认为在相同条件下防渗墙整体优于TRD工法墙,是一种先进可靠的防渗工艺,值得在超深基坑侧壁及坑底止水方面大力推广使用。

SEEPAGE ANALYSIS OF LANDFILL FOUNDATIONS IN SHANGHAI LAOGANG LANDFILL PHASE IV

A complex seepage flow field with unknown free surface was formed in the Shanghai Laogang Municipal Solid Waste （MSW） Landfill by the perimeter cut-off wall around the landfill site and the Prefabricated Vertical Drains （PVD） in the foundation of landfill. First, the equivalent vertical permeability was presented based on the drainage mechanism of PVD and the related calculation method was studied to macroscopically reflect the impact of PVD on the seepage flow status of the landfill foundation. With the influence of the cut-off wall and the PVD on the infiltration of groundwater, the total inflow was classified into two parts： the lateral inflow through the cut-off wall outside the landfill, and the upward infiltration through the PVD from the foundation of the landfill. Seepage analysis was conducted using the finite element method according to the actual scenario of Laogang Landfill, and the lateral infiltration and the upward infiltration were calculated, respectively. The results show that the total inflow into the landfill area was mostly supplied by the upward infiltration through the PVD and the perimeter cut-off wall was significantly effective to depressurize the seepage pressure and to reduce the flow rate.