渗流与渗透稳定问题是土石坝的关键技术问题。而对于建在深厚覆盖层上的堆石坝，由于深覆盖层一般具有结构松散、岩性不连续、成因类型复杂、岩性在水平和垂直两个方向上均有较大变化，物理力学性质呈现较大的不均匀性、透水较强等特性，而且由于堆石坝坝体本身防渗性能差，所以对这类坝的渗流分析就显得更加重要。本文用geoslope软件对旁多水电站深覆盖层沥青混凝土心墙堆石坝进行了渗流数值分析，就坝基设80m悬挂防渗墙和无防渗两种方案进行计算，对两者的渗流场进行分析比较，结果表明在坝基无防渗时，大坝渗流明显，坝体内部渗压大，覆盖层中的水力坡降超出了安全比降，影响坝体的安全稳定；而在设防渗墙时能有效降低坝体浸润线，降低坝体、覆盖层以及下游渗流出逸点的水力坡降，但是同时也存在一个问题就是防渗墙底部水力坡降过大的问题，说明了此工程对坝基设防的必要性以及选择80m防渗墙的可行性与限制性。
关 键 词：堆石坝；深覆盖层；数值计算；二维渗流；Geoslope
Seepage Analysis of Asphalt Concrete Core Wall Rockfill Dam in Deep Overburden of Pangduo Hydropower Station of Tibet
Abstract: Seepage and stability seepage problem is the key technical problems of earth-rockfill dam. Because of in general the loose structure, lithologic discontinuity, complicatedly genetic types, and the relatively large changes of lithology in the horizontal and vertical direction, the physical and mechanical properties of the deep overburden layers appear comparatively large non-uniformity, strong water features and so on，because of rockfill dam seepage control performance is poor， so the seepage problem we built rockfill dam on the deep overburden layers need more earnest analysis and calculation.This paper use the software of geoslope as the platform analysising seepage of asphalt concrete core wall rockfill dam of Pangduo Hydropower Station .Two schemes about whetherthe foundation of the dam protected are discussed and analyzed , obtained the corresponding conclusion about the seepage field which indicates the necessity of fortification for the dam., the results showed that without anti-seepage in the dam foundation, the dam seepage obviously, inside seepage pressure high, and in the cover the seepage slope gradient is excess of the safety line, impact the security and stability of the dam; But when established cut-off wall can effectively reduce the soakage line, reduce the dam, covering layers and downstream escaping seepage point , but at the same time there is a problem is at the bottom of the diaphragm wall has excessive penetration seepage , illustrates the necessity to built dam groundwork and also discuss the feasibility and boundedness of choose 80m diaphragm wall .
Key words: Rockfill Dam; Deep overburden; Numerical calculation; Two-dimensional seepage; Geoslope
第一章 概述
1.1深覆盖层建坝的渗流问题
我们知道对大坝整体安全构成威胁的诸多因素中，渗流的影响举足轻重。地表水流
的破坏作用常会引起人们注意，也较容易发现;而地下水流的渗流冲刷不易发现，常被忽视，有时一经发现工程已被破坏或难以易补救。根据国内外大坝失事原因的调查统计，因渗流问题而失事的比例高达30%-40%[1]-【2】。据统计，我国241座大型水库土石坝的千次事故中，由渗透破坏造成的占31.9%。在2391座水库跨坝事故中，由渗透破坏造成的占29%。据世界其他国家统计，渗透破坏所造成的土石坝失事率，美国为39%(统计失事坝206座)，日本为44%(统计失事坝119座)，西班牙为40%(统计失事坝117座)。另据不完全统计，国外建于软基及覆盖层上的水工建筑物，由于坝基渗透破坏、沉陷太大或滑动等因素导致失事的占到35%-40%[3]。
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