公路地下排水设计理论与土工合成材料

应用研究

研究生：刘建华

指导教师：郭忠印教授

二〇〇五年三月

摘要

公路排水系统是公路工程的重要组成部分，其中地下排水系统(包括路基地下排水、中央分隔带排水、支挡结构物排水及边坡排水等)对保证公路的使用性能和使用寿命具有重要的作用，而现有排水设计方法及传统的排水材料均无法适应复杂的地质地形条件和自然气候条件的要求。基于这种背景，本文主要从公路地下排水设计理论与土工合成材料在公路排水设计中的应用技术两个方面进行选题并开展研究。

在公路地下排水设计理论研究方面，主要工作有以下几个方面：

(1)首先在现行设计理论对基础上对复杂地质条件下的路基地下排水设计方法进行了扩充与完善，一方面深入分析了现有渗沟计算方法的局限性，针对不透水层坡底不水平以及渗沟未挖至不透水层的情况，对渗沟计算方法进行了很大程度的扩充和完善，另一方面提出了封闭式渗沟的新型地下排水设施构造型式，并研究了封闭式渗沟的相关计算理论与方法，最终总结归纳出低洼平坦地带各种地质地形条件下的公路排水设施布设方案。然后对公路工程支挡结构物(挡土墙)及边坡坡面排水的计算理论与方法进行了探讨。研究表明：存在稳定潜水渗流的挡土墙排水计算方法与路基地下排水是相同的；考虑挡土墙填土区域的非饱和特性是挡土墙排水计算的关键。

(2)采用渗流有限元的数值方法分析各种典型的公路地下排水问题，特别是计算区域边界不规则和边界条件难于用简单对数学式进行表达的复杂情况，如不完整渗沟、斜坡渗沟。数值方法可以考虑渗透介质的不均匀性、各向异性等特点，更准确的反映实际情况；可以直观地得到排水设施渗流场规律，包括流量、流速、压力水头分布及流网图等便于后期分析和工程设计。

(3)应用非饱和土理论，探讨了考虑非饱和渗流的公路排水设计方法，采用饱和一非饱和渗流有限元方法对几种具有代表性的公路渗沟进行分析，并与现行计算方法所得结果进行比较。由于没有考虑非饱和士的渗流情况，现行方法低估了渗流流量。所提出的饱和一非饱和渗流有限元法得到了工程实例的初步验证。

在土工合成材料应用技术研究方面，主要工作有以下几个方面：

(1)通过大量室内试验系统地测试了土工合成材料的关键性能指标并验证分析了相关测试方法，提出了新的评价指标。重点研究对土工织物滤层设计指标(等效孔径、渗透系数与梯度比)的概念和测试方法、土工膜损伤对渗漏量的影响以及复合士工排水材料(塑料盲沟)的通水能力指标。

(2)建立了土工防排水材料应用分类体系，并改善优化了公路土工合成材料防排水设计标准，提出了针对公路工程应用的土工合成材料分类指标体系与方法，同时归纳总结了土工合成材料在公路地卜．排水、支挡结构物(挡土墙)排水、路面中央分隔带排水、路面边缘排水及边坡排水等排水设施中应用的典型构造形式，最终形成了系统的土工合成材料应用于公路排水设施中的设计方法。

最后在两项公路工程中实际铺筑的多段试验路测试结果对理论研究及室内试验成果进行了初步验证。

关键词：道路工程，排水，设计理论，土工合成材料，渗沟，挡土墙，边坡，地下水，渗流，非饱和土，反滤，淤堵，通水能力系数

ABSTRACT

Drainage  system is all important part of highway engineering，and subsurface drainage system  including underground drainage，median separator drainage，retaining wall drainage and slope drainage is important in  ensuring the performance and life of highway．However，current drainage design method and traditional drainage material  can’t satisfy the requirement of complex terra and climate condition．The two main topics of the  dissertation is the improvement of the drainage design theory and the analyse  of the application technique of geosynthetics in highway drainage engineering．

The main  research work on the drainage design theory is as follow：

(1) Based on  the current design theory，underground drainage method is expanded all improved greatly．After analyzing the  limitation of the calculating method for underdrain，it is developed for underdrain  in complicated geology or terrain，especially when the underdrain is located in aquifer and the  bedrock is not even．Moreover，the close underdrain is introduced with the main structure，construction technique and  calculating method．Then，the  representative drainage problems of highway engineering in low-lying  flatterrain are summarized and the resolvent is put forward considering the terrain  characteristic．Afterward，the drainage calculating  theory and method on retaining wall and slope is developed．It is indicated that the  calculating method for retaining wall with stable seepage is same as underdrain  drainage and the unsaturated seepage is the main problem of retaining wall  drainage．

(2) The  subsurface drainage problems in highway engineering are analyzed with numerical  method-FEM seepage，especially the calculating zone is anomalistic and the boundary  condition is difficult to expressed with mathematics equation，such as unfull underdrain，the underdrain is located in  aquifer and the bedrock is not even．

(3) Based on unsaturated  soil mechanics，the  highway drainage design method considering unsaturated seepage is developed．Several typical underdrains  are analyzed by unsaturated seepage FEM and the result is compared with that  from the existing method．Without considering the unsaturated seepage，the existing method  underestimates the flux of seepage which is validated by a true project．

The main  research work on the application technique of geosynthetics in highway  drainage engineering is as follow：

(1)  The key performance  indexes are tested by a great deal of indoor experiments and the test methods  are validated at the same time．Then some new indexes ale put forward．The emphases of the research  is about the design indexes of geotextile filter(such as equivalent pore size，coefficient of permeability  and gradient ratio)，the influence of geomembrance damage to leakage and the drainage  ability index of geocomposite material．

(2)  The  classified index system of geosynthetics in highway wateproof and drainage  engineering was established．Thus，geosynthetic  materials were sorted in terms of product and application．Then the representative  construction format for geosynthetics application in highway drainage  engineering including underground drainage，retaining wall drainage，median separator drainage，edge drainage and slope  drainage Was introduced．Finally the systemic design method is formed．

In the end．the result from theory  research and indoor experiment is validated by several test sections of two  highways．

Keywords：Highway Engineering，Drainage，Design Theory，Geosynthetics，Underdrain，Retaining Wall，Slope，Seepage，Unsaturated Soil，Filtration，Clogging，Drainage Ability Coefficient