摘要
在膨胀土边坡工程中,国内铁道、公路、水利等部门曾多采用土钉墙、重力式挡土墙和抗滑桩三大加固措施,并采取短锚杆喷射混凝土和浆砌片石等全封闭措施对路堑边坡进行坡面防护,但工程处治的实际效果是刚性支护结构发生破坏的现象屡见不鲜。为进一步探讨刚性挡土墙是否适合支护膨胀土边坡,本文针对墙体绕基底转动的变位模式,尝试开展了以下分析研究:
第一,完成了广西百色膨胀土样的室内固结快剪、膨胀力及固结试验,确定了土样的相关力学指标,建立了膨胀力与起始含水率、膨胀变形量的关系,为推导土压力公式和开展数字分析做好准备。
第二,基于对已有研究成果及室内试验结果分析,将膨胀力沿墙背土层深度变化的量化式引入土压力水平层分析法中,推导了挡墙土压力公式;并编写matlab程序进行计算,获得土体增湿后的土压力大小、土压力作用点高度及其随墙顶位移的变化;根据墙身稳定要求,反算不同墙顶位移下考虑膨胀力作用时墙身所需截面尺寸,并与正常填土挡墙的算例进行对比,获得刚性墙支护膨胀土适用性的量化指标:填土初始含水率较小且增湿后,土压力显著增大,其作用点位置也明显升高;若挡墙静止,较正常填土墙顶宽需增大2.6倍才能维持墙身稳定;墙顶位移量需15cm时膨胀力作用才完全消散;
第三,运用FLAC软件的热、力学耦合分析功能,用材料温度场等效模拟土体湿度场,考虑大气影响深度范围内膨胀土体的增湿条件,对比分析了土体增湿前后墙与土体间的相互作用,数值模拟结果也表明:土体增湿后土压力强度峰值明显增大,挡土墙和墙后土体产生显著的侧向位移,需很大限度地增大截面尺寸才能保证膨胀土挡墙的稳定。因此,从安全和经济性考虑,刚性挡墙不适合支护膨胀土堑坡。
最后,运用灰色局势决策理论分析了柔性支护、刚性支护及刚柔结合三种膨胀土堑坡处治方案的优劣性,对比工程成本、施工难易及生态环保等指标,得出柔性支护处治膨胀土堑坡为最佳方案,刚性支护方案最差。
In the slope project of expansive soils, although reinforcement measures including soil nailing wall、gravity retaining wall and anti-slide pile and major protective measures including full closed short bolt shotcrete and mortar flag stone for expansive soil slope reinforcement and protection were used by the departments at home and abroad including railway、highway and water conservancy, the failure phenomena of rigid protection in practical project.For investigating the expansive soil slope supported by rigid retaining walls, according to movement modes of expansive soil retaining walls rotated basement, the paper analyzed as follows:
Firstly, the samples correlated mechanical properties were determined by the consolidated quick shear test、expansive force test and consolidation test the Bai-se expansive soil of the Bai-se expansive soil. And then, the variation relationships of the expansive force with initial water content and expansive deformation were established to the derivation of earth pressure formulas and numerical analysis.
Secondly, the mathematical expression of the variation relationship between the expansive force and depth of soil layer in the climate influenced layer was proposed by summarizing the result of the laboratory test and existing research results. Then, the mathematical expression was introduced to deduce the calculation formula of the soil pressure of expansive soil retaining walls in the rigid retaining walls horizontal layer analysis method, the calculation program of Matlab was compiled to analyze the value of earth pressure、height of earth pressure acted point and the variation of wall displacement resulting from the expansive soil after moistening. According to the stability requirements of the retaining wall, the wall body section size under the expansive force in the different of wall displacement was reverse calculated, and the quantitative indexes of applicability analysis of expansive soil retaining walls were obtained by comparing with wall body section size without expansive force. The test results are showed that the earth pressure acted point rose markedly with the earth pressure increasing after expansive soils water content was less humidifying. When the expansive soil retaining walls was stationary, the wall body section size were needed to increase 2.6 times for the retaining walls stability, and only the deflection on the top of wall reaching 15cm the expansive action would be completely dissipated.
Thirdiy, according to the material temperature field equivalent simulated the soil humidity field of FLAC, and the expansive soil humidifying conditions in the climate influenced layer was considered, the interaction between the soil and the retaining wall was comparative analysis. the numerical simulation results are showed the earth pressure rose markedly in the climate influenced layer after moistening, and the remarkable lateral displacement was produced between the retaining walls and the soils behind retaining wall. Considering the security and the project costiy, the rigid retaining wall is unsuitable to support the expansive soil slope.
Finally, the advantages and disadvantages of expansive soil slope treatment program such as flexible supporting and rigid and rigid-flexible support were analyzed by gray theory, In considering the project cost, difficulty of construction and ecological protection, compared the flexible support is the best way of treating expansive soil slope, rigid support is the worst.
引文
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[1]交通部西部膨胀土项目课题组.膨胀土地区公路修筑成套技术研究总报告.长沙:长沙理工大学,2007,11
[2]交通部西部膨胀土项目课题组.西部地区膨胀土路基工程典型案例的调研与分析报告.长沙:长沙理工大学,2006,12
[3]罗强、蔡英、邵启毫.成都粘土重力式挡土墙的工程试验.西南交通大学学报1995(6):270~274
[4]陈义深.裂土地区挡土墙承受的土压力.路基工程.1988,(21)
[5]顾慰慈,挡土墙土压力计算手册.北京:中国建材工业出版社,2004年
[6]窦斌,梅利芳等.无连接挡板高填方路堤薄壁挡土墙土压力模型试验研究.公路交通科技,2004,12(12),27~33
[7]刘超,宋飞等.各向异性砂土主动土压力的离心模型试验研究.岩石力学与工程学报,2009,5(28),3201~3206
[8]王年香,章为民,顾行文等.膨胀土挡墙侧向膨胀压力研究.水利学报,2008,39:580~587
[9]张颖钧.裂土挡土墙模型试验缓冲层设置的研究.岩土工程学报1995(1):38~45
[10] FANG Y S, ISHIBASHI I. Static earth pressure with various wall movements[J]. Journal of Geotechnical Engineering,1986,112(3):317~333
[11] Clayton C R I,Symons I F,Hiedra-Cobo. The pressure of clay backfill against retaining structures. Canadian Geotechnical Journal,1991,28(4):282~297
[12] Nakai, T. Finite element computations for active and passive earth pressure problems of retaining wall.Soils and Foundations,1985 (3):99~112
[13]吴顺从,金爱兵等.车辆荷载下路基挡土结构失稳机理数值模拟.岩土力学,2007,2(28),258~262
[14]廖文周.刚性挡土墙支护膨胀土边坡的适用性探讨[长沙理工大学硕士论文].长沙:长沙理工大学,2009
[15]邓子胜,邹银生等.考虑位移非线性影响的挡土墙土压力计算模型研究.中国公路学报,2004,17(2),24~27
[16]宰金珉,梅国雄.考虑位移的土压力模型研究.南京建筑工程学院学报,2001,1,9~19
[17]王元占,黄长虹.关于挡土墙主动土压力计算问题.港工技术,2003,NO.2,22~27
[18]王元占,王海龙等.挡土墙土压力分布.中国港湾建设,2000,4,1~5
[19]王元占,李新国等.挡土墙主动土压力分布与侧压力系数.岩土力学,2005,26(7),1019~1022
[20]王元占,李蔚等.墙体绕基础转动情况下挡土墙主动土压力分布.岩土工程学报,2003,25(2),208~211
[21]王元占,唐照评等.墙体绕墙顶转动情况下挡土墙主动土压力分布.应用数学和力学,2004,25(7),695~699
[22]龚慈,俞建霖等.绕墙底向外转动刚性挡土墙的土压力计算.浙江大学学报,2005,39(11),1690~1694
[23]张刚,孔亮等.考虑平动位移效应的黏性填土挡土墙土压力计算.宁夏大学学报,2008,29(4),325~328
[24]徐日庆,龚慈等.考虑平动位移效应的刚性挡土墙土压力理论.浙江大学学报,2005,39(1),119~122
[25]张颖钧.裂土挡墙的土压力分布.中国土木学会第七届土力学与基础工程学术会议论文集.北京:中国建筑工业出版社,1994.254~257
[26] Pufahl D E, Fredlund D G, Ranardjo H. Lateral earth pressures in expansive clay soils[J]. Canadian Geotechnical Journal, 1983, 20:228~241
[27]徐永福,刘松玉.非饱和土强度理论及其工程应用.南京:东南大学出版社,1999