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桩拱组合式挡土墙及其简化设计方法研究

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  摘 要:桩板式挡土墙是山区道路工程建设中经常采用的一种支挡结构,由于抵抗水平荷载的需要,传统桩板式挡土墙结构桩和板的尺寸通常做得较大,桩体的布置较密,不经济。基于此,提出一种新的适用于山区道路的桩拱组合式挡土墙,利用拱结构受压性能较好的特点,采用拱板代替传统的平板,拱板与桩基础的上部连接,整体结构可以通过装配式或者现浇制作而成。基于土压力和桩基水平承载力理论,分别建立拱板主动土压力计算模型和抗滑桩计算模型,利用拱板荷载传递给桩基的基本原理,建立桩拱挡土墙整体结构的力学平衡方程,通过求解平衡方程获得桩拱挡土墙整体结构的极限承载力。通过参数分析,分别讨论了不同的桩体几何尺寸、拱板几何尺寸以及土体参数对桩拱组合式挡土墙极限承载力的影响,结果表明,增加矩形截面的长宽比、桩体嵌入深度、土体摩擦角等可以有效提高桩拱组合式挡土墙的极限荷载。
  关键词:挡土墙;理论模型;土压力;极限荷载
  中图分类号:TU476 文献标志码:A 文章编号:2096-6717(2020)01-0001-08
  Abstract:Sheet-pile retaining wall is a very common retaining structure is widely used in construction of mountain road. However, in order to resist the lateral load, conventional sheet-pile retaining wall is of relatively large size, which is less economical. Under this condition, a new pile-arching retaining wall, which is suitable for mountain road construction, is proposed in this study. Considering that the arch structure is of good compression performance, the arching plate is used to replace the conventional plate structure, and the arch plate is connected with the pile foundation. The whole structure could be prefabricated or constructed in the way of cast-in-place. Based on the theories of earth pressure and lateral loaded pile, computational models were proposed for the active earth pressure of arch plate and the anti-slide pile. Then, the theoretical model was validated by comparing the predictions with the numerical results. Subsequently, parametric studies were conducted to investigate the influence of the geometric parameters of pile, geometric parameters of arch plate and the soil parameters on the limit load of the new pile-arching retaining wall structure. The results show that increase of ratio of length to width of the rectangular pile cross section, the embedded depth of pile as well as the friction angle of soil could effectively improve the limit load of pile-arching retaining wall structure.
  Keywords:retaining wall; theoretical model; earth pressure; limit load
  第1期
  周航,等:樁拱组合式挡土墙及其简化设计方法研究
  山区道路由于地形、地质复杂,不可避免地会形成高路堑、高路堤,其边坡稳定性直接影响道路的使用功能。此外,山区道路修建常会遇到结构松散岩土体,极易产生山体滑坍地质灾害,给交通安全留下隐患。挡土墙作为一种常用的支挡结构,广泛应用于山区道路工程中路堤、路堑边坡的加固。工程中常用的挡土墙有重力式挡土墙[1-2]、衡重式挡土墙[3-4]、悬臂式挡土墙[5]、扶壁式挡土墙[6-7]、锚杆式挡土墙[8]、锚定板式挡土墙[9-10]、加筋土挡土墙[11-14]、土钉式挡墙[15-16]、桩板式挡土墙[17-20]等,另外,也有学者提出一些新颖的挡墙结构,如土砌体组合挡土墙[21]、纤维增强塑料土工格栅挡土墙[22]、椅式桩板挡土墙[23]、树根桩挡土墙[24-25]、H形砌块挡土墙[26]等。
  传统的重力式挡土墙、衡重式挡土墙、悬臂式挡土墙、扶壁式挡土墙、锚杆式挡土墙、锚定板式挡土墙只能适用于低路堑和路堤边坡的情况,对于高路堑和高路堤的边坡,不宜使用,而加筋挡土墙属于柔性支挡结构,墙体变形较大,而且对墙厚填筑料的要求比较高,不经济。桩板式挡墙适用范围较广,主要用于表层土及强风化层较薄的均匀岩石地基,挡土墙墙高可较大,因此,该支挡结构非常适合用于山区道路边坡加固。但是,传统的桩板式结构由于抵抗水平荷载的需要,桩和板的尺寸通常做得较大,桩体的布置较密,不经济。因此,笔者基于水利工程中常常采用的高拱坝结构原理,提出一种用于山区道路的桩拱组合式挡土墙结构(专利公开号:ZL201810122638.0)[27],将传统的桩板挡土墙中的平板构件换成拱板构件,利用拱板受压的优势大大减小了板件的厚度,节省了造价,同时,挡土墙的承载力不会降低。   主要针对桩拱组合式挡土墙这一新型支挡结构,开展设计计算方法和结构优化的研究,通过理论推导,提出桩拱组合式挡土墙的简化设计计算方法,为桩拱组合式挡土墙的现场应用提供理论依据。
  1 桩拱组合式挡土墙结构形式
  如图1所示,桩拱组合式挡土墙主要有拱形挡板和抗滑桩组成,拱形挡板的弧线可以采用半圆,也可以采用圆弧,抗滑桩采用矩形截面桩。桩拱组合式挡土墙根据不同施工方法可以分为装配式桩拱组合式挡土墙和现浇式桩拱组合式挡土墙两种。对于装配式桩拱组合式挡土墙,拱形挡板和矩形截面桩可以预制,预制矩形桩通过静压或者其他方式打入地基,预制拱板通过螺栓与预制矩形桩连接,拱板稍微嵌入土层即可。现浇式桩拱组合式挡土墙拱形挡板和矩形截面桩通过现场钻孔灌注现浇而成,前者的施工速度较快,后者的整体性能更好,可以视现场调节選择不同的形式。
  为了方便分析,定义矩形桩桩长为H、桩体悬臂长度为h,矩形桩体截面长为a、宽为b,相邻两桩的间距为s,拱板的厚度为d,拱板的横跨为2R(净跨)。
  2 理论模型
  桩拱组合式挡土墙主要包含拱板和矩形截面抗滑桩两部分,拱板的作用是将土压力传递给抗滑桩,因此,理论模型需要分别考虑拱板的稳定性以及抗滑桩的稳定性。理论模型分为拱板主动土压力理论模型和抗滑桩受力理论模型。
  4 结论与建议
  提出一种适用于山区道路的新型桩拱组合式挡土墙结构形式,并给出简化的设计计算方法,得到以下主要结论:
  1)基于土压力和桩基水平承载力理论,分别建立拱板主动土压力计算模型和抗滑桩计算模型,利用拱板荷载传递给桩基的基本原理,建立桩拱挡土墙整体结构的力学平衡方程,通过求解平衡方程获得桩拱挡土墙整体结构的极限承载力计算公式。
  2)通过参数分析,分别讨论了不同的桩体几何尺寸、拱板几何尺寸以及土体参数  对桩拱组合式挡土墙的极限承载力的影响,结果表明,增加矩形截面的长宽比、桩体嵌入深度、土体摩擦角等可以有效提高桩拱组合式挡土墙的极限荷载。
  3)未来可以考虑在以下几个方面继续开展研究:开展大比例模型试验或者现场试验研究,进一步检验并细化本文的设计方法;开展粘性土中桩拱组合式挡土墙结构稳定理论设计方法研究;开展水流侵蚀(水毁)以及地震动力荷载等条件下桩拱组合式挡土墙的稳定性研究;开展地震作用下桩拱连接处抗震性能设计研究(针对装配式桩拱组合式挡土墙结构)。
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