地下水路堑段槽型挡土墙设计若干问题的探讨
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摘要
对于地下水路堑段槽型挡土墙,铁路设计人员一般采用边墙简化为悬臂梁、底板简化为弹性地基梁的结构计算模型。一个整体结构简化为两个分离的构件,计算模型本身存在一定的缺陷,一些设计者对此不甚了解;在边墙土压力计算理论的选择、边墙外侧活荷载侧压力的计算、抗浮措施的确定、抗浮稳定安全系数的选取、地基压缩模量的选用等方面也存在疑惑。通过多个荷载组合工况的内力及位移计算,结合国内外标准的有关规定,探讨了结构计算模型的合理性以及弥补其缺陷的措施,提出了设计参数选取的优先方向,得出如下结论:在地下水位较高时,弹性地基梁链杆出现负反力是其最大的缺陷;边墙位移小于产生主动土压力所需位移,土压力计算采用静止土压力更为合理,同时可以减小链杆负反力,弥补弹性地基梁模型缺陷;边墙外侧活荷载宜按非主可变荷载单独计算其侧压力,不宜合并入土压力;抗浮优先考虑底板外延方式;抗浮系数在限制结构重要性系数不小于1.0的条件下取1.05;弹性地基梁模型对地基压缩模量取值不敏感。
For groove retaining wall in groundwater cutting section, railway designers usually simplify the side wall to cantilever beam and the floor to elastic foundation beam. On one side, a whole structure is simplified into two separate members, it must has some defects, which some designers do not know much about; on the other hand, there are doubts in other aspects, such as the selection of calculation model of soil pressure on side wall, the calculation of lateral pressure on side wall under live load, the determination of anti-floating measures, the selection of safety factor of anti-floating stability, and the selection of compressive modulus of foundation. Based on the calculation of internal forces and displacements under multiple load combinations, and the relevant provisions of domestic and foreign standards, this paper discusses the rationality of the calculation model and the measures to remedy its defects, puts forward the priority direction of selecting design parameters, and draws the following conclusions: when the groundwater level is high, the negative reaction of the elastic foundation beam chain rod is the biggest defect; displacement of side wall is less than that needed to produce active soil pressure, so it is more reasonable to calculate static soil pressure, at the same time, the loading of static soil pressure can reduce negative chain reaction and make up for the defects of the elastic foundation beam model; lateral live load of side wall should be calculated separately according to non-principal variable load, and it is not suitable to merge into earth pressure; base plate extension is prioritized for floating resistance; floating resistance coefficient of 1.05 is taken when the structural importance coefficient is not less than 1.0; the elastic foundation beam model is not sensitive to the value of compressive modulus of foundation.
For groove retaining wall in groundwater cutting section, railway designers usually simplify the side wall to cantilever beam and the floor to elastic foundation beam. On one side, a whole structure is simplified into two separate members, it must has some defects, which some designers do not know much about; on the other hand, there are doubts in other aspects, such as the selection of calculation model of soil pressure on side wall, the calculation of lateral pressure on side wall under live load, the determination of anti-floating measures, the selection of safety factor of anti-floating stability, and the selection of compressive modulus of foundation. Based on the calculation of internal forces and displacements under multiple load combinations, and the relevant provisions of domestic and foreign standards, this paper discusses the rationality of the calculation model and the measures to remedy its defects, puts forward the priority direction of selecting design parameters, and draws the following conclusions: when the groundwater level is high, the negative reaction of the elastic foundation beam chain rod is the biggest defect; displacement of side wall is less than that needed to produce active soil pressure, so it is more reasonable to calculate static soil pressure, at the same time, the loading of static soil pressure can reduce negative chain reaction and make up for the defects of the elastic foundation beam model; lateral live load of side wall should be calculated separately according to non-principal variable load, and it is not suitable to merge into earth pressure; base plate extension is prioritized for floating resistance; floating resistance coefficient of 1.05 is taken when the structural importance coefficient is not less than 1.0; the elastic foundation beam model is not sensitive to the value of compressive modulus of foundation.
引文
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[2] 孙爱斌,吴连海.天津某封闭式路堑U型槽结构的设计与计算[J].铁道工程学报,2006,97(7):49-53.
[3] 丁兆锋,吴沛沛.U型槽结构设计与分析[J].铁道工程学报,2009,127(4):13-16.
[4] European Committee for Standardazation. Eurocode 7-BS EN1997 Geotechnical design[S]. Brussels: CEN/TC250, 2004.
[5] Canadian Geotechnical Society. 4thEditionCanadian Foundation Engineering Manual[S]. Richmond, BC: BiTech Publishers Ltd. 2006.
[6] 中华人民共和国交通运输部.公路路基设计规范:JTG D30—2015[S].北京:人民交通出版社股份有限公司,2015.
[7] 中华人民共和国铁道部.铁路路基支挡结构设计规范:TB 10025—2006/J127—2006[S].北京:中国铁道出版社,2009.
[8] 蔡四维.弹性地基梁解法[M].上海:上海科学技术出版社,1962.
[9] 铁道部第一勘测设计院.铁路工程设计技术手册·路基[M].修订版.北京:中国铁道出版社,1995.
[10] 龚晓南.土力学[M].北京:中国建筑工业出版社,2002.
[11] 李广信.土力学[M].4版.北京:清华大学出版社,2014.
[12] 中国铁路总公司.铁路路基设计规范(极限状态法):Q/CR9127—2018[S].北京:中国铁道出版社,2018.
[13] 刘昌清,罗一农,魏永幸.基于极限状态设计法的重力式挡墙设计研究[J].铁道工程学报,2014(9):30-34.
[14] Hartmut Freystein, Martin Muncke, Peter Sehollmeier.德国铁路基础设施设计手册[M].北京:中国铁道出版社,2007.
[15] 刘少飞.重力式支挡结构的荷载图式研究[D].成都:西南交通大学,2010.
[16] 郑伟国.地下结构抗浮设计的思路和建议[J].建筑结构,2013,43(5):88-91.
[17] 朱叔平.关于深基础施工中的抗浮问题[J].建筑技术,1998,29(3):181-182.
[18] 中华人民共和国住房和城乡建设部.地铁设计规范:GB50157—2013[S].北京:中国建筑工业出版社,2013.
[19] 广东省住房和城乡建设厅.建筑地基基础设计规范:DBJ 15—31—2016[S].北京:中国建筑工业出版社,2017.
[20] 中国工程建设标准化协会.给水排水工程钢筋混凝土水池结构设计规程:CECS138—2002[S].北京:中国建筑工业出版社,2012.