考虑基岩水平破坏的嵌岩桩嵌岩深度计算方法
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摘要
为了准确计算嵌岩桩的嵌固深度,既要考虑桩侧岩石的破坏特征,还应考虑基岩顶面水平力和弯矩的共同作用。根据嵌岩桩嵌岩段桩侧岩石的水平极限承载特性,建立了嵌岩桩嵌岩深度计算的简化分析模型,并基于Hoek–Brown强度准则和静力平衡原理,推导了考虑基岩顶面水平力和弯矩共同作用的嵌岩桩嵌岩深度理论计算公式。算例对比分析发现,通过理论公式计算得到的嵌岩深度值与规范方法的结果更为接近。在此基础上探讨了基岩顶面处水平荷载、桩径、桩侧岩石抗压强度、岩石质量分类指标对嵌岩桩嵌固深度的影响,计算结果表明:嵌岩深度随水平力增加近似呈现线性关系增大,随弯矩增加呈现非线性关系增大,而随桩径、岩石单轴抗压强度及岩体地质力学分类指标RMR增加呈现非线性关系减小。保持其他条件相同,当桩径由1.0 m增大到2.0 m和3.0 m时,对应的最小嵌岩深度约分别减小32%和44%;当岩石单轴抗压强度由15 MPa增加到30、45和60 MPa时,对应的最小嵌岩深度分别减小44.4%、59.7%及67.6%;当岩体地质力学分类指标RMR值由30增加到45、60和75时,对应的最小嵌岩深度分别减小48.9%、72.3%及84.2%。与岩石单轴抗压强度相比,岩体地质力学分类指标RMR对嵌岩深度的影响更为显著,当RMR值大于85时,嵌岩深度不足1.0 m。实际工程设计时,应综合考虑岩石的强度、质量以及桩径等方面以确定嵌岩桩的最佳嵌岩深度。
In order to calculate the rock-socketed depth of rock-socketed piles, the failure characteristics of rock outside piles and the horizontal force and bending moment on the top of bedrock should be taken into account. According to horizontal ultimate bearing characteristics of rocksocketed pile, a simplified analysis model of rock-socketed depth calculation was established. Based on the Hoek–Brown strength criterion and static balance principle, a theoretical calculation formula of rock-socketed depth of rock-socketed piles was deduced with the consideration of horizontal force and bending moment at the top of bedrock. Comparison and analysis of an engineering example showed that values of rock-socketed depth calculated by theoretical formulas are closer to the method of codes. And then the influences of horizontal load, pile diameter, rock uniaxial compressive strength and rock mass rating index RMR on rock-socketed depths were discussed. The results showed that the rock-socketed depth increases linearly with the increase of horizontal force, non-linearly with the increase of bending moment, and decreases non-linearly with the increase of pile diameter, rock uniaxial compressive strength and rock mass rating index RMR. At the same condition, when pile diameter increases from 1.0 m to 2.0 m and 3.0 m, rock-socketed depth decreases by 32% and 44%, respectively. When rock uniaxial compressive strength increases from 15 MPa to 30, 45 and 60 MPa, rock-socketed depth reduces by 44.4%, 59.7% and 67.6%, respectively. When the value of rock mass rating index RMR increases from 30 to 45, 60 and 75, rock-socketed depth reduces by 48.9%, 72.3% and 84.2%, respectively. Rock mass rating index RMR has a significant effect on rock-socketed depth. If the value of rock mass rating index RMR is more than 85, the rock-socketed depth will less than 1.0 m. When determining the optimum rock-socketed depth of actual rock socketed piles, the strength and quality of rocks and pile diameters should be considered comprehensively.
In order to calculate the rock-socketed depth of rock-socketed piles, the failure characteristics of rock outside piles and the horizontal force and bending moment on the top of bedrock should be taken into account. According to horizontal ultimate bearing characteristics of rocksocketed pile, a simplified analysis model of rock-socketed depth calculation was established. Based on the Hoek–Brown strength criterion and static balance principle, a theoretical calculation formula of rock-socketed depth of rock-socketed piles was deduced with the consideration of horizontal force and bending moment at the top of bedrock. Comparison and analysis of an engineering example showed that values of rock-socketed depth calculated by theoretical formulas are closer to the method of codes. And then the influences of horizontal load, pile diameter, rock uniaxial compressive strength and rock mass rating index RMR on rock-socketed depths were discussed. The results showed that the rock-socketed depth increases linearly with the increase of horizontal force, non-linearly with the increase of bending moment, and decreases non-linearly with the increase of pile diameter, rock uniaxial compressive strength and rock mass rating index RMR. At the same condition, when pile diameter increases from 1.0 m to 2.0 m and 3.0 m, rock-socketed depth decreases by 32% and 44%, respectively. When rock uniaxial compressive strength increases from 15 MPa to 30, 45 and 60 MPa, rock-socketed depth reduces by 44.4%, 59.7% and 67.6%, respectively. When the value of rock mass rating index RMR increases from 30 to 45, 60 and 75, rock-socketed depth reduces by 48.9%, 72.3% and 84.2%, respectively. Rock mass rating index RMR has a significant effect on rock-socketed depth. If the value of rock mass rating index RMR is more than 85, the rock-socketed depth will less than 1.0 m. When determining the optimum rock-socketed depth of actual rock socketed piles, the strength and quality of rocks and pile diameters should be considered comprehensively.
引文
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[9]Lei Yong,Zhao Minghua,Ma Binhui.Calculation method of socketed length of rock socketed pile based on requirement of pile top settlement[J].Journal of Highway and Transportation Research and Development,2011,28(5):86-91.[雷勇,赵明华,马缤辉.按桩顶沉降控制的嵌岩桩嵌岩深度计算方法[J].公路交通科技,2011,28(5):86-91.]
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[11]Zhao Minghua,Zhang Ling,Liu Jianhua.Calculation method for socketed length of rock-socketed pile[J].Central South Highway Engineering,2007,32(1):1-4.[赵明华,张玲,刘建华.公路桥梁嵌岩桩嵌岩深度计算[J].中南公路工程,2007,32(1):1-4.]
[12]Zhao Minghua,Feng Mingwei,Liu Meng,et al.A method to calculate socketed depth of large diameter rock socketed piles in soft rock ground[J].Advances in Science and Technology of Water Resources,2015,35(1):73-77.[赵明华,冯明伟,刘猛,等.大直径软岩嵌岩桩嵌岩深度计算模型[J].水利水电科技进展,2015,35(1):73-77.]
[13]Lei Yong,Liu Ze.A calculation method for rock-socketed depth of highway bridge pile based on Hoek-Brown strength criterion[J].Rock and Soil Mechanics,2015,36(2):457-462.[雷勇,刘泽.基于H-B准则的公路桥梁基桩嵌岩深度计算[J].岩土力学,2015,36(2):457-462.]
[14]Hock E,Brown E T.Empirical strength criterion for rock masses[J].Journal of Geotechnical Engineering Division ASCE,1980,106(GT9):1013-1035.
[15]You Mingqing.Study of mathematical equation and parameter determination of strength criteria for rock[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(11):2172-2184.[尤明庆.岩石强度准则的数学形式和参数确定的研究[J].岩石力学与工程学报,2010,29(11):2172-2184.]
[16]公路桥涵地基与基础设计规范:JTG D63-2007[S].北京:人民交通出版社,2007.
[2]Lyu Yaru,Liu Hanlong,Wang Xinquan,et al.A modified Geddes solution for estimating induced stress coefficient of subsoil and settlement of pile foundation[J].Journal of Sichuan University(Engineering Science Edition),2013,45(2):68-74.[吕亚茹,刘汉龙,王新泉,等.地基附加应力和桩基沉降计算的修正Geddes应力解[J].四川大学学报(工程科学版),2013,45(2):68-74.]
[3]Pells P J N,Turner R M.Elastic solutions for the design and analysis of rock-socketed piles[J].Canadian Geotechnical Journal,1979,16(3):481-487.
[4]Radhakrishnan R,Leung C F.Load transfer behavior of rock-socketed piles[J].Journal of Geotechnical Engineering,1989,115(6):755-768.
[5]Dai Guoliang,Gong Weiming,Chen Long.Modified method for shaft resistance of rock-socketed piles based on Hoek-Brown criterion[J].Chinese Journal of Geotechnical Engineering,2012,34(9):1746-1752.[戴国亮,龚维明,陈隆.基于Hoek-Brown准则嵌岩段桩-岩侧阻力修正计算方法[J].岩土工程学报,2012,34(9):1746-1752.]
[6]Xing H,Zhang Z,Meng M,et al.Centrifuge tests of superlarge-diameter rock-socketed piles and their bearing characteristics[J].Journal of Bridge Engineering,2014,19(6):4001-4010.
[7]Liu Shuya,Liu Zude.Issues on research and design of piles socketed in rock[J].Rock and Soil Mechanics,1999,20(4):86-92.[刘树亚,刘祖德.嵌岩桩理论研究和设计中的几个问题[J].岩土力学,1999,20(4):86-92.]
[8]Song Renqian,Zhang Zhongmiao.Study on socket length of rock-socketed piles in soft soil ground[J].Rock and Soil Mechanics,2003,24(6):1053-1056.[宋仁乾,张忠苗.软土地基中嵌岩桩嵌岩深度的研究[J].岩土力学,2003,24(6):1053-1056.]
[9]Lei Yong,Zhao Minghua,Ma Binhui.Calculation method of socketed length of rock socketed pile based on requirement of pile top settlement[J].Journal of Highway and Transportation Research and Development,2011,28(5):86-91.[雷勇,赵明华,马缤辉.按桩顶沉降控制的嵌岩桩嵌岩深度计算方法[J].公路交通科技,2011,28(5):86-91.]
[10]He Jie,Li Li,Feng Mingwei.The depth calculation of rocksocketed pile in weathered granite region[J].Highway Engineering,2012,37(6):11-13.[何杰,李力,冯明伟.风化花岗岩地区嵌岩桩嵌岩深度计算方法[J].公路工程,2012,37(6):11-13.]
[11]Zhao Minghua,Zhang Ling,Liu Jianhua.Calculation method for socketed length of rock-socketed pile[J].Central South Highway Engineering,2007,32(1):1-4.[赵明华,张玲,刘建华.公路桥梁嵌岩桩嵌岩深度计算[J].中南公路工程,2007,32(1):1-4.]
[12]Zhao Minghua,Feng Mingwei,Liu Meng,et al.A method to calculate socketed depth of large diameter rock socketed piles in soft rock ground[J].Advances in Science and Technology of Water Resources,2015,35(1):73-77.[赵明华,冯明伟,刘猛,等.大直径软岩嵌岩桩嵌岩深度计算模型[J].水利水电科技进展,2015,35(1):73-77.]
[13]Lei Yong,Liu Ze.A calculation method for rock-socketed depth of highway bridge pile based on Hoek-Brown strength criterion[J].Rock and Soil Mechanics,2015,36(2):457-462.[雷勇,刘泽.基于H-B准则的公路桥梁基桩嵌岩深度计算[J].岩土力学,2015,36(2):457-462.]
[14]Hock E,Brown E T.Empirical strength criterion for rock masses[J].Journal of Geotechnical Engineering Division ASCE,1980,106(GT9):1013-1035.
[15]You Mingqing.Study of mathematical equation and parameter determination of strength criteria for rock[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(11):2172-2184.[尤明庆.岩石强度准则的数学形式和参数确定的研究[J].岩石力学与工程学报,2010,29(11):2172-2184.]
[16]公路桥涵地基与基础设计规范:JTG D63-2007[S].北京:人民交通出版社,2007.