冲刷作用下水平承载单桩计算方法及承载特性
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摘要
考虑冲刷作用对桩基承载力的影响,传统设计常采用忽略最大冲刷深度以上土体效应且认为冲刷线下土体物理力学特性不变的方法,此简化方法忽略了局部冲刷坑的尺寸效应和桩周土体应力历史的变化,设计桩长冗余度较大。为了充分考虑现场实际情况,在Reese的研究基础上,基于修正的p-y曲线进行砂土中单桩水平承载力的理论推导,为了验证结果正确性,随后进行了相应室内模型试验,且同时利用LPILE软件进行了模拟计算。结果表明:基于桩端点极限土抗力不变原则计算的等效冲刷深度公式可靠,相应的p-y曲线导入LPILE中计算值与试验值的误差在13%~17%,能够较好模拟现场冲刷情况;随着冲刷深度增加,单桩基础水平承载能力减弱,自由长度增大,桩身最大弯矩增大而土抗力影响深度减小,最大弯矩位置向桩端移动;修正的p-y曲线考虑冲刷坑底以上土体的有利作用,最大水平承载力计算值与试验值误差为3.6%~6.0%,桩顶最大水平位移误差为13.9%~23.5%,最大弯矩误差为2.9%~4.4%,最大弯矩点位置误差为3.3%~7.7%。最后进行冲刷深度、冲刷坡角和冲刷宽度的参数敏感性分析,结果表明三者的影响程度依次下降,试验条件下,相比无冲刷工况,冲刷深度为15cm和30cm时,桩顶位移增幅高达51%和106%。相应试验进一步证实了冲刷作用对桩基承载力的重要影响和理论计算的正确性,可为工程设计提供参考。
The traditional method of investigating the effect of scouring on the foundation bearing capacity usually adopts an approach that removes the scoured soil above the maximum scour depth and assumes that the physical property of the subsoil remains unchanged.However,this method ignores the effect of the scouring hole size and the stress history around the foundation,leading tohigh redundancy of the pile length.The authors consider the effect of the size,and deduce the theoretical equation for the lateral bearing capacity of single pile based on the modified p-ycurves and the study by Reese.Then,simulation was carried out using LPILE and the results were compared with those obtained from model tests.The results show that the equivalent scour depth formula derived based on the principle of invariable ultimate soil resistance is reliable,and the relative error between the LPILE calculated value and the test value is 13%-17%,which indicates that the actual situation can be accurately predicted.As the scour depth increases,the lateral bearing capacity of the single pile weakens,the free length of the pile increases,and the maximum pile bending moment increases with increasing depth to the pile bottom.The modified p-y curves consider the beneficial effect of soil above the scour pit,and the relative errors between the calculated value and the test value for maximum lateral bearing capacity,pile top maximum lateral displacement,maximum moment,and pile depth of the maximum moment are3.6%-6.0%,13.9%-23.5%,2.9%-4.4%,and 3.3%-7.7%,respectively.The sensitivity of the scouring depth,scouring slope angle,and scouring width parameters were analyzed to determine their effects on the scouring hole and the validity of the theoretical equation;the results show that the impact of the three parameters decreased in turn,which can provide some reference for engineering design.
The traditional method of investigating the effect of scouring on the foundation bearing capacity usually adopts an approach that removes the scoured soil above the maximum scour depth and assumes that the physical property of the subsoil remains unchanged.However,this method ignores the effect of the scouring hole size and the stress history around the foundation,leading tohigh redundancy of the pile length.The authors consider the effect of the size,and deduce the theoretical equation for the lateral bearing capacity of single pile based on the modified p-ycurves and the study by Reese.Then,simulation was carried out using LPILE and the results were compared with those obtained from model tests.The results show that the equivalent scour depth formula derived based on the principle of invariable ultimate soil resistance is reliable,and the relative error between the LPILE calculated value and the test value is 13%-17%,which indicates that the actual situation can be accurately predicted.As the scour depth increases,the lateral bearing capacity of the single pile weakens,the free length of the pile increases,and the maximum pile bending moment increases with increasing depth to the pile bottom.The modified p-y curves consider the beneficial effect of soil above the scour pit,and the relative errors between the calculated value and the test value for maximum lateral bearing capacity,pile top maximum lateral displacement,maximum moment,and pile depth of the maximum moment are3.6%-6.0%,13.9%-23.5%,2.9%-4.4%,and 3.3%-7.7%,respectively.The sensitivity of the scouring depth,scouring slope angle,and scouring width parameters were analyzed to determine their effects on the scouring hole and the validity of the theoretical equation;the results show that the impact of the three parameters decreased in turn,which can provide some reference for engineering design.
引文
[1]PALMER H D.Wave Induced Scour on the Sea Floor[C]//Wiley.Civil Engineering in the Oceans.New York:Wiley,1969:703-716.
[2] REESE L C,WANG S T,LONG J H.Scour from Cyclic Lateral Loading of Pile[C]//Society of Petroleum Engineers. Offshore Technology Conference.Houston:Society of Petroleum Engineers,1989:395-402.
[3] KISHORE Y N,RAO S N,MANI J S.The Behavior of Laterally Loaded Piles Subjected to Scour in Marine Environment[J].KSCE Journal of Civil Engineering,2009,13(6):403-408.
[4] CHEN J W,KUO Y S,TSENG W C.The Required Embedded Length of Monopole Foundation with Respect to Scour[C]//ISOPE.Proceedings of the International Offshore and Polar Engineering Conference.Cupertino:ISOPE,2011:654-659.
[5] MOSTAFA Y E.Effect of Local and Global Scour on Lateral Response of Single Piles in Different Soil Conditions[J].Engineering,2012,4(6):297-306.
[6]汤虎.冲刷对海洋平台桩基水平承载性能影响的研究[D].武汉:武汉理工大学,2012.TANG Hu.Investigation of the Scouring Effect on Lateral Load Capability of Offshore Platform's Pile Foundation[D]. Wuhan:Wuhan University of Technology,2012.
[7] NI S H,HUANG Y H,LO K F.Numerical Investigation of the Scouring Effect on the Lateral Response of Piles in Sand[J].Journal of Performance of Constructed Facilities,2012,26(3):320-325.
[8]邵帅.局部冲刷影响下水中沉井基础的承载性能研究[D].成都:西南交通大学,2013.SHAO Shuai.Study on Bearing Capacity of Open Caisson Foundation in Water Under Local Scouring Effect[D].Chengdu:Southwest Jiaotong University,2013.
[9] LIN C.Evaluation of Lateral Behavior of Pile-supported Bridges Under Scour Conditions[D].Wichita:University of Kansas,2012.
[10] LIN C,BENNETT C,PARSONS R L.Analysis of Laterally Loaded Piles in Sand Considering Scour Hole Dimensions[J].Journal of Geotechnical&Geoenvironmental Engineering,2014,140(6):1-13.
[11] LIN C,HAN J,BENNETT C,et al.Behavior of Laterally Loaded Piles Under Scour Conditions Considering the Stress History of Undrained Soft Clay[J].Journal of Geotechnical&Geoenvironmental Engineering,2014,140(6):06014005.
[12] LIN C,BENNETT C,PARSONS R L.Scour Effects on the Response of Laterally Loaded Piles Considering Stress History of Sand[J].Computers and Geotechnics,2010,37(7/8):1008-1014.
[13] LI F,HAN J,LIN C.Effect of Scour on the Behavior of Laterally Loaded Single Piles in Marine Clay[J].Marine Georesources&Geotechnology,2013,31(3):271-289.
[14] LI F,HU D,YAN R J.Research on the Lateral Load Capacity of Offshore Platform Piles Under Scour Conditions[C]//ASCE.Second International Conference on Transportation. Reston:ASCE,2013:2228-2234.
[15]马殿滨,李志刚,段梦兰,等.冲刷后地基土体特性及平台桩基承载力研究[J].石油机械,2012,40(6):54-58.MA Dian-bin,LI Zhi-gang,DUAN Meng-lan,et al.Research on Foundation Soil Mass Property After Erosion and Bearing Capacity of Platform Pile Foundation[J].China Petroleum Machinery,2012,40(6):54-58.
[16]杨晓峰,张陈蓉,黄茂松,等.砂土中单桩基础冲刷的修正应变楔计算[J].地震工程学报,2016,38(4):549-553.YANG Xiao-feng,ZHANG Chen-rong, HUANG Mao-song,et al.Modified Strain Wedge Calculation of Single Pile in Sand Under Scour[J].China Earthquake Engineering Journal,2016,38(4):549-553.
[17]杨晓峰,张陈蓉,袁聚云.砂土中考虑冲刷的水平受荷桩等效应变楔方法[J].岩土力学,2015,36(10):2946-2950.YANG Xiao-feng,ZHANG Chen-rong,YUAN Juyun.Equivalent-strain Wedge Method for Laterally Loaded Pile in Sand Considering Scouring Effect[J].Rock and Soil Mechanics,2015,36(10):2946-2950.
[18]杨晓峰,张陈蓉,黄茂松,等.砂土中桩土侧向相互作用的应变楔模型修正[J].岩土力学,2016,37(10):2877-2884.YANG Xiao-feng,ZHANG Chen-rong, HUANG Mao-song,et al. Modification of Strain Wedge Method for Lateral Soil-pile Interaction in Sand[J].Rock and Soil Mechanics,2016,37(10):2877-2884.
[19]史佩栋.桩基工程手册[M].北京:人民交通出版社,2008.SHI Pei-dong.Pile and Pile Foundation Handbook[M].Beijing:China Communications Press,2008.
[20]张忠苗.桩基工程[M].北京:中国建筑工业出版社,2007.ZHANG Zhong-miao.Pile Foundation Engineering[M]. Beijing:China Architecture and Building Press,2007.
[21] REESE L C,COX W R,KOOP F D.Analysis of Laterally Loaded Piles in Sand[C]//Society of Petroleum Engineers.Offshore Technology.Houston:Society of Petroleum Engineers,1974:473-485.
[22] RICHARDSON E V,DAVIS S R.Evaluating Scour at Bridges[R].Washington DC:FHWA,1995.
[2] REESE L C,WANG S T,LONG J H.Scour from Cyclic Lateral Loading of Pile[C]//Society of Petroleum Engineers. Offshore Technology Conference.Houston:Society of Petroleum Engineers,1989:395-402.
[3] KISHORE Y N,RAO S N,MANI J S.The Behavior of Laterally Loaded Piles Subjected to Scour in Marine Environment[J].KSCE Journal of Civil Engineering,2009,13(6):403-408.
[4] CHEN J W,KUO Y S,TSENG W C.The Required Embedded Length of Monopole Foundation with Respect to Scour[C]//ISOPE.Proceedings of the International Offshore and Polar Engineering Conference.Cupertino:ISOPE,2011:654-659.
[5] MOSTAFA Y E.Effect of Local and Global Scour on Lateral Response of Single Piles in Different Soil Conditions[J].Engineering,2012,4(6):297-306.
[6]汤虎.冲刷对海洋平台桩基水平承载性能影响的研究[D].武汉:武汉理工大学,2012.TANG Hu.Investigation of the Scouring Effect on Lateral Load Capability of Offshore Platform's Pile Foundation[D]. Wuhan:Wuhan University of Technology,2012.
[7] NI S H,HUANG Y H,LO K F.Numerical Investigation of the Scouring Effect on the Lateral Response of Piles in Sand[J].Journal of Performance of Constructed Facilities,2012,26(3):320-325.
[8]邵帅.局部冲刷影响下水中沉井基础的承载性能研究[D].成都:西南交通大学,2013.SHAO Shuai.Study on Bearing Capacity of Open Caisson Foundation in Water Under Local Scouring Effect[D].Chengdu:Southwest Jiaotong University,2013.
[9] LIN C.Evaluation of Lateral Behavior of Pile-supported Bridges Under Scour Conditions[D].Wichita:University of Kansas,2012.
[10] LIN C,BENNETT C,PARSONS R L.Analysis of Laterally Loaded Piles in Sand Considering Scour Hole Dimensions[J].Journal of Geotechnical&Geoenvironmental Engineering,2014,140(6):1-13.
[11] LIN C,HAN J,BENNETT C,et al.Behavior of Laterally Loaded Piles Under Scour Conditions Considering the Stress History of Undrained Soft Clay[J].Journal of Geotechnical&Geoenvironmental Engineering,2014,140(6):06014005.
[12] LIN C,BENNETT C,PARSONS R L.Scour Effects on the Response of Laterally Loaded Piles Considering Stress History of Sand[J].Computers and Geotechnics,2010,37(7/8):1008-1014.
[13] LI F,HAN J,LIN C.Effect of Scour on the Behavior of Laterally Loaded Single Piles in Marine Clay[J].Marine Georesources&Geotechnology,2013,31(3):271-289.
[14] LI F,HU D,YAN R J.Research on the Lateral Load Capacity of Offshore Platform Piles Under Scour Conditions[C]//ASCE.Second International Conference on Transportation. Reston:ASCE,2013:2228-2234.
[15]马殿滨,李志刚,段梦兰,等.冲刷后地基土体特性及平台桩基承载力研究[J].石油机械,2012,40(6):54-58.MA Dian-bin,LI Zhi-gang,DUAN Meng-lan,et al.Research on Foundation Soil Mass Property After Erosion and Bearing Capacity of Platform Pile Foundation[J].China Petroleum Machinery,2012,40(6):54-58.
[16]杨晓峰,张陈蓉,黄茂松,等.砂土中单桩基础冲刷的修正应变楔计算[J].地震工程学报,2016,38(4):549-553.YANG Xiao-feng,ZHANG Chen-rong, HUANG Mao-song,et al.Modified Strain Wedge Calculation of Single Pile in Sand Under Scour[J].China Earthquake Engineering Journal,2016,38(4):549-553.
[17]杨晓峰,张陈蓉,袁聚云.砂土中考虑冲刷的水平受荷桩等效应变楔方法[J].岩土力学,2015,36(10):2946-2950.YANG Xiao-feng,ZHANG Chen-rong,YUAN Juyun.Equivalent-strain Wedge Method for Laterally Loaded Pile in Sand Considering Scouring Effect[J].Rock and Soil Mechanics,2015,36(10):2946-2950.
[18]杨晓峰,张陈蓉,黄茂松,等.砂土中桩土侧向相互作用的应变楔模型修正[J].岩土力学,2016,37(10):2877-2884.YANG Xiao-feng,ZHANG Chen-rong, HUANG Mao-song,et al. Modification of Strain Wedge Method for Lateral Soil-pile Interaction in Sand[J].Rock and Soil Mechanics,2016,37(10):2877-2884.
[19]史佩栋.桩基工程手册[M].北京:人民交通出版社,2008.SHI Pei-dong.Pile and Pile Foundation Handbook[M].Beijing:China Communications Press,2008.
[20]张忠苗.桩基工程[M].北京:中国建筑工业出版社,2007.ZHANG Zhong-miao.Pile Foundation Engineering[M]. Beijing:China Architecture and Building Press,2007.
[21] REESE L C,COX W R,KOOP F D.Analysis of Laterally Loaded Piles in Sand[C]//Society of Petroleum Engineers.Offshore Technology.Houston:Society of Petroleum Engineers,1974:473-485.
[22] RICHARDSON E V,DAVIS S R.Evaluating Scour at Bridges[R].Washington DC:FHWA,1995.