深基坑开挖地面位移的变化.doc

第 12 期 杨 敏，等. 基坑开挖引起的地面沉降估算 1837 第32卷 第12期 岩 土 工 程 学 报 Vol.32 No.12 2010年 .12月 Chinese Journal of Geotechnical Engineering Dec. 2010 Estimation of ground settlement aroused by deep excavation Yangmin 1,2, Suoyi Lu3(1. Key Laboratory of geotechnical and underground engineering, Tongji University; 2. Underground Department of Architecture and Engineering of Tongji University, Shanghai 200,092; 3. Changsha in Hunan Province Economic Development Zone Management Committee, Changsha, Hunan, 410,100)摘 要：基于 4 种不同的围护结构基本变形模式，对上海地区典型土层分布状况进行了多种工况下的基坑开挖数值模拟计算。计算结果发现，在 4 种不同的围护结构基本变形模式下，墙后最大沉降量和基坑围护结构最大侧向位移之间呈线性关系，墙后的地面沉降曲线呈明显的正态函数分布，并可拟合得到其正态函数曲线表达式。在此基础上，提出了基于围护结构变形模式的地面沉降估算方法。工程实例验证表明，该方法具有一定的实用性和可靠性，不失为一种方便实用的估算基坑开挖引起墙后地面沉降的方法。 关键词：基坑开挖；基坑变形；地面沉降；变形计算 中图分类号：TU463 文献标识码：A 文章编号：10004548(2010)12182108 作者简介：杨 敏(1960 )，男，博士，教授，博士生导师，主要从事岩土工程方面的教学与研究工作。E-mail: 。 Estimation of ground settlement aroused by deep excavation YANG Min1，2, LU Jun-yi3 (1. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China; 2. Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China; 3. Management Committee of Changsha National Economic & Technical Development Zone, Changsha 410100, China) Abstract: Based on four basic deformation modes of retaining structures, numerical simulations and calculations are carried out on deep excavations with typical soil layer distribution in Shanghai. The results show that the maximum ground settlement has a linear relationship with the maximum lateral wall deflection in the four basic deformation modes of the retaining structures. At the same time, the settlement curve shows a normal function distribution, and normal function expressions are obtained by fitting. Then, on this basis, an estimation method is proposed based on the four basic deformation modes of the retaining structures. The feasibility and reliability of the method is verified by two engineering examples and it proves to be a practical method for estimating ground settlement aroused by deep excavation. Key words: excavation; pit deformation; ground settlement; deformation calculation 0IntroductionAt present, the internal force and deformation of the retaining structure caused by Foundation Pit Excavation can get the practical application of beam Finite Element Method to Solve. And to the question of wall soil settlement caused by pit excavation ,the main method is numerical analysis and test statistics. In the area of measured by statistics, according to observation data of sheet pile and retaining structure in Oslo and Chicago, Peck has drawn relationship diagram of land subsidence behind pit wall and radial distance from the pit walls with massive experience. In Shanghai soft soil area, Lilin has collected a large amount of Foundation pit monitoring data , and he analyzed the relationship between excavation depth with maximum lateral deformation and locations of the retaining structure ,then he build this relationship between anti-Uplift safety factor with maximum lateral displacement and land subsidence out of pit walls of retaining structure .In numerical analysis ,according to 4 kinds of retaining structure ,Baijian Wang build a Numerical Analysis of Three - dimensional models ,which conduct a numerical simulation to land subsidence out of the pit walls with Mohr-Coulomb model and get a relation curve about the deformations of different retaining structure with land subsidence out of the pit walls .this paper are based on the research result of literature 5 and introduce Modified Cam-Clay Model studied typical distribution of soil in shanghai with 4 deformations of retaining structure to calculate the law of land settlement out of the pit walls and proposed a practical method of estimation of ground settlement induced by excavation .1. Simplification of retaining structure deformation By massive measured data, Goldberg and many believe that rigid enclosure structure would turn to inner of the pit around the wall-toe or top of the walls . theyre corresponding to the pictures 1(a),(b ),(c ) respectively ;However, the deformation of flexible envelopes is swollen to the inner of the pits, which is shown in the picture 1(d).Fig. 1 Deformation modes of retaining structures Any deformation pattern of retaining structure can be simplified to 4 kinds of basic deformation structure (pit walls ),there are walls shifting to inner pit, combined mode ,walls rotating to the inner pits around the walls-toe and swollen to the pits, walls shifting to the inner pits and rotating to the inner pits around the wall-toe ,walls shifting to the inner pits and rotating to the inner around the top of walls ,walls rotating to the inner pits round the walls-toes and swollen to the inner , they are correspond to the pic 1(e),(f), g），（h），（i）.The study of literature 5 shows that retaining structures settlement curve is a clearly regularity in the 4 kinds of basic deformations . then we can decompose any deformations into the 4 kinds of basic deformations ,and get the ground settlement regularity of the retaining structures which is outside of the pits walls .2.Ground settlement calculation of retaining structure deformation models out of the pit-walls 2.1 Calculation models (1)Modified Cambridge models Modified Cambridge models most popular elastoplastic models ever used in the field of soil mechanics calculation . The outcome is stable ,simple and regularly ,few the arguments that needed is and especially apply to soil of soft clay . Here is the yield equation and the yield track respectively as it shown in pic 2.(1+q2/M2p2)p = p0 (2)Boundary Condition Zero offset in the models front and back ,right and left. The upper surface are free , bottom surface and horizontal offset are fixed.(3) The calculation models assumption : The fourth deformation pattern of retaining structure are simplified to parabolic form , the apex of this parabolic line is right on the excavation surface . No consideration of underground water in the calculation . No consideration of influence of the bottom swollen to the land settlement . Fig. 2 Yield locus of modified Cam-clay model 2.2 Arguments and working conditions of pits (1)Cases of pits and related arguments To make it clearly , the meaning of symbols that shown in the article are in chart 3. Fig. 3 Definitions of deep excavation variables We pick up 4 special excavation works as our research object ,which are fully offering their available modified Cambridge Model arguments . A s theyre shown in table 1.Table 1 Cases and parameters of deep excavation 2.3calculation resultsThe calculation are based on 400 kinds of models calculations ，by sorting the calculation result ,we get different regularities of ground settlement outside the pit walls in deferent retaining deformations .(1) walls shifting in as it shown in chart 4, we get the relationship between the max settlement and the max lateral shift ,the range of variable is 1.141.24,by average ,the formula is dvmax =1.18dhmax.Table 2 Variation range of parameter for all conditions Variable AmountDeclaration Pit amount 4 4 example above DeformationMode4 4 formation modeExcavationDepth5 5，8，10，12，15 m Max lateral Offet5 15，30，45，60，75 mm Fig. 4 Relationship between maximum ground settlement and maximum lateral wall deflection in Mode (a)In chart 5，we can see the distribution of settlement points outside of the walls is clearly a spandrel type distribution . Fitting to these settlement points distribution with the settlement curve which is offered in the article 11 that considered excentricity of settlement through ,and its curve is : dv = dvmax exp -0.10(0.43 )2x 2 (2) Fig. 5 Distribution of ground settlement in Mode (a) (2)walls rotating around the toes chart 6 give us the maximum settlement to the inner pits and the relation between lateral shift with it .We can see from chart 6 that the linear relation range from 1.091.15,taking the average ,their formula is :dvmax =1.13dhmax (3) Fig. 6 Relationship between maximum ground settlement and maximum lateral wall deflection in Mode (b) Chart 7 gives us the settlement calculation of walls outside pits .We can learn that settlement points distribute like spandrel type and its fitting line is : dv = dvmax exp -0.26(x+ 0.67)2 (4) Fig. 7 Distribution of ground settlement in Mode (b) (3) Walls rotating to the inner around the top Chart 8 gives us the relationship between maximum settlement and maximum literal shifting ,we can learn that in different situations ,the relationship is linear range from 0.550.63,taking the average ,their formula is : dvmax = 0.58dhmax （5） Fig. 8 Relationship between maximum ground settlement and maximum lateral wall deflection in Mode (c) Chart 9 gives us calculation of ground settlement outside of the walls .By the chart ,we can learn its point distributing notch type ,their fitting line is : dv = dvmax exp-0.30(x1.54)2 (6) Fig. 9 Distribution of ground settlement in Mode (c) (4)swollen into the wall Chart 10 gives us the relationship between maximum and maximum literal shift which is linear in different situations. The variable range from 0.80 to 0.85 ,taking average ,the formula is :dvmax = 0.82dhmax (7) Fig. 10 Relationship between maximum ground settlement and maximum lateral wall deflection in Mode (d) Chart 11 gives the calculation results of ground settlements of pits walls in the swollen to inner mode. We can tell the settlement points distributing in notch mode, its fitting line is :dv = dvmax exp-0.250(x 0.93)2 (8) Fig. 11 Distribution of ground settlement in Mode (d) Based on the four pits project in shanghai and a data simulation, we can gain a lot of information about deformation and ground settlement in regular and approximate in pit excavation. As general research ,the writer analysis the average soil condition and found that of similar regularity ,the calculation results range from 4-11.2.4.Prediction waysBy the analyses above ,different deformation mode have some regularity in common which is very clear. Therefore, to one specific deformation mode ,if the maximum lateral deflection was given ,we can approximately get the settlement number at any point respectively .The same time ,with fig1,any ground settlement out of retaining structure deformation mode can be seen as a combination of 4 basic deformation above ,so we can get the points settlement. 2.Experiment VerificationCase1: The pit of SWFC located in Huangpu District ,Shanghai City ,which covers an area of 17576 m2 and its maximum digging depth is 16.78m, taking reinforced concrete diaphragm wall as retaining structure. When the pit was excavated ,people monitored the literal displacement of diaphragm wall and ground surface settlement outside pit, the monitoring data is shown in fig 12,13. Fig. 12 Lateral wall deflection and decomposition (case 1) Assuming deformation mode based on earlier ,the pit diaphragm wall of SWFC its lateral deformation can be decompose into translation, rotating around the pit-toes and swelling to inner of the pit. Basic displacement of decomposition showed in fig12,their peak is 22,22,60mm,substitute them into expression (1) ,(3),(7), we can get the maximum settlement dvmax under the 3 basic deformation above ,they are 26.0,24.9,49.2mm.,substitute them into expression (2),(4),(8),then we get ground surface outside the pit its settlement expression under these 3 deformation: dv1 = 26.0exp-0.10(x+ 0.43)2 (9) dv2 = 24.9exp-0.26(x+ 0.67)2 (10) dv3 = 49.2exp-2.50(x 0.93)2 (11)Combine them, we can get the ground settlement curve line expression :dv = dv1+dv2 +dv3 (12)Taking a 15m away from pit wall substitute x=15m into exp.(9),(10),(11),(12),we can get the surface ground settlement values are 21.5,13.2,31.9,60.6 respectively under 3 basic modes and they are combined .Fig 13 draws the surface ground settlement curve lines under 3 basic deformation above and the combined one . We can see the concordance in measuring results and the calculation using the method given by this article. Fig. 13 Comparison between calculated and measured results (Case 1) Case 2: A pit project of transformer station in Shanghai its diamond is 130m,its depth is 33.5m.The bottom of foundations attitude is -31m,its thickness is 2.5m,and a 0.2m bedding beneath it .the excavation depth is 33.7m ,pit area is 3273m2,its circumference is 408m.A monitoring was conducted when the pit was excavated ,fig14 gives us observation point CX48s lateral deformation curve in diaphragm wall .fig15gives us ground settlement curve of observation point B3. According to fig 14,the measured lateral deformation of walls can be calculated by then method given by this article with the argument of ground settlement outside the pit walls. Taking a cutting surface attitude -22.6m for example ,we can use the calculation method given by this article ,like :The excavation surface its attitude is -22.6m,and by this depth its lateral offset measuring curve are shown in fig 16, this deformation curve can be seen as a combination of translation、rotating around the top wall and swelling to the inner of pit whose decomposition basic offset is shown in fig 16,their max value is 4,3,20mm.We take them into expression (1),(5),(7) respectively ,so we can get the maximum value dvmax of settlement in each mode and they are 4.7,1.7,24.6mm.Get the max value of settlement into expression (2),(6),(8), we can get the settlement of the pit-walls in this 3 modes. dv1 = 4.7exp-0.10(x+0.43)2 (13) dv2 =1.7exp-0.30(x1.54)2 (14)dv3 = 24.6exp-2.50(x0.93)2 (15) Fig. 14 Lateral wall deflection (Case 2) Fig. 15 Curves of measured settlement (Case 2) Combining these 3 basic deformations, we get the ultimate ground settlement expression as it shown in exp(12).Fig17 draws the settlement curve both in decomposition and combined of these 3mode .Calculation in accordance with similar steps, using the lateral deformation curve given by fig14 ,we can still figure out the ultimate ground settlement ,which is shown fig18 to fig23.Fig. 16 Lateral wall deflection and decomposition (H=-22.6 m) Fig. 17 Comparison between calculated and measured results (H =-22.6 m) Fig. 18 Comparison between calculated and measured results (H =-7.6 m) Fig. 19 Comparison between calculated and measured results .(H =-12.9 m) Fig. 20 Comparison between calculated and measured results (H =-17.6 m) Fig. 21 Comparison between calculated and measured results .(H =-27.6 m) Fig. 22 Comparison between calculated and measured results (H =-30.9 m) Fig .23 Comparison between calculated and measured results (H =-33.7 m) Contrasting the calculation result and measured data , we found fig 17 and 20 match well, fig 18,19,20 matches.fig23 still have a long way to go match .Generally speaking, the deeper we dig, the bigger the lateral deformation are ,the bigger the ground settlement outside the pit-walls are. But its easier to find that when the digging depth is deeper than -22m,the settlement remains the same with fig15. The reason is unknown , which maybe related to the actual construction measures of the construction site, like using some measures to control land subsidence. But this article doesnt take these affects into consideration ,the same time the unknown reason tells us revaluation of land subsidence is a complex job, because influence factors are variable. However, with the large error in fig23, we can still believe this calculation method available . 4.conclusion This article based on the basic 4 deformation mode ,by massive numerical computing, proposed an estimation method and formulas of calculating ground settlement include by excavation of foundation pit in Shanghai. Engineering Verification shows that the method of practicality and reliability is better, be a more practical method for estimation of ground settlement.Reference： 1 杨 敏, 冯又全, 王瑞祥. 深基坑支挡结构的力学分析及与实测结果的比较J. 建筑结构学报, 1999(2): 6875. (YANG Min, FENG You-quan, WANG Rui-xiang. Comparison of mechanical analysis and measured results for retaining structure in deep excavationJ. Journal of Building Structures, 1999(2): 6875. (in Chinese) 2 JGJ12099 建筑基坑支护技术规程S. 北京: 中国建筑工业出版社, 1999. (JGJ12099 Technical specification for retaining and protection of building foundation excavationsS. Beijing: China Architecture & Building Press, 1999. (in Chinese) 3 PECK R B. Deep excavations and tunneling in soft ground. state-of-the-art reportC/ Proc 7th Int Conf Soil Mechanics Foundation Engineering, Mexico, 1969: 225290. 4 李 琳, 杨 敏, 熊巨华. 软土地区深基坑变形特性分析J. 土木工程学报, 2007, 40(4): 6672. (LI Lin, YANG Min, XIONG Ju-hua. Analysis of the deformation characteristics of deep excavations in soft clayJ. China Civil Engineering Journal, 2007, 40(4): 6672. (in Chinese) 5 王保建, 熊巨华，