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1、Direct loss Prediction on Buildings around Construction Pit Caused by Ground Water Pumping,SONG Jianxue,Zhengzhou University,1,in collaboration with SONG Danju,outline,BackgroundGround water table after pumpingGround settlement caused by water pumpingGround settlement and settlement gradientAdjacent
2、 building direct loss predictionPractical application,2,1 Study background,More and more skyscrapers: deep foundation pitsmore and more underground projects Metro underground shop mallResult in: Deep excavation,3,Zhengzhou International Conference and Exhibition Center (ICEC),4,Zhengzhou ICEC Hotel,
3、5,Zijingshan Metro Station:In the future, the L-2 Metro line will run beneath this station. Here will be a busy transfer center for travelers.,6,Adjacent ground settlement and crack caused by ground water pumping in construction pit,7,Pipeline cut by ground settlement that resulted from ground water
4、 pumping,8,Residential buildings damaged by ground settlement that resulted from ground water pumping,9,How far?,Magnitude?,Is settlement magnitude the only factor?,10,Construction pit ground water pumping,Determining of ground water table and contour after pumping,Building direct loss vs. ground se
5、ttlement gradient,Ground settlement gradient,Determining of ground settlement and contour,Adjacent building direct loss prediction,11,2 Ground water table and contour after pumping,2.1 General algorithm for water table determining,A-Solution of fluid mechanism: strict analytic solution,B-Solution of
6、 hydraulics: approximate solution,(3-D stable flow),(2-D stable flow),12,C- Numerical simulation,Pore water pressure numerical simulation-1,13,Pore water pressure numerical simulation-2,14,Ground settlement numerical simulation-1,15,Ground settlement numerical simulation-2,16,However, these algorith
7、ms are too complicated to be applied in practical project!,On the other hand, most of the Chinese civil engineers are used to following the national codes system,This must be taken into consideration!,17,18,Assumptions:2-dimension stable flow, without water cutting wall surrounding the pit,Determini
8、ng of ground water table after pumping,The ground water table may be obtained by,19,(Dupuits equation),20,Loess geological area,Alluvion geological area,21,Before applying, the validity of the formula has to be checked,Six projects are chosen as cases study, and only one is discussed here,Zhengzhou
9、Metro Station:Athlete Center Station,22,23,24,Calculated water table and monitored water table,25,26,Calculated water table and monitored water table,After verification in six projects, it is found that the Dupuits equation can be used to determine the water table after pumping,3.1 Algorithm-soil co
10、mpression accumulation (SCA),For the convenience of engineers, the algorithm stipulated in Chinese National Code (SCA) is employed:,3 Ground settlement caused by water pumping,27,S2-usually very small, may be neglected According to the National Code, in order to obtained S1, the modification factor
11、has to be determined first,28,modification factor : _determined by local engineering geology condition.,(3.1),Modification factor,29,modification factor ,30,Presume comply with the standard normal distribution,31,，,Take as 0.29, then the settlement calculation error,32,4 Building loss results from g
12、round settlement,4.1 Main assumption Only direct loss is taken into consideration,33,34,4.2 AlgorithmThe ground near the construction pit is divided into a series of donuts. (2) Equation (3.1) is employed to determine the settlement of each donut (the middle line of each donut is taken as target).(3
13、) Settlement gradient between bordered donuts is obtained.(4) Economic loss rate vs. ground settlement gradient is set up.(5) A certain scope around the pit is chosen, all buildings loss in the scope is accumulated.,35,4.3 Donuts4.3.1 Usually, the geometric center of pit is set as the center of all
14、donuts4.3.2 The affecting scope (taken as 5Sw, Sw-the depth of water table falling beneath the pit ground ) is divided into a series of donuts with the increment as 0.2Sw,36,4.4 ground settlement gradient,37,Ground settlement gradient in the Case Project,38,Generally, the further the distance from t
15、he pit edge is, the smaller the ground settlement gradient is.,39,However, if a donut runs across over the soil surface which is below and above the water table before and after pumping, the gradient here is likely to leap significantly.,40,For the sake of security, 1 is taken as the threshold of gr
16、ound settlement gradient.,4.5 The threshold of difference settlement building,41,4.6 The relationship between ground settlement gradient (G) and economic loss rate () of building,1 When G is smaller than 1 , = 0.2 Theoretically, when G approaches , = 1.3 Several historical cases are employed to set the relationship between G and , such as,(Above parameters are all from reference),Then, the form of the Equation is determined as,
