CN110263366B - Method for determining depth of suspended waterproof curtain inserted into precipitation aquifer - Google Patents
Method for determining depth of suspended waterproof curtain inserted into precipitation aquifer Download PDFInfo
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Abstract
The invention provides a method for determining the depth of a suspended water-stop curtain inserted into a precipitation aquifer, which is characterized in that a three-dimensional finite element model is established by combining a water pumping test according to engineering general information and geological information, and under the condition of setting the length of a filter pipe of a precipitation well, the hydraulic gradient of the inner side and the outer side of the water-stop curtain and the change rule of surface settlement outside a pit are analyzed by changing the depth of the water-stop curtain inserted into the precipitation aquifer, so that the reasonable depth of the water-stop curtain inserted into the precipitation aquifer is determined, and the requirements of engineering safety, environmental effect and economy are met.
Description
Technical Field
The invention relates to a method in the technical field of underground engineering construction, in particular to a method for determining the depth of a suspended waterproof curtain inserted into a precipitation aquifer.
Background
In order to ensure the safety and stability of foundation pit excavation, foundation pit dewatering is generally carried out before the foundation pit excavation. A common foundation pit dewatering scheme is a method for combining a waterproof curtain with in-pit dewatering, namely the waterproof curtain is arranged around a foundation pit to block hydraulic connection inside and outside the foundation pit, and a dewatering well is arranged inside the foundation pit to pump underground water so that the underground water level in the pit is lowered to the bottom of an excavation surface of the foundation pit for a certain distance. Precipitation in the pit may cause a drop in the groundwater level outside the pit, which in turn causes a number of geological and environmental problems, such as ground subsidence, damage to surrounding structures, etc. Theoretically, if the waterproof curtain can be inserted into a confined aquifer needing precipitation, namely the bottom of the precipitation aquifer, the hydraulic connection between the inside and the outside of the foundation pit can be completely cut off, and the influence of the precipitation of the foundation pit on the surrounding environment is very small. However, with the development of cities, the excavation depth of the foundation pit is larger and larger, and if the waterproof curtain is completely inserted into the bottom of the precipitation aquifer, the construction difficulty is increased and the method is not economical. Therefore, the method of combining the hanging type waterproof curtain with the precipitation in the pit is widely adopted. The suspended waterproof curtain is inserted into a precipitation aquifer to a certain depth, so that hydraulic connection inside and outside a foundation pit is partially isolated, and the waterproof effect is ensured and the economical efficiency is achieved. For the method of combining the suspended waterproof curtain with the precipitation in the pit, in order to meet the requirements of engineering safety, environmental effect and economy, it is very important to reasonably design the depth of the waterproof curtain inserted into the precipitation aquifer.
At present, no universal method is provided for the design of the depth of the suspended waterproof curtain inserted into the precipitation aquifer, and the engineering practice mostly depends on the experience of related personnel and has uncertainty.
Through the research of the literature, the depth of the waterproof curtain inserted into the precipitation aquifer is selected according to the allowable settlement of the surrounding soil body in the Song Yu field and the like in the article 'analysis of the insertion depth of the waterproof curtain of the deep foundation pit' (Shandong water conservancy, 2003 (08): 41-42) and the article 'optimization design of the waterproof curtain of the deep foundation pit' (the proceedings of the State institute of technology, 2008, 21 (S1): 119-121); the Thanksgiving army and the like compare the control effects of the waterproof curtain on the settlement of the surface outside the pit and the reduction of the underground water level under two different insertion depths in an article 'selection of the depth of a suspended waterproof curtain in foundation pit precipitation' (construction technology, 2017, 46 (S1): 61-64), thereby determining the final insertion depth; zhangjingxi et al, in article "calculation of inflow volume of suspended curtain foundation pit and influence effect of insertion depth" (geotechnical engineering technology, 2018, 32 (03): 109-.
The above documents all consider a method of adopting a scheme of comparing by assuming several curtain depths and then selecting the best among the assumed curtain depths according to the allowable extra-pit surface subsidence or groundwater level subsidence. The selection criteria used in the above-mentioned documents are not uniform and the optimal depth selected on the basis of the above-mentioned criteria is not universal due to the limited number of assumed curtain depths. In addition, the above document does not propose a method for determining the insertion depth of the waterproof curtain in consideration of the length of the filter pipe of the dewatering well.
In further search, no report on a method for determining the depth of the suspended waterproof curtain inserted into the rainfall aquifer is found at present.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for determining the depth of a suspended waterproof curtain inserted into a precipitation aquifer by comprehensively considering engineering safety, environmental effect and economic requirements.
In order to achieve the purpose, the invention combines a water pumping test to establish a three-dimensional finite element model according to engineering general information and geological information, and analyzes the hydraulic gradient of the inner side and the outer side of a water-stop curtain and the change rule of surface settlement outside a pit by changing the depth of the water-stop curtain inserted into a precipitation aquifer under the condition of setting the length of a filter pipe of the precipitation well, thereby determining the reasonable depth of the water-stop curtain inserted into the precipitation aquifer and ensuring that the water-stop curtain meets the requirements of engineering safety, environmental effect and economy.
Specifically, the method for determining the depth of the suspended waterproof curtain inserted into the aquifer of the precipitation comprises the following steps:
and S1, acquiring engineering overview, engineering geology and hydrogeology information through the engineering survey report.
Preferably, the engineering profile comprises: the plane geometry of foundation ditch, excavation depth, the plane position and the thickness of waterproof curtain.
Preferably, the engineering geological information comprises: dividing information of soil layers and parameters of physical and mechanical properties of each soil layer.
More preferably, the soil layer division information includes: the types of all soil layers and the buried depths of the top plate and the bottom plate.
More preferably, the physical-mechanical property parameters include: soil body gravity gamma, porosity ratio e and horizontal permeability coefficient khVertical permeability coefficient kvCompression modulus Es。
Preferably, the hydrogeological information comprises: hydrologic geological formation division information, initial water level of each aquifer.
More preferably, the hydrogeological stratification information comprises: the category and the top and bottom plate burial depth of each hydrologic geological layer.
More preferably, the initial water level of the aquifer comprises: the initial water level of the phreatic layer and the initial water level of the confined aquifer.
And S2, acquiring arrangement information, structural information, precipitation data and test data of the precipitation well and the observation well through the pumping test report.
Preferably, the arrangement information of the dewatering well and the observation well comprises: the number and the plane arrangement positions of the dewatering wells and the observation wells.
Preferably, the structural information of the dewatering well and the observation well comprises: the buried depth of the bottom of each well and the buried depths of the top and the bottom of the filter tube.
Preferably, the precipitation data refers to the water pumping quantity Q or the water level depth H of each precipitation wellw. Wherein: for the constant flow pumping test, the precipitation data is Q; for the fixed-depth-lowering water pumping test, the precipitation data is Hw。
More preferably, the fixed-depth pumping test refers to a pumping test performed under the condition that the water level of a given dewatering well is reduced; the constant-flow pumping test is a pumping test performed under the condition of giving the pumping quantity of the dewatering well.
Preferably, the test data refers to the water level lowering H of each observation wellJData over time t.
And S3, establishing a finite element model to simulate a water pumping test.
1) The finite element model is sized and gridded.
The dimensions of the finite element model comprise a plane X, Y direction dimension and a vertical Z direction dimension; the X, Y-direction sizes of the finite element models are all larger than the precipitation influence radius R; the Z-direction dimension is larger than or equal to the buried depth of the bottom plate of the weakly permeable layer under the precipitation aquifer;
the partitioning grid follows the following principle: a dense net is arranged in the pit on the plane, and the outside of the pit is gradually enlarged; dividing information coarse-dividing large layers vertically according to soil layers; the sub-layers are then further subdivided according to hydrogeological stratification information.
Preferably, the precipitation impact radius R is calculated using the following formula:
in the formula (I), the compound is shown in the specification,
the average level equivalent permeability coefficient of the precipitation aquifer is calculated according to the following formula
Wherein T is the thickness of the precipitation aquifer, u is the number of soil layers between the top and bottom of the precipitation aquifer, and khiIs the horizontal permeability coefficient of the ith soil layer between the top and the bottom of the precipitation water-bearing layer hiAnd the thickness of the ith soil layer is obtained according to S1.
H is the water level depth of the precipitation aquifer and is calculated according to the following formula:
in the formula, H0Is the initial water level of the precipitation aquifer; n is the number of soil layers from the top plate of the precipitation aquifer to the excavation surface of the foundation pit; gamma raysiIs the gravity of the i-th layer of soil between the top plate of the rainfall aquifer and the excavation surface of the foundation pit, hiThe thickness of the ith soil layer is obtained according to S1; gamma raywIs the severity of the water; fsThe construction safety factor is an engineering safety factor, and the value can be taken according to the basic design standard of the building foundation (GB 50007-2011).
2) Initial formation parameters are input.
The initial formation parameters include: soil body gravity gamma, porosity ratio e and permeability coefficient k of each soil layerx、ky、kzWater storage coefficient Ss。
Preferably, gamma and e of each soil layer are taken as S1.
Preferably, k of each soil layerx、kyK equal to S1h，kzK equal to S1v。
Preferably, S of each soil layersCalculated using the formula:
in the formula, gammawIs the heaviness of the water. EsThe compression modulus of the soil is obtained according to S1.
3) Initial conditions are set.
The initial conditions refer to the initial water level of each hydrogeological formation. Wherein: the initial water level of the aquifer is taken according to S1; the initial water level of the aquifer above the permeable-to-water layer is the same as the initial water level of the aquifer located above it.
4) A boundary condition is set.
The boundary includes a perimeter boundary and a bottom boundary. Wherein: the periphery boundary is a constant head boundary, and the bottom boundary is a water-resisting boundary.
5) And setting precipitation information.
The precipitation information includes: and (4) taking values of arrangement information, structure information and precipitation data of the precipitation well according to S2.
6) And (6) correcting the model.
The correction model is used for simulating a water pumping test of S2 by using a finite element model established based on 1) -5), comparing simulation data with test data and checking deviation of the simulation data and the test data. The model is corrected if the maximum deviation between the two is greater than a threshold (e.g., 5%).
Preferably, the specific steps of the correction model are as follows: firstly, adjusting the formation parameters in the step 2), then simulating the water pumping test again based on the finite element model reestablished in the steps 1) to 5), comparing the simulation data with the test data, and repeating the processes until the maximum deviation between the simulation data and the test data is less than a threshold value (such as 5%).
S4, adopting the finite element model determined by S3 to simulate and analyze the length ratio R of the filter pipe of the given dewatering wellLIn case of different waterproof curtain insertion depth ratio RDDrawing the simulation result into R according to the environmental effect of the lower foundation pit rainfallDInfluence graph, said RDThe influence graph contains RD- Δ i and RD-an S-relationship graph;
the R isLThe ratio of the length L of the filter pipe of the precipitation well to the thickness T of the precipitation aquifer is obtained;
the R isDFor inserting the waterproof curtain into the water-bearing stratum；
The environmental effect refers to: calculating the hydraulic gradient delta i of the well and the surface settlement value S of the settlement calculation point outside the pit on two sides of the waterproof curtain;
preferably, L is taken as S2; t is taken as S1.
Preferably, said R isDAt least 10 different values are taken.
More preferably, the calculation well is disposed at a distance of 4-6 times the thickness of the waterproof curtain from one side of the waterproof curtain, and the structural information is the same as that of the observation well in S2.
More preferably, the settlement calculation point is set at 3 excavation depths outside the pit.
More preferably, the Δ i is calculated by the following formula:
in the formula (I), the compound is shown in the specification,
calculating the water level difference of the well at two sides of the water stopping curtain, wherein l is the length of the shortest fold line passing through the midpoint of the well filter tube outside the pit, the bottom of the water stopping curtain and the midpoint of the well filter tube in the pit.
S5, fitting R obtained in S4 by using Boltzmann methodD- Δ i diagram, yielding RDBoltzmann curve of-. DELTA.i by plotting RDDerivation of Boltzmann curve of- Δ i to obtain RD-h1，RD-h2，RD-h3I.e. at a given RLIn the case of (1), considering R controlling the hydraulic gradient on both sides of the waterproof curtainDMinimum value of RD-h1Maximum value RD-h2Optimum value RD-h3；
Fitting R obtained by S4 by using Boltzmann methodD-S relationship diagram, resulting in RDBoltzmann curve of-S by pair RDDerivation of Boltzmann curve of-S to obtain RD-s1，RD-s2，RD-s3I.e. at a given RLIn the case of (2), R for controlling the sedimentation of the earth surface outside the pit is consideredDMinimum value of RD-s1Maximum value RD-s2At the mostFigure of merit RD-s3。
The R isD-h1Is RD-abscissa corresponding to the maximum of the second derivative of the Boltzmann curve for Δ i.
The R isD-h2Is RD-abscissa corresponding to the minimum of the second derivative of the Boltzmann curve for Δ i.
The R isD-h3Is RD-abscissa corresponding to the maximum of the first derivative of the Boltzmann curve for Δ i.
The R isD-s1Is RD-abscissa corresponding to the minimum of the second derivative of the Boltzmann curve of S.
The R isD-s2Is RD-abscissa corresponding to the maximum of the second derivative of the Boltzmann curve of S.
The R isD-s3Is RD-abscissa corresponding to the first derivative minimum of the Boltzmann curve of S.
S6, obtaining R by comparing the two groups of data obtained in S5D-1，RD-2，RD-3I.e. at a given RLIn the case of (1), R controlled in consideration of the combined environmental effectDMinimum value of RD-1Maximum value RD-2Optimum value RD-3。
The R isD-1To obtain RD-h1And RD-s1The larger of these.
The R isD-2To obtain RD-h2And RD-s2The larger of these.
The R isD-3To obtain RD-h3And RD-s3The larger of these.
S7, adding RD-1、RD-2、RD-3Multiplying by T respectively to obtain the minimum value D of D given L1Maximum value D2Optimum value D3。
Compared with the prior art, the invention can comprehensively consider the requirements of engineering safety, environmental effect and economy and scientifically determine the depth of the suspended waterproof curtain inserted into the precipitation aquifer. Compared with the method depending on experience, the method is more scientific. Compared with the method in the prior document, the method is more operable and accurate.
Drawings
FIG. 1 is a schematic view of a planar geometry and well point layout of a foundation pit according to an embodiment of the present invention;
FIG. 2 is a diagram of engineering geology and hydrogeology information in accordance with an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a dewatering well and an observation well according to an embodiment of the present invention;
FIG. 4 is a diagram of a finite element model according to an embodiment of the present invention;
FIG. 5 is a graph comparing pump test data and simulation data according to one embodiment of the present invention;
FIG. 6 shows an example of RD- Δ i diagram;
FIG. 7 shows an embodiment of RD-an S-relationship graph.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
The following describes the implementation process of the present invention in detail by taking the foundation pit engineering of a subway station as an example.
The first step, the engineering general view, engineering geology and hydrogeology information are obtained through an engineering investigation report.
The project of this embodiment includes a standard block region and a termination well region. Wherein: the standard section zone foundation pit is 157m long, 19.30m wide and 22.40m deep; the end well area is 15m long, 23.60m wide and 23.96m deep. The thickness of the waterproof curtain is 1 m. The plane geometry of the foundation pit and the plane position of the waterproof curtain are shown in figure 1.
The engineering geological formation that this embodiment engineering relates to includes 17 soil layers, by last to being in proper order: 11Artificial fill, 12A silty clay; 21Clay clay，22Muddy clay, 23A grey silty clay; 31Silt, 32A grey silty clay; 41Argillaceous clays, 42Clay; 51Mucky clay, 52 Powdery clay 53Silty sandy soil; 61A silty clay; 71A powdery clay; 81Powder sand; 91Powdery clay, 92A clay. The categories of the soil layers, the buried depths of the top plate and the bottom plate and the physical and mechanical property parameters are shown in figure 2.
The hydrological geological formation involved in the engineering of the present embodiment comprises 4 aquifers and 4 aquifers. The following steps are carried out from top to bottom in sequence: the permeable water-bearing stratum comprises a diving water-bearing stratum (Aq01), a first weak permeable stratum (AdI), a shallow confined water-bearing stratum (Aq02), a second weak permeable stratum (AdII), a first confined water-bearing stratum (AqI), a third weak permeable stratum (AdIII), a second confined water-bearing stratum (AqII) and a fourth weak permeable stratum (AdIV). The initial water level of the diving aquifer is-0.5 m (minus below the earth surface), the initial water level of the shallow confined aquifer is-2 m, and the initial water levels of the first confined aquifer and the second confined aquifer are-3.5 m and-4 m respectively. The types of the hydrogeological layers and the buried depths of the top and bottom plates are shown in fig. 2.
And secondly, acquiring arrangement information, structural information, precipitation data and test data of the precipitation well and the observation well through a pumping test report.
The pumping test of the project is provided with 6 dewatering wells (J1-J6) and 2 observation wells (G1, G2), and the plane arrangement of each well is shown in figure 1.
The bottom burial depth of each well and the top and bottom burial depths of the filter tubes are shown in fig. 3.
The pumping test of the project belongs to a fixed-depth-reducing pumping test, and the water level of each dewatering well is reduced by a depth HwAre all 15 m.
Water level lowering H of two observation wellsJThe data over time t are shown in fig. 5.
And thirdly, establishing a finite element model to simulate a water pumping test. The method comprises the following steps:
1) the finite element model is sized and gridded.
In this embodiment, the precipitation aquifer is AqI, its initial water levelH0Is-3.5 m, engineering safety factor FsTaking 1.05, and calculating the water level depth H of the precipitation aquifer to be 14.84m according to the formula (3); the thickness T of the precipitation aquifer is 12m, and the average equivalent horizontal permeability coefficient of the precipitation aquifer is calculated by the formula (2)
Is 8.99 m/d; calculating the precipitation influence radius R to be 494.95m according to the formula (1); the bottom plate buried depth of the weakly permeable layer under the precipitation aquifer is 50 m. The X, Y, Z-directional dimensions of the finally-built finite element model were 1600m, and 72m, respectively.
The mesh size in the pit on the plane is 4 × 4m, the pit is gradually enlarged, the maximum mesh size is 100 × 100m, the mesh size is roughly divided into 17 large layers according to the soil layer division information in the vertical direction, and the mesh size is further finely divided into 28 sub-layers according to the hydrological geological layer information, wherein 4 sub-layers are formed2、53、81The soil layers were subdivided on average into 2, 6 and 4 layers, the remaining soil layers each being 1 layer. The finite element model of the project is shown in FIG. 4.
2) Initial formation parameters are input.
The soil mass gravity gamma and the porosity e are taken as shown in figure 2; coefficient of permeability kx、kyAccording to k in FIG. 2hValue kzAccording to k in FIG. 2vTaking values; water storage coefficient SsCalculated according to the formula (4), wherein the compression modulus Es is taken according to the figure 2, SsThe values are shown in table 1:
table 1 shows the initial water storage coefficient table of each soil layer in the examples
| |
11 | 12 | 21 | 22 | 23 | 31 | 32 | 41 | 42 | 51 | 52 | 53 | 61 | 71 | 81 | 91 | 92 |
| Ss(×10-3m-1) | 3.75 | 0.19 | 0.20 | 0.19 | 0.20 | 8.20 | 0.15 | 0.16 | 0.15 | 0.15 | 0.16 | 2.06 | 0.30 | 3.11 | 3.08 | 0.29 | 0.30 |
3) Initial conditions are set.
The initial water level of the diving aquifer (Aq01) and the first weak permeable layer (AdI) is-0.5 m, the initial water level of the shallow confined aquifer (Aq02) and the second weak permeable layer (AdII) is-2 m, the initial water level of the first confined aquifer (AqI) and the third weak permeable layer (AdIII) is-3.5 m, and the initial water level of the second confined aquifer (AqII) and the fourth weak permeable layer (AdIV) is-4 m.
4) A boundary condition is set.
The periphery boundary of the model is a constant head boundary, and the bottom boundary is a water-resisting boundary.
5) And setting precipitation information.
And inputting the arrangement information, the structure information and the precipitation data of the precipitation well according to the second step.
6) And (6) correcting the model.
In this example, the maximum deviations of the simulated data of G1 and G2 from the experimental data calculated using the initial formation parameters are 11.23% and 9.52%, respectively, which are greater than 5%, and the model needs to be corrected. The comparison of the simulation data and the test data obtained after the formation parameters are adjusted repeatedly is shown in fig. 5, and the maximum deviation of the simulation data of G1 and G2 and the test data is respectively 2.01 percent and 1.18 percent, and is less than 5 percent, which meets the requirements. Of course, 5% is the threshold set in this embodiment, and in other embodiments, other thresholds may be adopted according to actual needs, which will be readily understood by those skilled in the art.
Fourthly, simulating and analyzing the length ratio R of the filter pipe of the given dewatering well by adopting the finite element model determined in the third stepLIn case of different waterproof curtain insertion depth ratio RDDrawing the simulation result into R according to the environmental effect of the lower foundation pit rainfallDThe influence graph.
In this embodiment, the length L of the filter pipe of the precipitation well is 6m, and the thickness T of the precipitation aquifer is 12m, namely RLIs 50%. The insertion depth D of the waterproof curtain is increased from 0 to 12m and is increased by 1m each time, namely RDIncreasing from 0 to 100%, RDA total of 13 different values were taken. In this embodiment, the thickness of the waterproof curtain is 1m, the distance between the computing well (JS1) inside the pit and the waterproof curtain is 4m, and the distance between the computing well (JS2) outside the pit and the waterproof curtain is 6 m. Obtaining different R by adopting finite element model analysis determined in the third stepDIn case of a water head difference between two calculation wells
And the corresponding hydraulic gradient Δ i is calculated using equation (5). In this embodiment, the excavation depth of the standard section foundation pit is 22.4m, and the distance between the settlement calculation point P and the outer side of the waterproof curtain is 68 m. Obtaining different R by adopting finite element model analysis determined in the third stepDThe surface subsidence S at point P in this case. The locations of the computing wells JS1, JS2, and the settlement computing point P are shown in fig. 1, and the structural information of JS1 and JS2 are shown in fig. 3.
Plotting the simulation result as RD- Δ i diagram and RD-S-relationship diagrams as shown in fig. 6 and 7, respectively.
Fifthly, fitting the R obtained in the fourth step by using a Boltzmann methodD- Δ i diagram, yielding RDBoltzmann curve for Δ i. By the pair RDDerivation of Boltzmann curve of- Δ i to obtain RD-h1，RD-h2，RD-h3I.e. at a given RLIn the case of (1), R is givenLIn the case of (1), considering R controlling the hydraulic gradient on both sides of the waterproof curtainDMinimum value of RD-h1Maximum value RD-h2Optimum value RD-h3。
In this example, R obtained by fittingDBoltzmann curve for- Δ i is shown in FIG. 6, and is determined at RLIn the case of 50%, RD-h1，RD-h2，RD-h350.6%, 59.7% and 55.2%, respectively.
In this embodiment, the above-mentioned passing pair RDDerivation of Boltzmann curve of- Δ i to obtain RD-h1，RD-h2，RD-h3The method specifically comprises the following steps: first to RDSolving a first derivative and a second derivative by using a Boltzmann curve of the-delta i, wherein abscissas corresponding to a maximum value, a minimum value and a maximum value of the first derivative are respectively taken as RD-h1，RD-h2，RD-h3(ii) a Then defining the three values as R for controlling hydraulic gradient on two sides of the waterproof curtainDMinimum value of RD-h1Maximum value RD-h2Optimum value RD-h3。
Sixthly, fitting the R obtained in the fourth step by using a Boltzmann methodD-S relationship diagram, resulting in RDThe Boltzmann curve of S. By the pair RDDerivation of Boltzmann curve of-S to obtain RD-s1，RD-s2，RD-s3I.e. at a given RLIn the case of (2), R for controlling the sedimentation of the earth surface outside the pit is consideredDMinimum value of RD-s1Maximum value RD-s2Optimum value RD-s3。
In this example, R obtained by fittingDBoltzmann curve for-S is shown in FIG. 7, determined at RLIn the case of 50%, RD-s1，RD-s2，RD-s340.1%, 70.8% and 55.5%, respectively.
In this embodiment, the above-mentioned passing pair RDDerivation of Boltzmann curve of-S to obtain RD-s1，RD-s2，RD-s3The method specifically comprises the following steps: to RDSolving a first derivative and a second derivative by using a Boltzmann curve of the-S, wherein abscissas corresponding to a minimum value, a maximum value and a minimum value of the first derivative of the second derivative are respectively taken as RD-s1，RD-s2，RD-s3(ii) a Then put this inThree values are defined as R for controlling the foreign surface settlement of the pitDMinimum value of RD-S1Maximum value RD-S2Optimum value RD-S3。
Seventhly, obtaining R by comparing the two groups of data obtained in the fifth step and the sixth stepD-1，RD-2，RD-3I.e. at a given RLIn the case of (1), R controlled in consideration of the combined environmental effectDMinimum value of RD-1Maximum value RD-2Optimum value RD-3。
In this example, it is determined that R isLIn the case of 50%, RD-1，RD-2，RD-350.6%, 70.8% and 55.5%, respectively.
In this embodiment, the larger of the two previous sets of data is selected and defined as R taking into account the control of the combined environmental effectsDMinimum value of RD-1Maximum value RD-2Optimum value RD-3。
The eighth step of adding RD-1、RD-2、RD-3Multiplying by T respectively to obtain the minimum value D of D in the case of given L1Maximum value D2Optimum value D3。
In this example, D was obtained when L was 6m1，D2、D3Respectively 6.1m, 8.5m and 6.7 m.
Finally, in the embodiment, under the condition that the length L of the precipitation well filter tube is 6m, the minimum value of the depth D of the waterproof curtain inserted into the precipitation aquifer is 6.1m, the maximum value is 8.5m, and the optimal value is 6.7 m.
According to the embodiment, the requirements of engineering safety, environmental effect and economy are comprehensively considered, and the depth of the suspended waterproof curtain inserted into the precipitation aquifer is scientifically determined. Compared with the method depending on experience, the method is more scientific; compared with the method in the prior document, the method is more operable and accurate.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (7)
1. A method of determining the depth to which a suspended waterproof curtain is inserted into a precipitation aquifer, comprising:
s1, acquiring engineering general, engineering geology and hydrogeology information through the engineering investigation report;
the engineering profile includes: the plane geometry, excavation depth and plane position and thickness of a waterproof curtain of the foundation pit;
the engineering geological information comprises: dividing information of soil layers and parameters of physical and mechanical properties of each soil layer; the soil layer division information includes: the categories of all soil layers and the buried depths of the top plate and the bottom plate; the physical mechanical property parameters comprise: soil body gravity gamma, porosity ratio e and horizontal permeability coefficient khVertical permeability coefficient kvCompression modulus Es；
The hydrogeological information comprises: hydrological geological layer division information and initial water levels of all aquifers; the hydrogeological stratification information comprises: the category and the top and bottom plate burial depth of each hydrological geological layer; the initial water level of the aquifer comprises: the initial water level of the diving layer and the initial water level of the confined aquifer;
s2, acquiring arrangement information, structure information, precipitation data and test data of the precipitation well and the observation well through the pumping test report;
the arrangement information of the dewatering well and the observation well comprises: the number and the plane arrangement positions of the dewatering wells and the observation wells are determined;
the structural information of precipitation well and observation well includes: the bottom embedded depth of each well and the top and bottom embedded depths of the filter pipes;
the precipitation data refers to the water pumping quantity Q or water level depth H of each precipitation wellwWherein: for the constant flow pumping test, the precipitation data is Q; for the fixed-depth-lowering water pumping test, the precipitation data is Hw；
The fixed-depth-lowering water pumping test is a water pumping test carried out under the condition of water level depth lowering of a given precipitation well; the constant-flow pumping test is a pumping test performed under the condition of setting the pumping quantity of the dewatering well;
the test data refers to the water level depth H of each observation wellJData that varies over time t;
s3, establishing a finite element model;
in S3, establishing a finite element model, including:
s301: determining the size of the finite element model and dividing meshes;
the dimensions of the finite element model comprise the dimension of a plane X, Y in the direction and the dimension of a vertical Z direction, the dimension of the finite element model in the X, Y direction is larger than the precipitation influence radius R, and the dimension of the Z direction is larger than or equal to the buried depth of a bottom plate of a weakly permeable layer under a precipitation aquifer;
the partitioning grid follows the following principle: a dense net is arranged in the pit on the plane, and the outside of the pit is gradually enlarged; dividing information coarse-dividing large layers vertically according to soil layers; then, further subdividing a sublayer according to hydrologic geological layer division information;
s302: inputting initial formation parameters;
the initial formation parameters include: soil body gravity gamma, porosity ratio e and permeability coefficient k of each soil layerx、ky、kzWater storage coefficient Ss(ii) a These parameters are obtained by S1;
s303: setting initial conditions;
the initial condition refers to an initial water level of each hydrogeological formation, wherein the initial water level of the aquifer is obtained by S1; the initial water level of the weak permeable layer is the same as that of the aquifer positioned above the weak permeable layer;
s304: setting a boundary condition;
the boundary includes a perimeter boundary and a bottom boundary, wherein: the periphery boundary is a constant head boundary, and the bottom boundary is a water-resisting boundary;
s305: setting precipitation information;
the precipitation information includes: arrangement information, structural information and precipitation data of the precipitation well are obtained by S2;
s306: correcting the model;
the correction model is a water pumping test of S2 simulated by using a finite element model established based on S301-S305, comparing simulated data with test data, checking the deviation of the simulated data and the test data, and correcting the model if the maximum deviation of the simulated data and the test data is greater than a threshold value;
s4, adopting the finite element model determined by S3 to simulate and analyze the length ratio R of the filter pipe of the given dewatering wellLIn case of different waterproof curtain insertion depth ratio RDDrawing the simulation result into R according to the environmental effect of the lower foundation pit rainfallDInfluence graph, said RDThe influence graph contains RD- Δ i and RD-an S-relationship graph;
the R isLThe ratio of the length L of the filter pipe of the precipitation well to the thickness T of the precipitation aquifer is obtained;
the R isDThe ratio of the depth D to the depth T of the waterproof curtain inserted into the precipitation aquifer;
the environmental effect refers to: calculating the hydraulic gradient delta i of the well and the surface settlement value S of the settlement calculation point outside the pit on two sides of the waterproof curtain;
s5, respectively fitting R obtained in S4 by using Boltzmann methodD- Δ i diagram, RD-S relationship diagram, resulting in RDBoltzmann curve, R, for Δ iD-Boltzmann curve of S, wherein:
by the pair RDBoltzmann curve derivation of- Δ i yields the difference at a given RLIn the case of (1), considering R controlling the hydraulic gradient on both sides of the waterproof curtainDMinimum value of RD-h1Maximum value RD-h2Optimum value RD-h3；
The R isD-h1Is RD-abscissa corresponding to the maximum of the second derivative of the Boltzmann curve for Δ i;
the R isD-h2Is RD-abscissa corresponding to the minimum of the second derivative of the Boltzmann curve for Δ i;
the R isD-h3Is RD-abscissa corresponding to the maximum of the first derivative of the Boltzmann curve for Δ i;
by the pair RDBoltzmann curve derivation of-S yields the difference at a given RLIn the case of (2), R for controlling the sedimentation of the earth surface outside the pit is consideredDMinimum value of RD-s1Maximum value RD-s2Optimum value RD-s3；
The R isD-s1Is RD-abscissa corresponding to the minimum of the second derivative of the Boltzmann curve of S;
the R isD-s2Is RD-abscissa corresponding to the maximum of the second derivative of the Boltzmann curve of S;
the R isD-s3Is RD-abscissa corresponding to the first derivative minimum of the Boltzmann curve of S;
s6, comparing the two groups of data obtained in S5 to obtain the data at the given RLIn the case of (1), R controlled in consideration of the combined environmental effectDMinimum value of RD-1Maximum value RD-2Optimum value RD-3；
The R isD-1R obtained for S5D-h1And RD-s1The larger of (a);
the R isD-2R obtained for S5D-h2And RD-s2The larger of (a);
the R isD-3R obtained for S5D-h3And RD-s3The larger of (a);
s7, adding RD-1、RD-2、RD-3Multiplying by T respectively to obtain the minimum value D of D given L1Maximum value D2Optimum value D3。
2. The method of claim 1, wherein the calibration model is selected from the group consisting of: firstly, adjusting the stratum parameters in S302, then simulating the water pumping test again based on the finite element model reestablished in S301-S305, and comparing the simulation data with the test data; this process is repeated until the maximum deviation of the simulated data from the experimental data is less than the threshold.
3. The method of determining the depth of insertion of a suspended waterproof curtain into a rainfall aquifer according to claim 1, wherein the radius of influence of precipitation R is calculated using the formula:
in the formula (I), the compound is shown in the specification,
the average level equivalent permeability coefficient of the precipitation aquifer is calculated according to the following formula
Wherein T is the thickness of the precipitation aquifer, u is the number of soil layers between the top and bottom of the precipitation aquifer, and khiIs the horizontal permeability coefficient of the ith soil layer between the top and the bottom of the precipitation water-bearing layer hiIs the thickness of the ith soil layer, obtained from S1; h is the water level depth of the precipitation aquifer and is calculated according to the following formula:
in the formula, H0Is the initial water level of the precipitation aquifer; n is the number of soil layers from the top plate of the precipitation aquifer to the excavation surface of the foundation pit; gamma raysiIs the gravity of the i-th layer of soil between the top plate of the rainfall aquifer and the excavation surface of the foundation pit, hiIs the thickness of the ith soil layer, obtained from S1; gamma raywIs the severity of the water; fsIs the engineering safety factor.
4. The method of determining the depth of insertion of a suspended waterproof curtain into a precipitation aquifer of claim 1, wherein the soil mass gravity γ, the void fraction e is determined by S1;
permeability coefficient k of each soil layerx、kyHorizontal permeability coefficient k equal to S1hCoefficient of permeability kzVertical permeability coefficient k equal to S1v；
Water storage coefficient S of each soil layersBy using the lower partCalculating the formula:
in the formula, gammawHeavy of water, EsThe compressive modulus of soil was obtained from S1.
5. The method for determining the depth of the suspended waterproof curtain inserted into the aquifer, according to any one of claims 1 to 4, wherein in S4, the calculation well is arranged 4 to 6 times the thickness of the waterproof curtain from one side of the waterproof curtain, and the structural information is the same as that of the observation well in S2.
6. The method of determining the depth of insertion of a suspended waterproof curtain into a precipitation aquifer of claim 5, wherein the settlement calculation point is located 3 excavation depths outside the pit.
7. The method of determining the depth of insertion of a suspended waterproof curtain into a rainfall aquifer according to claim 6, wherein Δ i is calculated using the formula:
in the formula (I), the compound is shown in the specification,
calculating the water level difference of the well at two sides of the water stopping curtain, wherein l is the length of the shortest fold line passing through the midpoint of the well filter tube outside the pit, the bottom of the water stopping curtain and the midpoint of the well filter tube in the pit.
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| CN105239611A (en) * | 2015-10-22 | 2016-01-13 | 上海交通大学 | Method for determining influence of waterproof curtain leakage below foundation pit excavation surface on surroundings |
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