CN112597673A - Method for determining effect of servo support system on foundation pit deformation control under rainfall condition - Google Patents
Method for determining effect of servo support system on foundation pit deformation control under rainfall condition Download PDFInfo
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Abstract
本发明提供了一种确定降雨条件下伺服支撑系统对基坑变形控制效果的方法，该方法根据土层信息及基坑资料，观测的实际降雨量情况，场区地表入渗面积以及基坑防渗措施；建立三维有限元模型，根据工程采取的防渗措施设置围护结构单元和地表的渗透性；按照伺服钢支撑系统在数值模型的相应位置设置自定义支撑单元；施加与实际降雨量对应的时间相关的降雨边界条件；对自定义支撑单元假设不同的伺服支撑轴力，并依次采用流固耦合模块模拟基坑开挖、渗流固结，最终确定降雨条件下伺服钢支撑系统对基坑变形的控制效果。本发明方法简单，便于推广，适用于降雨条件下的基坑变形控制问题。
The invention provides a method for determining the control effect of the servo support system on the deformation of the foundation pit under the condition of rainfall. seepage measures; establish a three-dimensional finite element model, set the permeability of the enclosure structure unit and the surface according to the anti-seepage measures taken in the project; set the custom support unit at the corresponding position of the numerical model according to the servo steel support system; apply corresponding to the actual rainfall The time-dependent rainfall boundary conditions are assumed; different servo support axial forces are assumed for the custom support unit, and the fluid-structure coupling module is used to simulate the excavation and seepage consolidation of the foundation pit in turn, and finally determine the effect of the servo steel support system on the foundation pit under rainfall conditions. Deformation control effect. The method of the invention is simple, easy to popularize, and suitable for the problem of deformation control of foundation pits under rainfall conditions.
Description
Technical Field
The invention relates to a method in the technical field of constructional engineering, in particular to a method for determining the effect of a servo support system on foundation pit deformation control under rainfall conditions.
Background
With the continuous development of underground space, more and more foundation pit projects are close to existing building structures, and the problem of how to control the excavation deformation of the foundation pit to reduce the influence on the surrounding environment becomes the concern of the engineering industry. In recent years, the servo steel support system has obvious control effect on foundation pit deformation, and is gradually applied and popularized in foundation pit engineering practice. The servo steel support system mainly comprises a hydraulic system module and an automatic control system module, and can automatically compensate the problem of axial force loss of the steel support through monitoring and regulation. However, due to lack of sufficient engineering practice experience and computational theory guidance, the application of the servo steel support system still has construction risks. Through the search of the prior art documents, the research on the servo steel support system mainly focuses on the aspects of the servo steel support device and the construction method.
Meanwhile, the existing literature data show that the rainfall infiltration can cause the deformation and sudden increase of the foundation pit, and serious threats are caused to the construction safety and the surrounding environment. How to effectively control the deformation of the foundation pit under the rainfall condition also becomes a problem to be solved urgently.
Through retrieval, the Chinese invention patent application number: 202010841498.X, application date: 2020-08-20, relates to a method for determining the critical water content of rainfall parameter weakening type foundation pit slope instability, and aims to achieve timely and effective early warning by adopting a uniform deformation control value to judge whether the foundation pit slope instability is unreasonable and a method for determining the critical water content of rainfall parameter weakening type foundation pit slope instability.
At present, no published engineering application case and relevant research about the control of the servo steel support system on the deformation of the foundation pit under the rainfall condition is published. However, the problem of controlling the deformation of the foundation pit under the rainfall condition by the servo steel supporting system cannot be solved by the above patent. The stress deformation characteristic of the foundation pit under the rainfall condition is greatly different from that of the conventional foundation pit, and the stability of the foundation pit under the action of the servo steel support system cannot be reasonably predicted according to the existing engineering experience. Therefore, the servo steel support system is adopted to control the deformation of the foundation pit under the rainfall condition, the deformation of the foundation pit is accurately predicted, and the method has important significance for construction risk control.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for determining the effect of a servo support system on foundation pit deformation control under the rainfall condition.
The invention is realized by the following technical scheme:
the invention provides a method for determining the effect of a servo support system on foundation pit deformation control under rainfall conditions, which comprises the following steps:
s1, acquiring soil layer information and relevant parameters of the foundation pit, including:
performing on-site investigation, determining soil layer division information and underground water distribution conditions, performing indoor geotechnical tests by drilling and taking soil, and acquiring physical and mechanical parameters and soil-water characteristic curves of soil layers;
acquiring the plane size, the excavation depth and the supporting structure form of the foundation pit, the thickness, the embedding depth, the elastic modulus and the hydraulic conductivity of the enclosure structure, and determining the equivalent elastic modulus considering the strength reduction effect;
acquiring the actual rainfall distribution condition in the early stage of the site and the surface infiltration area of the field area, and predicting the rainfall condition in the later stage;
s2, establishing a three-dimensional numerical model by using finite element software, setting initial conditions and boundary conditions of the three-dimensional numerical model and mechanical parameters of each soil layer and each structural unit according to the parameters obtained in S1, and setting permeability of an envelope structural unit and the earth surface in the three-dimensional numerical model;
s3, setting a self-defined supporting unit in the three-dimensional numerical model according to the arrangement condition of the servo steel supports;
s4, setting boundary conditions related to the time corresponding to the actual rainfall and the predicted rainfall condition in the three-dimensional numerical model after the self-defined supporting unit is set in S3;
and S5, assuming different servo support axial forces for the user-defined support unit in the three-dimensional numerical model after the boundary conditions are set in the S4, and sequentially simulating foundation pit excavation and seepage consolidation by adopting a fluid-solid coupling module, so that the control effect of excavation deformation of foundation pits with different servo support axial forces under the rainfall condition is determined.
Compared with the prior art, the embodiment of the invention has at least one of the following beneficial effects:
according to the method, the user-defined supporting unit is arranged in the foundation pit excavation numerical model applying the rainfall boundary condition, the influence of rainfall infiltration and supporting axial force on the foundation pit deformation can be considered at the same time, and the control effect of the servo steel supporting system on the foundation pit deformation under the rainfall condition is finally determined.
The method is simple, convenient to popularize, suitable for the problem of foundation pit deformation control under the rainfall condition and has important significance for construction risk control.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a flow chart of a method of a preferred embodiment of the present invention;
FIG. 2 is a diagram illustrating a distribution of rainfall in an embodiment of the present invention;
fig. 3 is a schematic diagram of final lateral movement of the foundation pit under the supporting action of the servo steel according to an embodiment of the invention.
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.
FIG. 1 is a flow chart of a method according to a preferred embodiment of the present invention. The embodiment of the invention provides a method for determining the effect of a servo support system on foundation pit deformation control under rainfall conditions, which is characterized in that a three-dimensional finite element model is established according to the observed rainfall infiltration condition on the basis of knowing soil layer information and foundation pit data; setting the permeability of the building envelope unit and the earth surface, and setting a rainfall boundary condition related to the time corresponding to the actual rainfall; setting a self-defined supporting unit at a corresponding position of the numerical model according to the servo steel supporting system; different servo supporting axial forces are assumed for the user-defined supporting unit, the fluid-solid coupling module is adopted to simulate foundation pit excavation and seepage consolidation in sequence, and finally the control effect of the servo steel supporting system on foundation pit deformation under the rainfall condition is determined.
Specifically, referring to fig. 1, the method for determining the effect of the servo support system on controlling the deformation of the foundation pit under the rainfall condition in the embodiment includes the following steps:
s100, carrying out on-site investigation on a foundation pit, determining soil layer division information and underground water distribution conditions, carrying out indoor geotechnical tests by drilling and taking soil, and obtaining physical and mechanical parameters of the soil layer and a soil-water characteristic curve;
in this step, the soil layer division means: dividing soil layers within a foundation pit depth range of 2.5 times below the ground surface in the foundation pit by a drilling and soil sampling method, then obtaining a construction site soil sample to perform an indoor soil test, obtaining construction site soil layer division information and geological information, and determining the soil property of each soil layer and the thickness of the corresponding soil layer.
In this step, the groundwater distribution condition means: adopting a drilling water detector to carry out underground water drilling detection on the foundation pit field, and judging the type and thickness of the aquifer according to the exposed soil type; and drilling to observe the stable water levels of different aquifers, and taking water-resisting measures to the confined aquifer to isolate the aquifer to be measured from other aquifers and then measuring the stable water levels.
In this step, the physical and mechanical parameters are as follows: the effective cohesive force, the effective friction angle and the elastic modulus of the soil body are measured through a soil test.
In this step, the soil-water characteristic curve means: the suction force of the soil body in the matrix changes along with the change of the water content.
S200, acquiring the plane size, the excavation depth, the supporting structure form, the thickness, the embedding depth, the elastic modulus and the hydraulic conductivity of the enclosure structure, and determining the equivalent elastic modulus considering the strength reduction effect;
in the step, the water conductivity of the enclosure structure is divided into a horizontal direction and a vertical direction, and is determined by the permeability and the thickness of the enclosure structure.
In the step, the reduction effect of the elastic modulus strength of the enclosure structure is caused by concrete cracks and other problems, and the equivalent elastic modulus E meets the following relation:
E＝ηEc
wherein: eta is modulus reduction coefficient, and is taken as 0.8; ecIs the modulus of elasticity of reinforced concrete.
S300, observing the actual rainfall distribution condition of the site and the surface infiltration area of the field, and predicting the later rainfall condition;
in this step, the distribution of rainfall is: distribution of rainfall over time;
in this step, the surface infiltration area refers to: the area and distribution of rainfall infiltration can occur at the earth surface within the main influence range of foundation pit excavation under the influence of the surrounding environment and buildings.
The steps S100 to S300 do not require strict sequence, may be performed in parallel, or may be performed in any sequence, and are mainly used to obtain soil layer information and parameters related to the foundation pit for setting the three-dimensional numerical model in the subsequent steps.
S400, establishing a three-dimensional numerical model by adopting finite element software, and setting permeability of an enclosure structure unit and the earth surface in the numerical model according to initial conditions and boundary conditions of the numerical model set by field investigation;
in this step, the initial conditions are: setting the pore pressure of a water line to be zero, carrying out ground stress balance and enabling displacement to return to zero;
in this step, the boundary conditions are: the periphery of the three-dimensional numerical model is set to be a constant head boundary, peripheral displacement is normal phase constraint, the bottom is a fixed boundary condition, and the surface boundary is set with virtual rainfall simulation daily rainfall.
S500, setting a self-defined supporting unit at a corresponding position of the numerical model according to the arrangement condition of the servo steel supports;
in this step, the custom support unit is a two-node elastic unit with constant elastic modulus, and the support unit and other entity units share a node in the numerical model, and have two basic parameters: modulus of elasticity E and cross-sectional area A.
S600, setting boundary conditions related to time corresponding to actual rainfall and predicted rainfall conditions in the three-dimensional numerical model;
in this step, the boundary condition related to the time corresponding to the actual rainfall amount refers to a rainfall function in which the rainfall amount changes with time, and the boundary condition may be expressed as:
wherein: h is boundary head; z is boundary position head;
the maximum value of the depth of the accumulated water; q is rainfall intensity; ssIs the infiltration capacity of the soil body. q. q.sxAnd q isyThe seepage flow rates in the horizontal direction and the vertical direction are respectively; n isxAnd nyHorizontal and vertical vectors, respectively;
is the total amount of seepage.
S700, assuming different servo supporting axial forces of the user-defined supporting unit, simulating foundation pit excavation and seepage consolidation by adopting the fluid-solid coupling module in sequence, and determining the control effect of excavation deformation of the foundation pit with different servo supporting axial forces under the rainfall condition.
In this step, the different servo support axial forces refer to the support axial forces after the excavation is controlled by the prestress of the support unit.
In this step, the excavation process of the foundation pit refers to: and sequentially freezing soil bodies on the inner side of the foundation pit, activating the structural units, and completing the excavation and supporting process of the foundation pit.
In order to better illustrate the technical solutions in the above embodiments of the present invention, the following detailed description is further described with reference to the accompanying drawings and application examples, but the present invention is not limited to the following embodiments.
In this embodiment, a method for determining a control effect of a servo support system on deformation of a foundation pit under a rainfall condition, where a certain foundation pit project is a rectangular foundation pit, an underground continuous wall is used as a building enclosure, and a process shown in fig. 1 is referred to, includes the following steps:
s1, performing on-site investigation on the foundation pit, determining soil layer division information and underground water distribution conditions, performing indoor geotechnical tests by drilling and taking soil, and acquiring physical and mechanical parameters and soil-water characteristic curves of the soil layer;
in this step, it can be determined by the drilling and borrowing method that the soil layer in which the foundation pit is located is from top to bottom:
the first layer is miscellaneous filling soil with the thickness of 2 m;
the second layer is a powdery clay with a thickness of 5 m;
the third layer is residual powder clay with the thickness of 6 m;
the fourth layer is a fully weathered rock with a thickness of 4 m;
the fifth layer is a conglomerate weathered rock with the thickness of 6 m;
the sixth layer is medium weathered granite.
The physical and mechanical properties of the soil body of the foundation pit soil layer obtained by taking soil for an indoor conventional test are shown in table 1:
TABLE 1 soil physical and mechanical Properties
S2, acquiring the plane size, excavation depth, supporting structure form, enclosure structure thickness, embedding depth, elastic modulus and hydraulic conductivity of the foundation pit, and determining the equivalent elastic modulus considering the strength reduction effect;
in this embodiment: the foundation pit is a rectangular foundation pit, the long side of the foundation pit is 50m, the short side of the foundation pit is 30m, and the excavation depth is 13 m; first supportConcrete supports are adopted, and the second support is a steel support; the thickness of the diaphragm wall is 0.8m, the depth is 20m, and the gravity is 25kN/m3The horizontal permeability coefficient and the vertical permeability coefficient are assumed to be 0. The envelope equivalent elastic modulus E considering the strength reduction effect meets the following formula:
E＝ηEc
wherein: eta is modulus reduction coefficient, and is taken as 0.8; ecThe elastic modulus of the reinforced concrete is obtained by the following values:
E＝ηEc＝0.8×200＝160GPa。
s3, observing the actual rainfall distribution situation and the ground infiltration area of the field
In this embodiment: the actual rainfall distribution is shown in fig. 2, no large-area building structures are arranged around the foundation pit, and rainfall can permeate into the ground surface in the field.
And S4, establishing a quasi-three-dimensional numerical model by using finite element software PLAAXIS. The numerical model is 90m long, 4m thick and 40m high to eliminate the influence of boundary conditions on the calculation result, and the whole model has 81498 nodes and 53272 units.
According to the field investigation result, the initial conditions of the three-dimensional numerical model are that the initial water level is 17m below the ground, the pore pressure at the water level is zero, and the displacement returns to zero after the ground stress is balanced;
the boundary conditions are that the periphery of the three-dimensional numerical model is set as a constant head boundary, the peripheral displacement is normal phase constraint, the bottom is a fixed boundary condition, and the surface boundary is set with 2mm/d of virtual rainfall simulation daily rainfall;
and according to the physical and mechanical properties of the soil body and the information of the foundation pit supporting structure obtained in the S1 and S2, setting mechanical parameters of the soil body and the structural units of each layer in the three-dimensional numerical model, and setting the permeability of the enclosure structural units and the surface boundary.
S5, setting a self-defined supporting unit at the corresponding position of the three-dimensional numerical model according to the arrangement condition of the servo steel supports;
s6, setting a time-dependent boundary condition corresponding to the actual rainfall in the three-dimensional numerical model;
wherein: h is boundary head; z is boundary position head;
the maximum value of the depth of the accumulated water; q is rainfall intensity;
s7, assuming different servo support axial forces for the user-defined support unit, sequentially simulating foundation pit excavation and seepage consolidation by adopting a fluid-solid coupling module, and determining the control effect of excavation deformation of the foundation pit with different servo support axial forces under rainfall conditions, as shown in FIG. 3.
According to the embodiment of the invention, the influence of rainfall infiltration and supporting axial force on the deformation of the foundation pit can be considered at the same time, and the control effect of the servo steel supporting system on the deformation of the foundation pit under the rainfall condition is finally determined, so that the method is suitable for the problem of the control of the deformation of the foundation pit under the rainfall condition.
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 and 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.
Claims (10)
1. A method for determining the effect of a servo support system on foundation pit deformation control under rainfall conditions is characterized by comprising the following steps:
s1, acquiring soil layer information and relevant parameters of the foundation pit, including:
performing on-site investigation, determining soil layer division information and underground water distribution conditions, performing indoor geotechnical tests by drilling and taking soil, and acquiring physical and mechanical parameters and soil-water characteristic curves of soil layers;
acquiring the plane size, the excavation depth and the supporting structure form of the foundation pit, the thickness, the embedding depth, the elastic modulus and the hydraulic conductivity of the enclosure structure, and determining the equivalent elastic modulus considering the strength reduction effect;
acquiring the actual rainfall distribution condition in the early stage of the site and the surface infiltration area of the field area, and predicting the rainfall condition in the later stage;
s2, establishing a three-dimensional numerical model by using finite element software, setting initial conditions and boundary conditions of the three-dimensional numerical model and mechanical parameters of each soil layer and each structural unit according to the parameters obtained in S1, and setting permeability of an envelope structural unit and the earth surface in the three-dimensional numerical model;
s3, setting a self-defined supporting unit in the three-dimensional numerical model according to the arrangement condition of the servo steel supports;
s4, setting boundary conditions related to the time corresponding to the actual rainfall and the predicted rainfall condition in the three-dimensional numerical model after the self-defined supporting unit is set in S3;
and S5, assuming different servo support axial forces for the user-defined support unit in the three-dimensional numerical model after the boundary conditions are set in the S4, and sequentially simulating foundation pit excavation and seepage consolidation by adopting a fluid-solid coupling module, so that the control effect of excavation deformation of foundation pits with different servo support axial forces under the rainfall condition is determined.
2. The method for determining the effect of the servo support system on foundation pit deformation control under rainfall conditions as claimed in claim 1, wherein in S1:
the soil layer division means that: dividing soil layers within a foundation pit depth range of 2.5 times below the ground surface in the foundation pit by a drilling and soil sampling method, then obtaining a construction site soil sample to perform an indoor soil test, obtaining construction site soil layer division information and geological information, and determining the soil property of each soil layer and the thickness of the corresponding soil layer;
the underground water distribution condition is as follows: adopting a drilling water detector to carry out underground water drilling detection on the foundation pit field, and judging the type and thickness of the aquifer according to the exposed soil type; drilling to observe the stable water levels of different aquifers, and taking water-resisting measures for the confined aquifer to isolate the measured aquifer from other aquifers and then measuring the stable water levels;
the physical and mechanical parameters are as follows: the effective cohesive force, the effective friction angle and the elastic modulus of the soil body are measured through a soil test;
the soil-water characteristic curve is as follows: the suction force of the soil body in the matrix changes along with the change of the water content.
3. The method for determining the effect of the servo support system on controlling the deformation of the foundation pit under the rainfall condition as claimed in claim 1, wherein in S1, the hydraulic conductivity of the enclosure is divided into horizontal direction and vertical direction, which are determined by the permeability and thickness of the enclosure.
4. The method for determining the effect of the servo support system on controlling the deformation of the foundation pit under the rainfall condition as claimed in claim 1, wherein in S1, the effect of reducing the elastic modulus strength of the enclosure structure is caused by concrete cracks, and the equivalent elastic modulus E satisfies the following relationship:
E＝ηEc
wherein: eta is modulus reduction coefficient, and is taken as 0.8; ecIs the modulus of elasticity of reinforced concrete.
5. The method for determining the effect of the servo support system on foundation pit deformation control under rainfall conditions as claimed in claim 1, wherein in S1:
the rainfall distribution condition is as follows: distribution of rainfall over time;
the surface infiltration area refers to: the area and distribution of the rainfall infiltration at the earth surface within the main influence range of the excavation of the foundation pit are influenced by the surrounding environment and buildings.
6. The method for determining the effect of the servo support system on foundation pit deformation control under rainfall conditions as claimed in claim 1, wherein in S2:
the initial conditions are as follows: setting the pore pressure of a water line to be zero, carrying out ground stress balance and enabling displacement to return to zero;
the boundary conditions are as follows: the periphery of the numerical model is set to be a constant head boundary, peripheral displacement is normal phase constraint, the bottom is a fixed boundary condition, and the surface boundary is set with virtual rainfall simulation daily rainfall.
7. The method according to claim 1, wherein in S3, the self-defined support unit is a two-node elastic unit with constant elastic modulus, and the self-defined support unit shares a node with other entity units in the three-dimensional numerical model, and has two basic parameters: modulus of elasticity E and cross-sectional area A.
8. The method according to claim 1, wherein in S4, the boundary condition related to the actual rainfall is a rainfall function setting the rainfall as a function of time, and the boundary condition is expressed as:
wherein: h is boundary head; z is boundary position head;
the maximum value of the depth of the accumulated water; q is rainfall intensity; ssThe infiltration capacity of the soil body; q. q.sxAnd q isyThe seepage flow rates in the horizontal direction and the vertical direction are respectively; n isxAnd nyHorizontal and vertical vectors, respectively;
is the total amount of seepage.
9. The method for determining the effect of the servo support system on controlling the deformation of the foundation pit under the rainfall condition as claimed in claim 1, wherein in S5, the different servo support axial forces are the support axial forces after the excavation of the foundation pit is controlled by setting the prestress of the self-defined support unit.
10. The method for determining the effect of the servo support system on controlling the deformation of the foundation pit under the rainfall condition as claimed in claim 1, wherein in S5, the excavation of the foundation pit refers to: and sequentially freezing soil bodies on the inner side of the foundation pit according to actual construction conditions, activating the structural units representing the horizontal supports, and completing the excavation and supporting processes of the foundation pit.
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