CN115795978B - Prediction method for existing tunnel floating caused by foundation pit excavation considering various influencing factors - Google Patents
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Abstract
The invention provides a prediction method for the floating up of an existing tunnel caused by excavation of a foundation pit in consideration of multiple influencing factors, which comprises the following steps: determining each influence factor of the foundation pit excavation enclosure, which leads to the floating of the existing tunnel: establishing the association between the maximum lateral displacement of the foundation pit support and each influence factor; establishing a finite element calculation model according to the actual excavation step sequence of the foundation pit; establishing the correlation between the floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit enclosure; obtaining the correlation between the floating quantity of the existing tunnel and each influence factor; and acquiring parameters of each influence factor of the existing tunnel floating caused by the foundation pit excavation enclosure in the to-be-constructed engineering, and predicting the floating quantity of the existing tunnel in the to-be-constructed engineering by the factors. The prediction method provided by the invention can predict the floating amount of the foundation pit excavation caused to the existing tunnel below according to the parameter factors of each influence factor of the foundation pit excavation enclosure caused to float in the to-be-constructed engineering, so that whether the existing design needs to be optimized and adjusted or not can be judged in advance, and the risk control cost is greatly reduced.
Description
Technical Field
The invention relates to the technical field of underground engineering construction, in particular to a prediction method for the floating up of an existing tunnel caused by excavation of a foundation pit in consideration of various influencing factors.
Background
Foundation pit engineering is a complex system engineering, the stress and deformation of which are comprehensively influenced by a plurality of factors, including: geological hydrologic condition of field soil, surrounding environmental condition (ground overload, surrounding buildings, underground pipelines and the like), foundation pit plane shape and scale and building enclosure rigidityThe embedded depth of the wall body, the supporting form, the plane rigidity, the supporting prestress and the construction method (the construction method of the retaining wall and the supporting, the construction quality, the excavation sequence, the soil excavation time and the like). By a single factor such as: foundation pit excavation depth H, foundation pit excavation width E1, unit width underground diaphragm wall rigidity EI, axial rigidity EA of supporting structure or clay normalized non-drainage strength Su/sigma v ' (Su is the non-drainage shear Strength, sigma) v ' effective vertical stress) and the like, the deformation discreteness of the ground surface after the foundation pit support structure and the wall is large, and the change relation between the ground surface deformation discreteness and the internal force and displacement of a foundation pit system cannot be well represented.
The comprehensive rigidity of the existing MVSS (multiple variaE1les system stiffness) mainly shows the rule between each influencing factor and the deformation of the foundation pit, and the deformation condition of the existing tunnel is not shown.
Research results show that the research on the floating of the tunnel caused by excavation of the foundation pit is mostly concentrated on the rule analysis of one or two influencing factors, but the factors influencing the floating of the tunnel are more, such as: the foundation pit depth, the vertical clear distance between the pit bottom and the tunnel, the foundation pit supporting form, the substrate reinforcing mode, the foundation pit excavation framing mode, the foundation pit dewatering construction, the excavation time effect and other factors.
Therefore, it is necessary to provide a prediction method for the existing tunnel to float up due to excavation of the foundation pit in consideration of various influencing factors.
Disclosure of Invention
In view of the defects of the prior art, the main purpose of the invention is to provide a prediction method for the floating up of the existing tunnel caused by the excavation of the foundation pit by considering various influencing factors, so as to solve the limitation of floating rule analysis on the existing tunnel caused by the excavation of the foundation pit in the prior art.
The technical scheme of the invention is as follows:
a prediction method for foundation pit excavation with various influencing factors considered to cause floating up of an existing tunnel comprises the following steps:
step one: determining each influence factor of the foundation pit excavation enclosure, which leads to the floating of the existing tunnel;
step two: establishing the association between the maximum lateral displacement of the foundation pit support and each influence factor;
step three: establishing a finite element calculation model according to the actual excavation step sequence of the foundation pit, and obtaining the existing tunnel floating quantity and the maximum lateral displacement of the foundation pit support corresponding to the excavation depth through simulation calculation;
step four: establishing the correlation between the floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit enclosure;
step five: according to the second step and the fourth step, the correlation between the floating quantity of the existing tunnel and each influence factor is obtained;
step six: and (3) acquiring parameters of each influence factor causing the floating of the existing tunnel by the foundation pit excavation enclosure in the construction project to be constructed, and predicting the floating amount of the existing tunnel in the construction project to be constructed according to the association between the floating amount of the existing tunnel and each influence factor.
In some embodiments, the foundation pit excavation takes the form of an internal support brace, including a concrete brace and/or a steel brace.
In some embodiments, in the first step, determining each influence factor of the pit excavation enclosure to cause the existing tunnel to float includes:
introducing the MVSS comprehensive rigidity of the foundation pit enclosure:
wherein k is t K is the integrated adjustment coefficient based on space-time effect and insertion ratio j Is a foundation reinforcement influencing factor, (mk) 1 +nk 2 )/[(m+n)k 1 ]For the influence factor of the supporting rigidity, m is the number of steel supporting channels, n is the number of concrete supporting channels, and k is the number of concrete supporting channels 1 For steel support stiffness, k 2 For the concrete support rigidity, EI is the fender post/wall rigidity, gamma w The gravity of water, H is the average vertical spacing of the supports, H is the depth of the foundation pit, and s is the average horizontal spacing of the supports.
In some embodiments, in the second step, the associating the maximum lateral displacement of the foundation pit support with each influence factor includes:
defining a dimensionless maximum lateral relative displacement y=δ of a foundation pit enclosure max /H；
Through finite element calculation and fitting, a functional relation between the dimensionless maximum lateral relative displacement y of the foundation pit enclosure and the MVSS comprehensive rigidity of the foundation pit enclosure is established:
wherein δmax is the maximum lateral displacement of the foundation pit enclosure, alpha 2 、β 2 Is a variable parameter of comprehensive rigidity.
In some embodiments, the computing and fitting by finite elements comprises:
determining a typical geological condition of foundation pit excavation;
the dimensionless maximum lateral relative displacement delta of the foundation pit enclosure is calculated through finite elements max /H；
Drawing the MVSS comprehensive rigidity of the foundation pit enclosure and the dimensionless maximum lateral relative displacement delta of the foundation pit enclosure max graph/H;
and fitting the graph to obtain a functional relation between the dimensionless maximum lateral relative displacement y of the foundation pit support and the MVSS comprehensive rigidity of the foundation pit support.
In some embodiments, the pit excavation typically includes:
class (1) formation: the foundation pit bottom is filled with silt soil, and the pit bottom is a thicker silt stratum;
class (2) formation: the foundation pit bottom and the upper surface of the foundation pit bottom are all in a silt stratum;
class (3) formation: the upper part of the foundation pit bottom and the pit bottom are both silt stratum.
In some embodiments, in the fourth step, the associating the existing tunnel float and the maximum lateral displacement of the foundation pit enclosure includes:
performing curve fitting on the floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit support to obtain a linear relation between the floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit support, wherein the linear function relation is as follows:
in the formula, P is the floating quantity of the existing tunnel, k is a constant, and δmax is the maximum lateral displacement of the foundation pit support.
In some embodiments, the constant k is obtained by:
the corresponding floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit enclosure under three types of strata are respectively obtained through finite element modeling calculation;
obtaining linear function relation between the corresponding floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit support under three stratum through curve fitting, and further obtaining a corresponding coefficient k;
respectively taking soil layer deformation moduli Es corresponding to the three types of strata;
curve fitting is carried out on the coefficient k and the soil deformation modulus Es, and a functional relation between the coefficient k and the soil deformation modulus Es is obtained as follows:
where k is a constant and Es is a soil layer deformation modulus.
In some embodiments, in the fifth step, the obtaining the association between the existing tunnel float and each influencing factor includes:
the foundation pit is supported to have dimensionless maximum lateral relative displacement y=delta max And (3) carrying into the formula (3) to obtain a functional relation between the floating quantity of the existing tunnel and the dimensionless maximum lateral relative displacement y of the foundation pit enclosure:
wherein P is the floating quantity of the existing tunnel, k is a constant, and H is the depth of the foundation pit.
In some embodiments, in step six, the predicting the floating amount of the existing tunnel includes:
acquiring parameters of each influence factor of the foundation pit excavation enclosure in the construction project to be constructed, which cause the floating of the existing tunnel;
substituting the functional relation between the foundation pit support dimensionless maximum lateral relative displacement y and the foundation pit support MVSS comprehensive rigidity to obtain the foundation pit support dimensionless maximum lateral relative displacement y;
and calculating the floating quantity of the existing tunnel according to a functional relation between the floating quantity of the existing tunnel and the dimensionless maximum lateral relative displacement y of the foundation pit enclosure.
Compared with the prior art, the invention has the beneficial effects that:
the prediction method for the floating of the existing tunnel caused by the excavation of the foundation pit taking various influencing factors into consideration can predict the floating amount of the foundation pit excavation on the existing tunnel below according to the parameters of each influencing factor of the floating of the existing tunnel caused by the excavation of the foundation pit in the construction project to be constructed, so that whether the existing design needs to be optimized and adjusted or not can be judged in advance, and the risk control cost is greatly reduced.
Based on the original comprehensive rigidity theoretical formula, the invention obtains the relation rule between the comprehensive rigidity and the existing tunnel floating deformation by means of finite element calculation and the like based on the prior engineering background, namely, the relation rule comprises the following steps: and building new association between the result of finite element calculation and the floating deformation of the existing tunnel under the action of various influence factors such as foundation pit supporting form, substrate reinforcing mode, excavation framing mode, time effect and the like, so as to obtain a quantifiable rule of influence of open cut foundation pit excavation on the floating of the existing tunnel below under the condition of various influence factors.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It will be apparent to those of ordinary skill in the art that the drawings in the following description are exemplary only and that other implementations can be obtained from the extensions of the drawings provided without inventive effort.
The structures, proportions, sizes, etc. shown in the present specification are shown only for the purposes of illustration and description, and are not intended to limit the scope of the invention, which is defined by the claims, but rather by the claims.
FIG. 1 is a schematic overall flow chart of a prediction method for excavating a foundation pit to cause floating up of an existing tunnel by considering various influencing factors according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a finite element computational model according to an embodiment of the present invention;
FIG. 3 is a graph showing a function fit between maximum lateral displacement of a foundation pit enclosure and the amount of floating up in an existing shield zone according to one embodiment of the present invention;
FIG. 4 shows the soil deformation modulus E according to an embodiment of the present invention S And (3) fitting a curve diagram with a function between coefficients k in a prediction formula.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention will be described in further detail with reference to the embodiments and the accompanying drawings. The exemplary embodiments of the present invention and their descriptions herein are for the purpose of explaining the present invention, but are not to be construed as limiting the invention.
It should be understood that the terms "comprises/comprising," "consists of … …," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a product, apparatus, process, or method that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such product, apparatus, process, or method as desired. Without further limitation, an element defined by the phrases "comprising/including … …," "consisting of … …," and the like, does not exclude the presence of other like elements in a product, apparatus, process, or method that includes the element.
At present, most of researches on tunnel floating caused by foundation pit excavation are focused on rule analysis of one or two influencing factors, but the factors influencing the tunnel floating are more, such as: the foundation pit depth, the vertical clear distance between the pit bottom and the tunnel, the foundation pit supporting form, the substrate reinforcing mode, the foundation pit excavation framing mode, the foundation pit dewatering construction, the excavation time effect and other factors. How to find the influence rule of foundation pit excavation on tunnel floating under the condition of combining various factors, the research is relatively few at present.
Based on the existing MVSS (multiple variaE E1les system stiffness) comprehensive rigidity theoretical formula, the invention provides a functional relation of foundation pit excavation on the floating quantity of the existing tunnel under the condition of containing various influencing factors, so as to effectively predict the deformation value of the existing tunnel and guide the safe construction similar to the actual project.
The implementation of the present invention will be described in detail with reference to the preferred embodiments.
As shown in fig. 1, the invention provides a prediction method for the existing tunnel floating caused by pit excavation considering various influencing factors, which comprises the following steps:
step one: determining each influence factor of the foundation pit excavation enclosure, which leads to the floating of the existing tunnel;
step two: establishing the association between the maximum lateral displacement of the foundation pit support and each influence factor;
step three: establishing a finite element calculation model according to the actual excavation step sequence of the foundation pit, and obtaining the existing tunnel floating quantity and the maximum lateral displacement of the foundation pit support corresponding to the excavation depth through simulation calculation;
step four: establishing the correlation between the floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit enclosure;
step five: according to the second step and the fourth step, the correlation between the floating quantity of the existing tunnel and each influence factor is obtained;
step six: and (3) acquiring parameters of each influence factor causing the floating of the existing tunnel by the foundation pit excavation enclosure in the construction project to be constructed, and predicting the floating amount of the existing tunnel in the construction project to be constructed according to the association between the floating amount of the existing tunnel and each influence factor.
According to the invention, the relation between the floating quantity of the existing tunnel and each influence factor of the floating of the existing tunnel caused by the foundation pit excavation enclosure is established, and for the construction project to be constructed, the floating quantity of the existing tunnel in the construction project to be constructed can be directly calculated by inquiring each influence factor parameter in the construction project before construction, so that whether the design scheme of the foundation pit excavation enclosure is required to be optimized and adjusted can be judged in advance, and the risk control cost is greatly reduced.
In the invention, the foundation pit excavation adopts an inner support supporting mode. It is readily understood that the foundation pit inner support includes concrete supports and steel supports, and the steel supports naturally also include steel section composite supports, such as concrete-type steel composite supports and steel section prestress composite supports.
In the invention, in the first step, each influence factor for determining that the foundation pit excavation enclosure causes the existing tunnel to float up comprises the following steps:
introducing the MVSS comprehensive rigidity of the foundation pit enclosure:
wherein k is t For the comprehensive adjustment coefficient based on the space-time effect, the insertion ratio and other influence factors, 1, k are generally taken j Is a foundation reinforcement influencing factor, (mk) 1 +nk 2 )/[(m+n)k 1 ]For the influence factor of the supporting rigidity, m is the number of steel supporting channels, n is the number of concrete supporting channels, and k is the number of concrete supporting channels 1 For steel support stiffness, k 2 For the concrete supporting rigidity, EI is the rigidity of the enclosure wall (pile), gamma w The gravity of water, H is the average vertical spacing of the supports, H is the depth of the foundation pit, and s is the average horizontal spacing of the supports.
The MVSS comprehensive rigidity characteristics of the foundation pit enclosure are as follows:
(1) The relationship contains the influence factors: the rigidity of the enclosure wall (pile), the depth of the foundation pit, the rigidity of the support, the horizontal and vertical spacing of the support, the reinforcement of the foundation, the space-time effect and the like.
(2) The comprehensive rigidity can reflect the integral attribute of the foundation pit support structure, and can establish a functional relation with the maximum deformation of the foundation pit support, namely, the same foundation pit MVSS comprehensive rigidity support system has the same wall displacement when the foundation pit is under the same inherent factors such as hydrogeological conditions, overload on the periphery of the foundation pit and construction factors such as overexcavation, construction period, construction method, engineering accident and the like.
(3) The comprehensive rigidity relation is simple and practical, the maximum lateral deformation of the enclosure can be rapidly predicted by calculating the comprehensive rigidity of the foundation pit enclosure, and the optimal enclosure design scheme can be selected more efficiently.
And a calculation formula of the comprehensive rigidity is introduced, and parameters related to the foundation pit (foundation pit supporting rigidity, foundation pit supporting form, foundation pit reinforcing measures, foundation pit space effect and the like) and the floating quantity of the existing tunnel are established in a functional relation by means of numerical simulation, so that the limitation that the influence of a certain factor on the floating quantity is only considered is solved.
In some embodiments, three typical geological conditions affecting deformation of a foundation pit enclosure include:
class (1) formation: the foundation pit bottom is filled with silt soil, and the pit bottom is a thicker silt stratum;
class (2) formation: the upper part of the foundation pit and the bottom of the pit are all silt stratum;
class (3) formation: the upper part and the bottom of the foundation pit are both silt stratum.
In the invention, as for construction factors, the maximum actual measurement deformation of the foundation pit enclosure under the conventional construction level condition of which the construction is completed is selected, and the unconventional monitoring data is removed.
In some embodiments, according to theoretical calculation and engineering practice verification of the deep foundation pit of the subway in the three stratum, the following relation can be established between the MVSS comprehensive rigidity of the foundation pit support structure and the dimensionless maximum lateral relative displacement delta max/H of the foundation pit support:
further, a dimensionless maximum lateral relative displacement y=δmax/H of the foundation pit support is defined.
Through finite element calculation and fitting, the following functional relation is established between the dimensionless maximum lateral relative displacement y of the foundation pit enclosure and the MVSS comprehensive rigidity of the foundation pit enclosure:
wherein δmax is the maximum lateral displacement of the foundation pit enclosure, H is the depth of the foundation pit, and alpha 2 、β 2 Is a variable parameter of comprehensive rigidity.
In the invention, the variable values in the foundation pit support MVSS comprehensive rigidity calculation formula are shown in table 1:
table 1 variable values in the foundation pit bracing MVSS integrated stiffness calculation
The method for calculating and fitting through finite elements specifically comprises the following steps:
determining a typical geological condition of foundation pit excavation;
calculating the dimensionless maximum lateral relative displacement delta max/H of the foundation pit support based on the finite element of the elastic foundation beam method;
drawing a graph of MVSS comprehensive rigidity of the foundation pit enclosure and a dimensionless maximum lateral relative displacement delta max/H of the foundation pit enclosure;
and fitting the graph to obtain a functional relation between the dimensionless maximum lateral relative displacement y of the foundation pit support and the MVSS comprehensive rigidity of the foundation pit support.
In the third step, the actual excavation step sequence of the foundation pit is as follows:
1) The self-weight stress of the stratum is balanced and the existing tunnel is arranged;
2) Constructing a foundation pit support structure;
3) Dewatering the foundation pit;
4) Excavating foundation pit layer by layer;
5) And excavating the foundation pit to a pit bottom position.
Further, in step four, referring to fig. 2, three-dimensional simulation calculation is performed by using PLAXIS finite element calculation software according to the actual excavation step of the foundation pit, the existing tunnel floating quantity corresponding to the excavation depth and the maximum lateral displacement of the foundation pit enclosure are obtained through simulation calculation, curve fitting is performed on the simulation calculation data by using origin software, the existing tunnel floating quantity obtained through fitting and the maximum lateral displacement of the foundation pit enclosure are in a linear relation, the larger the maximum lateral displacement of the foundation pit enclosure is, the larger the existing tunnel floating quantity is, and the linear function relation is:
in the formula, P is the floating quantity of the existing tunnel, k is a constant, and δmax is the maximum lateral displacement of the foundation pit support.
In the fifth step, the obtaining of the association between the existing tunnel floating quantity and each influence factor comprises the following steps:
bringing the maximum lateral relative displacement y=δmax/H of the foundation pit enclosure into formula (3), and obtaining a functional relation between the floating quantity of the existing tunnel and the maximum lateral relative displacement y of the foundation pit enclosure as follows:
wherein P is the floating amount of the existing tunnel, k is a constant, H is the depth of the foundation pit, and
，k t k is the integrated adjustment coefficient based on space-time effect and insertion ratio j Is a foundation reinforcement influencing factor, (mk) 1 +nk 2 )/[(m+n)k 1 ]For the influence factor of the supporting rigidity, m is the number of steel supporting channels, n is the number of concrete supporting channels, and k is the number of concrete supporting channels 1 For steel support stiffness, k 2 For the concrete supporting rigidity, EI is the rigidity of the enclosure wall (pile), gamma w Is the gravity of water, h is the average vertical spacing of supports, s is the average horizontal spacing of supports, alpha 2 、β 2 As a variable of integrated rigidityParameters.
With continued reference to fig. 2, the invention uses a 5 # line shield interval spanned on an air duct of a Nanning 4 # line flood interchange station as an engineering background, adopts PLAXIS finite element calculation software according to the actual excavation step of a foundation pit, performs three-dimensional simulation calculation, and obtains the existing tunnel floating quantity and the maximum lateral displacement of the foundation pit enclosure corresponding to the excavation depth through simulation calculation.
In the invention, the fact that the plane size of the foundation pit is calibrated is considered, different vertical excavation depths are adopted to describe different unloading amounts, namely, the excavation depths of the foundation pit are respectively valued as follows: 0.5m, 1m, 1.5m, 2m, 2.5m, 3m, 3.5m, 4m, 4.5m, 5m, 5.5m, 6m, 6.5m, 7m, 7.5m, 8m, 8.5m (pit bottom position).
The actual excavation step sequence of the foundation pit is as follows:
1) The self-weight stress of the stratum is balanced, and the existing tunnel is arranged (the buried depth of the tunnel top is 10.5 m);
2) Constructing foundation pit guard piles;
3) Dewatering the foundation pit;
4) Excavating foundation pit layer by layer (interval is 0.5 m);
5) And excavating the foundation pit to the burial depth of 8.5m.
The calculated data of the foundation pits at different excavation depths are arranged as shown in table 2:
TABLE 2 corresponding floating amount of existing shield zone and maximum lateral displacement of foundation pit support at different excavation depths
Referring to fig. 3, curve fitting the table 2 simulation calculation data using origin software yields:
in the invention, as the soil deformation modulus (weighting value is taken by a plurality of layers of soil layers) Es=46721 KPa in the tunnel crossing line 5 shield section engineering of the Nanning line 4 flood interchange station, namely when the soil deformation modulus is 46721KPa, k in the formula (5) is 0.5.
In addition, three-dimensional simulation calculation is performed on projects corresponding to the 3 types of strata by using PLAXIS finite element calculation software, so that corresponding functional relation formulas under the 3 types of strata are obtained, wherein P=0.42 δmax in the sandy stratum, P=0.32 δmax in the silty stratum and P=0.34 δmax in the clay stratum are obtained, corresponding coefficients k are obtained, and then corresponding soil deformation modulus Es (weighting values of multiple layers of soil layers) under the 3 types of strata are obtained.
The data corresponding to 4 groups of k and Es can be obtained through the steps, and the functional relation between the soil layer deformation modulus Es and the coefficient k is obtained through fitting on the basis, and is shown in the table 3:
TABLE 3 relation between soil deformation modulus Es and coefficient k
Fitting the data in Table 3 to obtain a fitted curve as shown in FIG. 4, and further obtaining the functional relationship between the coefficient k and the soil deformation modulus Es as follows:
can be obtained by substituting (4)
Wherein Es is soil deformation modulus (weighting value is taken by a plurality of layers of soil), and is obtained by inquiring related soil classification and corresponding parameters in engineering geological manuals.
According to the method, a functional relation between the shear modulus of the soil layer and the coefficient of the prediction formula is established, and further deformation prediction value calculation of the existing tunnel can be carried out by applying the prediction formula according to soil layer parameters in a specific engineering field.
Further, in the sixth step, obtaining the parameter of each influence factor to predict the floating amount of the existing tunnel includes:
acquiring parameters of each influence factor of the foundation pit excavation enclosure in the construction project to be constructed, which cause the floating of the existing tunnel;
substituting the functional relation between the foundation pit support dimensionless maximum lateral relative displacement y and the foundation pit support MVSS comprehensive rigidity to obtain the foundation pit support dimensionless maximum lateral relative displacement y;
and calculating the floating quantity of the existing tunnel according to a functional relation between the floating quantity of the existing tunnel and the dimensionless maximum lateral relative displacement y of the foundation pit enclosure.
And finally, comparing the predicted floating quantity of the existing tunnel with the floating quantity allowed in the standard of the prior art, and optimally adjusting each influence factor parameter until the design requirement is met if the predicted floating quantity is not met, so that the floating quantity value of the existing tunnel below by foundation pit excavation is predicted in advance, and further, whether the existing design scheme is required to be optimally adjusted or not can be judged in advance, thereby greatly reducing the risk control cost and optimizing the construction.
Based on the original comprehensive rigidity theoretical formula, the relation rule between the comprehensive rigidity and the existing tunnel floating deformation is obtained by means of finite element calculation and the like based on the existing engineering background. Namely, the comprehensive rigidity formula comprises the following steps: and building new association between the result of finite element calculation and the floating deformation of the existing tunnel under the action of various influence factors such as foundation pit supporting form, substrate reinforcing mode, excavation framing mode, time effect and the like, so as to obtain a quantifiable rule of influence of open cut foundation pit excavation on the floating of the existing tunnel below under the condition of various influence factors.
In a specific project, taking a 5-line shield section on an air duct of a Nanning 4-line flood interchange station as an example, the depth of an attached open excavation foundation pit of the Nanning 4-line flood interchange station is 8.5m, and a concrete support (C30) is arranged to support the horizontal spacing of 6 m-9 m. Based on the research results of the existing comprehensive rigidity, the variable values in the comprehensive rigidity of the foundation pit of the engineering are shown in table 4:
table 4 variable values in the integrated stiffness of the pit
Further, the values of various parameters in the foundation pit enclosure MVSS comprehensive rigidity formula in the 5 # line shield section engineering on the wind channel of the Nanning 4 # line-Nannon interchange station are as follows: alpha 2 =0.641，β 2 =0.262，k j =1.35，m=0，n=1，k t Because the engineering has no steel support, k is taken in the engineering 1 =k 2 =220MN/m，EI=180MN*m 2 ，γ w =9.8kN/m 3 ，H=8.5m，s=9m，h=8m。
Substituting each influence factor parameter into a relation formula (2) of the maximum lateral relative displacement y of the foundation pit enclosure dimensionless and the comprehensive rigidity of the foundation pit enclosure MVSS, and calculating to obtain the maximum lateral relative displacement y=2.78 of the foundation pit enclosure dimensionless, wherein the maximum lateral displacement δmax=yH=2.78×8.5= 23.67mm of the foundation pit enclosure, so as to obtain the floating quantity p= kHy =0.5×8.5×2.78= 11.815mm of the existing tunnel.
The invention compares the predicted dimensionless maximum lateral displacement of the foundation pit enclosure with the data of the floating quantity of the existing tunnel, wherein the data of the maximum lateral displacement of the foundation pit enclosure corresponds to the data of the floating quantity of the existing tunnel when the excavation depth of the foundation pit is 8.5m, which are obtained through simulation calculation in the table 2, and the data are shown in the table 5:
table 5 equation calculation prediction results and numerical simulation calculation results
The comparison result shows that the calculation formula prediction result after the comprehensive rigidity is introduced is basically consistent with the numerical simulation calculation result, so that the tunnel floating quantity obtained by the method can accurately reflect the influence of each influence factor parameter in the current engineering on the existing tunnel below, further whether the existing design needs to be optimized and adjusted or not can be judged in advance, the risk control cost is greatly reduced, the complicated simulation calculation process is omitted, and the construction is optimized.
It is easy to understand by those skilled in the art that the above preferred embodiments can be freely combined and overlapped without conflict.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Claims (6)
1. A prediction method for foundation pit excavation with consideration of various influencing factors to cause floating up of an existing tunnel is characterized by comprising the following steps:
step one: determining each influence factor of the foundation pit excavation enclosure, which leads to the floating of the existing tunnel; comprising the following steps: introducing the MVSS comprehensive rigidity of the foundation pit enclosure:
wherein k is t K is the integrated adjustment coefficient based on space-time effect and insertion ratio j Is a foundation reinforcement influencing factor, (mk) 1 +nk 2 )/[(m+n)k 1 ]For the influence factor of the supporting rigidity, m is the number of steel supporting channels, n is the number of concrete supporting channels, and k is the number of concrete supporting channels 1 For steel support stiffness, k 2 For the concrete support rigidity, EI is the fender post/wall rigidity, gamma w The gravity of water, H is the average vertical spacing of the supports, H is the depth of the foundation pit, and s is the average horizontal spacing of the supports;
step two: establishing the association between the maximum lateral displacement of the foundation pit support and each influence factor; comprising the following steps: defining a dimensionless maximum lateral relative displacement y=δ of a foundation pit enclosure max /H；
Through finite element calculation and fitting, a functional relation between the dimensionless maximum lateral relative displacement y of the foundation pit enclosure and the MVSS comprehensive rigidity of the foundation pit enclosure is established:
in delta max For the maximum lateral displacement of the foundation pit enclosure, alpha 2 、β 2 Is a variable parameter of comprehensive rigidity;
step three: establishing a finite element calculation model according to the actual excavation step sequence of the foundation pit, and obtaining the existing tunnel floating quantity and the maximum lateral displacement of the foundation pit support corresponding to the excavation depth through simulation calculation;
step four: establishing the correlation between the floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit enclosure; comprising the following steps: performing curve fitting on the floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit support to obtain a linear relation between the floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit support, wherein the linear function relation is as follows:
wherein P is the floating amount of the existing tunnel, k is a constant, delta max Maximum lateral displacement is provided for the foundation pit enclosure;
step five: according to the second step and the fourth step, the correlation between the floating quantity of the existing tunnel and each influence factor is obtained; comprising the following steps: the foundation pit is supported to have dimensionless maximum lateral relative displacement y=delta max And (3) carrying into the formula (3) to obtain a functional relation between the floating quantity of the existing tunnel and the dimensionless maximum lateral relative displacement y of the foundation pit enclosure:
step six: and (3) acquiring parameters of each influence factor causing the floating of the existing tunnel by the foundation pit excavation enclosure in the construction project to be constructed, and predicting the floating amount of the existing tunnel in the construction project to be constructed according to the association between the floating amount of the existing tunnel and each influence factor.
2. A predictive method as claimed in claim 1, wherein the pit excavation takes the form of an internal support, including a concrete support and/or a steel support.
3. The prediction method according to claim 1, wherein the calculating and fitting by finite elements comprises:
determining a typical geological condition of foundation pit excavation;
the dimensionless maximum lateral relative displacement delta of the foundation pit enclosure is calculated through finite elements max /H；
Drawing the MVSS comprehensive rigidity of the foundation pit enclosure and the dimensionless maximum lateral relative displacement delta of the foundation pit enclosure max graph/H;
and fitting the graph to obtain a functional relation between the dimensionless maximum lateral relative displacement y of the foundation pit support and the MVSS comprehensive rigidity of the foundation pit support.
4. A method of predicting as claimed in claim 3, wherein the pit excavation typically comprises:
class (1) formation: the foundation pit bottom is filled with silt soil, and the pit bottom is a silt stratum;
class (2) formation: the foundation pit bottom and the upper surface of the foundation pit bottom are all in a silt stratum;
class (3) formation: the upper part of the foundation pit bottom and the pit bottom are both silt stratum.
5. The prediction method according to claim 4, wherein the constant k is obtained by:
the corresponding floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit enclosure under three types of strata are respectively obtained through finite element modeling calculation;
obtaining linear function relation between the corresponding floating quantity of the existing tunnel and the maximum lateral displacement of the foundation pit support under three stratum through curve fitting, and further obtaining a corresponding coefficient k;
respectively taking soil layer deformation moduli Es corresponding to the three types of strata;
curve fitting is carried out on the coefficient k and the soil deformation modulus Es, and a functional relation between the coefficient k and the soil deformation modulus Es is obtained as follows:
where k is a constant and Es is a soil layer deformation modulus.
6. The method according to claim 1, wherein in the sixth step, the predicting the floating amount of the existing tunnel in the to-be-constructed engineering includes:
acquiring parameters of each influence factor of the foundation pit excavation enclosure in the construction project to be constructed, which cause the floating of the existing tunnel;
substituting the functional relation between the foundation pit support dimensionless maximum lateral relative displacement y and the foundation pit support MVSS comprehensive rigidity to obtain the foundation pit support dimensionless maximum lateral relative displacement y;
and calculating the floating quantity of the existing tunnel according to a functional relation between the floating quantity of the existing tunnel and the dimensionless maximum lateral relative displacement y of the foundation pit enclosure.
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| CN112989262A (en) * | 2021-02-02 | 2021-06-18 | 中铁十一局集团有限公司 | Method for predicting maximum horizontal displacement of adjacent tunnel by considering excavation process of foundation pit |
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| CN107476809B (en) * | 2017-09-05 | 2019-06-11 | 长安大学 | A kind of large deformation control method of chlorite schist stratum longspan tunnel |
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| CN112989262A (en) * | 2021-02-02 | 2021-06-18 | 中铁十一局集团有限公司 | Method for predicting maximum horizontal displacement of adjacent tunnel by considering excavation process of foundation pit |
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