CN112729232A - Method for predicting surface settlement outside pit and considering whole process of foundation pit excavation in soft soil area - Google Patents

Method for predicting surface settlement outside pit and considering whole process of foundation pit excavation in soft soil area Download PDF

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CN112729232A
CN112729232A CN202110040831.1A CN202110040831A CN112729232A CN 112729232 A CN112729232 A CN 112729232A CN 202110040831 A CN202110040831 A CN 202110040831A CN 112729232 A CN112729232 A CN 112729232A
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程康
张旭东
唐达昆
夏明锬
胡小银
梅灿
徐日庆
甘晓露
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China Railway 11th Bureau Group Co Ltd
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Abstract

The invention relates to a method for predicting surface subsidence outside a pit in a soft soil area by considering the whole process of foundation pit excavation, which comprises the following steps: monitoring the surface subsidence of the whole process of the foundation pit excavation, obtaining a first relation function of the transverse maximum subsidence value of the surface outside the pit and the excavation depth and a second relation function of the transverse maximum subsidence position of the surface outside the pit and the excavation depth based on monitoring data, and obtaining a prediction function of the transverse subsidence of the surface outside the pit considering the whole process of the foundation pit excavation based on the first relation function and the second relation function; obtaining a longitudinal settlement prediction function of the earth surface outside the pit considering the whole process of the excavation of the foundation pit based on the complementary error function and the transverse maximum settlement value of the earth surface outside the pit; and obtaining the settlement value of any point outside the pit at any excavation stage based on the curve of the transverse settlement prediction function of the surface outside the pit and the curve of the longitudinal settlement prediction function of the surface outside the pit. The method can dynamically predict the settlement of the ground surface outside the pit in the whole process of excavation of the foundation pit based on the deformation monitoring data of the foundation pit and by combining theoretical analysis, and can also evaluate the reliability of monitoring of the foundation pit.

Description

Method for predicting surface settlement outside pit and considering whole process of foundation pit excavation in soft soil area
Technical Field
The invention relates to the field of surface subsidence prediction, in particular to a method for predicting surface subsidence outside a foundation pit by considering the whole process of foundation pit excavation in a soft soil area.
Background
Along with the vigorous development of urban engineering construction activities, the demand of cities for land resources is gradually increased, and more foundation pit projects are close to buildings, subway stations, underground pipelines and the like. The foundation pit construction operation along the subway tunnel is difficult to avoid, and the foundation pit excavation in a soft soil area with dense buildings and pipelines inevitably brings disturbance to the adjacent environment, such as uneven settlement of the road surface and deformation of underground pipelines, and even cracking and damage of the structure can be caused by serious people. Therefore, it is very important to accurately, quickly and simply predict the surface settlement outside the pit induced in the whole process of excavation of the foundation pit.
The method for predicting the foundation pit excavation induced pit foreign surface settlement in the prior art comprises the following steps: theoretical analysis and numerical simulation.
In the aspect of theoretical analysis method research, the problem that foundation pit excavation induces pit foreign surface settlement is firstly converted into the problem that foundation pit retaining wall deformation induces pit foreign surface settlement; then, by means of an elastic mechanics means, assuming that the soil body is an isotropic elastomer, and then deducing the foundation pit retaining wall in different displacement modes from the problem of the elastic edge value: and (3) performing settlement analysis on the rear earth surface of the wall under the working conditions of rigid translation, rotation around the toe of the wall, rotation around the top of the wall and the like. However, the above analysis is mainly based on the assumption that the foundation soil is an elastomer, and the foundation soil in actual engineering practice may not be satisfied; meanwhile, the method can further give a predicted value of the surface subsidence outside the pit only by knowing the deformation of the foundation pit retaining wall. In actual engineering, the predicted value of the ground surface settlement of the foundation pit at each excavation stage can be preliminarily predicted before the foundation pit is not worked, and then corresponding engineering measures are taken in advance. Obviously, this is not considered by the above theoretical approach.
Compared with a theoretical analysis method, the numerical method can consider the deformation characteristics of the soil body and the complexity of deep foundation pit engineering in the foundation pit excavation process, and can be used for simulation by combining the foundation pit excavation and the construction sequence of the supporting structure, so that the method is widely applied to the foundation pit engineering, but the soil layer parameters and the boundary conditions need to be accurately determined to obtain a satisfactory result. However, numerical methods generally achieve better accuracy in predicting lateral movement of the enclosure wall, but tend to be less effective in predicting surface subsidence behind the wall.
Disclosure of Invention
The invention provides a prediction method for surface subsidence outside a pit considering the whole excavation process of a foundation pit in a soft soil area, aiming at the technical problems in the prior art, and solving the problem of poor prediction effect in the prior art.
The technical scheme for solving the technical problems is as follows: a method for predicting surface subsidence outside a foundation pit considering the whole process of foundation pit excavation in a soft soil area comprises the following steps:
step 1, performing surface subsidence monitoring on the whole process of foundation pit excavation, obtaining a relation function I of a lateral maximum subsidence value of the surface outside the pit and the excavation depth and a relation function II of a lateral maximum subsidence position of the surface outside the pit and the excavation depth based on monitoring data, and obtaining a lateral subsidence prediction function of the surface outside the pit considering the whole process of foundation pit excavation based on the relation function I and the relation function II, wherein the lateral direction is the direction vertical to the long edge of the foundation pit;
step 2, obtaining a longitudinal settlement prediction function of the pit and foreign surface in consideration of the whole excavation process of the foundation pit, wherein the longitudinal direction is parallel to the long side direction of the foundation pit, based on the complementary error function and the transverse maximum settlement value of the pit and foreign surface given by the transverse settlement prediction function of the pit and foreign surface;
and 3, obtaining the settlement value of any point outside the pit at any excavation stage based on the curve of the transverse settlement prediction function of the surface outside the pit and the curve of the longitudinal settlement prediction function of the surface outside the pit.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, the process of obtaining the first relation function and the second relation function in the step 1 includes:
taking a perpendicular bisector of the long side of the foundation pit as a ground surface settlement observation line ll, taking the direction of the perpendicular bisector as an x-axis direction, and taking the intersection point of the perpendicular bisector and the long side of the foundation pit as an x-axis zero point;
recording the transverse maximum settlement value delta on the earth surface settlement observation line ll under different excavation depths H of the foundation pitvmaxAnd the distance S between the position of the transverse maximum settlement point P and the long edge of the foundation pitmax；
Drawing delta of foundation pit at each excavation stagevmaxThe distribution curve of the/H along with the excavation depth H is fitted based on the distribution curve to obtain a relation function I; drawing S in each excavation stage of foundation pitmaxAnd fitting the distribution curve along with the excavation depth H to obtain a second relation function based on the distribution curve.
Further, the first relation function is:
δvmax/H＝0.01H2-0.17H+1.179。
further, the relationship function two is:
smax＝-0.072H2+2.23H-7.40。
further, the prediction function of the lateral settlement of the surface outside the pit is as follows:
Figure BDA0002895778120000031
wherein, deltavAnd (4) representing the lateral settlement predicted value of the surface outside the pit, and s represents the vertical distance from the long edge of the foundation pit.
Further, in step 2, the lateral maximum sedimentation value δ of the off-pit table is given based on the complementary error function erfc () and the lateral sedimentation prediction function of the off-pit tablevmaxAnd the obtained prediction function of the longitudinal settlement of the earth surface outside the pit is as follows:
Figure BDA0002895778120000032
wherein, delta (x) represents a settlement predicted value with a vertical distance of x from the end point of the foundation pit on a longitudinal settlement observation line selected at the outer side of the foundation pit, L is the length of the long edge of the foundation pit, and delta (x) represents the settlement predicted valuevmaxIs the maximum sedimentation value on the longitudinal sedimentation observation line, and the sedimentation value on the longitudinal sedimentation observation line is selected to be deltavmaxAnd/2, wherein A is the vertical distance from the point to the foundation pit adjacent to one end.
Further, the process of determining the vertical distance A between the reverse bending point and the short side of the near foundation pit comprises the following steps:
selecting a line segment which is at any vertical distance s from the long edge of the foundation pit and has the length equal to that of the long edge L of the foundation pit and is parallel to the y direction as a longitudinal settlement observation line L 'L' of the earth surface by taking the direction of the long edge of the foundation pit as the y direction;
recording settlement values of all points on a ground surface longitudinal settlement observation line l 'l' under different excavation depths H of the foundation pit;
the intersection point of the observation line l ' l ' of the longitudinal settlement of the earth surface and the x axis is the maximum settlement point P ' on l ' l ', and the settlement value is wvmaxFinding out the settlement amount of 0.5w on the observation line l 'l' of the longitudinal settlement on the ground surfacevmaxRecording the distance from the inflection point P ' to the end point of the near end of the longitudinal settlement observation line l ' l ' of the earth surface as A;
and taking the distance A from a recurved point of the foundation pit under different excavation depths H to an end point close to a longitudinal settlement observation line L 'L' of the ground surface as a data point, drawing a distribution curve of 2A/L along with H/L under each excavation depth H of the foundation pit, and fitting based on the distribution curve to obtain a relation function of the 2A/L and the H/L.
Further, the fitted relation function of 2A/L and H/L is as follows:
Figure BDA0002895778120000041
the prediction function of the vertical settlement of the surface outside the pit is obtained as follows:
Figure BDA0002895778120000042
the invention has the beneficial effects that: the invention provides a method for predicting the settlement of the surface outside the pit in the whole process of foundation pit excavation, which can dynamically predict the settlement of the surface outside the pit in the whole process of foundation pit excavation on the one hand and evaluate the reliability of foundation pit monitoring on the other hand on the basis of the deformation monitoring data of the foundation pit and theoretical analysis, thereby providing an effective basis for the evaluation and optimization of the construction influence of the foundation pit and verifying and supplementing the monitoring data in the process of foundation pit excavation. The method is simple, convenient and practical, and has the following three advantages: 1. compared with the existing method which only can consider the lateral settlement of the ground surface outside the pit when the foundation pit is excavated to the bottom of the pit, the proposed method can consider the settlement of the ground surface outside the pit at any excavation depth in the excavation process of the foundation pit; 2. the method can predict the horizontal settlement of any earth surface outside the pit and can also predict the longitudinal settlement of any earth surface outside the pit; 3. by using the prediction method, the settlement of any earth surface outside the pit can be predicted in advance without excavating the foundation pit, and meanwhile, according to the settlement, the method is beneficial to taking corresponding engineering measures in advance.
Compared with the simplified calculation method which mainly focuses on the final stage of excavation in the existing research, the simplified semi-analytical engine provided by the invention has the advantages of stronger applicability and wider application range.
Drawings
FIG. 1 is a flow chart of a method for predicting the settlement of the surface outside a pit in a soft soil area in consideration of the whole process of foundation pit excavation;
FIG. 2 shows the excavation depth H and the maximum surface subsidence δ of the foundation pit according to the embodiment of the present inventionv maxA plot of the/H relationship;
FIG. 3 shows the excavation depth H of the foundation pit and the maximum settlement position S of the ground surface according to the embodiment of the present inventionmaxA relationship graph;
fig. 4 is a schematic diagram illustrating a surface subsidence analytic solution comparison under different excavation depths H of a foundation pit according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a complementary error function provided in accordance with an embodiment of the present invention;
fig. 6 is a schematic diagram of longitudinal settlement parameters of an external surface of a foundation pit provided by the embodiment of the invention;
FIG. 7 is a graph showing a relationship between a distance A between a reverse bend point and a short side, a half L/2 of a long side length of a foundation pit, and a excavation depth H of the foundation pit, and a long side length L of the foundation pit, according to an embodiment of the present invention;
fig. 8(a) is a schematic diagram illustrating a comparison of surface longitudinal settlement solutions for different excavation depths at a distance of 5 m according to an embodiment of the present invention;
fig. 8(b) is a schematic diagram illustrating a comparison of surface longitudinal settlement solutions for different excavation depths at a distance of 10 meters according to an embodiment of the present invention;
fig. 8(c) is a schematic diagram illustrating a comparison of surface longitudinal settlement solutions for different excavation depths at a distance of 15 meters according to an embodiment of the present invention;
fig. 8(d) is a schematic diagram illustrating a comparison of surface longitudinal settlement solutions for different excavation depths at a distance of 20 meters according to an embodiment of the present invention.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
The method for predicting the subsidence of the surface outside the pit in the soft soil area considering the whole process of the excavation of the foundation pit is based on actual measurement analysis and prediction, the actual measurement analysis and prediction adopts a method combining theory and actual measurement, and the relationship between the surface subsidence form and the subsidence quantity and the relevant physical and mechanical parameters of the foundation pit is discussed by utilizing a statistical analysis method based on actual measurement data of the foundation pit which can better reflect the comprehensive conditions of an engineering field. The method has better guiding function for understanding the deformation character of the earth surface behind the wall, predicting the earth surface settlement behind the wall and verifying the numerical analysis result. Theoretical analysis can better summarize and reconcile the law reflected by the actual measurement data and add mathematical expression, thereby facilitating popularization and application.
At present, most of methods based on actual measurement or theoretical analysis are focused on the prediction of the longitudinal settlement of the surface outside the pit during the final excavation stage of the foundation pit, the transverse settlement of the surface outside the pit is ignored, and the dynamic process of the whole excavation of the foundation pit cannot be considered.
As shown in fig. 1, the present invention provides a flowchart of a method for predicting surface subsidence outside a pit in a soft soil area in consideration of the whole process of excavation of a foundation pit, and as can be seen from fig. 1, the method for predicting surface subsidence outside a pit in a soft soil area in consideration of the whole process of excavation of a foundation pit includes:
step 1, performing surface subsidence monitoring on the whole process of foundation pit excavation, obtaining a relation function I of a lateral maximum subsidence value of the surface outside the pit and the excavation depth and a relation function II of a lateral maximum subsidence position of the surface outside the pit and the excavation depth based on monitoring data, and obtaining a lateral subsidence prediction function of the surface outside the pit considering the whole process of the foundation pit excavation based on the relation function I and the relation function II, wherein the lateral direction is perpendicular to the long side direction of the foundation pit.
And 2, obtaining a longitudinal settlement prediction function of the surface outside the pit considering the whole excavation process of the foundation pit, wherein the longitudinal direction is parallel to the long side direction of the foundation pit, based on the complementary error function and the transverse maximum settlement value of the surface outside the pit, which is given by the transverse settlement prediction function of the surface outside the pit.
And 3, obtaining the settlement value of any point outside the pit at any excavation stage based on the curve of the transverse settlement prediction function of the surface outside the pit and the curve of the longitudinal settlement prediction function of the surface outside the pit.
The invention provides a method for predicting the settlement of the surface outside the pit in the whole process of foundation pit excavation, which can dynamically predict the settlement of the surface outside the pit in the whole process of foundation pit excavation on the one hand and evaluate the reliability of foundation pit monitoring on the other hand on the basis of the deformation monitoring data of the foundation pit and theoretical analysis, thereby providing an effective basis for the evaluation and optimization of the construction influence of the foundation pit and verifying and supplementing the monitoring data in the process of foundation pit excavation. The method is simple, convenient and practical, and has the following three advantages: 1. compared with the existing method which only can consider the lateral settlement of the surface outside the pit when the foundation pit is excavated to the bottom of the pit, the proposed method can consider the settlement of the surface outside the pit when the excavation depth is arbitrary in the excavation process of the foundation pit; 2. the method can predict the horizontal settlement of any earth surface outside the pit and can also predict the longitudinal settlement of any earth surface outside the pit; 3. by using the prediction method, the arbitrary surface subsidence outside the pit can be predicted in advance without excavation of the foundation pit, and meanwhile, according to the subsidence size, corresponding engineering measures can be taken in advance.
Compared with the simplified calculation method which mainly focuses on the final stage of excavation in the existing research, the simplified semi-analytical engine provided by the invention has the advantages of stronger applicability and wider application range.
Example 1
The embodiment 1 provided by the invention is an embodiment of a method for predicting the subsidence of the surface outside a pit in a soft soil area by considering the whole process of foundation pit excavation, and the embodiment comprises the following steps:
step 1, performing surface subsidence monitoring on the whole process of foundation pit excavation, obtaining a relation function I of a lateral maximum subsidence value of the surface outside the pit and the excavation depth and a relation function II of a lateral maximum subsidence position of the surface outside the pit and the excavation depth based on monitoring data, and obtaining a lateral subsidence prediction function of the surface outside the pit considering the whole process of the foundation pit excavation based on the relation function I and the relation function II, wherein the lateral direction is perpendicular to the long side direction of the foundation pit.
Preferably, the process of obtaining the first relation function and the second relation function includes:
and (5) monitoring the surface subsidence of the subway foundation pit in the whole excavation process, and analyzing the surface subsidence displacement characteristics.
And taking the perpendicular bisector of the long side of the foundation pit as a ground surface settlement observation line ll, taking the direction of the perpendicular bisector as the x-axis direction, and taking the intersection point of the perpendicular bisector and the long side of the foundation pit as an x-axis zero point o.
Recording the transverse maximum settlement value delta on the earth surface settlement observation line ll under different excavation depths H of the foundation pitv maxAnd the distance S between the position of the transverse maximum settlement point P and the long edge of the foundation pitmax。
And (5) taking the monitoring data of the maximum settlement point of the foundation pit under different excavation depths H as data points, and drawing delta under each excavation stage of the foundation pitv maxThe method comprises the following steps that A, a distribution curve of/H along with the excavation depth H is obtained, and a relation function I is obtained on the basis of the distribution curve; drawing S in each excavation stage of foundation pitmaxAnd fitting the distribution curve along with the excavation depth H to obtain a second relation function based on the distribution curve.
Specifically, in the embodiment of the present invention, as shown in fig. 2, the excavation depth H and the maximum surface subsidence δ of the foundation pit according to the embodiment of the present invention are providedv maxThe graph of the relationship/H can be obtained based on the distribution curve in FIG. 2: the relation function one is deltav max/H＝0.01H2-0.17H+1.179。
As shown in fig. 3, the excavation depth H and the maximum ground subsidence position S of the foundation pit according to the embodiment of the present inventionmaxThe relationship graph can be obtained based on the distribution curve in fig. 3: the second relation function is smax＝-0.072H2+2.23H-7.40。
According to deltav max/H、SmaxFurther, the prediction formula of the lateral settlement of the ground surface outside the pit, which can consider the whole process of the excavation of the foundation pit, is provided as follows:
Figure BDA0002895778120000081
wherein, deltavAnd (4) representing the lateral settlement predicted value of the surface outside the pit, and s represents the vertical distance from the long edge of the foundation pit.
After a prediction result is obtained based on the prediction function of the lateral settlement of the external surface of the pit, the measured lateral settlement of the external surface of the pit under different excavation depths H and the lateral settlement distribution curve of the external surface of the pit given by the prediction function of the lateral settlement of the external surface of the pit can be drawn; and calculating a prediction error and evaluating the prediction effect. Fig. 4 is a schematic diagram illustrating a comparison of surface subsidence analytic solutions for different excavation depths H of a foundation pit according to an embodiment of the present invention.
And 2, obtaining a longitudinal settlement prediction function of the surface outside the pit considering the whole excavation process of the foundation pit, wherein the longitudinal direction is parallel to the long side direction of the foundation pit, based on the complementary error function and the transverse maximum settlement value of the surface outside the pit, which is given by the transverse settlement prediction function of the surface outside the pit.
As shown in fig. 5, which is a schematic diagram of the complementary error function provided by the embodiment of the present invention, the complementary error function erfc () is defined as:
Figure BDA0002895778120000082
where u is the normalization variable of the normalization gaussian function, erf (0) ═ 0, and erf (∞) ═ 1.
The general formula based on the complementary error function deformation curve is: y ═ C · erfc [ (x-a)/B ] + D.
As shown in fig. 6, which is a schematic diagram of a longitudinal settlement parameter of the ground surface outside the foundation pit according to an embodiment of the present invention, it can be known from fig. 5 and 6 that, on a longitudinal settlement observation line selected on the outer side of the foundation pit, x represents a vertical distance to an end point of the foundation pit, and δ representsv maxIs the maximum sedimentation value on the longitudinal sedimentation observation line, and the sedimentation value on the longitudinal sedimentation observation line is selected to be deltav maxAnd/2, wherein A is the vertical distance from the point to the foundation pit at the adjacent end, namely the distance from the reverse bending point of the complementary error function to the corner of the foundation pit, B is the shape parameter of the slope at the reverse bending point, C is the amplitude parameter, and D is the vertical offset parameter.
According to the complementary error function form and the excavation-induced surface subsidence distribution relation, the following steps are known:
D＝δv max，C＝-D/2。
for conventional foundation pit excavation, the analysis side is the long side of the foundation pit with the length of L, and the middle position of the foundation pit is not difficult to find, namely the position which is delta from the L/2 position of the cornerv maxIs at, i.e. y(x＝L/2)Substituting D into a general formula based on a deformation curve of a complementary error function：
Figure BDA0002895778120000091
When x increases to infinity, the complementary error function goes to zero and a reasonable truncation must be performed to compute the function. Finding that the complementary error function is approximately zero based on least squares fit, the following condition may be taken:
B≈[(L/2)-A]/2.8。
based on the formula, the longitudinal settlement prediction function of the surface outside the pit can be obtained as follows:
Figure BDA0002895778120000092
from this formula, it can be seen that only A and δ need be obtainedv maxThe control equation of the deformation curve can be obtained.
For different excavation depths H of the foundation pit, the different back-bending points of the settlement curve are obviously corresponded.
Preferably, the process of determining the vertical distance a between the inflection point and the short side of the foundation pit closer comprises the following steps:
and selecting any vertical distance s from the long edge of the foundation pit by taking the direction of the long edge of the foundation pit as the y direction, wherein the length of the line segment which is equal to the long edge L of the foundation pit and is parallel to the y direction is taken as a longitudinal settlement observation line L ' L ' of the earth's surface.
And recording the settlement values of all points on the longitudinal settlement observation line l 'l' of the ground surface under different excavation depths H of the foundation pit.
According to the symmetry, the intersection point of the longitudinal surface settlement observation line l ' l ' and the x axis is the maximum settlement point P ' on l ' l ', and the settlement value is wv maxFinding out the settlement amount of 0.5w on the observation line l 'l' of the longitudinal settlement on the ground surfacev maxAnd recording the distance from the inflection point P ' to the end point of the nearby end of the longitudinal surface settlement observation line l ' l ' as A.
And taking the distance A from a recurved point of the foundation pit under different excavation depths H to an end point close to a longitudinal settlement observation line L 'L' of the ground surface as a data point, drawing a distribution curve of 2A/L along with H/L under each excavation depth H of the foundation pit, and fitting based on the distribution curve to obtain a relation function of the 2A/L and the H/L.
In the embodiment provided by the present invention, as shown in fig. 7, a graph of a relationship between a distance a between a recurved point and a short side, a half of a length a of a long side of a foundation pit, L/2, and an excavation depth of the foundation pit, H, and a length L of the long side of the foundation pit, provided by the embodiment of the present invention, is shown, and a relationship function between 2A/L and H/L, which can be obtained by fitting according to a distribution curve in fig. 7, is:
Figure BDA0002895778120000101
the prediction function of the longitudinal settlement of the surface outside the pit considering the whole process of the excavation of the foundation pit can be obtained as follows:
Figure BDA0002895778120000102
and delta (x) represents a predicted settlement value with a vertical distance x from the end point of the foundation pit on a longitudinal settlement observation line selected on the outer side of the foundation pit. After a prediction result is obtained based on the prediction function of the longitudinal settlement of the external surface of the pit outside the pit, the actual measurement longitudinal settlement of the external surface of the pit under different excavation depths H and the transverse settlement distribution curve of the external surface of the pit given by the prediction function of the transverse settlement of the external surface of the pit can be drawn; and calculating a prediction error and evaluating the prediction effect. Fig. 8(a) -8 (d) are schematic diagrams illustrating the analysis and comparison of the longitudinal subsidence of the ground surface at different excavation depths at distances of 5 m, 10 m, 15 m and 20 m according to the embodiment of the present invention.
And 3, obtaining the settlement value of any point outside the pit at any excavation stage based on the curve of the transverse settlement prediction function of the surface outside the pit and the curve of the longitudinal settlement prediction function of the surface outside the pit.
When any point on the curve of the lateral settlement prediction function outside the pit can be taken, the corresponding lateral maximum settlement value delta can be obtainedv maxWill deltav maxThe longitudinal settlement distribution curve of any point can be obtained by taking the longitudinal settlement prediction function of the surface outside the pit. Namely: combining the steps 1-3, any excavation stage (excavation depth) can be obtainedH) The sedimentation value of any point outside the pit.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (8)

1. A method for predicting the settlement of the surface outside a pit in a soft soil area by considering the whole process of foundation pit excavation is characterized by comprising the following steps:
step 1, performing surface subsidence monitoring on the whole process of foundation pit excavation, obtaining a relation function I of a lateral maximum subsidence value of a surface outside the pit and the excavation depth and a relation function II of a lateral maximum subsidence position of the surface outside the pit and the excavation depth based on monitoring data, and obtaining a lateral subsidence prediction function of the surface outside the pit considering the whole process of the foundation pit excavation based on the relation function I and the relation function II, wherein the lateral direction is the direction vertical to the long side of the foundation pit;
step 2, obtaining a longitudinal settlement prediction function of the pit and foreign surface in consideration of the whole excavation process of the foundation pit, wherein the longitudinal direction is parallel to the long side direction of the foundation pit, on the basis of the complementary error function and the maximum horizontal settlement value of the pit and foreign surface obtained by the prediction function;
and 3, obtaining the settlement value of any point outside the pit at any excavation stage based on the curve of the transverse settlement prediction function of the surface outside the pit and the curve of the longitudinal settlement prediction function of the surface outside the pit.
2. The method for predicting subsidence of an underground surface according to claim 1, wherein the step 1 of obtaining the first relation function and the second relation function comprises:
taking a perpendicular bisector of a long side of the foundation pit as a ground surface settlement observation line ll, taking the direction of the perpendicular bisector as an x-axis direction, and taking the intersection point of the perpendicular bisector and the long side of the foundation pit as an x-axis zero point;
recording the transverse maximum settlement value delta on the earth surface settlement observation line ll under different excavation depths H of the foundation pitvmaxAnd the position of occurrence of the transverse maximum settlement point PDistance S from long side of foundation pitmax；
Drawing delta of foundation pit at each excavation stagevmaxThe distribution curve of the/H along with the excavation depth H is fitted based on the distribution curve to obtain the first relation function; drawing S in each excavation stage of foundation pitmaxAnd fitting the distribution curve along with the excavation depth H to obtain the second relation function based on the distribution curve.
3. The method of predicting subsidence of an out-of-pit surface according to claim 2, wherein the first relation function is:
δvmax/H＝0.01H2-0.17H+1.179。
4. the method of predicting subsidence of an out-of-pit surface according to claim 2, wherein the second relation function is:
smax＝-0.072H2+2.23H-7.40。
5. the method of claim 1, wherein the off-pit surface lateral subsidence prediction function is:
Figure FDA0002895778110000021
wherein, deltavAnd (4) representing the lateral settlement predicted value of the surface outside the pit, and s represents the vertical distance from the long edge of the foundation pit.
6. Method for prediction of the subsidence of a foreign table from a pit according to claim 1, wherein in step 2, the lateral maximum subsidence value δ of a foreign table from a pit based on the complementary error function erfc () and the lateral maximum subsidence value δ of a foreign table from a pit given by the lateral subsidence prediction function of the foreign table from a pitvmaxAnd the obtained prediction function of the longitudinal settlement of the surface outside the pit is as follows:
Figure FDA0002895778110000022
wherein, delta (x) represents a settlement predicted value with a vertical distance of x from the end point of the foundation pit on a longitudinal settlement observation line selected at the outer side of the foundation pit, L is the length of the long edge of the foundation pit, and delta (x) represents the settlement predicted valuevmaxIs the maximum sedimentation value on the longitudinal sedimentation observation line, and the sedimentation value on the longitudinal sedimentation observation line is selected to be deltavmaxAnd/2, wherein A is the vertical distance from the point to the foundation pit adjacent to one end.
7. The method for predicting subsidence of an underground ground surface according to claim 6, wherein the process of determining the vertical distance A of the recurved point from the short side of the nearer foundation pit comprises:
selecting a line segment which is at any vertical distance s from the long edge of the foundation pit and has the length equal to that of the long edge L of the foundation pit and is parallel to the y direction as a longitudinal settlement observation line L 'L' of the earth surface by taking the direction of the long edge of the foundation pit as the y direction;
recording settlement values of all points on the longitudinal settlement observation line l 'l' of the ground surface under different excavation depths H of the foundation pit;
the intersection point of the longitudinal settlement observation line l ' l ' of the earth surface and the x axis is the maximum settlement point P ' on l ' l ', and the settlement value is wvmaxFinding out the settlement amount of 0.5w on the observation line l 'l' of the longitudinal settlement on the earth surfacevmaxThe settlement point is marked as a recurved point P 'on the longitudinal settlement observation line l' l 'on the earth surface, and then the distance from the recurved point P' to the end point of the nearby end of the longitudinal settlement observation line l 'l' on the earth surface is recorded as A;
and taking the distance A from a recurved point of the foundation pit under different excavation depths H to the end point of the near end of the ground surface longitudinal settlement observation line L 'L' as a data point, drawing a distribution curve of 2A/L along with H/L under each excavation depth H of the foundation pit, and fitting based on the distribution curve to obtain a relation function of the 2A/L and the H/L.
8. The method of predicting subsidence of an extra-excavation surface according to claim 7, wherein the fitted 2A/L to H/L relation function is:
Figure FDA0002895778110000031
the prediction function of the longitudinal settlement of the surface outside the pit is obtained as follows:
Figure FDA0002895778110000032
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