CN114818046B - Method for determining foundation pit safety of deformation super-early-warning-value pile anchor supporting structure - Google Patents
Method for determining foundation pit safety of deformation super-early-warning-value pile anchor supporting structure Download PDFInfo
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Abstract
According to the foundation pit safety determination method for the deformation super-early-warning pile anchor supporting structure, provided by the invention, from the angle of energy conservation, the energy change of the whole process of the anchor rod pulling resistance is analyzed, and the pulling resistance-displacement curve of the anchor rod in the whole process of the anchor rod pulling resistance is obtained. And taking the pile body and the anchor rod as a supporting system, and obtaining the soil pressure matched with the displacement data of the monitored pile body through iterative inversion calculation, so as to obtain the internal force of the pile body under the action of the soil pressure, thereby judging the safety of the pile body. Because the whole process of the pullout resistance of the anchor rod is considered, the anchor rod is in P u ‑P r The pulling resistance of the anchor rod can be accurately obtained in the process, and the residual pulling resistance P of the anchor rod is not simply used r The internal force of the pile body is calculated, so that the internal force of the pile body can be more accurately analyzed, the most accurate foundation pit safety judgment result is made, the pile body is convenient to rescue and strengthen by taking a chance in practical engineering application, and the pile body has great economic benefit.
Description
[ field of technology ]
The invention relates to the technical field of foundation pit support, in particular to a foundation pit safety determination method for a deformation super-early-warning pile anchor support structure.
[ background Art ]
In the field of constructional engineering, in order to ensure the safety of a foundation pit, deformation of a supporting structure is generally monitored in the foundation pit construction process, and corresponding treatment is required once the deformation of the supporting structure exceeds a designed early warning value, so that emergency work is required to be adopted if necessary. However, before the treatment, the internal force of the foundation pit supporting structure needs to be determined, and then the safety state of the foundation pit is determined, so that the emergency measure can be determined. If the foundation pit safety is still a certain margin through analysis, manual equipment can be mobilized to carry out emergency reinforcement, so that accident potential is eliminated; if the foundation pit safety is analyzed to be not excessive, the foundation pit can only be backfilled or any of the foundation pit can collapse.
The safety of the pile anchor supporting structure can be judged by comparing the internal force of the pile in the pile anchor supporting structure with the bearing capacity in the design parameters of the pile body, and the internal force of the pile body can be calculated by a structural mechanics method. The internal force of the pile body in the pile anchor supporting structure is calculated by adopting a structural mechanics method, and the following 4 basic data are needed: (1) a foundation resistance parameter; (2) geometric and material characteristics of the piles; (3) deformation monitoring data of the supporting structure; (4) and (5) pulling resistance-deformation curves of the anchor rods of each row. Wherein (1) and (2) can be obtained by referring to survey and design data; (3) the method comprises the steps of monitoring through a foundation pit; (4) and the anchor rod is obtained through an anchor rod drawing test.
The anchor rod anti-pulling test is also called as an acceptance test, and the acceptance test is only used for determining whether the bearing capacity of the anchor rod is larger than a design value, so that the anchor rod cannot be pulled to be damaged. Therefore, the pulling resistance-deformation curve of the anchor rod obtained by the acceptance test is only a section of the pulling force-deformation curve before the pulling force of the anchor rod reaches the peak value, and the pulling resistance P of the anchor rod reaching the limit is not included u After entering the residual pulling resistance P r The tension versus deflection section of the state is thus an incomplete tension versus deflection curve. And after the anchor rod is drawn to reach the limit pulling resistance, namely damaged, part of the anchor rod remains in the soil layer, the remaining part still has certain pulling resistance, and the pulling resistance becomes the residual pulling resistance P r . Engineering experience shows that the residual pulling resistance P r Ultimate pullout resistance P is generally achievable u 30 to 60 percent of the total weight of the composition. For the foundation pit with overlarge deformation and alarm, the residual pulling resistance P of the anchor rod r Is still important for maintaining the stability of the foundation pitIs used. If the residual pulling resistance P is not taken into consideration r The influence on the stability of the foundation pit can be used for judging the unsafe condition of the foundation pit in advance under the condition that the foundation pit has unsafe surplus degree, so that huge economic loss is caused. Therefore, it is necessary to provide a method for determining the safety of the foundation pit of the deformed pile anchor supporting structure to solve the above problems.
[ invention ]
The technical problem to be solved by the invention is to provide the foundation pit safety determination method of the deformation super-early-warning-value pile anchor supporting structure, which considers the influence of the residual pulling resistance of the anchor rod on the stability of the foundation pit, can make more accurate judgment on the safety of the foundation pit, and can avoid making unsafe judgment in advance under the condition that the foundation pit has unsafe surplus degree.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
the foundation pit safety determination method for the deformation super-early-warning pile anchor supporting structure comprises a pile body and a plurality of layers of anchor rods connected with the pile body, and comprises the following steps:
s1: constructing an adhesion model of the anchor rod and the soil layer, wherein the adhesion model is expressed as:
wherein P is u Representing the ultimate pulling resistance of the anchor rod, S u Indicating the ultimate pulling resistance P of the anchor rod u Displacement amount of the lower part; p (P) r Representing the residual pullout resistance of the anchor rod; l (L) a Representing the length of the anchor rod anchoring section; u represents the perimeter of the anchor rod anchoring section; e (E) S And A S Respectively representing the elastic modulus and the cross section area of the free section of the anchor rod; e and A respectively represent the elastic modulus and the cross-sectional area of the anchor rod anchoring section; l (L) f Representing the length of the free section of the anchor rod; alpha represents an intermediate parameter; τ m Representing the ultimate strength of the bonding of the anchor rod anchoring section and the soil layer; τ r Representing the residual strength of the bonding of the anchor rod anchoring section and the soil layer; s is(s) m Representing the maximum shear displacement of the anchor rod anchoring section; l (L) ar The length of the debonded part of the anchor rod and the soil layer under the limit pulling resistance is represented; λ represents the coefficient of friction resistance transfer between the anchor rod anchoring section and the soil layer;
s2: setting anchor rod basic experiments aiming at different soil layers respectively, and recording P of the test anchor rod u 、S u P r Substituting the value into the cohesive force model to obtain tau by back calculation m 、τ r Lambda and s m Completing the establishment of a cohesive force model;
s3: for the safety determination of the pile anchor supporting structure, randomly sampling the installed anchor rods to obtain sample anchor rods, performing acceptance test on the sample anchor rods, analyzing the energy change of the sample anchor rods in the whole pulling-resistant process based on energy conservation, and calculating to obtain that the pulling-resistant force of the sample anchor rods just reaches P r Displacement S at the time r The method comprises the steps of carrying out a first treatment on the surface of the Establishing an anchor rod pulling resistance-displacement coordinate system, and obtaining (0, 0) and (P) u ,S u )、(P r ,S r )、(P r Infinity) are sequentially connected by straight lines to obtain a pulling resistance-displacement curve of the whole pulling resistance process of the sample anchor rod;
s4: setting an initial value of a soil layer intensity coefficient, taking the pile body and the anchor rod as a supporting system bearing the action of soil pressure, and calculating the soil pressure P borne by the pile body a Obtaining displacement of the pile body under the initial value of the soil layer intensity coefficient through iterative inversion calculation, comparing the displacement with the displacement in pile body detection data, if the two errors exceed 5%, adjusting the soil layer intensity coefficient to recalculate until the two errors do not exceed 5%, finishing the determination of the actual soil layer intensity coefficient, and solving based on a structural mechanics method to obtain the internal force of the pile body under the actual soil layer intensity coefficient;
s5: and directly acquiring the bearing capacity of the pile body from the design parameters of the pile anchor supporting structure, comparing the internal force of the pile body with the bearing capacity, and judging the safety of the pile anchor supporting structure.
Preferably, in the step S3, "the energy change of the sample anchor rod in the whole pulling-resistant process is analyzed based on energy conservation", and the pulling-resistant force of the sample anchor rod is calculated to just reach P r Displacement S at the time r The method comprises the following steps:
s21: increasing from 0 to P according to the sample anchor rod pulling resistance u In-process energy conservation, calculating the surface energy E required to be dissipated for forming a new surface by the unit area of the anchoring section of the sample anchor rod and the debonded part of the soil layer b ；
S22: according to the pulling resistance of the sample anchor rod from P u Down to P r In-process energy conservation, calculating that the pulling resistance of the sample anchor rod just reaches the residual pulling resistance P r When in use, the displacement S corresponding to the sample anchor rod r 。
Preferably, the step S21 specifically includes the following steps:
s211: according to the cohesive force model, calculating to obtain the pulling force P of the sample anchor rod u Length L of debonded portion of the sample anchor rod with soil layer ar ；
S212: calculation of sample Anchor rod pullout resistance increasing from 0 to P u In the process, energy E externally applied to the top of the sample anchor Top ：
Wherein P is max For the maximum pulling force born by the sample anchor rod in the acceptance test, S max Is P max The displacement of the anchor rod under the action;
s213: calculating the energy E accumulated by the elongation of the free section of the sample anchor rod f ：Wherein L is f The free section length of the sample anchor rod;
s214: calculating the energy E dissipated by friction force between the anchoring section of the sample anchor rod and the debonded part of the soil layer Friction wheel ：
S215: calculating the energy E accumulated by the extension of the sample anchor rod anchoring section and the soil layer debonding part Anchor extension ：
S216: calculating elastic potential energy E accumulated by non-debonded part of sample anchor rod anchoring section and soil layer Anchor bullet ：
Wherein L is ae The length of the non-debonded part of the sample anchor rod and the soil layer is the length of the non-debonded part of the sample anchor rod and the soil layer;
s217: calculating the surface energy required to be dissipated for forming a new surface by unit area of an anchoring section of a sample anchor rod and a debonded part of a soil layer
Preferably, the step S22 specifically includes the following steps:
s221: calculating the drawing force of the sample anchor rod from P u Down to P r In the process, elastic potential energy E released by free section of sample anchor rod 2 ：
S222: calculating elastic potential energy E released by rebound of sample anchor rod anchoring section and soil layer debonding part 3 ：
Wherein x is the length of the anchor rod anchoring section and the new debonded part of the soil layer;
s223: calculating elastic potential energy E accumulated by new debonding part of sample anchor rod anchoring section and soil layer 4 ：
Wherein:
s224: calculating the energy E dissipated by friction force between the anchoring section of the sample anchor rod and the debonded part of the soil layer 5 ：
S225: calculating the surface energy consumed by the sample anchor rod anchoring section and the soil layer debonding part:
E surface energy ＝U(L a -L ar )E b
S226: elastic potential energy E released by anti-pulling device in acceptance test 1 Constructing an equation, and solving to obtain that the pulling resistance of the anchor rod just reaches the residual pulling resistance P r In the process, the displacement S of the anchor rod r ：
Preferably, in the step S4, the soil pressure P a Expressed as:
wherein, gamma, c,The soil layer weight, cohesion and internal friction angle are respectively; k is the soil layer intensity coefficient, and k is less than or equal to 1.0; z represents the distance from the node on the pile body to the bottom of the foundation pit; p is p 0 Is ground load;
in the step S4, the soil pressure P is solved a The solving process of the displacement of each node of the pile body under the action is as follows:
wherein:
P a1 ，P a2 …P ai ，P aj …P am soil pressure acting on pile body nodes 1,2,3 … i, j … m respectively;
x 1 ，x 2 …x i ，x j …x m the horizontal displacement amounts of pile body nodes 1,2 and 3 … i and j … m are respectively;
θ 1 ，θ 2 …θ i ，θ j …θ m the corners of pile body nodes 1,2 and 3 … i and j … m are respectively;
P mgi the anchor rod tension corresponding to the pile body node i is calculated according to the following formula:
P mgi ＝K mgi ·x i
wherein K is mgi The rigidity coefficient K of the anchor rod corresponding to the pile body node i mgi The calculation process of (1) is as follows:
wherein: h is a i The horizontal displacement quantity h of the anchor rod corresponding to the pile body node i i ∈x i The method comprises the steps of carrying out a first treatment on the surface of the Delta is the inclination angle of the anchor rod;
K djn k is the foundation rigidity coefficient of pile body node below the bottom surface of foundation pit djn The calculation process of (1) is as follows:
K djn ＝gzb 1 l
wherein g is the proportionality coefficient of the horizontal resistance coefficient of the stratum foundation; b 1 Calculating the width of the pile body; l is the sum of 50% of the lengths of the units at two sides of the pile body node.
Compared with the related art, the method for determining the safety of the foundation pit of the deformation super-early-warning-value pile anchor supporting structure provided by the invention is from the angle of energy conservationAnd (3) analyzing the energy change of the whole process of the anchor rod pulling resistance, and obtaining a pulling resistance-displacement curve of the whole process of the anchor rod pulling resistance. And taking the pile body and the anchor rod as a supporting system, and obtaining the soil pressure matched with the displacement data of the monitored pile body through iterative inversion calculation, so as to obtain the internal force of the pile body under the action of the soil pressure, thereby judging the safety of the pile body. Because the whole process of the pullout resistance of the anchor rod is considered, the anchor rod is in P u -P r The pulling resistance of the anchor rod can be accurately obtained in the process, and the residual pulling resistance P of the anchor rod is not simply used r The internal force of the pile body is calculated, so that the internal force of the pile body can be more accurately analyzed, the most accurate foundation pit safety judgment result is made, the pile body is convenient to rescue and strengthen by taking a chance in practical engineering application, and the pile body has great economic benefit.
[ description of the drawings ]
For a clearer description of the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly introduced below, it being obvious that the drawings in the description below are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art, wherein:
FIG. 1 is a schematic diagram of a pile-anchor supporting structure in a method for determining the safety of a foundation pit of a pile-anchor supporting structure with a deformation super-early warning value;
fig. 2 is a schematic structural diagram of an anchor rod in the method for determining the safety of a foundation pit of a deformation super-early-warning pile anchor supporting structure;
FIG. 3 is a flowchart showing the steps of iterative inversion calculation in step S4;
FIG. 4 is a schematic view showing the installation structure of three anchors MG-1, MG-2, MG-3 in the first embodiment;
FIG. 5 is a basic experimental result diagram of anchor rods of three different soil layers in the first embodiment;
FIG. 6 is a graph of the acceptance test results of three anchors MG-1, MG-2, MG-3;
FIG. 7 is a graph showing the pulling resistance versus displacement of the three anchors MG-1, MG-2, MG-3 during the entire pulling process.
[ detailed description ] of the invention
In order to better understand the technical solution in the embodiments of the present invention and make the above objects, features and advantages of the present invention more obvious, the following detailed description of the present invention will be further described with reference to the accompanying drawings of the present application.
Referring to fig. 1-7 in combination, the invention provides a method for determining foundation pit safety of a deformed pile anchor supporting structure, wherein the pile anchor supporting structure comprises a pile body and a plurality of layers of anchor rods connected with the pile body, and the method comprises the following steps:
s1: constructing an adhesion model of the anchor rod and the soil layer, wherein the adhesion model is expressed as:
wherein P is u Representing the ultimate pulling resistance of the anchor rod, S u Indicating the ultimate pulling resistance P of the anchor rod u Displacement amount of the lower part; p (P) r Representing the residual pullout resistance of the anchor rod; l (L) a Representing the length of the anchor rod anchoring section; u represents the perimeter of the anchor rod anchoring section; e (E) S And A S Respectively representing the elastic modulus and the cross section area of the free section of the anchor rod; e and A respectively represent the elastic modulus and the cross-sectional area of the anchor rod anchoring section; l (L) f Representing the length of the free section of the anchor rod; alpha represents an intermediate parameter; τ m Representing the ultimate strength of the bonding of the anchor rod anchoring section and the soil layer; τ r Representing the residual strength of the bonding of the anchor rod anchoring section and the soil layer; s is(s) m Representing the maximum shear displacement of the anchor rod anchoring section; l (L) ar The length of the debonded part of the anchor rod and the soil layer under the limit pulling resistance is represented; λ represents the coefficient of friction resistance transfer between the anchor rod anchoring section and the soil layer;
the binding force model is used for representing the binding condition of the anchor rod and the soil layer, the design parameters of the anchor rod are considered, and the anchor rods with different design parameters can be solved and calculated by adopting the binding model. Therefore, different anchors can be obtained by only carrying out basic anchor rod experiments once aiming at each different soil layerModel parameters of the rod under different soil layer conditions: τ m 、s m 、L ar 。
S2: setting anchor rod basic experiments aiming at different soil layers respectively, and recording P of the test anchor rod u 、S u P r Substituting the value into the cohesive force model to obtain tau by back calculation m 、τ r Lambda and s m And (5) finishing the establishment of the adhesive force model.
Aiming at different application scenes, the basic experiment is carried out again, the parameter adjustment of the adhesive force model is completed, and a new adhesive force model which is applicable to the current scene and has different parameters can be obtained, so that the operation is quick and convenient.
S3: for the safety determination of the pile anchor supporting structure, randomly sampling the installed anchor rods to obtain sample anchor rods, performing acceptance test on the sample anchor rods, analyzing the energy change of the sample anchor rods in the whole pulling-resistant process based on energy conservation, and calculating to obtain that the pulling-resistant force of the sample anchor rods just reaches P r Displacement S at the time r The method comprises the steps of carrying out a first treatment on the surface of the Establishing an anchor rod pulling resistance-displacement coordinate system, and obtaining (0, 0) and (P) u ,S u )、(P r ,S r )、(P r And (infinity) are sequentially connected by straight lines to obtain a pulling resistance-displacement curve of the whole pulling resistance process of the sample anchor rod.
For the installed anchor rod, as long as the parameters of the soil layer and the design parameters of the anchor rod are consistent with those in the basic experiment of the anchor rod, tau in the acceptance test m 、s m 、L ar The method is also consistent with the basic experiment, and the ultimate pulling resistance P of the anchor rod under the soil layer condition can be solved by using the cohesive force model u Ultimate pull-out resistance P u Corresponding displacement S u Residual pullout resistance P r 。
In the step S3, the energy change of the sample anchor rod in the whole pulling-resistant process is analyzed based on energy conservation, and the pulling-resistant force of the sample anchor rod is calculated to just reach P r Displacement S at the time r The method comprises the following steps:
s21: increasing from 0 to P according to the sample anchor rod pulling resistance u Conservation of energy in a processCalculating the surface energy E required to be dissipated for forming a new surface by the unit area of the anchoring section of the sample anchor rod and the debonded part of the soil layer b ；
S22: according to the pulling resistance of the sample anchor rod from P u Down to P r In-process energy conservation, calculating that the pulling resistance of the sample anchor rod just reaches the residual pulling resistance P r When in use, the displacement S corresponding to the sample anchor rod r 。
The anchor rod is subjected to a pulling force increasing from 0 to a limit pulling force P u The deformation of the anchor rod is as follows:
(1) The free section of the anchor rod is subjected to outward force, and is pulled out to generate elastic deformation at the same time, so as to store elastic potential energy;
(2) The anchor rod anchoring section is divided into a debonded part and a non-debonded part, wherein the debonded part generates elastic deformation under the action of drawing force, and elastic potential energy is accumulated; meanwhile, the debonded part and the soil layer are debonded to form a new surface, so that certain surface energy needs to be dissipated; in addition, as the debonded part is tightly contacted with soil before debonding, the soil layer provides reverse friction force in the process of being pulled out outwards, and therefore the friction force in the pulling process also works;
(3) The non-debonded part of the anchoring section can also generate elastic deformation under the action of the drawing force, and elastic potential energy is accumulated.
Based on the above-mentioned deformation, the step S21 specifically includes the following steps:
s211: according to the cohesive force model, calculating to obtain the pullout resistance of the sample anchor rod as P u When in use, the debonding length L of the sample anchor rod and the soil layer ar ；
S212: calculation of sample Anchor rod pullout resistance increasing from 0 to P u In the process, energy E externally applied to the top of the sample anchor Top ：
Wherein P is max For the maximum pulling force born by the sample anchor rod in the acceptance test, S max Is P max The displacement of the anchor rod under the condition;
s213: calculating the energy E accumulated by the elongation of the free section of the sample anchor rod f ：Wherein L is f The free section length of the sample anchor rod;
s214: calculating the energy E dissipated by friction force between the anchoring section of the sample anchor rod and the debonded part of the soil layer Friction wheel ：
S215: calculating the energy E accumulated by the extension of the sample anchor rod anchoring section and the soil layer debonding part Anchor extension ：
S216: calculating elastic potential energy E accumulated by non-debonded part of sample anchor rod anchoring section and soil layer Anchor bullet ：
Wherein L is ae The length of the non-debonded part of the sample anchor rod and the soil layer is the length of the non-debonded part of the sample anchor rod and the soil layer;
s217: calculating the surface energy E required to be dissipated for forming a new surface by the unit area of the anchoring section of the sample anchor rod and the debonded part of the soil layer b ：
The anchor rod receives a drawing force from a limit drawing force P u Reduced to residual bearing capacity P r The deformation of the anchor rod is as follows:
(1) The free section of the anchor rod is lowered by the outward force to generate rebound, and elastic potential energy is released;
(2) The debonded part of the anchor rod anchoring section also generates rebound under the condition of the stress falling, and elastic potential energy is released; simultaneously, friction force does work and consumes energy;
(3) Although the force is reduced, the anchor rod is pulled outwards, so that a new debonding part is generated in the anchor section, and the elastic potential energy is accumulated in the new debonding part; in addition, the anchor segment debonds from the soil layer to form a new surface, which requires dissipation of a certain surface energy.
Based on the above-mentioned deformation, the step S22 specifically includes the following steps:
s221: calculating the drawing force of the sample anchor rod from P u Down to P r In the process, elastic potential energy E released by free section of sample anchor rod 2 ：
S222: calculating elastic potential energy E released by rebound of sample anchor rod anchoring section and soil layer debonding part 3 ：
Wherein x is the length of the anchor rod anchoring section and the new debonded part of the soil layer;
s223: calculating elastic potential energy E accumulated by new debonding part of sample anchor rod anchoring section and soil layer 4 ：
Wherein:
s224: calculating the energy E dissipated by friction force between the anchoring section of the sample anchor rod and the debonded part of the soil layer 5 ：
S225: calculating the surface energy consumed by the sample anchor rod anchoring section and the soil layer debonding part:
E surface energy ＝U(L a -L ar )E b
S226: elastic potential energy E released by anti-pulling device in acceptance test 1 Constructing an equation, and solving to obtain the displacement S of the anchor rod when the pulling resistance of the anchor rod just reaches the residual pulling resistance r ：
When the pulling force of the anchor rod just reaches the residual pulling resistance P r When the anchor rod anchoring section is completely debonded with the soil layer, the anchor rod can be pulled out by small pulling force.
S4: setting an initial value of a soil layer intensity coefficient, taking the pile body and the anchor rod as a supporting system bearing the action of soil pressure, and calculating the soil pressure P borne by the pile body a And (3) obtaining the displacement of the pile body under the initial value of the soil layer intensity coefficient through iterative inversion calculation, comparing the displacement with the displacement in the pile body detection data, if the error of the displacement and the displacement exceeds 5%, adjusting the soil layer intensity coefficient to recalculate until the error of the displacement and the displacement does not exceed 5%, finishing the determination of the actual soil layer intensity coefficient, and solving based on a structural mechanical method to obtain the internal force of the pile body under the actual soil layer intensity coefficient.
Soil pressure P a Expressed as:
wherein, gamma, c,The soil layer weight, cohesion and internal friction angle are respectively; k is the soil layer intensity coefficient, and k is less than or equal to 1.0; z represents the distance from the node on the pile body to the bottom of the foundation pit; p is p 0 Is ground surfaceLoad;
the solving process of the displacement of each node of the pile body is as follows:
wherein:
P a1 ，P a2 …P ai ，P aj …P am soil pressure acting on pile body nodes 1,2,3 … i, j … m respectively;
x 1 ，x 2 …x i ，x j …x m horizontal displacement on pile body nodes 1,2,3 … i and j … m respectively;
θ 1 ，θ 2 …θ i ，θ j …θ m the corners of pile body nodes 1,2 and 3 … i and j … m are respectively;
P mgi the anchor rod tension corresponding to the pile body node i is calculated according to the following formula:
P mgi ＝K mgi ·x i
wherein K is mgi The rigidity coefficient K of the anchor rod corresponding to the pile body node i mgi The calculation process of (1) is as follows:
wherein: h is a i The horizontal displacement quantity h of the anchor rod corresponding to the pile body node i i ∈x i The method comprises the steps of carrying out a first treatment on the surface of the Delta is the inclination angle of the anchor rod;
the anchor rod is connected with a specific node on the pile body, the horizontal displacement of the node on the pile body is the horizontal displacement of the anchor rod, the horizontal displacement of the anchor rod can be obtained after the displacement of each node of the pile body is solved, and the relationship between the horizontal displacement of the anchor rod and the displacement of the anchor rod is as follows: h is a i ＝S i ·cosδ，S i Indicating the displacement of the anchor rod.
K djn Foundation rigidity coefficient of pile body node below foundation pit bottom surface，K djn The calculation process of (1) is as follows:
K djn ＝gzb 1 l
wherein g is the proportionality coefficient of the horizontal resistance coefficient of the stratum foundation; b 1 Calculating the width of the pile body; l is the sum of 50% of the lengths of the units at two sides of the pile body node.
As can be seen in connection with fig. 7, the stiffness coefficient K of the anchor rod mgi Namely the slope of the anchor rod in the pulling resistance-displacement curve, and the rigidity coefficient K of the anchor rod in different stress stages mgi If the difference exists, the calculated tension of the anchor rod is deviated if the tension of the anchor rod is calculated by constant rigidity coefficient, so that the calculation of the internal force of the pile body is influenced.
Referring to fig. 3, the iterative calculation process is:
(1) Firstly, setting an initial value P for the anchor rod tension corresponding to a pile body node i pi Calculating an initial value P by adopting a pile displacement solving formula pi Displacement x of each node of lower pile body i Obtaining the horizontal displacement h of the anchor rod i ；
(2) According to a calculation formula of the anchor rod stiffness coefficient, determining the horizontal displacement h of the anchor rod i Lower rigidity coefficient K mgi ；
(3) P is calculated according to the calculation formula of the anchor rod tension mgi Judgment of P mgi And P pi Error of (2);
(4) If the error exceeds 5%, the calculated P is calculated mgi Setting the pulling force of the anchor rod as an initial value, repeating the steps (1) - (3) until the error of the pulling force and the pulling force is not more than 5%, and obtaining the pulling force of the anchor rod as the assigned value P in the iteration pi ；
(5) And substituting the obtained anchor rod tension into a solving formula of the displacement of the pile body again to obtain the displacement of each node of the pile body.
The internal force solving process of the pile body is achieved by adopting a conventional technology in the art, for example, a calculating method of the prior art 1 (finite element calculation and application of a prestressed anchor cable slide-resistant pile, wei Ning and the like, university of Chinese university (engineering edition), 37 th roll, 5 th period and 10 month in 2004) is adopted, and the calculating method can be used for compiling a corresponding calculating program by applying MATLAB language, directly calculating the internal force of the pile body, drawing a graph and being rapid and convenient to use.
The value of k is different, the deformation of the pile body and the internal force of the pile body are different, an initial value k=1.0 is given to k before calculation starts, the k value is corrected by comparing the calculated displacement of the pile body with monitoring data of the displacement of the pile body until the calculated displacement of the pile body is matched with the detection data of the displacement of the pile body, and the determination of the k value can be completed. After the k value is determined, solving the internal force of each node of the pile body again.
S5: and directly acquiring the bearing capacity of the pile body from the design parameters of the pile anchor supporting structure, comparing the internal force of the pile body with the bearing capacity, and judging the safety of the pile anchor supporting structure.
The judging process is as follows: calculating the ratio of the bearing capacity to the internal force of the pile body, if the ratio is greater than 1, the internal force of the pile body does not reach the bearing capacity of the pile body yet, the pile body is in a safe and stable state, the displacement of the pile body can be continuously monitored, reinforcement operation is not needed, and the greater the ratio is, the higher the safety margin of the pile body is represented; if the ratio is less than or equal to 1, the internal force of the pile body reaches or exceeds the bearing capacity of the pile body, the pile body is in an unsafe state, and the greater the ratio, the higher the unsafe degree of the pile body. A threshold value may be set by an empirical value, and when the ratio is less than 1 but greater than the threshold value, the reinforcement work is performed; when the ratio is less than or equal to the threshold, the risk of reinforcement is high, and the foundation pit can only be backfilled or collapsed.
The steps in the steps S1-S5 can be directly packaged in a computer program, and the computer executes the processes of operation, processing and judgment, so that the final judgment result can be obtained only by inputting corresponding test measurement data according to the actual application scene, and the operation speed can be greatly improved. Aiming at different application scenes, the binding force model is adjusted by only carrying out primary experiments, and the binding force model is rapid and convenient to use.
Example 1
In this embodiment, a deep foundation pit engineering of a commercial center to be built in the M city center is selected for illustration: 8 building on the ground of the planned building is a 2-24-layer connected building, the underground is two layers and a half, and the foundation is in the form of a raft foundation. The elevation of the terrace of the planned site is 39.5-42.5 m, the elevation of the bottom of the foundation pit is 27.2m, the depth of the foundation pit is 12.3-15.3 m, and the length of the pile anchor supporting structure is about 617.0m. The formations buried in the field include a fourth system of fresh system earth fill, silt silty clay, a fourth system of updated system silty clay, silt, round gravel, chalk system silt silty sandstone, etc.
And selecting any section of pile anchor supporting structure of the foundation pit for calculation, wherein supporting structure parameters of the foundation pit and the selected supporting section are shown in table 1, and geological condition information and soil layer parameter information are shown in table 2.
TABLE 1 Foundation pit design parameter information Table
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Table 2 geological conditions and soil layer parameters take on value table
In the embodiment, a certain supporting section of the foundation pit is selected, three layers of anchor rods are adopted, as shown in fig. 4, the anchor rods are numbered as MG-1, MG-2 and MG-3 from top to bottom, wherein an MG-1 anchoring stratum is a fine sand round gravel layer, an MG-2 anchoring stratum is a round gravel layer, and an MG-3 main anchoring stratum is a strong-weathered argillaceous silty sandstone layer. Basic tests were performed on anchors with fine sand round gravel layer, round gravel layer and stroke-cemented argillite respectively, the results of the basic tests are shown in fig. 5, wherein:
anchor rods anchored in a fine sand round gravel layer: p (P) u ＝784kN，P r ＝306kN，S u ＝0.058m；
Anchored in a circleAnchor rods in the gravel layer: p (P) u ＝865kN，P r ＝407kN，S u ＝0.065m；
Anchor rod anchored in strongly weathered argillaceous silty rock stratum: p (P) u ＝630kN，P r ＝243kN，S u ＝0.052m。
The parameters of the model obtained based on the inverse calculation of the cohesive force model in the step S1 are shown in the following table:
TABLE 3 calculation parameter back calculation result table
| Calculating parameters | Fine sand round gravel layer | Round gravel layer | Strong weathering argillaceous silty sandstone layer |
| Residual strength of anchor and stratum bond, τ r (kPa) | 34.18 | 45.46 | 27.14 |
| Ultimate strength of anchor and stratum bond, τ m (kPa) | 563.91 | 586.39 | 350.11 |
| Limited shear displacement S m (m) | 0.00266 | 0.00229 | 0.00295 |
| Length of debonding section corresponding to ultimate pulling resistance L ar (m) | 14.5 | 15 | 13.5 |
The MG-1, MG-2 and MG-3 are respectively sampled and subjected to acceptance test, in the acceptance test, based on the principle of energy conservation, the energy released by the system is equal to the consumed energy, and the surface energy E required to be dissipated is calculated and obtained by debonding the anchor rod anchoring section and the unit area of the soil layer debonding part to form new surface energy b Maximum pulling force P in acceptance test max Can be directly obtained from FIG. 5, the result of the acceptance test is shown in FIG. 6, E b The calculation results of (2) are shown in Table 4:
table 4 acceptance test calculation results table
| P max (kN) | S max (m) | E b (J/m 2 ) | |
| MG-1 | 782 | 0.056 | 131.30 |
| MG-2 | 873 | 0.058 | 124.02 |
| MG-3 | 560 | 0.036 | 103.11 |
Based on the adhesive force model provided in the step S1, the ultimate pulling resistance P of the three rows of anchor rods is calculated respectively u Ultimate pull-out resistance P u Corresponding displacement S u ：
MG-1：P u1 ＝804.31kN，S u1 ＝0.059m；
MG-2：P u2 ＝910.46kN，S u2 ＝0.0628m；
MG-3：P u3 ＝597.38kN，S u3 ＝0.039m。
And (2) respectively calculating residual pulling resistance P of the three rows of anchor rods by using the energy conservation analysis method provided in the step (S2) r Just reaching the residual pulling resistance P r Displacement S at the time r ：
MG-1：P r1 ＝322.11kN，S r1 ＝0.0804m；
MG-2：P r2 ＝417.71kN，S r2 ＝0.0649m；
MG-3：P r3 ＝243.12kN，S r3 ＝0.0463m。
Building a tensile-displacement (P-S) coordinate system of each row of anchor rods, and obtaining (0, 0), (P) u ,S u )、(P r ,S r )、(P r And infinity) are sequentially connected by straight lines to obtain a pulling resistance-displacement curve of the whole pulling resistance process of the three rows of anchor rods, as shown in figure 7.
In the pile internal force calculation process, the pile body is divided into 17 units, 18 nodes are formed in total, the node 1 is a pile top, the node 18 is a pile bottom, the first row of anchor rods MG-1 is arranged on the node 2, the second row of anchor rods MG-2 is arranged on the node 6, and the third row of anchor rods MG-3 is arranged on the node 10. The rigidity coefficient values of the three-layer anchor rod are respectively as follows:
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the displacement and stress conditions of each node of the pile body are calculated by adopting a matrix displacement method, and calculation results under a design working condition (k=1.0) and an early warning working condition (the maximum displacement of the pile body exceeds 0.020 m) are shown in tables 5 and 6 respectively, wherein the calculation results are positive in a foundation pit and negative outside the foundation pit.
Table 5 calculation results table of each node of pile body (design condition: rock-soil intensity coefficient k=1.0)
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When k=1.0, the displacement and the stress condition of each node indicate that the maximum bending moment appears at the node 9, which is 964.5 kN.m, which is smaller than the bending-resistant bearing capacity of the pile body; the maximum node displacement is 0.01411m, and the maximum node displacement occurs at the node 10, namely the third-layer anchor rod; meanwhile, the pulling force of the three-layer anchor rods is smaller than the calculated maximum pulling resistance, and the fact that the foundation pit supporting structure is in a stable state is proved that the foundation pit supporting structure is loaded with larger surplus under the design working condition.
TABLE 6 calculation results table of each node of pile body (early warning condition: maximum displacement of pile body exceeds 0.020 m)
When the maximum displacement of the pile body exceeds 0.020m, back calculation is carried out to obtain k=0.85, and the tension of the third row of anchor rods is larger than P u3 Namely, the third row of engineering anchor rods are damaged, only residual bearing capacity can be provided, and the pulling resistance of the third row of engineering anchor rods is 505kN and is larger than the residual pulling resistance P according to the displacement of the third row of anchor rods r3 。
The maximum bending moment appears at the node 11 and is 1244.6 kN.m, the bending resistance bearing capacity of the pile body is still smaller than that of the pile body, the pile body is in a safe state, and the ratio of the bending resistance bearing capacity of the pile body to the bending moment of the pile body is: 1467/1244.6 =1.18 >1.15, which shows that the pile body has certain safety and has the condition of monitoring and reinforcing.
Comparative example
Directly analyzing the displacement and stress conditions of the pile body under the early warning working condition by using a structural mechanics method, wherein the tension of the third row of anchor rods is calculated according to P r3 The soil layer strength coefficient k was 0.85, and the obtained results are shown in table 7.
Table 7 calculation results table of each node of pile body (early warning condition: tension of third row anchor rod=p) r3 )
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Wherein the maximum bending moment appears at the node 10 and is 1847 kN.m, the bending bearing capacity of the pile body is exceeded, and the ratio of the bending bearing capacity of the pile to the bending moment of the pile body is: 1467/1847=0.8<1.05, presenting a destructive state; and the pulling force of the second layer of anchor rod exceeds the maximum value P u2 I.e. the second layer of anchor rods are also damaged, so the reinforcement operation is very dangerous, and only has two options of backfilling the foundation pit or appearing to collapse.
By comparing the embodiment 1 with the comparative example, it can be found that under the early warning working condition, the method adoptsThe determination method provided by the invention has the following conclusion: the pile body has a certain margin of safety, and the safety of the foundation pit can be improved in a reinforcing mode; the determination method provided by the structural mechanics method in the prior art is adopted to draw the conclusion that: the pile body has no safety and no reinforcing condition, and can only be backfilled or collapsed. Therefore, the determination method provided by the invention can generate great economic benefit in practical engineering application. The invention is based on the technical proposal that the energy change of the whole process of the anchor rod pulling resistance is analyzed from the angle of energy conservation, the tension-displacement curve of the anchor rod in the whole process of the anchor rod pulling resistance is obtained, and the analysis of the tension-displacement curve can find that when the load born by the anchor rod exceeds the limit pulling resistance P u When it is not a direct broken layer, it reaches the residual pulling resistance P r Still coming to the residual resistance P in a linear descent r During the descending process, the pulling resistance of the anchor rod is larger than the residual pulling resistance P r If the anchor rod breaks directly with residual resistance P r And calculating, namely loading redundant pulling resistance on the pile body to ensure balance of forces, and bearing by the pile body, so that the load of the pile body is increased, the calculated pile body internal force is increased, and unsafe judgment of the pile body is easy to make.
Compared with the related art, the foundation pit safety determination method for the deformation super-early warning value pile anchor supporting structure provided by the invention analyzes the energy change of the whole process of the anchor rod pulling resistance from the angle of energy conservation, and obtains the pulling resistance-displacement curve of the anchor rod in the whole process of the anchor rod pulling resistance. And taking the pile body and the anchor rod as a supporting system, and obtaining the soil pressure matched with the displacement data of the monitored pile body through iterative inversion calculation, so as to obtain the internal force of the pile body under the action of the soil pressure, thereby judging the safety of the pile body. Because the whole process of the pullout resistance of the anchor rod is considered, the anchor rod is in P u -P r The pulling resistance of the anchor rod can be accurately obtained in the process, and the residual pulling resistance P of the anchor rod is not simply used r The internal force of the pile body is calculated, so that the internal force of the pile body can be more accurately analyzed, and the most accurate foundation pit installation is madeAnd the judgment result of the completeness is convenient for the practical engineering application, the opportunity is taken for emergency reinforcement, and the economic benefit is relatively high.
The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.
Claims (5)
1. The foundation pit safety determination method for the deformation super-early-warning-value pile anchor supporting structure is characterized by comprising a pile body and a plurality of layers of anchor rods connected with the pile body, and the method comprises the following steps of:
s1: constructing an adhesion model of the anchor rod and the soil layer, wherein the adhesion model is expressed as:
wherein P is u Representing the ultimate pulling resistance of the anchor rod, S u Indicating the ultimate pulling resistance P of the anchor rod u Displacement amount of the lower part; p (P) r Representing the residual pullout resistance of the anchor rod; l (L) a Representing the length of the anchor rod anchoring section; u represents the perimeter of the anchor rod anchoring section; e (E) S And A S Respectively representing the elastic modulus and the cross section area of the free section of the anchor rod; e and A respectively represent the elastic modulus and the cross-sectional area of the anchor rod anchoring section; l (L) f Representing the length of the free section of the anchor rod; alpha represents an intermediate parameter; τ m Representing the ultimate strength of the bonding of the anchor rod anchoring section and the soil layer; τ r Representing the residual strength of the bonding of the anchor rod anchoring section and the soil layer; s is(s) m Representing the maximum shear displacement of the anchor rod anchoring section; l (L) ar The length of the debonded part of the anchor rod and the soil layer under the limit pulling resistance is represented; λ represents the coefficient of friction resistance transfer between the anchor rod anchoring section and the soil layer;
s2: setting anchor rod basic experiments aiming at different soil layers respectively, and recording P of the test anchor rod u 、S u P r Substituting the value into the cohesive force model to obtain tau by back calculation m 、τ r Lambda and s m Completing the establishment of a cohesive force model;
s3: for the safety determination of the pile anchor supporting structure, randomly sampling the installed anchor rods to obtain sample anchor rods, performing acceptance test on the sample anchor rods, analyzing the energy change of the sample anchor rods in the whole pulling-resistant process based on energy conservation, and calculating to obtain that the pulling-resistant force of the sample anchor rods just reaches P r Displacement S at the time r The method comprises the steps of carrying out a first treatment on the surface of the Establishing an anchor rod pulling resistance-displacement coordinate system, and obtaining (0, 0) and (P) u ,S u )、(P r ,S r )、(P r Infinity) are sequentially connected by straight lines to obtain a pulling resistance-displacement curve of the whole pulling resistance process of the sample anchor rod;
s4: setting an initial value of a soil layer intensity coefficient, taking the pile body and the anchor rod as a supporting system bearing the action of soil pressure, and calculating the soil pressure P borne by the pile body a Obtaining displacement of the pile body under the initial value of the soil layer intensity coefficient through iterative inversion calculation, comparing the displacement with the displacement in pile body detection data, if the two errors exceed 5%, adjusting the soil layer intensity coefficient to recalculate until the two errors do not exceed 5%, finishing the determination of the actual soil layer intensity coefficient, and solving based on a structural mechanics method to obtain the internal force of the pile body under the actual soil layer intensity coefficient;
s5: and directly acquiring the bearing capacity of the pile body from the design parameters of the pile anchor supporting structure, comparing the internal force of the pile body with the bearing capacity, and judging the safety of the pile anchor supporting structure.
2. The method for determining the safety of a foundation pit of a deformed super-early-warning pile anchor supporting structure according to claim 1, wherein in the step S3, the pulling resistance of the sample anchor rod is calculated to be just up to P based on energy conservation analysis of energy change of the sample anchor rod in the whole pulling resistance process r Displacement S at the time r The method comprises the following steps:
s21: increasing from 0 to P according to the sample anchor rod pulling resistance u Conservation of energy in the process, calculating the sampleThe unit area of the anchoring section of the anchor rod and the debonded part of the soil layer form a new surface energy E needing dissipation b ；
S22: according to the pulling resistance of the sample anchor rod from P u Down to P r In-process energy conservation, calculating that the pulling resistance of the sample anchor rod just reaches the residual pulling resistance P r When in use, the displacement S corresponding to the sample anchor rod r 。
3. The method for determining the safety of the foundation pit of the deformed super-early-warning pile anchor supporting structure according to claim 2, wherein the step S21 specifically comprises the following steps:
s211: according to the cohesive force model, calculating to obtain the pulling force P of the sample anchor rod u Length L of debonded portion of the sample anchor rod with soil layer ar ；
S212: calculation of sample Anchor rod pullout resistance increasing from 0 to P u In the process, energy E externally applied to the top of the sample anchor Top ：
Wherein P is max For the maximum pulling force born by the sample anchor rod in the acceptance test, S max Is P max The displacement of the anchor rod under the action;
s213: calculating the energy E accumulated by the elongation of the free section of the sample anchor rod f ：
Wherein L is f The free section length of the sample anchor rod;
s214: calculating the energy E dissipated by friction force between the anchoring section of the sample anchor rod and the debonded part of the soil layer Friction wheel ：
S215: meter with a meter bodyCalculating the energy E accumulated by the extension of the anchor section of the sample anchor rod and the debonded part of the soil layer Anchor extension ：
S216: calculating elastic potential energy E accumulated by non-debonded part of sample anchor rod anchoring section and soil layer Anchor bullet ：
Wherein L is ae The length of the non-debonded part of the sample anchor rod and the soil layer is the length of the non-debonded part of the sample anchor rod and the soil layer;
s217: calculating the surface energy E required to be dissipated for forming a new surface by the unit area of the anchoring section of the sample anchor rod and the debonded part of the soil layer b ：
4. The method for determining the safety of a foundation pit of a deformed super-early-warning pile anchor supporting structure according to claim 3, wherein the step S22 specifically comprises the following steps:
s221: calculating the drawing force of the sample anchor rod from P u Down to P r In the process, elastic potential energy E released by free section of sample anchor rod 2 ：
S222: calculating elastic potential energy E released by rebound of sample anchor rod anchoring section and soil layer debonding part 3 ：
Wherein x is the length of the anchor rod anchoring section and the new debonded part of the soil layer;
s223: calculating elastic potential energy E accumulated by new debonding part of sample anchor rod anchoring section and soil layer 4 ：
Wherein:
s224: calculating the energy E dissipated by friction force between the anchoring section of the sample anchor rod and the debonded part of the soil layer 5 ：
S225: calculating the surface energy consumed by the sample anchor rod anchoring section and the soil layer debonding part:
E surface energy ＝U(L a -L ar )E b
S226: elastic potential energy E released by anti-pulling device in acceptance test 1 Constructing an equation, and solving to obtain that the pulling resistance of the anchor rod just reaches the residual pulling resistance P r In the process, the displacement S of the anchor rod r ：
5. The method for determining the safety of a foundation pit of a deformed super-early-warning pile-anchor supporting structure according to claim 4, wherein in the step S4, the soil pressure P a Expressed as:
wherein, gamma, c,The soil layer weight, cohesion and internal friction angle are respectively; k is the soil layer intensity coefficient, and k is less than or equal to 1.0; z represents the distance from the node on the pile body to the bottom of the foundation pit; p is p 0 Is ground load;
in the step S4, the soil pressure P is solved a The solving process of the displacement of each node of the pile body under the action is as follows:
wherein:
P a1 ，P a2 …P ai ，P aj …P am soil pressure acting on pile body nodes 1,2,3 … i, j … m respectively;
x 1 ，x 2 …x i ，x j …x m the horizontal displacement amounts of pile body nodes 1,2 and 3 … i and j … m are respectively;
θ 1 ，θ 2 …θ i ，θ j …θ m the corners of pile body nodes 1,2 and 3 … i and j … m are respectively;
P mgi the anchor rod tension corresponding to the pile body node i is calculated according to the following formula:
P mgi ＝K mgi ·x i
wherein K is mgi The rigidity coefficient K of the anchor rod corresponding to the pile body node i mgi The calculation process of (1) is as follows:
wherein: h is a i The horizontal displacement quantity h of the anchor rod corresponding to the pile body node i i ∈x i The method comprises the steps of carrying out a first treatment on the surface of the Delta is the inclination angle of the anchor rod;
K djn k is the foundation rigidity coefficient of pile body node below the bottom surface of foundation pit djn The calculation process of (1) is as follows:
K djn ＝gzb 1 l
wherein g is the proportionality coefficient of the horizontal resistance coefficient of the stratum foundation; b 1 Calculating the width of the pile body; l is the sum of 50% of the lengths of the units at two sides of the pile body node.
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