CN114818046A - Method for determining safety of foundation pit of pile-anchor supporting structure with deformation exceeding early warning value - Google Patents
Method for determining safety of foundation pit of pile-anchor supporting structure with deformation exceeding early warning value Download PDFInfo
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Abstract
According to the method for determining the safety of the foundation pit of the pile-anchor supporting structure with the deformation exceeding the early warning value, the energy change of the overall pulling-resistant process of the anchor rod is analyzed from the aspect of energy conservation, and a pulling-resistant force-displacement curve of the overall pulling-resistant process of the anchor rod is obtained. And taking the pile body and the anchor rod as a supporting system, obtaining the soil pressure matched with the displacement data of the monitored pile body through iterative inversion calculation, and further obtaining the internal force of the pile body under the action of the soil pressure, thereby judging the safety of the pile body. Due to the consideration of the whole process change of the pulling resistance of the anchor rod, the method is carried out at P u ‑P r ProcedureThe pulling resistance of the anchor rod can be accurately obtained, and the residual pulling resistance P of the anchor rod is not simply used r The internal force of the pile body can be more accurately analyzed by calculating the internal force of the pile body, so that the most accurate foundation pit safety judgment result is made, the foundation pit safety judgment method is convenient for practical engineering application, and the opportunity is caught to carry out emergency repair reinforcement, so that the method has great economic benefit.
Description
[ technical field ] A method for producing a semiconductor device
The invention relates to the technical field of foundation pit supporting, in particular to a method for determining the safety of a foundation pit of a pile-anchor supporting structure with deformation exceeding an early warning value.
[ background of the invention ]
In the field of building engineering, in order to ensure the safety of a foundation pit, the deformation of a supporting structure is generally monitored in the construction process of the foundation pit, corresponding treatment is required once the deformation of the supporting structure exceeds a designed early warning value, and emergency work is required when necessary. Before treatment is carried out, 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 which emergency measures are adopted can be determined. If the safety of the foundation pit has a certain margin after analysis, the manpower equipment can be adjusted to carry out emergency repair and reinforcement, and the accident potential is eliminated; if the foundation pit safety is not redundant after analysis, the foundation pit can only be backfilled or allowed to collapse.
The safety of the pile anchor supporting structure can be judged by comparing the internal force of the pile body in the pile anchor supporting structure with the bearing capacity in the pile body design parameters, and the internal force of the pile body can be calculated by a structural mechanics method. The internal force of a pile body in the pile anchor supporting structure is calculated by adopting a structural mechanics method, and the following 4 basic data are required: firstly, foundation resistance parameters; geometric and material characteristics of the pile; thirdly, monitoring deformation data of the supporting structure; fourthly, the uplift resistance-deformation curve of each row of anchor rods. Wherein, the first and the second can be obtained by looking up the survey and design data; thirdly, the monitoring is carried out through the foundation pit; and fourthly, obtaining the product through an anchor rod drawing test.
Wherein, the anti-pulling test of the anchor rod is also called as 'acceptance test', and the acceptance test is only to determine the anchor rodAnd if the bearing capacity is larger than the designed value, the anchor rod cannot be pulled to be damaged. Therefore, the anchor rod anti-pulling force-deformation curve obtained by the acceptance test is only a tension-deformation curve section before the tension of the anchor rod reaches the peak value, and does not include that the tension of the anchor rod reaches the limit anti-pulling force P u Later entering residual pulling resistance P r The tension versus deflection for a state is a paragraph and is thus an incomplete tension versus deflection curve. And after the anchor rod is pulled to reach the limit pulling resistance and is 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 withdrawal resistance P r The ultimate pull-out resistance P can be reached u 30-60% of the total. For foundation pit with excessive deformation and alarming, residual uplift resistance P of anchor rod r The method still plays an important role in maintaining the stability of the foundation pit. If the residual pull-out resistance P is not taken into consideration r The influence on the stability of the foundation pit can make the judgment of the unsafe foundation pit in advance under the condition that the foundation pit has the unsafe surplus degree, thereby causing huge economic loss. Therefore, it is actually necessary to provide a method for determining the safety of the foundation pit of the pile-anchor supporting structure with deformation exceeding the early warning value so as to solve the above problems.
[ summary of the invention ]
The invention aims to provide a method for determining the safety of a foundation pit of a pile-anchor supporting structure with deformation exceeding an early warning value, which considers the influence of the residual uplift resistance of an 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 no safety margin.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a method for determining the safety of a foundation pit of a pile-anchor supporting structure with deformation exceeding an early warning value is provided, 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 a binding power model of the anchor rod and the soil layer, wherein the binding power model is expressed as:
in the formula, P u Indicating the ultimate pullout resistance of the anchor rod, S u Indicating that the anchor rod is at the limit withdrawal resistance P u A downward displacement amount; p r The residual uplift resistance of the anchor rod is represented; l is a Indicating the length of the anchor rod anchoring section; u represents the perimeter of the anchor rod anchoring section; e S And A S Respectively showing the elastic modulus and the cross-sectional area of the free section of the anchor rod; e and A respectively represent the elastic modulus and the cross-sectional area of the anchoring section of the anchor rod; l is f Indicating the length of the free section of the anchor rod; α represents an intermediate parameter; tau is m The ultimate strength of the bonding of the anchor rod anchoring section and the soil layer is shown; tau is r The bonding residual strength of the anchor rod anchoring section and the soil layer is shown; s m Representing the maximum shear displacement of the anchor rod anchoring section; l is ar The length of the debonding part of the anchor rod and the soil layer under the ultimate uplift resistance is shown; lambda represents the friction resistance transfer coefficient of the anchor rod anchoring section and the soil layer;
s2: aiming at different soil layers, basic experiments of anchor rods are respectively arranged, and P of the anchor rods in the experiments is recorded u 、S u And P r Substituting the value into the adhesion model to obtain tau through inverse calculation m 、τ r λ and s m Completing the establishment of a binding force model;
s3: the method comprises the steps of aiming at the safety determination of a pile anchor supporting structure, randomly sampling an installed anchor rod to obtain a sample anchor rod, carrying out acceptance test on the sample anchor rod, analyzing the energy change of the sample anchor rod in the whole anti-pulling process based on energy conservation, and calculating to obtain the anti-pulling force of the sample anchor rod which just reaches P r Amount of displacement S of time r (ii) a Establishing anchor rod drawing resistance-displacement coordinate system, and connecting (0,0), (P) u ,S u )、(P r ,S r )、(P r And infinity) are sequentially connected by a straight line to obtain an anti-pulling force-displacement curve of the sample anchor rod in the whole anti-pulling process;
s4: setting an initial value of soil layer strength coefficient, taking the pile body and the anchor rod as a supporting system bearing the soil pressure, and calculating the soil pressure P borne by the pile body a Obtaining the pile by iterative inversion calculationComparing the displacement of the pile body under the initial value of the soil layer strength coefficient with the displacement in the pile body detection data, if the error between the displacement and the displacement exceeds 5%, adjusting the soil layer strength coefficient for recalculation until the error between the displacement and the displacement does not exceed 5%, completing the determination of the actual soil layer strength coefficient, and solving to obtain the internal force of the pile body under the actual soil layer strength coefficient based on a structural mechanics method;
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 anti-pulling process is analyzed based on energy conservation, and the anti-pulling force of the sample anchor rod is calculated to be just P r Amount of displacement S of time r The method specifically comprises the following steps:
s21: increasing the pullout resistance of the anchor rod from 0 to P according to the sample u In the process of energy conservation, calculating the surface energy E to be dissipated when the new surface is formed by the anchoring section of the sample anchor rod and the soil layer debonding part in unit area b ；
S22: according to the sample anchor rod pulling resistance force from P u Down to P r The energy conservation in the process is realized, and the anti-pulling force of the sample anchor rod is calculated to just reach the residual anti-pulling force P r Then, the corresponding displacement S of the sample anchor rod r 。
Preferably, the step S21 specifically includes the following steps:
s211: according to the adhesion model, the pulling force P of the sample anchor rod is obtained through calculation u The length L of the debonding part of the sample anchor rod and the soil layer ar ；
S212: calculating the increase of the pullout resistance of the sample anchor rod from 0 to P u In the process, energy E is externally applied to the top of the sample anchor Top roof ：
In the formula, P max Maximum drawing force S borne by sample anchor rod in acceptance test max Is P max Displacement of the anchor rod under action;
s213: calculating the energy E accumulated by the elongation of the free section of the sample anchor rod f ：
In the formula, L f The length of a free section of the sample anchor rod is determined;
s214: calculating the energy E dissipated by the friction force between the sample anchor rod anchoring section and the soil layer debonding part Massage device ：
S215: calculating the energy E accumulated by the extension of the anchoring section of the sample anchor rod and the debonding part of the soil layer Anchor extension ：
S216: calculating elastic potential energy E accumulated by the anchoring section of the sample anchor rod and the un-debonded part of the soil layer Anchor bullet ：
In the formula, L ae The length of the part of the sample anchor rod which is not debonded from the soil layer is taken as the length of the sample anchor rod;
s217: calculating the surface energy to be dissipated when the new surface is formed by the anchoring section of the sample anchor rod and the debonding part of the soil layer in unit area
Preferably, the step S22 specifically includes the following steps:
s221: calculating sample anchor rod pullout force from P u Down to P r In the process, the elastic potential energy E released by the free section of the sample anchor rod 2 ：
S222: calculating elastic potential energy E released by resilience of the anchoring section of the sample anchor rod and the debonding part of the soil layer 3 ：
Wherein x is the length of the new debonding part between the anchor rod anchoring section and the soil layer;
s223: calculating the elastic potential energy E accumulated by the newly debonded part of the sample anchor rod anchoring section and the soil layer 4 ：
Wherein:
s224: calculating the energy E dissipated by the friction force between the sample anchor rod anchoring section and the soil layer debonding part 5 ：
S225: calculating the consumed surface energy of the anchoring section of the sample anchor rod and the soil layer debonding part:
E surface energy of ＝U(L a -L ar )E b
S226: elastic potential energy E released by pulling-out resistant device in acceptance test 1 An equation is constructed, and the anchor rod withdrawal resistance obtained by solving is just up to the residual withdrawal resistance P r While the displacement S of the anchor rod r ：
Preferably, in the step S4, the soil pressure P is a Expressed as:
wherein gamma, c,
the soil layer gravity, the cohesion and the internal friction angle are respectively; k is the soil layer strength coefficient, and k is less than or equal to 1.0; z represents the distance from a node on the pile body to the bottom of the foundation pit; p is a radical of 0 Is a 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 comprises the following steps:
wherein:
P a1 ，P a2 …P ai ，P aj …P am the soil pressure acting on the 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 the pile body nodes 1, 2, 3 … i, j … m are respectively;
θ 1 ，θ 2 …θ i ，θ j …θ m the corners of the pile body nodes 1, 2, 3 … i, j … m are respectively;
P mgi and calculating the anchor rod tension corresponding to the pile body node i according to the following formula:
P mgi ＝K mgi ·x i
wherein, K mgi The rigidity coefficient, K, of the anchor rod corresponding to the pile body node i mgi The calculation process of (2) is as follows:
in the formula: h is i The horizontal displacement amount h of the anchor rod corresponding to the pile body node i i ∈x i (ii) a Delta is the inclination angle of the anchor rod;
K djn is the foundation stiffness coefficient of the pile body node below the bottom surface of the foundation pit, K djn The calculation process of (2) is as follows:
K djn ＝gzb 1 l
in the formula, g is a proportionality coefficient of a horizontal resistance coefficient of a stratum foundation; b 1 Calculating the width of the pile body; l is the sum of the lengths of 50% of the units on the two sides of the pile body node.
Compared with the prior art, the method for determining the safety of the foundation pit of the pile-anchor supporting structure with the deformation exceeding the early warning value analyzes the energy change of the anchor rod in the whole pulling-resisting process from the angle of energy conservation, and obtains the pulling-resisting force-displacement curve of the anchor rod in the whole pulling-resisting process. And taking the pile body and the anchor rod as a supporting system, obtaining the soil pressure matched with the displacement data of the monitored pile body through iterative inversion calculation, and further obtaining the internal force of the pile body under the action of the soil pressure, thereby judging the safety of the pile body. Due to the consideration of the whole process change of the pulling resistance of the anchor rod, the method is carried out at P u -P r The anti-pulling force of the anchor rod can be accurately obtained in the process, and the residual anti-pulling force P of the anchor rod is not simply used r The internal force of the pile body can be more accurately analyzed by calculating the internal force of the pile body, so that the most accurate foundation pit safety judgment result is made, the foundation pit safety judgment method is convenient for practical engineering application, and the opportunity is caught to carry out emergency repair reinforcement, so that the method has great economic benefit.
[ description of the drawings ]
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without inventive efforts, 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 exceeding an early warning value, provided by the invention;
fig. 2 is a schematic structural diagram of an anchor rod in a method for determining the safety of a foundation pit of a deformation exceeding early warning value pile anchor supporting structure provided by the invention;
FIG. 3 is a flowchart of the steps of the iterative inversion calculation in step S4;
FIG. 4 is a schematic view of the mounting structure of three anchor rods MG-1, MG-2 and MG-3 in the first embodiment;
FIG. 5 is a graph showing the basic experimental results of the anchor rods of three different soil layers in the first embodiment;
FIG. 6 is a diagram showing the results of the acceptance tests of three anchors MG-1, MG-2 and MG-3;
FIG. 7 is a graph of resistance to pullout force versus displacement for three types of anchors MG-1, MG-2, and MG-3.
[ detailed description ] embodiments
In order to make the technical solutions in the embodiments of the present invention better understood and make the above objects, features and advantages of the present invention more comprehensible, specific embodiments of the present invention are described below with reference to the accompanying drawings of the present application.
Referring to fig. 1 to 7, the present invention provides a method for determining the safety of a foundation pit of a pile-anchor supporting structure with a deformation exceeding an early warning value, 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 a binding power model of the anchor rod and the soil layer, wherein the binding power model is expressed as:
in the formula, P u Indicating the ultimate pullout resistance of the anchor rod, S u Indicating that the anchor rod is at the limit withdrawal resistance P u A downward displacement amount; p r The residual uplift resistance of the anchor rod is represented; l is a Indicating the length of the anchor rod anchoring section; u represents the perimeter of the anchor rod anchoring section; e S And A S Respectively indicating the elasticity of the free section of the boltModulus and cross-sectional area; e and A respectively represent the elastic modulus and the cross-sectional area of the anchoring section of the anchor rod; l is f Indicating the length of the free section of the anchor rod; α represents an intermediate parameter; tau is m The ultimate strength of the bonding of the anchor rod anchoring section and the soil layer is shown; tau is r The bonding residual strength of the anchor rod anchoring section and the soil layer is shown; s is m Representing the maximum shear displacement of the anchor rod anchoring section; l is ar The length of the debonding part of the anchor rod and the soil layer under the ultimate uplift resistance is shown; lambda represents the friction resistance transfer coefficient of the anchor rod anchoring section and the soil layer;
the adhesion model is used for representing the adhesion 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 all adopt the adhesion model to carry out solution calculation. Therefore, model parameters of different anchor rods under different soil layer conditions can be obtained only by carrying out an anchor rod basic experiment for each different soil layer: tau is m 、s m 、L ar 。
S2: aiming at different soil layers, basic experiments of anchor rods are respectively arranged, and P of the anchor rods in the experiments is recorded u 、S u And P r Substituting the value into the cohesive force model to obtain tau through inverse calculation m 、τ r λ and s m And finishing the establishment of the adhesion model.
Aiming at different application scenes, only one basic experiment needs to be carried out again to complete parameter adjustment of the adhesion model, so that a new adhesion model which is suitable for the current scene and has different parameters can be obtained, and the operation is quick and convenient.
S3: the method comprises the steps of aiming at the safety determination of a pile anchor supporting structure, randomly sampling an installed anchor rod to obtain a sample anchor rod, carrying out acceptance test on the sample anchor rod, analyzing the energy change of the sample anchor rod in the whole anti-pulling process based on energy conservation, and calculating to obtain the anti-pulling force of the sample anchor rod which just reaches P r Amount of displacement S of time r (ii) a Establishing anchor rod drawing resistance-displacement coordinate system, and connecting (0,0), (P) u ,S u )、(P r ,S r )、(P r And infinity) are sequentially connected by straight lines to obtain the anti-pulling force-displacement curve of the sample anchor rod in the whole anti-pulling process.
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 of the anchor rod in the basic experiment, the tau in the acceptance test m 、s m 、L ar The method is also consistent with the basic experiment, and the limit withdrawal resistance P of the anchor rod under the soil layer condition can be solved by utilizing the cohesive force model u Ultimate pull-out resistance P u Corresponding displacement S u And residual pull-out resistance P r 。
In the step S3, the energy change of the sample anchor rod in the whole anti-pulling process is analyzed based on energy conservation, and the anti-pulling force of the sample anchor rod is calculated to be just up to P r Amount of displacement S of time r The method specifically comprises the following steps:
s21: increasing the pullout resistance of the anchor rod from 0 to P according to the sample u In the process of energy conservation, calculating the surface energy E to be dissipated when the new surface is formed by the anchoring section of the sample anchor rod and the soil layer debonding part in unit area b ；
S22: according to the sample anchor rod pulling resistance force from P u Down to P r The energy conservation in the process is realized, and the anti-pulling force of the sample anchor rod is calculated to just reach the residual anti-pulling force P r Then, the corresponding displacement S of the sample anchor rod r 。
The anchor rod is subjected to a pulling force which increases from 0 to a limit pulling force P u The deformation condition of the anchor rod is as follows:
(1) the free section of the anchor rod is subjected to outward force, and generates elastic deformation while being pulled out, so that elastic potential energy is accumulated;
(2) the anchor rod anchoring section is divided into a debonding part and a non-debonding part, wherein the debonding part generates elastic deformation under the action of drawing force to accumulate elastic potential energy; meanwhile, the debonding part is debonded from the soil layer to form a new surface, and certain surface energy needs to be dissipated; in addition, because the debonding part is in close contact with soil before debonding, and in the process of being pulled out, the soil layer provides reverse friction force, so the friction force also works in the pulling process;
(3) the un-debonded part of the anchoring section can also generate elastic deformation under the action of drawing force, and elastic potential energy is accumulated.
Based on the above modification, the step S21 specifically includes the following steps:
s211: according to the binding force model, the uplift resistance of the sample anchor rod is calculated to be P u In time, the debonding length L of the sample anchor rod and the soil layer ar ；
S212: calculating the increase of the pullout resistance of the sample anchor rod from 0 to P u In the process, energy E is externally applied to the top of the sample anchor Top roof ：
In the formula, P max Maximum drawing force S borne by sample anchor rod in acceptance test max Is P max Displacement of the anchor under conditions;
s213: calculating the energy E accumulated by the elongation of the free section of the sample anchor rod f ：
In the formula, L f The length of a free section of the sample anchor rod is determined;
s214: calculating the energy E dissipated by the friction force between the sample anchor rod anchoring section and the soil layer debonding part Massage device ：
S215: calculating the energy E accumulated by the extension of the anchoring section of the sample anchor rod and the debonding part of the soil layer Anchor extension ：
S216: calculating elastic potential energy E accumulated by the anchoring section of the sample anchor rod and the un-debonded part of the soil layer Anchor bullet ：
In the formula, L ae The length of the part of the sample anchor rod which is not debonded from the soil layer is taken as the length of the sample anchor rod;
s217: calculating the surface energy E to be dissipated when the new surface is formed by the anchoring section of the sample anchor rod and the soil layer debonding part in unit area b ：
The anchor rod is subjected to a drawing force from a limit drawing force P u Reduced to residual bearing capacity P r The deformation condition of the anchor rod is as follows:
(1) the free section of the anchor rod is descended by an outward force to generate rebound and release elastic potential energy;
(2) the debonding part of the anchor rod anchoring section also generates resilience under the condition of descending of the force borne by the anchor rod anchoring section, and elastic potential energy is released; meanwhile, the friction force works and consumes energy;
(3) the anchor rod is pulled outwards even though the force is reduced, so that a new debonding part is generated in the anchoring section, and elastic potential energy is accumulated in the new debonding part; in addition, the anchoring section and the soil layer are debonded to form a new surface, and a certain surface energy needs to be dissipated.
Based on the above modification, the step S22 specifically includes the following steps:
s221: calculating sample anchor rod pullout force from P u Down to P r In the process, the elastic potential energy E released by the free section of the sample anchor rod 2 ：
S222: calculating elastic potential energy E released by resilience of the anchoring section of the sample anchor rod and the debonding part of the soil layer 3 ：
In the formula, x is the length of a new debonding part of the anchor rod anchoring section and the soil layer;
S223: calculating the elastic potential energy E accumulated by the newly debonded part of the sample anchor rod anchoring section and the soil layer 4 ：
Wherein:
s224: calculating the energy E dissipated by the friction force between the sample anchor rod anchoring section and the soil layer debonding part 5 ：
S225: calculating the surface energy consumed by the debonding part of the sample anchor rod anchoring section and the soil layer:
E surface energy of ＝U(L a -L ar )E b
S226: elastic potential energy E released by pulling-out resistant device in acceptance test 1 An equation is constructed, and when the anchor rod anti-pulling force is solved and just reaches the residual anti-pulling force, the displacement S of the anchor rod is obtained r ：
When the drawing force of the anchor rod just reaches the residual anti-drawing force P r And when the anchor rod anchoring section is completely debonded from the soil layer, the anchor rod can be pulled out by smaller pulling force.
S4: setting an initial value of soil layer strength coefficient, taking the pile body and the anchor rod as a supporting system bearing the soil pressure, and calculating the soil pressure P borne by the pile body a Obtaining the displacement of the pile under the initial value of the soil layer strength coefficient through iterative inversion calculation, comparing the displacement with the displacement in the pile detection data, and if the error between the displacement and the displacement in the pile detection data exceeds 5%, adjusting the soil layer strength systemAnd recalculating the number until the error between the two is not more than 5%, determining the actual soil layer strength coefficient, and solving based on a structural mechanics method to obtain the internal force of the pile body under the actual soil layer strength coefficient.
Pressure P of the earth a Expressed as:
wherein gamma, c,
the soil layer gravity, the cohesion and the internal friction angle are respectively; k is soil layer strength coefficient, and k is less than or equal to 1.0; z represents the distance from a node on the pile body to the bottom of the foundation pit; p is a radical of formula 0 Is a ground load;
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 the soil pressure acting on the 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, j … m respectively;
θ 1 ，θ 2 …θ i ，θ j …θ m the corners of the pile body nodes 1, 2, 3 … i, j … m are respectively;
P mgi and calculating the anchor rod tension corresponding to the pile body node i according to the following formula:
P mgi ＝K mgi ·x i
wherein, K mgi The rigidity coefficient, K, of the anchor rod corresponding to the pile body node i mgi The calculation process of (2) is as follows:
in the formula: h is i The horizontal displacement h of the anchor rod corresponding to the pile body node i i ∈x i (ii) a 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 horizontal displacement of the anchor rod and the displacement of the anchor rod are related: h is i ＝S i ·cosδ，S i Indicating the amount of displacement of the anchor.
K djn Is the foundation stiffness coefficient of the pile body node below the bottom surface of the foundation pit, K djn The calculation process of (2) is as follows:
K djn ＝gzb 1 l
in the formula, g is a proportionality coefficient of a horizontal resistance coefficient of a stratum foundation; b 1 Calculating the width of the pile body; l is the sum of the lengths of 50% of the units on the two sides of the pile body node.
The stiffness coefficient K of the anchor rod is shown in the figure 7 mgi Namely the slope of the anchor rod in the anti-pulling force-displacement curve, and the rigidity coefficient K of the anchor rod at different stress stages mgi If the tension of the anchor rod is always calculated by a constant rigidity coefficient, the calculated tension of the anchor rod can generate deviation, and therefore the calculation of the force in 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 using a pile body 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) Determining the horizontal displacement h of the anchor rod according to a calculation formula of the stiffness coefficient of the anchor rod i Lower coefficient of stiffness K mgi ；
(3) According to the calculation formula of the tension of the anchor rodCalculating to obtain P mgi Judgment of P mgi And P pi The error of (2);
(4) if the error between the two exceeds 5%, P to be calculated mgi Setting the initial value of the anchor rod tension, repeating the steps (1) to (3) until the error between the initial value and the anchor rod tension is not more than 5%, wherein the anchor rod tension is the value P in the iteration pi ；
(5) And substituting the obtained anchor rod tension into a solving formula of the pile body displacement to solve to obtain the displacement of each node of the pile body.
The internal force solving process of the pile body can be realized by adopting conventional technologies in the field, for example, a calculation method in the prior art 1 (finite element calculation and application of the prestressed anchor cable slide-resistant pile, Weining and the like, Wuhan university journal (engineering edition), volume 37, No. 5, and year 2004-10 month) is adopted, and the calculation method can be used for compiling a corresponding calculation program by applying MATLAB language, directly calculating the internal force of the pile body, drawing a graph, and is quick and convenient to use.
k has different values, solved pile body deformation and the different internal force of the pile body, before the calculation starts, an initial value k is given to k as 1.0, the solved pile body displacement is compared with monitoring data of the pile body displacement, the k value is corrected until the calculated pile body displacement is matched with the detection data of the pile body displacement, and the determination of the k value can be completed. And 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, indicating that the internal force of the pile body does not reach the bearing capacity of the pile body, the pile body is in a safe and stable state, the displacement of the pile body can be continuously monitored, additional reinforcement operation is not needed, and the larger the ratio is, the higher the safe surplus degree of the pile body is represented; if the ratio is less than or equal to 1, the bearing capacity of the pile body is reached or exceeded by the internal force of the pile body, the pile body is in an unsafe state, and the larger the ratio is, the higher the unsafe degree of the pile body is represented. 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 operation is high, and only the foundation pit can be backfilled or collapsed.
The steps in steps S1-S5 may be directly encapsulated in a computer program, and the computer executes the processes of operation, processing and determination, so that the final determination result can be obtained only by inputting the corresponding test measurement data according to the actual application scenario, thereby greatly improving the operation speed. Aiming at different application scenes, only one basic experiment needs to be carried out to adjust parameters of the adhesion model, and the method is fast and convenient to use.
Example one
In the embodiment, a deep foundation pit project of a to-be-built business center in the city center M is selected for illustration: the 8 buildings to be built on the ground are 2-24 layers of connected buildings, the underground is two-layer and half-layer, and the foundation is in the form of a raft foundation. The elevation of the terrace of the proposed 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 617.0 m. The stratum buried in the field comprises a fourth system of completely new system filling soil, silty clay, a fourth system of updated system silty clay, silty sand, round gravel, chalky system silty sand and the like.
And selecting any section of pile-anchor supporting structure of the foundation pit for calculation, wherein the supporting structure parameters of the foundation pit and the selected supporting section are shown in a table 1, and the geological condition information and the soil layer parameter information are shown in a table 2.
Table 1 foundation pit design parameter information table
TABLE 2 geological Condition and soil layer parameter evaluation Table
In this embodiment, a certain supporting section of the foundation pit is selected, three layers of anchor rods are provided, and as shown in fig. 4, the numbers of the anchor rods from top to bottom are respectively MG-1, MG-2 and MG-3, wherein the MG-1 anchoring stratum is a fine sand gravel layer, the MG-2 anchoring stratum is a gravel layer, and the MG-3 main anchoring stratum is a strongly weathered argillaceous silty stratum. Basic tests are respectively carried out on the anchor rods of which the anchoring stratums are a fine sand round gravel layer, a round gravel layer and weathered argillaceous siltstone, and the results of the basic tests are shown in fig. 5, wherein:
anchor rod anchored in fine sand gravel layer: p u ＝784kN，P r ＝306kN，S u ＝0.058m；
Anchor rod anchored in the gravel layer: p u ＝865kN，P r ＝407kN，S u ＝0.065m；
Anchor in strongly weathered argillaceous silty rock: p u ＝630kN，P r ＝243kN，S u ＝0.052m。
The parameters of the model obtained based on the reverse calculation of the adhesion model in step S1 are shown in the following table:
TABLE 3 back calculation result table of calculation parameters
| Calculating parameters | Fine sand round gravel layer | Layer of round gravel | Strongly weathered argillaceous silty rock formations |
| Residual strength of adhesion of anchor to formation, τ r (kPa) | 34.18 | 45.46 | 27.14 |
| Ultimate bond strength, τ, of the anchor to the formation m (kPa) | 563.91 | 586.39 | 350.11 |
| Ultimate shear displacement, S m (m) | 0.00266 | 0.00229 | 0.00295 |
| Length of debonding segment corresponding to ultimate pullout resistance, L ar (m) | 14.5 | 15 | 13.5 |
Respectively sampling MG-1, MG-2 and MG-3 to perform acceptance test, wherein in the acceptance test, based on the principle of energy conservation, the energy released by the system is equal to the consumed energy, and calculating to obtain the surface energy E to be dissipated for forming new surface energy by debonding the anchoring section of the anchor rod and the debonding part of the soil layer in unit area b Maximum pulling force P in acceptance test max Can be taken directly from FIG. 5, the results of the acceptance test are shown in FIG. 6, E b The calculation results are shown in table 4:
table 4 acceptance test calculation result 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 |
Respectively calculating the ultimate pullout resistance P of the three rows of anchor rods based on the bonding force model provided in the step S1 u And ultimate pullout 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。
Respectively calculating the residual uplift resistance P of the three rows of anchor rods by using the energy conservation analysis method provided in the step S2 r And just reach the residual pull-out resistance P r Amount of displacement S of 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。
Establishing a stretching resistance-displacement (P-S) coordinate system of each row of anchor rods, and comparing (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 fig. 7.
In the process of calculating the internal force of the pile body, the pile body is divided into 17 units, 18 nodes are provided, the node 1 is the pile top, the node 18 is the pile bottom, the first row of anchor rods MG-1 is arranged on the first 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 coefficients of the three layers of anchor rods take values as follows:
the displacement and the stress condition of each node of the pile body are calculated by adopting a matrix displacement method, and the calculation results under the design working condition (k is 1.0) and the early warning working condition (the maximum displacement of the pile body exceeds 0.020m) are shown in tables 5 and 6, wherein the calculation results in the tables take the inside of the foundation pit as positive and the outside of the foundation pit as negative.
Table 5 pile body each node calculation result table (design condition: rock strength coefficient k is 1.0)
When k is 1.0, the maximum bending moment appears at the node 9, which is 964.5kN m and is smaller than the bending-resistant bearing capacity of the pile body, according to the displacement and the stress condition of each node; the maximum node displacement is 0.01411m, and occurs at node 10, i.e. the third layer of anchors; meanwhile, the pulling force of the three layers of anchor rods is smaller than the calculated maximum uplift force, so that the foundation pit supporting structure is proved to be in a stable state under the design working condition with larger surplus.
Table 6 calculation result table for each node of pile body (early warning condition: maximum displacement of pile body exceeds 0.020m)
When the maximum displacement of the pile body exceeds 0.020m, k is obtained by back calculation to be 0.85, and the tension of the third row of anchor rods is larger than P u3 That is, the third row of engineering anchor rods are damaged, only residual bearing capacity can be provided, and the pulling resistance is calculated to be 505kN and larger than the residual pulling resistance P according to the displacement of the third row of anchor rods r3 。
The maximum bending moment is 1244.6kN m at the node 11, which is still smaller than the bending-resistant bearing capacity of the pile body, the pile body is in a safe state, and the ratio of the bending-resistant bearing capacity of the pile body to the bending moment of the pile body is as follows: 1467/1244.6 is 1.18>1.15, which shows that the pile body still has certain safety and has the condition of monitoring and reinforcing.
Comparative example
The pile body displacement and stress condition under the early warning working condition are directly analyzed by a structural mechanics method, wherein the tension of the third row of anchor rods is P r3 Taking the value, the soil layer strength coefficient k is 0.85, and the obtained results are shown in table 7.
Table 7 pile body node calculation result table (early warning condition: tension of third row anchor rod is P) r3 )
The maximum bending moment occurs at the node 10, which is 1847kN m and exceeds the bending resistance bearing capacity of the pile body, and the ratio of the bending resistance bearing capacity of the pile to the bending moment of the pile body is as follows: 1467/1847 ═ 0.8<1.05, a destruction state is presented; and the tension of the second layer anchor rod exceeds the maximum value P u2 Namely, the second layer of anchor rods are also damaged, so that the reinforcing operation risk is high, and only two options of backfilling a foundation pit or collapsing are provided.
By comparing the example 1 with the comparative example, it can be found that, also under the early warning condition, the conclusion obtained by adopting the determination method provided by the invention is as follows: the pile body has certain redundant safety, and the safety of the foundation pit can be improved in a reinforcing mode; the conclusion obtained by adopting the determination method provided by the structural mechanics method in the prior art is as follows: the pile body has no safety, has 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 technical scheme provided by the invention analyzes the energy change of the anchor rod in the whole pulling-resistant process from the energy conservation angle to obtain a tensile force-displacement curve of the anchor rod in the whole pulling-resistant process, and the analysis of the tensile force-displacement curve can find that when the load borne by the anchor rod exceeds the limit pulling-resistant force P u When it is not a direct split layer, the residual pull-out resistance P is achieved r The residual pull-out resistance P is still reached in a linearly decreasing manner r During the descending process, the pulling resistance of the anchor rod is greater than the residual pulling resistance P r If the residual withdrawal force P is directly applied after the anchor is broken r The calculation is carried out, in order to ensure the balance of the force, the redundant uplift force is loaded on the pile body and borne by the pile body, so that the load of the pile body is increased, the internal force of the calculated pile body is increased, and the pile body uneasiness is easily causedAnd (6) carrying out full judgment.
Compared with the prior art, the method for determining the safety of the foundation pit of the pile-anchor supporting structure with the deformation exceeding the early warning value analyzes the energy change of the anchor rod in the whole pulling-resisting process from the angle of energy conservation, and obtains the pulling-resisting force-displacement curve of the anchor rod in the whole pulling-resisting process. And taking the pile body and the anchor rod as a supporting system, obtaining the soil pressure matched with the displacement data of the monitored pile body through iterative inversion calculation, and further obtaining the internal force of the pile body under the action of the soil pressure, thereby judging the safety of the pile body. Due to the consideration of the whole process change of the pulling resistance of the anchor rod, the method is characterized in that u -P r The anti-pulling force of the anchor rod can be accurately obtained in the process, and the residual anti-pulling force P of the anchor rod is not simply used r The internal force of the pile body can be more accurately analyzed by calculating the internal force of the pile body, so that the most accurate foundation pit safety judgment result is made, the foundation pit safety judgment method is convenient for practical engineering application, and the opportunity is caught to carry out emergency repair reinforcement, so that the method has great economic benefit.
The embodiments of the present invention have been described in detail, but the present invention is not limited to the described embodiments. Various changes, modifications, substitutions and alterations to these embodiments will occur to those skilled in the art without departing from the spirit and scope of the present invention.
Claims (5)
1. The method for determining the safety of the foundation pit of the pile-anchor supporting structure with the deformation exceeding early warning value is characterized by comprising the following steps of:
s1: constructing a binding power model of the anchor rod and the soil layer, wherein the binding power model is expressed as:
in the formula, P u Indicating the ultimate pullout resistance of the anchor rod, S u Indicating that the anchor rod is at the limit withdrawal resistance P u A downward displacement amount; p r Indicating anchor rodsResidual pull-out resistance; l is a Indicating the length of the anchor rod anchoring section; u represents the perimeter of the anchor rod anchoring section; e S And A S Respectively showing the elastic modulus and the cross-sectional area of the free section of the anchor rod; e and A respectively represent the elastic modulus and the cross-sectional area of the anchoring section of the anchor rod; l is f Indicating the length of the free section of the anchor rod; α represents an intermediate parameter; tau is m The ultimate strength of the bonding of the anchor rod anchoring section and the soil layer is shown; tau is r The bonding residual strength of the anchor rod anchoring section and the soil layer is shown; s m Representing the maximum shear displacement of the anchor rod anchoring section; l is ar The length of the debonding part of the anchor rod and the soil layer under the ultimate uplift resistance is shown; lambda represents the friction resistance transfer coefficient of the anchor rod anchoring section and the soil layer;
s2: aiming at different soil layers, basic experiments of anchor rods are respectively arranged, and P of the anchor rods in the experiments is recorded u 、S u And P r Substituting the value into the adhesion model to obtain tau through inverse calculation m 、τ r λ and s m Completing the establishment of a binding force model;
s3: the method comprises the steps of aiming at the safety determination of a pile anchor supporting structure, randomly sampling an installed anchor rod to obtain a sample anchor rod, carrying out acceptance test on the sample anchor rod, analyzing the energy change of the sample anchor rod in the whole anti-pulling process based on energy conservation, and calculating to obtain the anti-pulling force of the sample anchor rod which just reaches P r Amount of displacement S of time r (ii) a Establishing anchor rod drawing resistance-displacement coordinate system, and connecting (0,0), (P) u ,S u )、(P r ,S r )、(P r And infinity) are sequentially connected by a straight line to obtain an anti-pulling force-displacement curve of the sample anchor rod in the whole anti-pulling process;
s4: setting an initial value of soil layer strength coefficient, taking the pile body and the anchor rod as a supporting system bearing the soil pressure, and calculating the soil pressure P borne by the pile body a Obtaining the displacement of the pile body under the initial value of the soil layer strength coefficient through iterative inversion calculation, comparing the displacement with the displacement in the pile body detection data, if the error between the displacement and the displacement exceeds 5%, adjusting the soil layer strength coefficient to recalculate until the error between the displacement and the displacement does not exceed 5%, finishing the determination of the actual soil layer strength coefficient, and solving the displacement based on a structural mechanics methodSolving to obtain the internal force of the pile body under the actual soil layer strength 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 the foundation pit of the deformation super-early-warning-value pile-anchor supporting structure according to claim 1, wherein in the step S3, the energy change of the sample anchor rod in the whole anti-pulling process is analyzed based on energy conservation, and the anti-pulling force of the sample anchor rod is calculated to be just P r Amount of displacement S of time r The method specifically comprises the following steps:
s21: increasing the pullout resistance of the anchor rod from 0 to P according to the sample u In the process of energy conservation, calculating the surface energy E to be dissipated when the new surface is formed by the anchoring section of the sample anchor rod and the soil layer debonding part in unit area b ；
S22: according to the sample anchor rod pulling resistance force from P u Down to P r The energy conservation in the process is realized, and the anti-pulling force of the sample anchor rod is calculated to just reach the residual anti-pulling force P r Then, the corresponding displacement S of the sample anchor rod r 。
3. The method for determining the safety of the foundation pit of the deformation exceeding early warning value pile-anchor supporting structure according to claim 2, wherein the step S21 specifically comprises the following steps:
s211: calculating to obtain the pulling force P of the sample anchor rod according to the bonding force model u The length L of the debonding part of the sample anchor rod and the soil layer ar ；
S212: calculating the increase of the pullout resistance of the sample anchor rod from 0 to P u In the process, energy E is externally applied to the top of the sample anchor Top roof ：
In the formula, P max Maximum pull borne by sample anchor rod in acceptance testPulling force, S max Is P max Displacement of the anchor rod under action;
s213: calculating the energy E accumulated by the elongation of the free section of the sample anchor rod f ：
In the formula, L f The length of a free section of the sample anchor rod is determined;
s214: calculating the energy E dissipated by the friction force between the sample anchor rod anchoring section and the soil layer debonding part Massage device ：
S215: calculating the energy E accumulated by the extension of the anchoring section of the sample anchor rod and the debonding part of the soil layer Anchor extension ：
S216: calculating elastic potential energy E accumulated by the anchoring section of the sample anchor rod and the un-debonded part of the soil layer Anchor bullet ：
In the formula, L ae The length of the part of the sample anchor rod which is not debonded from the soil layer is taken as the length of the sample anchor rod;
s217: calculating the surface energy E to be dissipated when the new surface is formed by the anchoring section of the sample anchor rod and the soil layer debonding part in unit area b ：
4. The method for determining the safety of the foundation pit of the deformation exceeding early warning value pile-anchor supporting structure according to claim 3, wherein the step S22 specifically comprises the following steps:
s221: calculating sample anchor rod pullout force from P u Down to P r In the process, the elastic potential energy E released by the free section of the sample anchor rod 2 ：
S222: calculating elastic potential energy E released by resilience of the anchoring section of the sample anchor rod and the debonding part of the soil layer 3 ：
In the formula, x is the length of a new debonding part of the anchor rod anchoring section and the soil layer;
s223: calculating the elastic potential energy E accumulated by the newly debonded part of the sample anchor rod anchoring section and the soil layer 4 ：
Wherein:
s224: calculating the energy E dissipated by the friction force between the sample anchor rod anchoring section and the soil layer debonding part 5 ：
S225: calculating the surface energy consumed by the debonding part of the sample anchor rod anchoring section and the soil layer:
E surface energy of ＝U(L a -L ar )E b
S226: elastic potential energy E released by pulling-out resistant device in acceptance test 1 An equation is constructed, and the anchor rod withdrawal resistance obtained by solving is just up to the residual withdrawal resistance P r While the displacement S of the anchor rod r ：
5. The method for determining the safety of the foundation pit of the deformation super-early-warning-value pile-anchor supporting structure according to claim 4, wherein in the step S4, the soil pressure P is a Expressed as:
wherein gamma, c,
the soil layer gravity, the cohesion and the internal friction angle are respectively; k is the soil layer strength coefficient, and k is less than or equal to 1.0; z represents the distance from a node on the pile body to the bottom of the foundation pit; p is a radical of formula 0 Is a 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 comprises the following steps:
wherein:
P a1 ，P a2 …P ai ，P aj …P am the soil pressure acting on the 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 the pile body nodes 1, 2, 3 … i, j … m are respectively;
θ 1 ，θ 2 …θ i ，θ j …θ m the corners of the pile body nodes 1, 2, 3 … i, j … m are respectively;
P mgi and calculating the anchor rod tension corresponding to the pile body node i according to the following formula:
P mgi ＝K mgi ·x i
wherein, K mgi The rigidity coefficient, K, of the anchor rod corresponding to the pile body node i mgi The calculation process of (2) is as follows:
in the formula: h is i The horizontal displacement amount h of the anchor rod corresponding to the pile body node i i ∈x i (ii) a Delta is the inclination angle of the anchor rod;
K djn is the foundation stiffness coefficient of the pile body node below the bottom surface of the foundation pit, K djn The calculation process of (2) is as follows:
K djn ＝gzb 1 l
in the formula, g is a proportionality coefficient of a horizontal resistance coefficient of a stratum foundation; b 1 Calculating the width of the pile body; l is the sum of the lengths of 50% of the units on the two sides of the pile body node.
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