A processor for calculating critical data of a supporting pile and a calculation method thereof

Abstract

The present application relates to a kind of processors for calculating the critical data of supporting pile rock-socketing and its computing method, processor is configured as: in the embedded pile stage, based on the first active soil parameter above rock-socketing surface outside foundation pit, the rock mass horizontal resistance resultant force parameter provided by rock mass below rock-socketing surface calculates critical rock-socketing depth parameter;Select the minimum rock-socketing depth value that meets the first mechanical model as critical rock-socketing depth parameter;First mechanical model is: E p1 h p1 +T c1 (h T1 +h d )‑K e E a1 h a1 ≥0;E p1 It indicates that rock mass horizontal resistance resultant force parameter;h a1 It indicates the first distance parameter from the fifth support point to pile bottom;h p1 It indicates the second distance parameter from the sixth support point to pile bottom;T c1 It indicates upper layer support point axial force parameter in embedded pile stage;h T1 It indicates the vertical distance from the first support point to foundation pit excavation surface;h d It indicates critical rock-socketing depth parameter;K e It indicates rock-socketing stability safety factor;E a1 It indicates active soil resistance parameter.The critical rock-socketing depth obtained according to limit condition and first mechanical model in the present application is the minimum rock-socketing depth, and better supporting effect is realized.

Description

[0001] The original basis of the divisional application is a patent application with the application number 202410618741X, the application date of 2024.5.17, and the invention name of "Supporting pile rock-socketing stability checking system and method for rigid-flexible composite foundation pit". TECHNICAL FIELD

[0002] The present application relates to the technical field of geotechnical engineering, and particularly relates to a processor for calculating the critical data of supporting pile rock-socketing and a calculation method thereof. BACKGROUND

[0003] With the development of urban rail transit construction in China, complex and differentiated engineering geological environments are constantly emerging, bringing new challenges and opportunities to urban rail transit engineering construction. Soil and rock combined stratum is a typical complex engineering geological environment, the strength, stiffness, permeability and stability of the upper soil layer and the lower rock layer are significantly different, so the excavation method and the difficulty of pile forming are very different, and the overall stratum presents the characteristics of "soft on top and hard on bottom". Open excavation method is the most commonly used and most economical method for constructing subway stations, and is widely used in the urban rail transit engineering construction industry. In the city with upper soil and lower rock, a rigid-flexible composite support system is needed to ensure the safety of the open excavation deep foundation pit. At present, the "hanging foot pile" with partial rock-socketing is widely used in the industry as the foundation pit support structure of the upper soft soil layer of the soil and rock combined stratum. This foundation pit support system with upper "hanging foot pile" and lower jet anchor support is called rigid-flexible composite foundation pit support system.

[0004] "Hanging foot pile" refers to a supporting pile in foundation pit engineering, which refers to a retaining pile with the pile bottom above the foundation pit bottom and the entire pile body exposed. In recent years, hanging foot piles have been applied to deep foundation pit engineering support in many places, achieving good support effect and significant benefits. However, the theoretical research on hanging foot piles still lags far behind the engineering, and the traditional foundation pit enclosure structure calculation method in soft soil areas is still followed in structure calculation, which will lead to two problems. First, in the rigid-flexible composite support system, the upper supporting pile will go through two stages of rock-socketed pile and hanging foot pile. When the foundation pit is excavated below the pile bottom, the supporting pile enters the hanging foot pile stage, and the horizontal resistance provided by the rock mass in the rock-socketed section to the hanging foot pile will be greatly reduced, which is the main difference between the hanging foot pile and the rock-socketed pile. The traditional calculation method only calculates the supporting pile structure as a rock-socketed pile, without considering the structure calculation of the hanging foot pile below the foundation pit excavation. Second, the stratum difference between the upper soil and the lower rock is not considered; the traditional calculation method of active and passive soil pressure is based on the Rankine soil pressure theory, which is more suitable for soft soil characteristics. If the Rankine soil pressure theory is used to calculate the active and passive soil pressure of the rock-socketed part of the harder supporting pile, some problems will arise.

[0005] Therefore, the present application, in view of the above-mentioned defects, through intensive research and design, and the experience and results of long-term engagement in the relevant industry, applies the widely used Hoek-Brown strength criterion in the international to the calculation of the horizontal resistance of the rock-embedded part of the supporting pile. The structural stress characteristics and failure modes of the whole process of the construction of the hanging foot pile are deeply researched, the calculation method and system of the rock-embedded depth and the reserved rock shoulder width of the upper supporting pile in the hanging foot pile stage are proposed, and the guiding stability checking method and system of the rock-embedded stability of the rigid-flexible composite foundation pit supporting system are formed.

[0006] In addition, on the one hand, there are differences in the understanding of those skilled in the art; on the other hand, a large number of literatures and patents have been studied by the applicant when making the present application, but due to the limitation of space, all the details and contents are not listed in detail, but this is not a feature of the present application without these prior art, on the contrary, the present application has all the characteristics of the prior art, and the applicant reserves the right to add relevant prior art in the background art. SUMMARY

[0007] In the prior art, the traditional soft soil area foundation pit retaining structure calculation method is still followed in the structural calculation, which will lead to two problems. First, in the rigid-flexible composite supporting system, the upper supporting pile will go through two stages of embedded pile and hanging foot pile. When the foundation pit is excavated below the pile bottom, the supporting pile enters the hanging foot pile stage, and the horizontal resistance provided by the rock mass of the rock-embedded section to the hanging foot pile will be greatly reduced, which is the main difference between the hanging foot pile and the embedded pile. The traditional calculation method only calculates the supporting pile structure as an embedded pile without considering the calculation of the hanging foot pile structure below the pile bottom. Second, the stratigraphic difference of the upper soil and the lower rock is not considered, and the traditional active soil pressure and passive soil pressure calculation method is formed based on the Rankine soil pressure theory, which is more suitable for the characteristics of soft soil. If the Rankine soil pressure theory is used to calculate the active soil pressure and passive soil pressure for the rock-embedded part of the supporting pile, some problems will be caused.

[0008] In view of the deficiencies of the prior art, the present application provides, from a first aspect, a support pile rock-socketing stability checking system for a rigid-flexible composite foundation pit, comprising a processor. The processor is configured to: establish a model of the relative position relationship between the foundation pit position and the stratum based on the geological parameters related to the foundation pit position, and set a rock-socketing depth parameter and a design width parameter of a rock shoulder; in the rock-socketing pile stage, calculate a critical rock-socketing depth parameter based on a first active soil parameter outside the foundation pit above the rock-socketing surface, a rock mass horizontal resistance resultant parameter provided by the rock mass below the rock-socketing surface, and a second distance parameter from the sixth support point to the pile bottom; in the overhanging pile stage, calculate a critical rock shoulder width parameter based on a second active soil parameter outside the foundation pit below the second support point and a fourth distance parameter from the second support point to the fourth support point; and determine whether the rock-socketing depth parameter and the design width parameter of the rock shoulder meet the stability checking condition according to the first mechanical model and the second mechanical model. The rock shoulder horizontal resistance resultant can be understood as the resultant effect of the active soil pressure and the passive soil pressure of the rock-socketing section.

[0009] The present application improves the calculation method of the horizontal resistance provided by the rock mass below the rock-socketing surface in the rock-socketing pile stage by using the Hoek-Brown strength criterion, and divides the support pile calculation into the rock-socketing pile stage and the overhanging pile stage. In the rock-socketing pile stage, the critical rock-socketing depth of the support pile is calculated according to the stability requirement of the foundation pit, and the critical rock-socketing depth is obtained in the rock-socketing pile stage. In the overhanging pile stage, the critical rock shoulder width is obtained through the stability calculation of the overhanging pile. The present application considers the problem that when the foundation pit is excavated below the pile bottom and the support pile enters the overhanging pile stage, the horizontal resistance provided by the rock mass of the rock-socketing section to the overhanging pile will be greatly reduced. By analyzing two different stability failure modes of the rock-socketing pile stage and the overhanging pile stage, two limit equilibrium equations (the first mechanical model and the second mechanical model) are obtained, thereby providing a method that can help determine the two key design parameters of the critical rock-socketing depth and the critical rock shoulder width, and can help check the rock-socketing stability of the support pile of the rigid-flexible composite foundation pit support system.

[0010] According to a preferred embodiment, the processor calculates the first active soil parameter outside the foundation pit above the rock-socketing surface in the following manner: calculating the active soil pressure parameter outside the foundation pit above the rock-socketing surface; calculating the active soil resistance parameter outside the foundation pit above the rock-socketing surface and the first distance parameter from the fifth support point to the pile bottom. The fifth support point is the action point of the active soil resistance on the support pile. Above the rock-socketing surface, the soil pressure action point outside the support pile is basically located between the active soil pressure action point and the static soil pressure action point. By calculating the active soil pressure parameter outside the foundation pit above the rock-socketing surface and the first distance parameter, the resultant force on the support pile part above the rock-socketing surface can be determined.

[0011] According to one preferred embodiment, the processor calculates the rock mass horizontal resistance resultant force parameter provided by the rock mass below the rock-embedded surface in the following manner: calculating the pile side ultimate resistance parameter of the rock mass inside the foundation pit below the rock-embedded surface according to the Hoek-Brown strength criterion; and calculating the rock mass horizontal resistance resultant force parameter provided by the rock mass below the rock-embedded surface in the rock-embedded pile stage and the second distance parameter from the sixth support point to the pile bottom, the sixth support point being the action point of the rock mass horizontal resistance resultant force on the supporting pile. Below the rock-embedded surface, because the lower bedrock has better properties and the rock mass exists inside and outside the supporting pile, the horizontal displacement of the pile body is greater than the displacement of the rock mass, and the overhanging pile is extremely likely to have been separated from the moderately weathered granite or relaxed, that is, a gap is generated with the rock mass, so the active soil pressure outside the supporting pile at the soil-rock interface is zero. The passive soil pressure below the rock-embedded surface is quite different from the Rankine passive soil pressure in terms of distribution and value. By calculating the resultant force and the second distance parameter of the supporting pile part below the rock-embedded surface, the numerical simulation result shows that the soil pressure inside the supporting pile at the rock-embedded surface position is the largest, and decreases with the increase of the rock-embedded depth of the supporting pile.

[0012] According to one preferred embodiment, the processor calculates the critical rock-embedded depth parameter in the following manner: selecting the minimum rock-embedded depth value meeting the first mechanical model as the critical rock-embedded depth parameter; wherein the first mechanical model is: p1 h p1 +T c1 (h T1 +h d )-K e E a1 h a1 ≥0;E p1 represents the rock mass horizontal resistance resultant force parameter; h a1 represents the first distance parameter from the fifth support point to the pile bottom; h p1 represents the second distance parameter from the sixth support point to the pile bottom; T c1 represents the upper support point axial force parameter in the rock-embedded pile stage; h T1 represents the vertical distance from the first support point to the foundation pit excavation surface; h d represents the critical rock-embedded depth parameter; K e represents the rock-embedded stability safety factor; E a1 represents the active soil resistance parameter. For the rock-embedded depth of the supporting pile, the present application designs the supporting structure according to the most unfavorable effect working condition. In the construction process considered in the present application, the most unfavorable effect working condition in the rock-embedded pile stage is the working condition 3 in the embodiment, at this time the foundation pit is excavated below the soil-rock interface, and the lowermost row of anchor cables / supports has not been constructed, and if the rock-embedded depth is insufficient, damage is likely to occur. The damage mode mainly considers the rotation and displacement of the supporting pile around the pile bottom. The critical rock-embedded depth obtained according to this limit condition and the first mechanical model is the minimum rock-embedded depth. Only the rock-embedded depth greater than the critical rock-embedded depth can achieve a better supporting effect.

[0013] According to a preferred embodiment, the processor calculates the second active soil parameter outside the foundation pit below the second fulcrum in the following manner: calculating the active soil pressure resultant parameter outside the foundation pit below the second fulcrum; calculating the third distance parameter from the second fulcrum to the third fulcrum, the third fulcrum being the point of action of the active soil pressure resultant on the supporting pile outside the foundation pit below the second fulcrum. By calculating the resultant of the rock mass below the rock-embedded surface on the supporting pile and the third distance parameter, data support can be provided for the calculation of the second mechanical model.

[0014] According to a preferred embodiment, the processor calculates the critical rock shoulder width parameter in the following manner: selecting the minimum rock shoulder width value that meets the second mechanical model as the critical rock shoulder width parameter; wherein the second mechanical model is: E P2 h p2 ≥ K T E a2 h a2 ; E P2 represents the rock shoulder horizontal resistance resultant parameter; h p2 represents the fourth distance parameter from the second fulcrum to the fourth fulcrum, the fourth fulcrum being the point of action of the rock shoulder horizontal resistance resultant on the supporting pile; K T represents the kick stability safety factor; E a2 represents the active soil pressure parameter outside the foundation pit below the second fulcrum; h a2 represents the third distance parameter from the second fulcrum to the third fulcrum.

[0015] The design problem of the critical rock shoulder width of the supporting pile is mainly reflected in working condition 5 in the embodiment. Due to the excavation of the "inner pit", only the rock within the rock shoulder width range exerts a restraining action on the rock-embedded section of the supporting pile, so the rock shoulder part is prone to danger due to insufficient strength. In the calculation of the critical rock shoulder width, the kick stability is mainly considered. When the restraining action on the rock-embedded section is limited, the displacement of the upper part of the supporting pile is very small, but a large positive displacement is generated at the bottom of the supporting pile, which is manifested as rotation around the anchor cable or support fulcrum. Therefore, the second mechanical model is designed and the critical rock-embedded depth parameter obtained thereby provides very favorable reference information for the rock-embedded stability of the supporting pile for construction personnel.

[0016] According to a preferred embodiment, the processor is further configured to: in the case that the embedded depth parameter does not meet the condition of the first mechanical model, the information generated by the processor includes: increasing the embedded depth; in the case that the design width parameter of the rock shoulder does not meet the condition of the second mechanical model, the information generated by the processor includes: increasing the design width of the rock shoulder. The processor of the present application can use the first mechanical model and the second mechanical model to quickly check the rock-embedded stability of the supporting system of the rigid-flexible composite foundation pit, and give appropriate support suggestions.

[0017] The application provides a support pile rock-socketing stability checking method for a rigid-flexible composite foundation pit from a second aspect.

[0018] In the prior art, the structural calculation method for the hanging pile still follows the traditional foundation pit enclosure structure calculation method in soft soil areas, and the support pile structure is calculated as a rock-socketed pile without considering the calculation of the hanging pile structure below the bottom of the foundation pit, and without considering the stratum difference between the upper soil and the lower rock. The calculation method of the traditional active soil pressure and passive soil pressure is formed based on the Rankine soil pressure theory. The Rankine soil pressure theory is more suitable for the characteristics of soft soil, and some problems will be caused if the Rankine soil pressure is used to calculate the rock-socketed part of the support pile. In view of the defects of the prior art, the application distinguishes the rock-socketed pile stage and the hanging pile stage, and proposes a calculation method and a checking method of the critical rock-socketing depth and the critical rock shoulder width. The checking method of the application provides important guidance for the design of the support structure, and is more conducive to the stability of the support structure design and the construction safety.

[0019] According to a preferred embodiment, the method further comprises: increasing the rock-socketing depth when the rock-socketing depth parameter does not satisfy the condition of the first mechanical model; and increasing the design width of the rock shoulder when the design width parameter of the rock shoulder does not satisfy the condition of the second mechanical model. On the basis of the calculation method of the critical rock-socketing depth and the critical rock shoulder width, the application can also give clear and instructive suggestions, and provide reliable adjustment suggestions for the construction personnel or the design personnel of the support structure.

[0020] According to a preferred embodiment, the method further comprises: selecting a minimum rock-socketing depth value meeting the first mechanical model as the critical rock-socketing depth parameter; and selecting a minimum rock shoulder width value meeting the second mechanical model as the critical rock shoulder width parameter; the first mechanical model is: E p1 h p1 +T c1 (h T1 +h d )-K e E a1 h a1 ≥0; and the second mechanical model is: E P2 hp2 K T E a2 h a2 K p1 denotes the horizontal resistance force parameter of the rock mass; h a1 denotes the first distance parameter from the fifth support point to the pile bottom; h p1 denotes the second distance parameter from the sixth support point to the pile bottom; T c1 denotes the upper support point axial force parameter of the embedded pile stage; h T1 denotes the vertical distance from the first support point to the foundation pit excavation surface; h d denotes the critical rock-embedded depth parameter; K e denotes the rock-embedded stability safety factor; E a1 denotes the active soil resistance parameter; E P2 denotes the horizontal resistance force parameter of the rock shoulder; h p2 denotes the fourth distance parameter from the second support point to the fourth support point; K T denotes the toe stability safety factor; E a2 denotes the active soil pressure parameter outside the foundation pit below the second support point; h a2 denotes the third distance parameter from the second support point to the third support point.

[0021] Considering the two different stability failure modes of the embedded pile stage and the overhanging pile stage, the first mechanical model and the second mechanical model, i.e., two limit equilibrium equations, are provided, so as to determine the two design variables of the critical rock-embedded depth and the critical rock shoulder width, which can not only perform stability checking, but also provide effective guidance for the supporting structure based on the checking results. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the checking flowchart of the rock-embedded stability checking system of the supporting pile provided by the application;

[0023] Figure 2 is the construction flowchart of the rigid-flexible composite foundation pit provided by the application;

[0024] Figure 3 is the grading value diagram of the geological strength index GSI of the rock-embedded section rock mass;

[0025] Figure 4 is the schematic diagram of the first mechanical model of the rock-embedded stability checking of the embedded pile stage;

[0026] Figure 5 is the schematic diagram of the second mechanical model of the rock-embedded stability checking of the overhanging pile stage;

[0027] Figure 6 is the schematic diagram of the stratum condition of the upper supporting pile of one kind of rigid-flexible composite supporting system provided by the application.

[0028] List of reference signs

[0029] 100: processor; 200: information interaction component; 300: support pile; 310: first fulcrum; 320: second fulcrum; 330: third fulcrum; 340: fourth fulcrum; 350: fifth fulcrum; 360: sixth fulcrum; 370: pile bottom; 400: rock-embedded surface; 500: rock shoulder; 600: stratum condition; 610: miscellaneous fill; 620: strongly weathered granite; 630: moderately weathered granite. DETAILED DESCRIPTION

[0030] The following will be described in detail with reference to the accompanying drawings.

[0031] The support pile 300 is a pile mainly bearing lateral thrust. The support pile 300 is generally used for foundation pit support, slope support and landslide treatment, and bears horizontal soil pressure or landslide thrust. The support pile 300 generally needs higher reinforcement than the foundation pile bearing vertical force, and is often used together with anchor rods (cables) (pile-anchor structure).

[0032] Unlike the concept of the hanging foot pile in the field of traditional construction technology, the hanging foot pile in the present application refers to a support pile 300 in a foundation pit project, and the pile bottom 370 of the support pile 300 is above the bottom of the foundation pit, and the pile body is a full-exposed soil retaining pile.

[0033] Hoek-Brown strength criterion: Hoek-Brown strength criterion is an empirical formula for predicting rock failure.

[0034] The first fulcrum 310: because the hanging foot pile is generally shorter than the depth of the foundation pit, it is assumed here that the hanging foot pile will only be supported by two supports (or anchor rods), and the first fulcrum 310 refers to the action point of the first support (or anchor rod) from top to bottom in the vertical direction on the support pile 300.

[0035] The second fulcrum 320: because the hanging foot pile is generally shorter than the depth of the foundation pit, it is assumed here that the hanging foot pile will only be supported by two supports (or anchor rods), and the second fulcrum 320 refers to the action point of the second support (or anchor rod) from top to bottom in the vertical direction on the support pile 300.

[0036] The third fulcrum 330: the action point of the active soil pressure on the outside of the foundation pit on the support pile 300.

[0037] The fourth fulcrum 340: the action point of the resultant force of the rock shoulder horizontal resistance on the support pile 300.

[0038] The fifth fulcrum 350: the action point of the active soil resistance on the support pile 300.

[0039] The sixth fulcrum 360: the action point of the resultant force of the rock mass horizontal resistance provided by the rock mass below the rock-embedded surface 400 on the support pile 300.

[0040] Rock-embedded surface 400: refers to the top surface of the rock mass after the first excavation inside the foundation pit during the rock-embedded pile stage, i.e. Figure 2 The positions of the foundation pit excavated in working conditions 3, 4 and 5.

[0041] Rock shoulder 500: refers to the remaining rock mass that can provide horizontal resistance to the supporting pile 300 after the second excavation inside the foundation pit during the hanging pile stage, and this part of the remaining rock mass is called a rock shoulder.

[0042] The present application provides a supporting pile rock-embedded stability checking system and method for a rigid-flexible composite foundation pit, which can also be a supporting pile rock-embedded stability checking system and method for a rigid-flexible composite foundation pit supporting system, and can also be a rigid-flexible composite foundation pit supporting stability verification device and method. The present application can also provide a terminal for analyzing the supporting stability of a rigid-flexible composite foundation pit. The present application can also provide a storage medium for analyzing the supporting stability of a rigid-flexible composite foundation pit, and the storage medium stores an encoding program for checking the rock-embedded stability of the supporting pile of a rigid-flexible composite foundation pit.

[0043] The present application provides a processor 100 provided with an encoding program of a supporting pile rock-embedded stability checking method for a rigid-flexible composite foundation pit, which can execute the supporting pile rock-embedded stability checking method for a rigid-flexible composite foundation pit. The processor 100 of the supporting pile rock-embedded stability checking method for a rigid-flexible composite foundation pit can be a CPU or a special integrated chip, and can be provided in a computer, a portable terminal or the like. The portable terminal is, for example, a tablet computer, a smart phone, a smart watch, smart glasses or the like. The processor 100 can also be connected to an information interaction component 200 in a wired or wireless manner. The information interaction component 200 is used to input various geometric parameters of the foundation pit, and can also be used to output or display the processing information of the processor 100. The information interaction component 200 can be a keyboard, a mouse, a display or the like.

[0044] The processor 100 can also be a server or a cloud server, which is connected to a remote terminal in a wired or wireless manner to provide a service of a supporting pile rock-embedded stability checking algorithm for a rigid-flexible composite foundation pit.

[0045] The method for calculating the horizontal resistance provided by the rock mass below the rock-embedded surface 400 of the embedded pile in the stage of the embedded pile according to the Hoek-Brown strength criterion is improved (the horizontal resistance can be understood as the combined force effect of the active soil pressure and the passive soil pressure of the rock-embedded section), and the calculation of the supporting pile 300 is divided into the stage of the embedded pile and the stage of the overhanging pile. In the stage of the embedded pile, the critical rock-embedded depth of the supporting pile 300 is calculated according to the stability requirement of the foundation pit, and the critical rock shoulder width is calculated by the stability of the overhanging pile in the stage of the overhanging pile according to the minimum rock-embedded depth obtained in the stage of the embedded pile.

[0046] Numerical simulation tests are performed on the mechanical behavior of the whole process of the construction of the supporting pile of the rigid-flexible composite foundation pit supporting system according to the numerical results, the action point of the external soil pressure of the supporting pile 300 is located between the action point of the active soil pressure (i.e. the third supporting point 330) and the action point of the static soil pressure above the rock-embedded surface 400. Below the rock-embedded surface 400, because the lower bedrock has good properties, and there are rock masses inside and outside the supporting pile 300, the horizontal displacement of the pile body is greater than the displacement of the rock mass, and the overhanging pile is extremely likely to have been separated from the moderately weathered granite 630 or relaxed, that is, a gap is generated between the pile body and the rock mass, so the external active soil pressure of the supporting pile 300 at the soil-rock interface is zero. The passive soil pressure below the rock-embedded surface 400 is quite different from the Rankine passive soil pressure in terms of distribution and numerical value, and the numerical simulation results show that the soil pressure inside the position of the rock-embedded surface 400 is the largest, and decreases with the increase of the rock-embedded depth of the supporting pile 300.

[0047] It is considered through the above numerical simulation tests that there are obvious differences in the mechanical behavior of the upper soil body and the lower rock mass, the traditional Rankine soil pressure theory is established on the basis of the Mohr-Coulomb strength criterion, which assumes that the soil body is a continuous and uniform material, and the shear stress is the fundamental reason for the material failure. For the rock mass, the rock mass is composed of rock blocks and structural planes, and the rock mass strength is influenced and controlled by the rock mass structure plane to a certain extent, and if the Rankine soil pressure theory is continuously applied in the rock mass, it will deviate from the actual situation, so the Hoek-Brown strength criterion widely applied internationally is applied to the horizontal resistance of the rock-embedded part of the supporting pile 300. Research shows that the Hoek-Brown strength criterion more comprehensively reflects the influence of the characteristics of the rock mass structure on the strength of the rock mass, and is the most perfect method, which reflects the inherent characteristics and nonlinear failure characteristics of the rock mass, as well as the influence of rock strength, structural plane group number, excavation disturbance and rock mass fragmentation degree on the strength.

[0048] Embodiment 1

[0049] The following assumptions are followed in the embedded pile rock stability checking method and model derivation of the rigid-flexible composite foundation pit supporting system proposed in the patent:

[0050] (1) This embodiment aims to provide a calculation method. In order to make the calculation process relatively clear, a rigid-flexible composite support system construction process of a simple soil-rock foundation pit is considered here, as shown in Figure 2 Figure 2 Five construction conditions of working condition 1 to working condition 5 are shown. Working condition 1 and working condition 2 can be considered as the foundation pit not being excavated to the rock layer, at this time the support pile 300 is in the soft soil foundation pit embedded pile stage. Working condition 3 and working condition 4 can be considered as the foundation pit being excavated below the rock-embedded surface 400, at this time the support pile 300 is in the soil-rock foundation pit embedded pile stage. Working condition 5 can be considered as the foundation pit continuing to excavate after the rock shoulder 500 is reserved, at this time the support pile 300 is in the soil-rock foundation pit kick pile stage.

[0051] (2) The soil pressure of the rock-soil body above the rock-embedded surface 400 on the support pile 300 is calculated according to the Rankine active soil pressure theory.

[0052] (3) Below the rock-embedded surface 400, the difference between the soil and the rock is considered, the Hoek-Brown strength criterion considering the rock joint, excavation disturbance and other factors is used to calculate the passive horizontal resistance of the rock on the support pile 300, and the distribution of the passive soil pressure adopts the inverted triangular form.

[0053] (4) For the rock-embedded depth of the support pile 300, the support structure is designed according to the most unfavorable effect working condition, in the construction process considered in the present application, the most unfavorable effect working condition of the embedded pile stage is working condition 3, at this time the foundation pit is excavated below the soil-rock interface, and the lowermost row of anchor cables / supports has not been constructed, if the rock-embedded depth is not enough, it is easy to be damaged, and the damage mode mainly considers the rotation of the support pile 300 around the pile bottom 370 and displacement.

[0054] (5) The design problem of the critical rock shoulder width of the support pile 300 mainly reflects in working condition 5, due to the excavation of the "inner pit", only the rock within the rock shoulder width range has a restraining effect on the rock-embedded section of the support pile 300, therefore the rock shoulder 500 part is easy to be dangerous due to insufficient strength. In the calculation of the critical rock shoulder width, the stability of the kick is mainly considered, when the restraining effect on the rock-embedded section is limited, the upper displacement of the support pile 300 is very small, but the bottom of the support pile 300 will produce a large positive displacement, which is manifested as rotation around the anchor cable or support point.

[0055] The support pile rock-embedded stability checking system for the rigid-flexible composite foundation pit of the present application can include one or more processors 100. The processor 100 is configured to execute the support pile rock-embedded stability checking method for the rigid-flexible composite foundation pit of the present application. The processor 100 is a CPU, a special integrated chip and a server provided with a coded program of the support pile rock-embedded stability checking method.

[0056] The steps of the support pile rock-embedded stability checking method for the rigid-flexible composite foundation pit include: ​

[0057] S1: Establish a model of the relative position relationship between the foundation pit location and the stratum based on the geological parameters related to the foundation pit location, and set the embedded depth parameter and the design width parameter of the rock shoulder 500.

[0058] Obtain the basic geological data of the foundation pit range, and establish a model of the relative position relationship between the foundation pit location and the stratum. Determine the recommended values of the geotechnical parameters of each stratum and the geometric parameters of the foundation pit and its support system in the environment, especially the design embedded depth h of the support pile 300 and the design width B of the rock shoulder 500.

[0059] S2: In the embedded pile stage, calculate the critical embedded rock depth parameter based on the first active soil parameter above the rock-embedded surface 400 outside the foundation pit and the rock mass horizontal resistance force parameter provided by the rock mass below the rock-embedded surface 400.

[0060] S21: Calculate the active soil pressure parameter p above the rock surface outside the foundation pit ak .

[0061] For water-soil combined strata or strata above the groundwater level,

[0062] For water-soil combined strata or strata above the groundwater level,

[0063] where σ ak is the vertical stress of the calculation point, is the friction angle of the rock-soil mass at the calculation point position.

[0064] S22: Calculate the active soil resistance parameter E above the rock surface outside the foundation pit a1 and the first distance parameter h between the fifth support point 350 and the pile bottom 370 a1 . The active soil resistance refers to the resultant force of the active soil pressure above the rock surface, which is a horizontal force, h a1 is the vertical distance between the fifth support point 350 and the pile bottom 370.

[0065] The active soil resistance parameter E a1 is the resultant force of the active soil pressure.

[0066] The active soil resistance parameter E a1 is obtained by integrating the active soil pressure parameter p ak , and the first distance parameter h a1 is determined according to the moment of force theorem in mechanics.

[0067] S23: Calculate the pile side ultimate resistance parameter P below the rock surface inside the foundation pit according to the Hoek-Brown strength criterion L .

[0068] S231: According to the rock type of the rock-socketed section, find its Hoek-Brown constant m by Table 1 i .

[0069] Table 1 Hoek-Brown constant determined by rock type

[0070]

[0071] The values in Table 1 represent the Hoek-Brown constant m i .

[0072] S232: According to the classification value chart of the geological strength factor GSI of the rock mass of the rock-socketed section shown in Figure 3 , find the geological strength factor GSI value of the rock mass of the rock-socketed section.

[0073] S233: Obtain the disturbance degree coefficient D of the rock mass under external load such as excavation or blasting. The disturbance degree coefficient D is between 0 and 1, 0 represents no disturbance, and 1 represents severe disturbance. There are two methods to obtain the disturbance degree coefficient D, one is to take the value according to experience, and the specific value can be taken according to Table 2; the other is to estimate according to the measured data of previous excavation engineering according to the following formula:

[0074]

[0075] Where, V UP is the average longitudinal wave velocity of the undisturbed rock mass, and V P is the average longitudinal wave velocity of the rock mass after excavation and blasting disturbance.

[0076] Table 2 Disturbance degree coefficient D value table

[0077]

[0078] S234: Calculate the second distance parameter of the sixth fulcrum 360 to the pile bottom 370 provided by the rock mass under the rock-socketed surface 400 in the rock-socketed pile stage.

[0079] According to the Hoek-Brown constant m i , GSI coefficient D value obtained by steps S231, S232, S233, calculate the horizontal resistance provided by the rock mass under the rock-socketed surface 400:

[0080]

[0081] Where:

[0082]

[0083] γ is the unit weight of the rock mass, z is the depth of the excavation point below the top surface of the rock mass, f rc is the uniaxial compressive strength of the intact rock specimen.

[0084] According to Figure 4 It can be known that the horizontal resistance inside the foundation pit is in the shape of an inverted triangle. Through the integral relationship, the resultant force of the horizontal resistance of the rock mass is The distance h p1 is the distance from the center of gravity of the inverted triangle to the pile bottom 370,

[0085] S24: Calculate the critical rock-embedded depth parameter h d .

[0086] According to assumption (4), the most unfavorable effect working condition of the rock-embedded pile stage is working condition 3, at which time the foundation pit is excavated below the soil-rock interface, and the lowermost row of anchor cables / supports has not yet been constructed. If the rock-embedded depth is insufficient, damage is likely to occur, and the damage mode mainly considers the rotation of the supporting pile 300 around the pile bottom 370 and displacement.

[0087] Therefore, as Figure 4 shown, to ensure the stability of the pile bottom 370, the critical rock-embedded depth parameter h d needs to satisfy the first model: E p1 h p1 + T c1 (h T1 +h d )- K e E a1 h a1 ≥ 0;

[0088] (501.57 / 3)*h d ^2-1.25*(20.6077*(5.667+h d )+80.42465*

[0089] (1.978+h d ))>0;

[0090] h d >2.8627m.

[0091] In order to facilitate design and construction, h d = 3m.

[0092] E p1 represents the resultant force parameter of the horizontal resistance of the rock mass; h a1 represents the first distance parameter from the fifth support point 350 to the pile bottom 370; h p1 represents the second distance parameter from the sixth support point 360 to the pile bottom 370; T c1 represents the upper support point axial force parameter of the rock-embedded pile stage; h T1 represents the vertical distance from the first support point 310 to the foundation pit excavation surface; h d represents the critical rock-embedded depth parameter; K edenotes the safety factor of rock-socketed stability; E a1 denotes the active soil resistance parameter.

[0093] The minimum rock-socketed depth value conforming to the first mechanical model is selected as the critical rock-socketed depth parameter.

[0094] S3: In the overhanging pile stage, as shown in FIG. 3B, the critical rock shoulder width parameter is calculated based on the second active soil parameter of the outer side of the foundation pit below the second fulcrum 320 and the distance from the resultant force of the horizontal resistance of the rock shoulder to the pile bottom 370. Figure 5

[0095] S31: The horizontal resistance curve of the rock shoulder 500 to the pile is calculated. As shown in FIG. 4A, the horizontal resistance curve of the rock shoulder 500 to the pile is triangularly distributed, taking the rock-socketed surface 400 as the coordinate origin, and the horizontal resistance curve equation of the overhanging pile stage is Figure 5

[0096]

[0097] F x =(24.5×tan55°×h)·B min 0≤h≤3m.

[0098] γ is the unit weight of the rock shoulder 500, h is the burial depth of the calculation point, is the friction angle of the rock shoulder 500, c is the cohesion of the rock shoulder 500, B min is the critical rock shoulder width.

[0099] S32: The active soil pressure resultant force parameter E P2 is calculated.

[0100]

[0101] The fourth distance parameter h p2 from the second fulcrum 320 to the fourth fulcrum 340 is calculated.

[0102] S33: The active soil pressure resultant force parameter E a2 of the outer side of the foundation pit below the second fulcrum 320 is calculated.

[0103] The third distance parameter h from the second fulcrum 320 to the third fulcrum 330 below it is calculated.

[0104] The active soil pressure resultant force parameter E a2 is obtained by integrating the active soil pressure parameter p ak , and the third distance parameter h a2 is determined according to the resultant moment theorem in mechanics.

[0105] S34: The critical rock shoulder width B min is calculated. ​

[0106] According to assumption (5) and Figure 2 It can be known that the most unfavorable working condition of the hanging foot pile stage is working condition 5, considering the kicking foot around the anchor cable or support fulcrum rotation working condition. There is a second mechanical model as Figure 5 shown, to ensure the stability of the pile bottom 370, the critical rock shoulder width B min needs to meet:

[0107] E P2 h p2 ≥K T E a2 h a2 ;

[0108]

[0109] wherein K T is the kicking foot stability safety factor, for a first, second, and third foundation pit, K T is respectively taken as 1.25, 1.2, and 1.15.

[0110] E P2 represents the rock shoulder horizontal resistance resultant force parameter; h p2 represents the fourth distance parameter from the second fulcrum 320 to the fourth fulcrum 340; K T represents the kicking foot stability safety factor; E a2 represents the active soil pressure parameter outside the foundation pit below the second fulcrum 320; h a2 represents the third distance parameter from the second fulcrum 320 to the third fulcrum 330.

[0111] As shown above, the minimum rock shoulder width value selected according to the second mechanical model is the critical rock shoulder width parameter.

[0112] S4: As Figure 1 shown, according to the first mechanical model and the second mechanical model, it is judged whether the embedded depth parameter and the design width parameter of the rock shoulder 500 meet the stability checking condition.

[0113] S41: In the case where the embedded depth parameter does not meet the condition of the first mechanical model, the information generated by the processor 100 includes: increasing the embedded depth.

[0114] S42: In the case where the design width parameter of the rock shoulder 500 does not meet the condition of the second mechanical model, the information generated by the processor 100 includes: increasing the design width of the rock shoulder 500.

[0115] Considering the stratum difference of the upper soil and lower rock, the Hoek-Brown strength criterion widely applied internationally is applied to the horizontal resistance calculation of the rock-embedded part of the supporting pile, and the problem that when the foundation pit is excavated to below 370 of the pile bottom, the supporting pile 300 enters the overhanging pile stage, and the horizontal resistance provided by the rock-embedded section to the overhanging pile is greatly reduced. Through the analysis of two different stability failure modes of the embedded pile stage and the overhanging pile stage, two limit equilibrium equations are obtained, thereby providing a method which can help construction personnel to determine two key design parameters of the critical rock-embedded depth and the critical rock shoulder width, and can help construction personnel to check the rock-embedded stability of the supporting pile of the rigid-flexible composite foundation pit supporting system.

[0116] Embodiment 2

[0117] This embodiment is an example of the rock-embedded stability checking method of the supporting pile of the rigid-flexible composite foundation pit of the application.

[0118] S1: A model of the relative position relationship between the foundation pit position and the stratum is established based on the geological parameters related to the foundation pit position, and the embedded depth parameter and the design width parameter of the rock shoulder 500 are set.

[0119] Figure 6 It is a schematic diagram of the stratum condition 600 of the upper supporting pile 300 of the rigid-flexible composite supporting system of a certain first-level foundation pit. Figure 6 In the embodiment, the supporting pile 300 is embedded into the medium weathered granite 630. The elastic modulus of the medium weathered granite 630 is 5000 Mpa, wherein the thickness of the miscellaneous fill 610 is 2 m, the unit weight γ1 = 17.5 kN / m 3 , the friction angle The thickness of the strong weathered granite 620 is 5 m, the unit weight γ2 = 23.5 kN / m 3 , the friction angle The unit weight γ3 = 24.5 kN / m 3 of the medium weathered granite 630, the friction angle The uniaxial compressive strength f rc of the intact rock specimen = 30 MPa, the Hoek-Brown constant m i = 30, the geological strength factor GSI = 40, the disturbance coefficient D = 0.5,

[0120] S2 embedded pile stage:

[0121] S21: Calculate the active soil pressure parameter p ak

[0122] For the water-soil separate calculation stratum, u a represents the pressure outside the supporting structure.

[0123] For water-soil combined stratum or stratum above groundwater level,

[0124] σ ak For vertical stress of calculation point, For friction angle of rock-soil mass at calculation point position.

[0125] Then active earth pressure at point A is 0.

[0126] Active earth pressure at point B (filling 610) is

[0127] p ak = 17.5 x 2 x tan (45°- 15° / 2) = 20.6077 kN / m. 2

[0128] Active earth pressure at point B (strong weathering) is

[0129] p ak = 17.5 x 2 x tan (45°- 45° / 2) = 6.0050 kN / m. 2

[0130] Active earth pressure at point C (strong weathering) is

[0131] p ak = (17.5 x 2 + 23.5 x 5) x tan (45°- 45° / 2) = 26.16486 kN / m. 2

[0132] S22: Calculate resultant force of active earth pressure outside foundation pit above rock surface, i.e. active earth resistance E a1 and first distance h of fifth support point 350 to pile bottom 370 a1 .

[0133] Active earth resistance of AB section:

[0134]

[0135] First distance h of fifth support point 350 to pile bottom 370 of AB section: a1

[0136]

[0137] Active earth resistance of BC section:

[0138]

[0139] First distance h of fifth support point 350 to pile bottom 370 of BC section: a1

[0140] h a1 ​​​​​= 5 * (2 * 6.0050 + 26.16486) / 3 (6.0050 + 26.16486) + h d =

[0141] 1.978 + h d .

[0142] S23: Calculate the ultimate resistance of the pile side below the rock surface inside the foundation pit according to the Hoek-Brown strength criterion P L , specifically, comprising the following steps:

[0143] S231: According to the rock type of the rock-embedded section, find its Hoek-Brown constant m by Table 1 i .

[0144] The rock-embedded section is a medium weathered granodiorite, and m i = 30 is taken.

[0145] S232: According to Figure 3 , find the geological strength factor GSI value of the rock mass of the rock-embedded section.

[0146] The rock of the rock-embedded section is a medium weathered rock mass, which contains angular block folds formed by many discontinuous sets, and GSI = 40 is taken.

[0147] S233: Obtain the disturbance degree coefficient D of the rock mass under external load such as excavation or blasting.

[0148] According to the past engineering experience, D = 0.5 is taken.

[0149] S234: Calculate the horizontal resistance provided by the rock mass below the rock-embedded surface 400 according to the Hoek-Brown constant m i , GSI coefficient D value obtained in steps S231, S232, S233:

[0150] Wherein:

[0151]

[0152] S235: Calculate the critical rock-embedded depth h d .

[0153] As shown in Figure 4 , according to the first mechanical model, to ensure the stability of the pile bottom 370, the critical rock-embedded depth h d must satisfy:

[0154] E p1 h p1 + T c1 (h T1 + h d ) - K e E a1h a1 ≥0;

[0155] (501.57 / 3)*h d ^2-1.25*(20.6077*(5.667+h d +80.42465*

[0156] (1.978+h d ))>0;

[0157] h d >2.8627m;

[0158] For ease of design and construction, h is taken. d =3m.

[0159] S3: Suspended pile stage.

[0160] S31: Calculate the horizontal resistance curve of the 500-pair piles at the rock shoulder. The horizontal resistance curve of the 500-pair piles at the rock shoulder is as follows: Figure 4 As shown, the rock-embedded surfaces are distributed in an equilateral triangle. With the rock-embedded surface at 400° as the origin, the equation of the horizontal resistance curve for the suspended pile stage is:

[0161]

[0162] F x = (24.5 × tan55° × h) · B min 0≤h≤3m.

[0163] S32: Calculate the resultant force E of the horizontal resistance of the rock shoulder P2 :

[0164]

[0165] S33: Calculate the active earth pressure E on the outside of the foundation pit below the second support point (320). a2 The calculation method is the same as steps S21 and S22.

[0166] Active soil resistance E in section CD a2 :

[0167] E a2 = (17.5×2+23.5×5)×tan 2 (45°-55° / 2)×3=45.48kN:

[0168] The third distance h between the second fulcrum 320 and the third fulcrum 330 of segment CD a2 :

[0169]

[0170] S34: Calculate the critical shoulder width Bmin .

[0171] As shown in Figure 5 , according to the second mechanical model, to ensure the stability of the pile bottom 370, the critical rock shoulder width B min needs to satisfy:

[0172] E P2 h p2 ≥ K T E a2 h a2 ;

[0173]

[0174] B min ≥ 0.3 m.

[0175] It should be noted that the above specific embodiments are exemplary, and those skilled in the art can think of various solutions under the inspiration of the disclosure of the present application, and these solutions also belong to the disclosed range of the present application and fall within the protection scope of the present application. Those skilled in the art should understand that the specification and drawings of the present application are illustrative and do not constitute a limitation on the claims. The protection scope of the present application is defined by the claims and their equivalents. The specification of the present application contains multiple inventive concepts, such as "according to one preferred embodiment", which means that the corresponding paragraph discloses an independent concept, and the applicant reserves the right to file a divisional application according to each inventive concept.

Claims

1. A processor for calculating critical data for a support pile rock socket, the processor comprising: The processor (100) is configured to: During the embedded pile stage, the critical embedded depth parameter is calculated based on the first active soil parameter on the outside of the foundation pit above the embedded rock surface (400) and the resultant force parameter of the horizontal resistance of the rock mass provided by the rock mass below the embedded rock surface (400); among them, the minimum embedded rock depth value that conforms to the first mechanical model is selected as the critical embedded rock depth parameter. The first mechanical model is: ; denotes a parameter of the horizontal resistance force resultant of the rock mass; denotes a first distance parameter from the fifth fulcrum (350) to the pile bottom (370); denotes a second distance parameter from the sixth fulcrum (360) to the pile bottom (370); denotes a parameter of the axial force of the overlying fulcrum of the embedded pile stage; denotes a vertical distance from the first fulcrum (310) to the foundation pit excavation surface; denotes a critical rock-embedded depth parameter; denotes a rock-embedded stability safety factor; denotes a parameter of the active soil resistance force.

2. The processor of claim 1, wherein, During the suspended pile stage, the critical rock shoulder width parameter is calculated based on the second active soil parameter on the outside of the foundation pit below the second support point (320) and the distance from the resultant force of the horizontal resistance of the rock shoulder to the pile bottom (370); among them, the minimum rock shoulder width value that conforms to the second mechanical model is selected as the critical rock shoulder width parameter.

3. The processor according to claim 2, characterized in that, The second mechanical model is: ; represents a rock shoulder horizontal resistance resultant force parameter; represents a fourth distance parameter from the second fulcrum (320) to the fourth fulcrum (340); the fourth fulcrum (340) is a point of action of the rock shoulder horizontal resistance resultant force on the supporting pile (300); represents a toe stability safety factor; represents a active earth pressure parameter outside the foundation pit below the second fulcrum (320); represents a third distance parameter from the second fulcrum (320) to the third fulcrum (330).

4. The processor according to claim 1, characterized in that, The step of the processor (100) calculating the first active soil parameters outside the foundation pit above the rock-socketed surface (400) is configured as follows: Calculate the active earth pressure parameters on the outside of the foundation pit above the rock surface; Calculate the active soil resistance parameters on the outside of the foundation pit above the rock surface and the first distance parameter from the fifth support point (350) to the bottom of the pile (370); the fifth support point (350) is the point of action of the active soil resistance on the support pile (300).

5. The processor according to claim 1, characterized in that, The step of the processor (100) calculating the resultant force parameters of the horizontal resistance of the rock mass provided by the rock mass below the rock-embedded surface (400) is configured as follows: Calculate the ultimate resistance parameters of the pile side inside the foundation pit below the rock surface according to the Hoek-Brown strength criterion; Calculate the resultant force parameters of the horizontal resistance of the rock mass provided by the rock mass below the embedded rock surface (400) in the embedded pile stage and the second distance parameter from the sixth support point (360) to the bottom of the pile (370). The sixth support point (360) is the point of action of the resultant force of the horizontal resistance of the rock mass on the support pile (300).

6. The processor according to claim 2, characterized in that, The step of the processor (100) calculating the second active soil parameters outside the foundation pit below the second support point (320) is configured as follows: Calculate the resultant parameters of the active earth pressure on the outside of the foundation pit below the second support point (320); Calculate the third distance parameter from the second support point (320) to the third support point (330); the third support point (330) is the point of action of the resultant force of the active earth pressure on the outside of the foundation pit below the second support point (320) on the support pile (300).

7. A method for calculating critical data for rock-socketed support piles, characterized in that, The method includes: During the embedded pile stage, the critical embedded depth parameter is calculated based on the first active soil parameter on the outside of the foundation pit above the embedded rock surface (400) and the resultant force parameter of the horizontal resistance of the rock mass provided by the rock mass below the embedded rock surface (400); among them, the minimum embedded rock depth value that conforms to the first mechanical model is selected as the critical embedded rock depth parameter. The first mechanical model is: ; Indicates the resultant force parameter of the horizontal resistance of the rock mass; This represents the first distance parameter from the fifth support point (350) to the bottom of the pile (370); This represents the second distance parameter from the sixth support point (360) to the bottom of the pile (370); This indicates the axial force parameters at the upper support point during the embedded pile stage; This represents the vertical distance from the first support point (310) to the excavation surface of the foundation pit; Indicates the critical rock embedding depth parameter; Indicates the safety factor for rock-embedded stability; This represents the active soil resistance parameter.

8. The calculation method according to claim 7, characterized in that, The method further includes: calculating the critical rock shoulder width parameter based on the second active soil parameter outside the foundation pit below the second support point (320) and the distance from the resultant force of the horizontal resistance of the rock shoulder to the pile bottom (370); wherein, the minimum rock shoulder width value that conforms to the second mechanical model is selected as the critical rock shoulder width parameter; The second mechanical model is: ; This indicates the resultant force parameter of the horizontal resistance of the rock shoulder; The fourth distance parameter represents the distance from the second support point (320) to the fourth support point (340); the fourth support point (340) is the point of action of the resultant force of the horizontal resistance of the rock shoulder on the support pile (300); Indicates the stability and safety factor of the kicking motion; This represents the active earth pressure parameters on the outside of the foundation pit below the second support point (320); The third distance parameter represents the distance from the second fulcrum (320) to the third fulcrum (330).

9. The calculation method according to claim 7 or 8, characterized in that, The steps for calculating the first active soil parameters on the outside of the foundation pit above the rock-socketed surface (400) include: Calculate the active earth pressure parameters on the outside of the foundation pit above the rock surface; Calculate the active soil resistance parameters on the outside of the foundation pit above the rock surface and the first distance parameter from the fifth support point (350) to the bottom of the pile (370); the fifth support point (350) is the point of action of the active soil resistance on the support pile (300).

10. The calculation method according to claim 8, characterized in that, The steps for calculating the second active soil parameters on the outer side of the foundation pit below the second support point (320) are configured as follows: Calculate the resultant parameters of the active earth pressure on the outside of the foundation pit below the second support point (320); Calculate the third distance parameter from the second support point (320) to the third support point (330); the third support point (330) is the point of action of the resultant force of the active earth pressure on the outside of the foundation pit below the second support point (320) on the support pile (300).

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