Cooperative structure design method for foundation pit engineering

Abstract

The invention relates to a foundation pit engineering collaborative structure design method, which comprises the following steps of: 1, obtaining a stress monitoring value of a main reinforcement of an enclosure structure by calibrating the correlation between a scale distance length convergence value of a sensor and strain of a sensing optical fiber; step 2, obtaining a stress change rule of the main reinforcement of the enclosure structure; 3, the soil pressure around the foundation pit structure is obtained through calculation according to the Rankine soil pressure, and the transfer rule of the soil pressure between the enclosure structure and the side wall of the underground structure is obtained; and step 4, respectively obtaining the stress contribution value of the retaining structure and the stress contribution value of the retaining structure. According to the method, the stress-strain changes of the enclosure structure in the foundation pit excavation process, the underground structure construction process and the backfill completion are measured through the distributed optical fibers, and the stress distribution conditions of the enclosure structure and the underground structure are obtained in combination with the stress-strain change conditions, measured through the distributed optical fibers, of the side wall of the underground structure; and the internal force sharing ratio of the wall-attached type structure is obtained, and the foundation pit wall-attached type underground structure side wall design reinforcing bars are optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical design and construction of civil engineering, and more particularly to a collaborative structure design method for foundation pit engineering. Background Art

[0002] At present, in some large integrated transportation hubs, high-speed railways, urban subways, buses, etc. are distributed vertically underground in the same area, resulting in deep foundation pit excavation. The open excavation pits of some underground hubs are as long as one kilometer, and the excavation depth exceeds 30m (super-deep foundation pits), which leads to large lateral forces on the underground main structure, thick walls, and high reinforcement. In the actual implementation process, temporary retaining structures are often used to support the excavation and then the main structure is constructed. The main structure and the support structure are constructed against the wall. The main structure rarely considers the role of the early foundation pit retaining structure, and the two cannot clearly share the force when they are constructed together. As a result, the main structure of the foundation pit against the wall often takes no consideration of the force contribution of the temporary retaining structure. This makes the safety of the existing main structure of the foundation pit against the wall much higher than it actually is, and causes high construction costs.

[0003] Therefore, it is necessary to propose a collaborative structural design method for foundation pit engineering, which can reduce construction costs while ensuring safety performance, and is of great significance to controlling the construction costs of foundation pit engineering. Summary of the Invention

[0004] The present invention provides a collaborative structure design method for foundation pit engineering, so as to solve the technical problem that the existing foundation pit engineering does not consider the stress contribution of temporary enclosure structures at all, resulting in excessively high engineering costs.

[0005] According to one aspect of the present invention, a collaborative structure design method for foundation pit engineering is provided, comprising the following steps:

[0006] Step 1: Based on the Brillouin optical time-domain distributed optical fiber sensing method, the correlation between the sensor gauge length convergence value and the sensing optical fiber strain is calibrated to obtain the force monitoring value of the main reinforcement of the enclosure structure;

[0007] Step 2: Based on the linear correlation between Brillouin frequency shift, strain and temperature, the force variation law of the main reinforcement of the enclosure structure is obtained;

[0008] Step 3: Obtain the soil pressure around the foundation pit structure according to the Rankine earth pressure calculation, and obtain the earth pressure of the retaining structure and the earth pressure borne by the side walls of the underground structure according to step 2 to obtain the transfer law of the earth pressure between the retaining structure and the side walls of the underground structure;

[0009] Step 4: Based on the transfer law of soil pressure between the retaining structure and the side wall of the underground structure, the retaining structure force contribution value and the retaining structure force contribution value are obtained respectively.

[0010] Preferably, based on the above scheme, step 1 specifically includes:

[0011] Step 11: densely distributed grating optical fibers are laid along the main reinforcement direction of the foundation pit retaining pile reinforcement cage, and measurement lines are drawn out to continuously monitor the stress and strain changes of the retaining structure reinforcement;

[0012] Step 12: laying dense distributed grating optical fibers along the main reinforcement direction in the side wall reinforcement of the foundation pit retaining structure, and leading out measurement lines, and then continuously monitoring the stress and strain changes of the retaining structure wall reinforcement;

[0013] Step 13 is to obtain the force monitoring value of the main reinforcement of the enclosure structure and the stress monitoring value of the reinforcement of the enclosure structure wall.

[0014] Based on the above solution, in step 3, the soil pressure around the foundation pit structure is obtained according to the Rankine soil pressure calculation, and the calculation formula is as follows:

[0015]

[0016] in,

[0017] E0 is the Rankine earth pressure on the foundation pit structure; K0 is the Rankine earth pressure coefficient; y(h) is the earth pressure function; h is the excavation depth of the foundation pit; represents the internal friction angle of soil.

[0018] Based on the above scheme, in step 3, the formula for calculating the earth pressure of the retaining structure is as follows:

[0019]

[0020] E1 is the monitoring value of the earth pressure borne by the foundation pit retaining structure; f a,1 ,f a,2 ,…,f a,n It is the monitoring value of soil stress borne by the retaining structure after temperature compensation at each monitoring point of the optical fiber sensor.

[0021] Based on the above solution, in step 3, the calculation formula for the earth pressure on the side wall of the underground structure is as follows:

[0022]

[0023] E2 is the monitoring value of the earth pressure on the side wall of the underground structure; f b,1 ,f b,2 ,…,f b,n It is the soil stress monitoring value of the underground structure side wall after temperature compensation at each monitoring point of the optical fiber sensor.

[0024] Based on the above scheme, the transmission law of soil pressure between the retaining structure and the side wall of the underground structure is as follows:

[0025] E2 = α(E0-E1) (5);

[0026] E2 is the monitored value of the soil pressure borne by the side wall of the underground structure; E0 is the Rankine soil pressure borne by the foundation pit structure; E1 is the monitored value of the soil pressure borne by the foundation pit retaining structure; α is the soil pressure transfer coefficient between the foundation pit retaining structure and the side wall of the underground structure. After obtaining α (α < 1), the reinforcement design of the subsequent underground structure can be carried out according to this parameter.

[0027] The collaborative structure design method for foundation pit engineering of the present invention is applicable to the main structure engineering of underground stations that are superimposed on the wall with the retaining structure. The stress and strain changes of the retaining structure (retaining piles or retaining walls) during the foundation pit excavation process, the underground structure construction process and after the backfilling are completed are measured by distributed optical fiber. Combined with the stress and strain changes of the side walls of the underground structure measured by distributed optical fiber, the force distribution of the retaining structure and the underground structure are obtained respectively, the internal force sharing ratio of the wall-mounted structure is obtained, and the reinforcement design of the side walls of the foundation pit wall-mounted underground structure is optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without inventive efforts. In the drawings:

[0029] Figure 1 A flowchart of the collaborative structure design method for foundation pit engineering of the present invention is provided;

[0030] Figure 2 This is a first state diagram of the deep foundation pit engineering cross-section construction working condition of the present invention;

[0031] Figure 3 This is a second state diagram of the deep foundation pit engineering section construction working condition of the present invention;

[0032] Figure 4 This is a third state diagram of the deep foundation pit engineering cross-section construction working condition of the present invention;

[0033] Figure 5 This is a fourth state diagram of the deep foundation pit engineering cross-section construction working condition of the present invention;

[0034] Figure 6 This is a fifth construction working condition diagram of the deep foundation pit engineering cross-section construction working condition of the present invention;

[0035] Description of Figure Numbers:

[0036] 1. Support piles; 2. Foundation pit retaining pile reinforcement cage; 3. Dense distributed grating optical fiber; 4. Survey line; 6. Prestressed anchor cable; 7. Crown beam; 9. Pad layer; 10. DETAILED DESCRIPTION

[0037] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0038] It will be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections.

[0039] To simplify the drawings, only the parts relevant to the present invention are schematically shown in each figure. They do not represent the actual structure of the product. Furthermore, to simplify the drawings and facilitate understanding, in some figures, only one of the components with the same structure or function is schematically depicted or labeled. As used herein, "one" not only means "only one" but also "more than one."

[0040] It should be further understood that the term "and / or" used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0041] In the embodiments shown in the accompanying drawings, directional indications (such as up, down, left, right, front, and rear) used to explain the structure and movement of various components of the present invention are not absolute but relative. These descriptions are applicable when the components are in the positions shown in the accompanying drawings. If the descriptions of the positions of these components are changed, the directional indications will also change accordingly.

[0042] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive work.

[0044] See also Figure 1 , and combined with Figure 2 and Figure 3As shown, a collaborative structure design method for foundation pit engineering of the present invention comprises the following steps:

[0045] Step 1: Based on the Brillouin optical time-domain distributed optical fiber sensing method, the correlation between the sensor gauge length convergence value and the sensing optical fiber strain is calibrated to obtain the force monitoring values ​​of the main reinforcement and the side wall reinforcement of the enclosure structure;

[0046] The specific method involves creating grooves approximately 1mm deep in the main reinforcement of the enclosure structure and the reinforcement of the side walls. Fiber optic sensors are placed in these grooves and secured with glue. Vertically, data collection points are set every 1m, and extended measurement lines are run to the data collection points. Temperature-sensing optical fibers are placed on the outside of the main reinforcement to monitor changes in the temperature and stress of the steel bars. Horizontally, a group of fiber optic Bragg grating sensors can be deployed at 5m intervals to monitor stress changes in different sections of the structure.

[0047] During testing, Optical Frequency Domain Reflectometry (OFDR) technology is used. Laser emitters at both ends of the optical fiber inject a pulsed light beam and a continuous light beam into the optical fiber, respectively. When the frequency difference between the pulsed light and the continuous light is equal to the Brillouin frequency shift in a certain region of the optical fiber, a stimulated Brillouin amplification effect occurs in that region, allowing the deformation of the steel bar to be determined. Specifically, for example, a Bragg grating sensor is used. Due to the photosensitivity of the optical fiber, the refractive index changes. Exposing the photosensitive optical fiber to the light wave fringes caused by the mutual interference of ultraviolet light beams forms a refractive index modulation distribution. The relationship between stress and strain is as follows: σ = E * ε, where, within the elastic deformation range, σ represents stress, ε represents strain, and E is the elastic modulus, also known as Young's modulus.

[0048] Step 2: Based on the linear correlation between Brillouin frequency shift and strain, the force variation law of the main reinforcement and the side wall reinforcement of the enclosure structure is obtained;

[0049] Step 3: Obtain the soil pressure around the foundation pit structure according to the Rankine earth pressure calculation, and obtain the earth pressure of the retaining structure and the earth pressure borne by the side walls of the underground structure according to step 2 to obtain the transfer law of the earth pressure between the retaining structure and the side walls of the underground structure;

[0050] Step 4: Based on the transfer law of soil pressure between the retaining structure and the side wall of the underground structure, the retaining structure force contribution value and the retaining structure force contribution value are obtained respectively.

[0051] In step 3, the soil pressure around the foundation pit structure is obtained according to the Rankine soil pressure calculation. The calculation formula is as follows:

[0052]

[0053] in,

[0054] E0 is the Rankine soil pressure on the foundation pit structure; K0 is the Rankine soil pressure coefficient; y(h) is the soil pressure function; h is the excavation depth of the foundation pit;.

[0055] In step 3, the formula for calculating the earth pressure of the retaining structure is as follows:

[0056]

[0057] E1 is the monitoring value of the earth pressure borne by the foundation pit retaining structure; f a,1 ,f a,2 ,…,f a,n It is the monitoring value of soil stress borne by the retaining structure after temperature compensation at each monitoring point of the optical fiber sensor.

[0058] In step 3, the calculation formula for the earth pressure on the side walls of the underground structure is as follows:

[0059]

[0060] E2 is the monitoring value of the earth pressure on the side wall of the underground structure; f b,1 ,f b,2 ,…,f b,n It is the soil stress monitoring value of the underground structure side wall after temperature compensation at each monitoring point of the optical fiber sensor.

[0061] Among them, the transmission law of earth pressure between the retaining structure and the side wall of the underground structure is as follows:

[0062] E2 = α(E0-E1) (5);

[0063] E2 is the monitored value of the soil pressure borne by the side wall of the underground structure; E0 is the Rankine soil pressure borne by the foundation pit structure; E1 is the monitored value of the soil pressure borne by the foundation pit retaining structure; α is the soil pressure transfer coefficient between the foundation pit retaining structure and the side wall of the underground structure. After obtaining α (α < 1), the reinforcement design of the subsequent underground structure can be carried out according to this parameter.

[0064] Wherein, step 1 specifically includes:

[0065] Step 11: Lay dense distributed grating optical fiber 3 along the main reinforcement direction of the foundation pit retaining pile reinforcement cage 2, and lead out the measuring line 4, and then continuously monitor the stress and strain changes of the retaining structure reinforcement 2; please refer to the construction structure diagram Figure 2 As shown, multiple densely distributed grating optical fibers 3 are arranged at intervals along the length direction of the steel cage of the support pile 1, and the measuring line 4 is led out for easy connection.

[0066] Subsequently, the foundation pit is excavated until the bottom of the first anchor cable is reached, and the first prestressed anchor cable 6 and crown beam 7 are constructed. For the construction structure diagram, please refer to Figure 3As shown, after the first prestressed anchor cable 6 and crown beam 7 are completed, the remaining prestressed anchor cables 6 are excavated layer by layer, and the foundation pit is excavated to the bottom and a cushion layer 9 is set. After completion, the structure is as shown in the figure. Figure 4 shown.

[0067] Furthermore, the present invention continues to construct the structural bottom plate and structural side wall reinforcement, and fills the gap between the supporting pile 1 and the structural side wall with concrete to form a wall-attached structure, so that the structural side wall 11 is connected to the supporting pile 1 to form a whole to facilitate mechanical conduction.

[0068] Among them, the present invention also lays dense distributed grating optical fiber 3 along the main reinforcement direction in the structural side wall reinforcement 11, and leads to the measurement line 4, and then continuously monitors the stress and strain changes of the structural wall reinforcement. After completion, the structure diagram is as follows Figure 5 shown.

[0069] Finally, the structural side wall 11 is constructed and backfilled with soil 10 to the design elevation. For the construction conditions of the deep foundation pit engineering section, please refer to Figure 6 shown.

[0070] Step 12: laying dense distributed grating optical fibers 3 along the main reinforcement direction in the side wall reinforcement of the foundation pit retaining structure, and leading out the measuring line 4, and then continuously monitoring the stress and strain changes of the retaining structure wall reinforcement to obtain the influence of the retaining structure on the optimized main structure stress;

[0071] Step 13 is to obtain the force monitoring value of the main reinforcement of the enclosure structure and the stress monitoring value of the reinforcement of the enclosure structure wall.

[0072] The collaborative structure design method for foundation pit engineering of the present invention is applicable to the main structure engineering of underground stations that are superimposed on the wall with the retaining structure. The stress and strain changes of the retaining structure (retaining piles or retaining walls) during the foundation pit excavation process, the underground structure construction process and after the backfilling are completed are measured by distributed optical fiber. Combined with the stress and strain changes of the side walls of the underground structure measured by distributed optical fiber, the force distribution of the retaining structure and the underground structure are obtained respectively, the internal force sharing ratio of the wall-mounted structure is obtained, and the reinforcement design of the side walls of the foundation pit wall-mounted underground structure is optimized.

[0073] Finally, the method of this application is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A collaborative structure design method for foundation pit engineering, characterized in that: The following steps are involved: Step 1: Based on the Brillouin optical time-domain distributed optical fiber sensing method, the correlation between the sensor gauge length convergence value and the sensing optical fiber strain is calibrated to obtain the force monitoring value of the main reinforcement of the enclosure structure; Step 2: Based on the linear correlation between Brillouin frequency shift, strain and temperature, the force variation law of the main reinforcement of the enclosure structure is obtained; Step 3: Obtain the soil pressure around the foundation pit structure according to the Rankine earth pressure calculation, and obtain the earth pressure of the retaining structure and the earth pressure borne by the side walls of the underground structure according to step 2 to obtain the transfer law of the earth pressure between the retaining structure and the side walls of the underground structure; Step 4: Based on the transfer law of soil pressure between the retaining structure and the side wall of the underground structure, the retaining structure force contribution value and the retaining structure force contribution value are obtained respectively.

2. A collaborative structure design method for foundation pit engineering according to claim 1, characterized in that: The step 1 specifically includes: Step 11: densely distributed grating optical fibers are laid along the main reinforcement direction of the foundation pit retaining pile reinforcement cage, and measurement lines are drawn out to continuously monitor the stress and strain changes of the retaining structure reinforcement; Step 12: laying dense distributed grating optical fibers along the main reinforcement direction in the side wall reinforcement of the foundation pit retaining structure, and leading out measurement lines, and then continuously monitoring the stress and strain changes of the retaining structure wall reinforcement; Step 13 is to obtain the force monitoring value of the main reinforcement of the enclosure structure and the stress monitoring value of the reinforcement of the enclosure structure wall.

3. A collaborative structure design method for foundation pit engineering according to claim 2, characterized in that: In step 3, the soil pressure around the foundation pit structure is obtained according to the Rankine soil pressure calculation. The calculation formula is as follows: Where, E0 is the Rankine earth pressure on the foundation pit structure; K0 is the Rankine earth pressure coefficient; y(h) is the earth pressure function; h is the excavation depth of the foundation pit; represents the internal friction angle of soil.

4. A collaborative structure design method for foundation pit engineering according to claim 2, characterized in that: In step 3, the formula for calculating the earth pressure of the retaining structure is as follows: E1 is the monitoring value of the earth pressure borne by the foundation pit retaining structure; f a,1 ,f a,2 ,…,f a,n It is the monitoring value of soil stress borne by the retaining structure after temperature compensation at each monitoring point of the optical fiber sensor.

5. A collaborative structure design method for foundation pit engineering according to claim 4, characterized in that: In step 3, the calculation formula for the earth pressure on the side walls of the underground structure is as follows: E2 is the monitoring value of the earth pressure on the side wall of the underground structure; f b,1 ,f b,2 ,…,f b,n It is the soil stress monitoring value of the underground structure side wall after temperature compensation at each monitoring point of the optical fiber sensor.

6. A collaborative structure design method for foundation pit engineering according to claim 5, characterized in that: The transfer law of earth pressure between the retaining structure and the side wall of the underground structure is as follows: E2 = α(E0-E1) (5); E2 is the monitored value of the earth pressure borne by the side walls of the underground structure; E0 is the Rankine earth pressure borne by the foundation pit structure; E1 is the monitored value of the earth pressure borne by the foundation pit retaining structure; α is the earth pressure transfer coefficient between the foundation pit retaining structure and the side walls of the underground structure. After obtaining α, the reinforcement design of the subsequent underground structure is carried out according to this parameter.

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