Support device and support device design method

Abstract

The application provides a supporting device and a supporting device design method. The supporting device comprises a steel arch, a plurality of steel arch segments, each steel arch segment is sequentially assembled to form an arch frame body, a first buffer part, a plurality of first buffer pads, and a connection between two adjacent steel arch segments. Wherein, in the case that the pressure exceeds the yield strength of the first buffer pad, the first buffer pad generates a circumferential pressure relief deformation; a second buffer part, at least one second buffer pad, arranged on the back of the steel arch close to the surrounding rock, continuously arranged along the circumference of the steel arch and basically covering the back of the steel arch; in the case that the pressure exceeds the yield strength of the second buffer pad, the second buffer pad generates a radial pressure relief deformation; wherein, in the case that the steel arch is under pressure, the second buffer part is configured to be deformed after the first buffer part to achieve a staged pressure relief.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel and underground engineering support, and particularly relates to a support device and a support device design method. BACKGROUND

[0002] In a deep-buried soft rock tunnel, high ground stress causes continuous large deformation of surrounding rock, which often causes the traditional steel arch to yield, twist and even break. If the steel arch can be deformed within a certain range after being supported, the deformation energy of the surrounding rock can be dissipated to a certain extent, which will greatly reduce the pressure of the surrounding rock acting on the steel arch.

[0003] In the prior art, structures such as U-shaped steel telescopic joints, I-beams or square steel sleeves are often used to set telescopic nodes between the arch segments of the steel arch, and the telescopic nodes are used to realize the telescopic effect in the radial direction by sliding along the ring direction between the segments, thereby generating a radial yielding effect.

[0004] However, in a deep-buried soft rock tunnel, due to high ground stress, the surrounding rock often produces uneven convergence deformation, and the deformation rate and direction of different parts are different. If the rigidity of the support structure is too large or the response is too concentrated, it is easy to cause local stress peak, node yield and overall instability. Further, when the telescopic node reaches the critical state, sudden sliding often occurs, which causes stress concentration of the node, sudden drop of local rigidity, discontinuous energy release process, poor coordination of the surrounding rock support system, and a large decrease in the residual bearing capacity of the support after yielding of the node.

[0005] Therefore, the existing telescopic or sliding yielding structure cannot coordinate the stress and deformation process of the arch in time and space, and it is difficult to balance the node stability and overall deformation coordination. SUMMARY

[0006] The present application provides a support device and a design method for the support device, which solves the defects of sudden yielding caused by setting telescopic nodes between the steel arch segments in the prior art, poor coordination of the surrounding rock-support system, and continuous connection of the stress process of the node and the back of the arch through the staged yielding of the two-stage buffer, smooth energy absorption process, thereby realizing the coordinated deformation and stability control of the surrounding rock-support system.

[0007] The application provides a supporting device, which comprises a steel arch frame, a plurality of steel arch frame segments, each of the steel arch frame segments is sequentially assembled to form an arch frame body, a first buffer part, a plurality of first buffer pads, the first buffer pads are arranged at the connection of two adjacent steel arch frame segments, wherein, in the case that the pressure exceeds the yield strength of the first buffer pad, the first buffer pad generates a circumferential pressure relief deformation, and a second buffer part, at least one second buffer pad, the second buffer pad is arranged at the back of the steel arch frame close to the surrounding rock, is continuously arranged along the circumference of the steel arch frame and substantially covers the back of the steel arch frame, and in the case that the pressure exceeds the yield strength of the second buffer pad, the second buffer pad generates a pressure relief deformation, wherein, in the case that the steel arch frame is under pressure, the second buffer part is configured to generate a pressure relief deformation later than the first buffer part, so as to realize a staged pressure relief.

[0008] According to the supporting device provided by the application, the yield strength of the second buffer pad is less than or equal to the yield strength of the first buffer pad.

[0009] According to the supporting device provided by the application, the thickness of the second buffer pad is greater than the thickness of the first buffer pad.

[0010] According to the supporting device provided by the application, the two ends of the steel arch frame segment are provided with a connecting plate, the area of the connecting plate is greater than the cross-sectional area of the steel arch frame segment along the circumference of the steel arch frame, so that the first buffer pad forms a stable pressure interface between adjacent steel arch frame segments.

[0011] According to the supporting device provided by the application, adjacent steel arch frame segments are fixedly connected through threaded holes on the connecting plate by bolts; the first buffer pad is provided with a perforation corresponding to the threaded hole on the connecting plate; wherein the initial pre-tightening force of the bolt is set to keep the first buffer pad in the elastic deformation stage.

[0012] According to the supporting device provided by the application, the first buffer pad is a polyurethane foam plate, and the second buffer pad is a polyethylene closed-cell foam plate.

[0013] The application also provides a supporting device design method for designing the above-mentioned supporting device, which comprises the following steps: determining the reserved deformation amount of a target tunnel where the supporting device is installed; determining the design deformation threshold of the steel arch frame based on the geometric parameters and material parameters of the steel arch frame; determining the design pressure relief total amount based on the design deformation threshold and the reserved deformation amount, and determining the thicknesses of the first buffer pad and the second buffer pad based on the design pressure relief total amount.

[0014] According to the supporting device design method provided by the application, the reserved deformation amount of the target tunnel where the supporting device is installed is determined, including: determining the reserved deformation amount according to the surrounding rock deformation monitoring value after the initial support of the tunnel section near the target tunnel; or determining the reserved deformation amount of the target tunnel according to the numerical simulation result.

[0015] According to the supporting device design method provided by the application, the thickness of the first buffer pad and the second buffer pad is determined based on the design compression amount, including: preferentially determining the thickness of the second buffer pad according to the design compression amount and the design compression performance of the second buffer pad; in the case that the compression amount of the second buffer pad does not meet the design compression amount, determining the thickness of the first buffer pad according to the number and design compression performance of the first buffer pad, so that the compression amount of the first buffer pad and the second buffer pad meets the requirement of the design compression amount; wherein the design compression performance includes the volume compression rate of the buffer pad in the plastic deformation stage.

[0016] According to the supporting device design method provided by the application, in the case that the steel arch segment is provided with a connecting plate and connected by bolts, the method further includes: determining the initial pre-tightening force of the bolt based on the yield strength of the first buffer pad and the net contact area of the connecting plate, so that the first buffer pad is in the elastic deformation stage; wherein the net contact area of the connecting plate is the difference between the area of the connecting plate and the area of the threaded hole on the connecting plate.

[0017] The supporting device and the supporting device design method provided by the application set the first buffer pad at the connecting part between the steel arch segments, provide the ring-shaped compression amount between the segments of the steel arch, set the second buffer part at the back of the steel arch, and continuously arrange the second buffer pad in the second buffer part along the circumference of the steel arch to basically cover the back of the steel arch. During the convergence and deformation of the surrounding rock, the connecting part between the steel arch segments often bears a large concentrated stress, which needs to be released by the compression of the first buffer pad. However, the convergence and deformation of the surrounding rock is often uneven, and after the local compression of the first buffer pad, the overall arch structure will still bear a high radial convergence. If the stiffness of the whole system suddenly changes, the surrounding rock cannot slowly release energy, and there is still a risk of overall buckling of the steel arch. Therefore, after the compression of the first buffer pad, the second buffer pad is used for compression, and the second buffer pad basically covers the back of the steel arch along the circumference, which can bear pressure as evenly as possible. Thus, the energy of the surrounding rock can be continuously and smoothly released, and the large-range and uniform deformation energy is dissipated. The two-stage compression absorbs and dissipates the deformation energy of the surrounding rock in different time periods and with different intensities, increases the total compression amount, prolongs the effective action time of the compression and dissipation of the deformation energy of the surrounding rock, has higher efficiency and reliability, and has higher adaptability to the uncertainty of the surrounding rock pressure change.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] (1) The construction is simple, the core material is a common foam board, and no precise mechanical parts are needed. Only binding and installation are needed on site, overcoming the problem of high installation precision requirement of traditional ring-shaped telescopic nodes, greatly reducing the construction difficulty and cost;

[0020] (2) The inherent stress difference existing in the area where the two buffer parts are located is used to form the pressure release sequence of "node first, back part later", and then form the phased coordinated pressure release, which conforms to the mechanical principle and law, making the design more reliable and realistic;

[0021] (3) The second buffer pad is arranged behind the steel arch support, which absorbs the deformation energy of the surrounding rock by plastic deformation under pressure, realizes the radial direct pressure release of the continuous surface of the whole circumference, and the pressure release method is simple and effective, overcoming the problem of limited pressure release direction of the traditional ring-shaped telescopic mechanism;

[0022] (4) Through the combination of two densities and two thicknesses of the buffer pad, the smooth transition from "point (node) high stress concentration release" to "surface (back part) large deformation uniform adaptation" is realized, the pressure release process is clear in level, the energy absorption efficiency is high, the bearing capacity of the arch support changes smoothly, and the problems of traditional ring-shaped telescopic node such as jamming risk and poor sliding stability are overcome;

[0023] (5) A double protection mechanism is formed, the node pressure release layer effectively releases the concentrated stress in the node area, preventing stress concentration damage at the arch support connecting plate; the arch support back pressure release layer provides continuous, full-circumferential, relatively large displacement radial pressure release, uniformly absorbing the deformation energy of the surrounding rock, avoiding arch support distortion and fracture, and systematically improving the reliability and safety of the support system. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0025] Figure 1 is a schematic view of a support device according to an exemplary embodiment of the present application;

[0026] Figure 2 is a schematic view of a steel arch support segment provided with a second buffer pad according to an exemplary embodiment of the present application;

[0027] Figure 3 is a schematic view of a steel arch support segment connection according to an exemplary embodiment of the present application,Figure 3 (a) shows a side view of the connection between the steel arch frame segments. Figure 3 (b) shows a front view of the connection between the steel arch frame segments;

[0028] Figure 4 This is a flowchart illustrating a design method for a support device according to an illustrative embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram illustrating the pressure relief of the second buffer pad in an illustrative embodiment of the present invention;

[0030] Figure 6 This is a schematic diagram of the surrounding rock pressure and relief amount borne by the support device according to an illustrative embodiment of the present invention.

[0031] Figure label:

[0032] 10-Steel arch frame;

[0033] 11-Steel arch frame segment;

[0034] 12-Connecting plate;

[0035] 121 - Threaded hole;

[0036] 13- Bolt;

[0037] 20 - First cushioning pad;

[0038] 30 - Second cushioning pad;

[0039] 31-Galvanized steel wire. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] It should be noted that in the field of tunnel and underground engineering support technology, circumferential and radial directions are two fundamental concepts describing the stress and deformation directions of the arch frame. Taking the tunnel axis as a reference, the direction extending along the circumference of the tunnel cross-section is called the circumferential direction (also known as the ring direction), which corresponds to the assembly and connection direction of the steel arch frame; while the direction pointing from the center of the tunnel to the surrounding rock is called the radial direction, which corresponds to the deformation direction of the surrounding rock convergence or the arch frame inward contraction.

[0042] In the prior art, only a telescopic joint is usually arranged at the connection of a steel arch segment to absorb the energy released by the deformation of surrounding rock. However, the deformation of surrounding rock is often uneven, and the telescopic joint is poor in sliding stability along the curved profile, and is prone to jamming or sudden sliding, so that the overall stress of the steel arch is unbalanced, and the risk of buckling or instability exists.

[0043] Therefore, embodiments of the present application provide a supporting device and a supporting device design method.

[0044] Figure 1 is a schematic view of a supporting device according to an illustrative embodiment of the present application; Figure 2 is a schematic view of a steel arch segment provided with a second buffer pad according to an illustrative embodiment of the present application; Figure 3 is a schematic view of a connection of a steel arch segment according to an illustrative embodiment of the present application, Figure 3 (a) of which shows a side view of the connection of a steel arch segment, Figure 3 (b) of which shows a front view of the connection of a steel arch segment.

[0045] As shown in Figures 1-3 , the supporting device comprises a steel arch 10, a first buffer part and a second buffer part.

[0046] The steel arch 10 comprises a plurality of steel arch segments 11, and each steel arch segment 11 is sequentially assembled to form an arch frame body.

[0047] The first buffer part comprises a plurality of first buffer pads 20 arranged at the connection of two adjacent steel arch segments 11. In the case where the pressure received exceeds the yield strength of the first buffer pad 20, the first buffer pad 20 generates circumferential compression deformation.

[0048] The second buffer part comprises at least one second buffer pad 30 arranged on the back of the steel arch 10 close to the surrounding rock, and is continuously arranged along the circumference of the steel arch 10 and substantially covers the back of the steel arch 10. In the case where the pressure received exceeds the yield strength of the second buffer pad 30, the second buffer pad 30 generates radial compression deformation.

[0049] In the case where the steel arch 10 is under pressure, the second buffer part is configured to deform in compression after the first buffer part, so as to realize staged compression.

[0050] According to embodiments of the present application, the steel arch 10 can be an arch in the shape of a circle, a horseshoe or a city gate, and the present application does not limit the shape of the arch.

[0051] According to embodiments of the present application, the first buffer pad 20 and the second buffer pad 30 are both selected from materials with a volume compression rate greater than 50% in the plastic deformation stage.

[0052] According to the embodiment of the present application, the second buffer pad 30 can be arranged in multiple layers along the radial direction at the back of the steel arch 10.

[0053] Preferably, the first buffer pad 20 and the second buffer pad 30 can be foam boards. Considering that the soft rock large deformation tunnel is generally high stress + high water content surrounding rock, the water seepage is high during construction, and the volume change and strength attenuation of the buffer pad will be caused once the buffer pad absorbs water. Since the foam board has good waterproofness, the performance stability of the supporting yield structure can be ensured, and the foam board has buffering and durability, absorbs the surrounding rock deformation energy through compression deformation, and realizes the yield of the arch.

[0054] According to the embodiment of the present application, the first buffer pad 20 is arranged at the connection of adjacent steel arch segments 11, which is the first to bear concentrated pressure when the surrounding rock is initially deformed, so that at least part of the first buffer pad 20 is first compressed to release the node stress in the initial compression stage of the steel arch system. The second buffer pad 30 is arranged on the back of the steel arch 10 close to the surrounding rock and is continuously arranged along the circumference of the steel arch 10. Since its stress surface is larger, it mainly bears the radial distributed pressure from the surrounding rock, so the second buffer pad 30 gradually enters the compression state in the stage of further development of the overall convergence deformation of the surrounding rock.

[0055] According to the embodiment of the present application, the steel arch 10 can be an H-shaped steel, an I-shaped steel or a box-type arch.

[0056] According to the embodiment of the present application, before the steel arch segments 11 are assembled along the circumference of the tunnel, the second buffer pad 30 can be fixed to the back of the steel arch 11 by galvanized steel wire 31 with a binding interval of 30-50 cm to prevent the second buffer pad 30 from falling off.

[0057] Preferably, the second buffer pad 30 is as wide as the steel arch 10 and completely covers the back of the steel arch 10.

[0058] In the deep soft rock tunnel with high ground stress, the connection of the steel arch segment 11 will first bear the concentrated stress from the surrounding rock in the case of convergence of the surrounding rock, and if no buffering is performed, the instability of the segment connection may be caused, therefore, the first buffering pad 20 is arranged between the steel arch segments in the embodiment of the present application, and when the pressure at the node reaches a certain level, the circumferential yielding deformation occurs to dissipate the concentrated stress at the node, but with the further development of the convergence deformation of the surrounding rock, the pressure of the surrounding rock against the whole steel arch 10 will continuously increase, and the local yielding of the first buffering pad 20 cannot coordinate the deformation of the whole, which is easy to cause the overall buckling of the steel arch 10 along the haunch or the crown part. For this purpose, the second buffering pad 30 is arranged on the back of the steel arch 10 close to the surrounding rock and is continuously arranged along the circumference of the steel arch 10, so that it can uniformly absorb the distributed radial pressure from the surrounding rock.

[0059] Through the above arrangement, the first buffering pad 20 and the second buffering pad 30 cooperatively yield in stages in the process of bearing pressure: the first buffering pad 20 yields and deforms in response to the high concentrated stress in the initial stage of force to protect the connection, and with the further convergence of the surrounding rock, the overall pressure increases, and the second buffering pad 30 further yields and deforms, and the continuous circumferential yielding realizes the stable release of the energy of the surrounding rock. Thus, the steel arch 10 can realize the staged energy absorption from local yielding to overall yielding in the process of bearing force, and effectively improves the overall stability and adaptability of the supporting structure.

[0060] In an exemplary embodiment, the yield strength of the second buffering pad 30 is less than or equal to the yield strength of the first buffering pad 20.

[0061] According to the embodiment of the present application, the yielding triggering time and the mechanical behavior of the first buffering pad 20 and the second buffering pad 30 present the characteristics of staged cooperation due to the different positions and stress states. Assuming that the steel arch 10 is circular, the steel arch 10 is uniformly pressed p, the width of the arch is b, and the equivalent radius of the center line is R, and thus the stress of the connection of the steel arch segment 11 is σ L :

[0062] σ L =p • b • R / A S

[0063] In the formula, σ L is the stress borne by the first buffering pad 20 at the connection; A S is the cross-sectional area of the H-shaped, I-shaped steel and the like.

[0064] Since the cross-sectional area of the steel is relatively small, the stress σ LGenerally, p is two orders of magnitude greater than the inherent stress difference between the first cushion 20 and the second cushion 30. Therefore, the first cushion 20 yields to compression first, and the second cushion 30 yields to compression to trigger stress to further release the deformation energy of the surrounding rock when the load on the steel arch support is further increased.

[0065] Through the above setting mode, the initial high stress can be limited to the node, and the large displacement in the later stage can be dispersed to the whole circumference, so that the bearing-deformation process of the arch support is changed from sudden change to gradual change, the peak stress and secondary stress concentration are significantly reduced, buckling instability is inhibited, and the deformation coordination and long-term stability of the support are improved.

[0066] In an illustrative embodiment, the thickness of the second cushion 30 is greater than the thickness of the first cushion 20.

[0067] According to the embodiment of the present application, because the thickness of the first cushion 20 is small, the controllable yielding displacement is mainly provided; and because the thickness of the second cushion 30 arranged on the back of the steel arch support is large, the yielding amount of the second cushion 30 contributes greatly to the total yielding amount. Through the two-stage yielding effect, the bearing capacity of the steel arch support 10 changes smoothly, and a phased and coordinated yielding system is formed.

[0068] In an illustrative embodiment, the steel arch support segment 11 is provided with a connecting plate 12 at both ends, the area of the connecting plate 12 is greater than the cross-sectional area of the steel arch support segment along the circumferential direction of the steel arch support, and the first cushion 20 is arranged between the connecting plates 12 of the adjacent two steel arch support segments, so that the first cushion 20 forms a stable compression interface between the adjacent steel arch support segments 11.

[0069] According to the embodiment of the present application, the connecting plates 12 of the adjacent two steel arch support segments 11 can be fixedly connected in a pin shaft connection, welding or hoop type connection manner. The above manners can achieve effective force transmission through interface compression or fitting, so as to ensure stable deformation of the first cushion 20 under compression.

[0070] As shown in Figure 3 the adjacent steel arch support segments 11 are fixedly connected through the threaded holes 121 on the connecting plates 12 by bolts 13; and the first cushion 20 is provided with perforations corresponding to the threaded holes 121 on the connecting plates 12. The initial pretightening force of the bolt 13 is set to keep the first cushion 20 in the elastic deformation stage, and to keep the integrity and stability of the arch support 10 during installation and in the initial stage of surrounding rock deformation.

[0071] Through the above setting mode, in the installation stage, the first buffer pad 20 is in the elastic deformation stage by controlling the initial pre-tightening force of the bolt 13, avoiding the buffer pad yielding in advance in the process. When the external stress borne by the steel arch node is further increased to exceed the yield strength of the buffer pad, the buffer pad enters the yield compression stage, thereby realizing controllable yielding triggering and energy absorption, and ensuring that the node connection remains stable and continuous deformation ability in the whole stress process.

[0072] In an illustrative embodiment, the first buffer pad 20 is a polyurethane foam plate, and the second buffer pad 30 is a polyethylene closed-cell foam plate.

[0073] Through the above setting mode, since the yield strength of the polyurethane foam plate is high, it can bear larger concentrated load in the early stage, and can provide higher yield strength at the node position. The yield strength of the second buffer pad 30 is low (good flexibility), and provides a full-ring continuous, flexible and waterproof radial yielding layer at the back of the steel arch. In this way, the overall staged yielding and uniform energy absorption can be realized, and the durability and construction adaptability of the supporting system are improved.

[0074] Another aspect of the present application also provides a supporting device design method for designing the above supporting device.

[0075] Figure 4 is a flowchart of the supporting device design method of an illustrative embodiment of the present application; Figure 5 is a schematic diagram of the yielding amount of the second buffer pad of an illustrative embodiment of the present application. Wherein, T2 is the thickness of the second buffer pad under no pressure, T2' is the thickness of the second buffer pad after yielding deformation, and Δu2 is the yielding amount of the second buffer part in the case of arranging one layer of second buffer pad in the radial direction of the second buffer part.

[0076] As shown in Figure 4 and Figure 5 , the supporting device design method according to the embodiment of the present application includes operations S110-S130.

[0077] In operation S110, the reserved deformation amount of the target tunnel where the supporting device is installed is determined.

[0078] In operation S120, the design deformation threshold of the steel arch is determined based on the geometric parameters and material parameters of the steel arch.

[0079] According to the embodiment of the present application, in the process of determining the thickness of the first buffer pad 20 and the second buffer pad 30, it is necessary to consider that the steel arch 10 itself structure can also bear a certain incremental deformation, but it should be controlled within the range of elastic safety state. Assuming that the yield strength of the steel arch material is σ S , the incremental deformation that the steel arch structure itself can bear is:

[0080] Δu3= σ S • R / E

[0081] wherein Δu3 is a design deformation threshold of the steel arch structure itself; σ S is a yield strength of the arch material, E is an elastic modulus of the material, and R is an equivalent radius of the center line of the arch.

[0082] In operation S130, a total design compression amount is determined based on the design deformation threshold and the reserved deformation amount, and thicknesses of the first and second buffer pads 20 and 30 are determined based on the total design compression amount.

[0083] According to embodiments of the present application, the total design compression amount of the first and second buffer portions is related to the design deformation threshold of the steel arch structure itself and the reserved deformation amount of the tunnel as follows:

[0084] Δu1+Δu2+Δu3≈ u y

[0085] wherein Δu1 and Δu2 are compression amounts of the first and second buffer portions, respectively, and Δu2 can be directly equal to a compression amount of the second buffer pad 30 in the case that only one layer of the second buffer pad 30 is arranged in the radial direction of the second buffer portion, and u y is the reserved deformation amount.

[0086] In an illustrative embodiment, operation S110 includes determining the reserved deformation amount according to monitored values of the deformation of the surrounding rock after initial support of a tunnel section similar to the target tunnel, or determining the reserved deformation amount of the target tunnel according to numerical simulation results.

[0087] According to embodiments of the present application, a tunnel section similar to the target tunnel in terms of geological conditions, depth of burial, and support structure form can be monitored in the field to obtain a radial convergence deformation curve of the surrounding rock after initial support. Further in combination with the category of the surrounding rock and the level of in-situ stress, the maximum convergence amount of the surrounding rock before stabilization in this section is determined, and an average value or a corrected value thereof is taken as the reserved deformation amount of the target tunnel.

[0088] According to embodiments of the present application, finite element analysis of the target tunnel can be performed by using open-source or commercial numerical simulation software to obtain a convergence deformation curve of the surrounding rock, and the convergence displacement of the surrounding rock before stabilization obtained by numerical calculation is taken as the reserved deformation amount of the target tunnel.

[0089] In an illustrative embodiment, operation S130 includes:

[0090] The thickness of the second buffer pad 30 is determined preferentially according to the total design compression amount and the design compression performance of the second buffer pad 30.

[0091] In the case that the yielding amount of the second buffer pad 30 does not satisfy the design total yielding amount, the thickness of the first buffer pad 20 is determined according to the number of the first buffer pad 20 and the design compression performance, so that the yielding amount of the first buffer pad 20 and the second buffer pad 30 satisfies the requirement of the design total yielding amount.

[0092] The design compression performance includes the volume compression rate of the buffer pad in the plastic deformation stage.

[0093] According to the embodiment of the present application, since the yielding mode of the second buffer pad 30 is radial yielding, which contributes more directly to the total yielding amount, the thickness of the second buffer pad 30 is determined preferentially, so that the second buffer pad 30 can satisfy the requirement of the design total yielding amount as much as possible. In the case that there is only one second buffer pad 30 in the second buffer part, the yielding amount Δu2 of the second buffer part is:

[0094] Δu2=T2• ε z2

[0095] T2 is the thickness of the second buffer pad 30, and ε z2 is the volume compression rate of the second buffer pad 30 in the plastic deformation stage.

[0096] However, T2 cannot be increased indefinitely, and is limited by the diameter of the tunnel and the arrangement space between the steel arch and the surrounding rock. The second buffer pad 30 has a maximum preset thickness T 2,max .

[0097] If the requirement of the design total yielding amount can be satisfied in the case that T2≤ T 2,max , the first buffer pad 20 only needs to have a minimum preset thickness T 1,min , which is used to ensure the stability of the pressure at the segment connection and the initial stress release;

[0098] If T2 reaches T 2,max , the requirement of the design total yielding amount still cannot be satisfied, and the remaining yielding amount is supplemented by increasing the thickness T1 of the first buffer pad 20. In the case that the steel arch 10 is a circular arch, the total yielding amount Δu1 of the first buffer part is:

[0099] Δu1=n • T1• ε z1 / (2π)

[0100] T1 is the thickness of the first buffer pad 20, and ε z1 is the volume compression rate of the first buffer pad 20 in the plastic deformation stage.

[0101] In an illustrative embodiment, in the case that the steel arch segment 11 is provided with a connecting plate 12 and connected by a bolt 13, the supporting device design method further comprises:

[0102] The initial pre-tightening force of the bolt 13 is determined based on the yield strength of the first buffer pad 20 and the net contact area of the connecting plate 12, so that the first buffer pad 20 is in the elastic deformation stage, and the arch support 10 remains integrity and stability during the initial deformation of the surrounding rock.

[0103] The net contact area of the connecting plate 12 is the difference between the area of the connecting plate 12 and the area of the threaded hole 121 on the connecting plate.

[0104] According to the embodiment of the present application, the initial pre-tightening force of the bolt should meet the initial installation and fixation of the arch support connecting plate, ensure the integrity and stability of the connecting plate during the initial deformation of the surrounding rock, and prevent the connecting plate from slipping or loosening, while keeping the buffer layer in an elastic state, and participating in pressure relief after the stress of the buffer layer increases to a certain extent. After the foam board buffer layer is fully compacted, the bolt is further tightened. According to the above principle, the initial pre-tightening force of the bolt can be set at 80% of the yield stress of the buffer layer:

[0105] F p = 0.8σ z1 • A contact

[0106] F p is the initial pre-tightening force of the bolt; σ z1 is the yield strength of the first buffer pad 20; A contact is the net contact area of the node connecting plate.

[0107] Figure 6 is a schematic diagram of the pressure and pressure relief amount of a supporting device according to an exemplary embodiment of the present application.

[0108] As Figure 6 shown, the curve presents a double pressure relief platform shape, when the first buffer part starts to pressure relief, the bearing capacity enters the platform period; after the first stage of pressure relief, the second buffer part continues to work, and the bearing capacity rises again and maintains at a new stable platform; this stepwise bearing characteristic is more convenient for on-site control and monitoring, avoiding the disastrous consequences of single-point sudden failure, so that the supporting system can provide relatively stable and reliable supporting resistance during the entire deformation process, greatly enhancing the ductility and safety redundancy of the steel arch support.

[0109] To further illustrate how to design the supporting device through the above supporting device design method, the following specific embodiments are given:

[0110] Embodiment 1

[0111] In this example, the tunnel cross-sectional type is circular, the excavation radius is 9.8m, and other projects can be adjusted according to actual conditions.

[0112] The lithology of the tunnel section is argillaceous sandstone interbedded with carbonaceous mudstone, the steel arch is made of H150 steel, the measuring points are arranged on the steel arch after the initial support, the average deformation monitoring value of the measuring points is 11.5 cm, the steel arch of some tunnel sections is yielded, twisted or even broken, and the surrounding rock deformation invades the limit. Therefore, the tunnel section is treated by replacing the arch, and the supporting device and supporting design method are used during the replacement of the arch, the pressure borne by the supporting device and the pressure release amount are as shown in Figure 6 .

[0113] (1) Determine the reserved deformation of the tunnel: according to the initial support deformation monitoring value before the replacement of the arch, the reserved deformation u y = 11.5 cm is determined.

[0114] (2) The design deformation threshold Δu3 of the steel arch structure itself is determined according to the steel arch material and radius, the steel arch is made of Q235 steel, the arch radius R = 980 cm / 2 - 15 cm / 2 = 482.5 cm, and the elastic modulus of the steel is 200 GPa.

[0115] Calculate Δu3= σ S • R / E = 235 MPa • 482.5 cm / 200000 MPa = 0.57 cm.

[0116] (3) Determine the thickness of the first buffer pad 20 and the second buffer pad 30: the second buffer pad 30 is made of low-density (90 kg / m³), low-strength (0.4 MPa) polyethylene closed-cell foam board, the volume compression rate is 65%, the thickness of the second buffer pad 30 is 14 cm, and the radial pressure release amount is: Δu2= T2• ε z2 = 14 cm • 65% = 9.1 cm.

[0117] The total pressure release amount required to be supplemented by each first buffer pad 20 in the first buffer part is: Δu1≈ u y - Δu2- Δu3≈ 1.83 cm.

[0118] The steel arch is divided into 10 sections for assembly, the first buffer pad 20 is made of high-density (100 kg / m³), high-yield stress (2.0 MPa) polyurethane foam board, the volume compression rate is 55%, the thickness of the first buffer pad 20 is T1= 2π•Δu1 / (n • ε z1 )≈2.09 cm, therefore, T1= 2 cm is taken.

[0119] (4) The connecting plate is connected by 4 bolts, and the initial pre-tightening force of the bolts is determined: F p = 0.8σ z1 • A contact , the yield stress of the buffer layer is σ z1 = 2.0 MPa, and the net contact area is 0.035 m2 Solving the bolt pre-tightening force is 56kN, and the single bolt pre-tightening force is 14kN.

[0120] (5) Two-stage collaborative yielding process: before the steel arch support, the initial deformation of the surrounding rock of the tunnel exists, and the initial deformation is u0; after the double-yielding steel arch support, the contact pressure between the arch and the surrounding rock gradually rises to P1=0.011MPa, and σ L =P1• b •R / A S It is calculated that the first buffer pad 20 has reached its yield strength (σ L =σ z1 =2MPa) and starts to yield, and the total yielding displacement of the first buffer part is 1.75cm, which releases the high pressure stress concentrated at the connecting plate. After the first buffer pad is compacted, the contact pressure between the arch and the surrounding rock is further increased to P2=0.4MPa, and the second buffer pad reaches its yield strength of 0.4MPa, further yielding to release the deformation energy of the surrounding rock, and the yielding displacement is 9.1cm (at this time, the stress of the first buffer pad reaches σ L =P1• b • R / A S =73MPa). After the yielding of the two buffer parts is completed, the rigidity of the arch structure is completely excited, and further bears the pressure of the surrounding rock, and reaches a balanced state of the supporting resistance and the pressure of the surrounding rock.

[0121] Under the action of high surrounding rock pressure before the arch replacement of the tunnel section, part of the arches of the tunnel section are twisted, fractured, deformed and intruded, and after the supporting device provided by the application is used, the steel arches do not appear the phenomenon of yielding and twisting, and the construction quality and structural safety are effectively guaranteed.

[0122] As can be seen from the above, the supporting device and the supporting device design method provided by the application have at least the following beneficial effects:

[0123] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, but not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application.

Claims

1. A support device, characterized in that, The steel arch frame comprises: a steel arch frame comprising a plurality of steel arch frame segments, each of the steel arch frame segments being sequentially assembled to form an arch frame body; a first buffer portion comprising a plurality of first buffer pads arranged at the connection between two adjacent steel arch frame segments; wherein the first buffer pads generate circumferential yielding deformation when the pressure exceeds the yield strength of the first buffer pads; a second buffer portion comprising at least one second buffer pad arranged between the back surface of the steel arch frame close to the surrounding rock and the surrounding rock, and continuously arranged along the circumference of the steel arch frame and substantially covering the back surface of the steel arch frame; the second buffer pad generates radial yielding deformation when the pressure exceeds the yield strength of the second buffer pad; wherein the second buffer portion is adapted to withstand the radial distributed pressure from the surrounding rock to smoothly release the energy of the surrounding rock; wherein, in the case of pressure bearing of the steel arch frame, the first buffer pad is configured to yield stress yielding first, and when the load borne by the steel arch frame further increases, the second buffer pad reaches the yielding trigger stress to further release the deformation energy of the surrounding rock, so as to realize graded yielding.

2. The support device of claim 1, wherein The yield strength of the second buffer pad is less than or equal to the yield strength of the first buffer pad.

3. The support device of claim 2, wherein The thickness of the second buffer pad is greater than the thickness of the first buffer pad.

4. The support device of claim 1, wherein The two ends of the steel arch frame segment are provided with a connecting plate, and the area of the connecting plate is greater than the cross-sectional area of the steel arch frame segment along the circumference of the steel arch frame, so that the first buffer pad forms a stable pressure interface between adjacent steel arch frame segments.

5. The support device of claim 4, wherein The adjacent steel arch frame segments are fixedly connected through threaded holes on the connecting plate by bolts; the first buffer pad is provided with a perforation corresponding to the threaded hole on the connecting plate; wherein, the initial pre-tightening force of the bolt is set to keep the first buffer pad in the elastic deformation stage.

6. The support device of claim 1, wherein The first buffer pad is a polyurethane foam plate, and the second buffer pad is a polyethylene closed-cell foam plate.

7. A method for designing a support device according to any one of claims 1-6, characterized in that The steel arch frame comprises: determining the reserved deformation amount of the target tunnel where the supporting device is installed; determining the design deformation threshold of the steel arch frame based on the geometric parameters and material parameters of the steel arch frame; determining the total amount of design yielding based on the design deformation threshold and the reserved deformation amount, and determining the thickness of the first buffer pad and the second buffer pad based on the total amount of design yielding.

8. The method of designing according to claim 7, wherein, The determination of the reserved deformation amount of the target tunnel where the supporting device is installed comprises: determining the reserved deformation amount according to the surrounding rock deformation monitoring value after the initial support of the tunnel section near the target tunnel; or determining the reserved deformation amount of the target tunnel according to the numerical simulation result.

9. The method of claim 7, wherein, The determination of the thickness of the first buffer pad and the second buffer pad based on the total amount of design yielding comprises: preferentially determining the thickness of the second buffer pad according to the total amount of design yielding and the design compression performance of the second buffer pad; in the case that the yielding amount of the second buffer pad does not meet the total amount of design yielding, determining the thickness of the first buffer pad according to the number and design compression performance of the first buffer pad, so that the yielding amount of the first buffer pad and the second buffer pad meets the requirement of the total amount of design yielding; wherein, the design compression performance includes the volume compression rate of the buffer pad in the plastic deformation stage.

10. The method of claim 7, wherein, In the case that the steel arch segment is provided with a connecting plate and connected by bolts, the method further comprises: determining the initial pre-tightening force of the bolts based on the yield strength of the first buffer pad and the net contact area of the connecting plate, so that the first buffer pad is in the elastic deformation stage; wherein the net contact area of the connecting plate is the difference between the area of the connecting plate and the area of the threaded hole on the connecting plate.

Images