A variable stiffness high bearing capacity sprayed concrete-steel frame support structure and construction method thereof

Abstract

A variable stiffness high-bearing capacity sprayed concrete-steel frame support structure and its construction method are used to dynamically adjust the spatial position distribution of steel sections and constrain the deformation of sprayed concrete, so as to achieve the stiffness requirements of the support structure to control tunnel deformation. The steel section components include female plug T-steels and male plug T-steels with plug-in connection structures. In the early stage of tunnel construction, the female plug T-steels and the sprayed concrete layer installed at intervals along the extension direction of the tunnel constitute a support structure system with the first stiffness level. According to the longitudinal spatial deformation of the tunnel, the male plug T-steels are installed in a targeted manner in the sections with larger deformations, and they are combined with the corresponding female plug T-steels to form a quasi-I-shaped steel section, and the female plug T-steels and the quasi-I-shaped steel section, or the quasi-I-shaped steel section and the sprayed concrete layer constitute a support structure system with the second stiffness level, or a constraint panel is set outside the male plug T-steels of adjacent quasi-I-shaped steel sections to connect the two into one, and the quasi-I-shaped steel section, the constraint panel and the sprayed concrete layer constitute a support structure system with the third stiffness level.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnels and underground engineering, and relates to a variable-rigidity high-bearing-capacity sprayed concrete-steel frame supporting structure and a construction method thereof. Background Art

[0002] In my country's tunnel construction, the initial support is generally composed of steel skeletons (steel or grid steel frames) and shotcrete. It is an important support structure that directly bears the surrounding rock load and ensures the safety of tunnel construction. Especially in railway and highway tunnels, the initial support bears most of the surrounding rock load, and the secondary lining is only used as a safety reserve. However, due to my country's complex geological conditions and construction technology level, the initial support still has problems such as cracking, falling blocks, and severe deformation during construction, affecting the progress and safety of tunnel construction.

[0003] Through research, it is shown that, taking the steel frame as an example, after the initial support construction is completed, the steel has a large stiffness relative to the sprayed concrete, and bears a large amount of load in the initial stage. The steel flange and web undergo a complex stress change process, especially in areas with high rock pressure such as high ground stress. The stress of the steel web and its intersection with the flange is relatively large. If the nearby sprayed concrete is not close to the steel, then this point is very likely to become the breakthrough point of the steel damage, thereby causing continuous damage to the structure. However, due to the obstruction of the steel flange on the clearance side, the sprayed concrete often cannot fill the internal corners of the steel flange tightly, thus causing the loss of the bearing capacity of the support structure. In addition, concrete has good compressive properties. If the three-way confining pressure of concrete is increased, the structural bearing capacity will be further improved. However, since the clearance side of the sprayed concrete is unconstrained, compared with the three-way constraint, the bearing capacity of the sprayed concrete cannot be further exerted.

[0004] In the current tunnel design, support parameters such as steel skeleton spacing are still mainly designed based on experience. However, due to the complex geological conditions of the tunnel, it is inevitable that the empirical design does not match the actual geological conditions during construction. Specifically, the initial support is severely deformed, and the surrounding rock can only be reinforced by grouting at this time, and the initial support still needs to be replaced, which seriously affects the normal construction progress of the tunnel and causes huge economic losses. On the contrary, in order to control the deformation of the surrounding rock, the support structure is prone to have excessive stiffness, which also causes a certain degree of waste.

[0005] In summary, in the initial support structure system based on shotcrete-steel frame, the ultimate bearing capacity of the support structure cannot be fully utilized due to the limitations of the steel skeleton's own structural form and the lack of constraint boundaries of shotcrete. At the same time, the design parameters of the support structure are mostly determined by experience and cannot be dynamically adjusted once constructed. Therefore, it cannot adapt to the stability of the support structure under complex geological conditions, especially in areas with large deformation risks, which can easily lead to an increase in the economic cost of the project. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a variable stiffness and high-bearing capacity sprayed concrete-steel frame support structure, which can dynamically adjust the spatial position distribution of steel sections and constrain the deformation of sprayed concrete, thereby achieving the stiffness requirements of the support structure for controlling tunnel deformation and solving the technical problem of loss of bearing capacity of the support structure due to the loose spraying caused by the limitation of traditional steel frame forms. The invention also has convenient and quick construction, good deformation control and economy.

[0007] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0008] The invention discloses a variable stiffness high-bearing capacity sprayed concrete-steel frame supporting structure, comprising a sprayed concrete layer and a steel member, wherein the sprayed concrete layer comprises a primary sprayed concrete layer and a secondary sprayed concrete layer, wherein the primary sprayed concrete layer covers the surrounding rock, and the steel member is arranged on the surface of the primary sprayed concrete layer at intervals along the extension direction of the tunnel, and the secondary sprayed concrete layer covers the steel member, wherein the steel member comprises a female plug-in T-shaped steel, a male plug-in T-shaped steel and a restraining panel, and the female plug-in T-shaped steel and the male plug-in T-shaped steel have a plug-in connection structure with each other; in the initial stage of tunnel construction, the female plug-in T-shaped steel and the sprayed concrete layer arranged at intervals along the extension direction of the tunnel form a first stiffness A horizontal support structure system; according to the longitudinal spatial deformation of the tunnel, male T-steels are installed in sections with larger deformation, which are combined with corresponding female T-steels to form I-shaped steels, and the female T-steels and I-shaped steels, or the I-shaped steels and the shotcrete layer form a support structure system with the second level of stiffness; or a constraint panel is arranged outside the male T-steels of adjacent I-shaped steels to connect the two into one, and the I-shaped steels, the constraint panel and the shotcrete layer form a support structure system with the third level of stiffness; the male T-steels and the constraint panel are locally installed at the parts of the tunnel with larger deformation.

[0009] Another technical problem to be solved by the present invention is to provide a construction method for the above-mentioned variable stiffness high bearing capacity sprayed concrete-steel frame support structure. The construction method comprises the following steps:

[0010] Step 1: The initial sprayed concrete layer covers the surrounding rock to form a flat surface, and female T-shaped steel is installed along the longitudinal direction of the tunnel with a spacing of 0.4m / frame.

[0011] Step 2: spray the first composite sprayed concrete layer to the height of the mother insert web, at which point a support structure system with the first stiffness level is formed;

[0012] Step 3: Conduct deformation monitoring regression analysis on the tunnel. If the deformation rate exceeds 5mm / d, install male T-shaped steel in the section with larger deformation to form a steel frame layout of "1 frame of I-shaped steel + 2 frames of female T-shaped steel + 1 frame of I-shaped steel", that is, the spacing between I-shaped steel is 1.2m / frame, and a support structure system with the second-level stiffness is formed;

[0013] Step 4: Continue to conduct deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5mm / d, continue to install male T-shaped steel in the section where the deformation is still large. Among the remaining 2 female T-shaped steels without male T-shaped steels, select one to install male T-shaped steel, forming a steel frame layout of "2 I-shaped steels + 1 female T-shaped steel + 2 I-shaped steels", that is, the spacing of a group of 2 I-shaped steels is 0.8m / frame. At this time, the stiffness of the support structure is one level higher than the stiffness level of the Ⅱa, that is, the support structure system of the Ⅱb stiffness level;

[0014] Step 5: Continue to conduct deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5mm / d, continue to install male T-shaped steel in the section where the deformation is still large, forming a layout of I-shaped steel with a spacing of 0.4m / frame. At this time, the stiffness of the support structure is one level higher than the stiffness level of the Ⅱb, that is, the support structure system of the Ⅱc stiffness level;

[0015] Step 6: Continue to conduct deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5mm / d, install the restraint panel in the section where the deformation is still large. At this time, first fill the area where the restraint panel needs to be installed with the second composite sprayed concrete layer to the height of the male plug flange, then install the restraint panel and weld both sides to the male plug flange of the I-shaped steel to limit the deformation of the sprayed concrete between the steels. At this time, a support structure system with the third stiffness level is formed;

[0016] Step 7: After forming a new stage of the support structure system with a stiffness level, if the monitored tunnel deformation rate does not exceed 3mm / d, spray the third re-sprayed concrete layer to cover the female T-steel, male T-steel or restraint panel, and then carry out the waterproof layer construction after the re-spraying is completed.

[0017] The beneficial effects of the present invention are mainly reflected in the following aspects:

[0018] 1. Effectively improve the bearing capacity of the support structure system. On the one hand, by improving the form of I-beams, the technical problem of loose concrete spraying in the corners of the steel sections due to the obstruction of the flange plate during spraying concrete is avoided, thereby reducing the probability of the steel sections yielding and even breaking due to local de-airing under the action of external high stress, thereby improving the bearing performance of the support structure; on the other hand, by constructing new "I"-shaped steel sections and restraint panels, the steel section skeleton is densified, the role of restrained concrete is fully utilized, and the overall bearing capacity of the support structure is improved;

[0019] Second, a stiffness adaptive structural system has been formed to improve the construction flexibility of the support structure. By monitoring the deformation in the tunnel, targeted and phased construction of structural steel or constraint panels is carried out to achieve dynamic adjustment of the stiffness of the support structure as the construction situation changes. At the same time, when the deformation of the tunnel is unknown, it avoids the slowdown of excavation progress caused by the one-time installation of a large number of structural steels, or the inability to reinforce the structure later due to insufficient installation of structural steels. In addition, local installation can be carried out on the parts with larger deformation, which greatly improves the flexibility of the structure.

[0020] 3. Convenient and economical construction. According to the tunnel deformation monitoring data, the overall structure or local parts can be reinforced, and the stiffness of the support structure can be dynamically adjusted to achieve a balance between the deformation control requirements and the stiffness and bearing capacity of the support structure, avoiding the problem of poor economy caused by excessive or insufficient bearing capacity of the support structure, reducing material input, and having the characteristics of being green and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] This specification includes the following twelve drawings:

[0022] Figure 1 It is a longitudinal section of a variable stiffness high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0023] Figure 2 It is a cross-sectional view of a female T-shaped steel in a variable-rigidity high-bearing-capacity sprayed concrete-steel frame support structure of the present invention;

[0024] Figure 3 It is a partial enlarged view of the female insert web of the female insert T-shaped steel in a variable stiffness and high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0025] Figure 4 It is a longitudinal section of a female T-shaped steel in a variable stiffness and high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0026] Figure 5 It is a cross-sectional view of a male T-shaped steel in a variable-rigidity high-bearing-capacity sprayed concrete-steel frame support structure of the present invention;

[0027] Figure 6 It is a partial enlarged view of the male web of the male T-shaped steel in a variable stiffness and high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0028] Figure 7 It is a longitudinal section of a male T-shaped steel in a variable stiffness and high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0029] Figure 8 It is a schematic longitudinal section diagram of a support structure system of the first level of stiffness in a variable stiffness high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0030] Fig. 9 It is a schematic longitudinal section diagram of a support structure system of the second a stiffness level in a variable stiffness high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0031] Fig.10 It is a schematic longitudinal section diagram of a support structure system of the second b stiffness level in a variable stiffness high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0032] Fig.11 It is a schematic longitudinal section diagram of a support structure system of the Ⅱcth stiffness level in a variable stiffness high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0033] Fig.12 It is a schematic longitudinal section diagram of a support structure system of the third level of stiffness in a variable stiffness high bearing capacity sprayed concrete-steel frame support structure of the present invention;

[0034] The figure shows the names of the main components and the corresponding marks: surrounding rock 10, primary shotcrete layer 21, first re-shotcrete layer 22, second re-shotcrete layer 23, third re-shotcrete layer 24, female T-shaped steel 30, female flange 31, female web 32, groove 33, sealing strip 34, male T-shaped steel 40, male flange 41, male web 42, protrusion 43, constraint panel 50, tunnel clearance side A, tunnel surrounding rock side B, tunnel excavation direction C. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings.

[0036] Reference Figure 1 The invention discloses a variable stiffness high bearing capacity sprayed concrete-steel frame support structure, comprising a sprayed concrete layer and a steel member, wherein the sprayed concrete layer comprises a primary sprayed concrete layer 21 and a secondary sprayed concrete layer, wherein the primary sprayed concrete layer 21 covers the surrounding rock 10, and the steel member is arranged on the surface of the primary sprayed concrete layer 21 at intervals along the tunnel extension direction, and the secondary sprayed concrete layer covers the steel member. Figure 2 , Figure 5 and Fig.12 The steel structure includes a female T-shaped steel 30, a male T-shaped steel 40 and a restraining panel 50, and the female T-shaped steel 30 and the male T-shaped steel 40 have a plug-in connection structure. Figure 8 In the early stage of tunnel construction, the mother plug T-shaped steel 30 installed at intervals along the tunnel extension direction and the sprayed concrete layer constitute the support structure system with the first stiffness level. Figures 9 to 11 According to the longitudinal spatial deformation of the tunnel, male T-shaped steel 40 is installed in the larger deformation section, which is combined with the corresponding female T-shaped steel 3 to form a quasi-I-shaped steel. The female T-shaped steel 30, the quasi-I-shaped steel and the sprayed concrete layer form a support structure system with the second stiffness level. Fig.12, or a restraint panel 50 is arranged outside the male T-steel 40 of the adjacent I-shaped steel to connect the two into one, and the I-shaped steel, the restraint panel 50 and the shotcrete layer constitute a support structure system with the third stiffness level; the male T-steel 40 and the restraint panel 50 are locally installed at the part where the tunnel deformation is larger, rather than being installed in the whole ring or arch wall range.

[0037] The female T-shaped steel 30 in the present invention does not have a flange plate located on the clear side A of the tunnel, which effectively avoids the problem of loose concrete spraying in the corners of the steel during spraying, and improves the bearing performance of the support structure; at the same time, by applying a new type of I-shaped steel and a constraint panel 50, the principle of constrained concrete is fully utilized to improve the overall ultimate bearing capacity of the support structure. At the same time, due to the early application of the female T-shaped steel 30, a space for targeted and phased collaborative reinforcement using the male T-shaped steel 40 and the constraint panel 50 is reserved, and the dynamic adjustment of the stiffness of the support structure with the construction situation is realized, which greatly improves the flexibility of the structure. In addition, the present invention can dynamically adjust the stiffness of the support structure to achieve a balance between the deformation control requirements and the stiffness and bearing capacity of the support structure, avoid the situation where the bearing capacity of the support structure is insufficient and causes a replacement project or a large number of strengthening measures are invested due to excessive bearing capacity, improve the economy of the support structure system, and reduce carbon emissions in tunnel construction to a certain extent.

[0038] In general, the present invention effectively improves the bearing capacity of the support structure system; forms a stiffness adaptive structural system, and improves the construction flexibility of the support structure; the construction is convenient and economical, and can improve the standardization and mechanization level of tunnel construction.

[0039] Reference Figures 2 to 7 The male T-shaped steel 40 has a male flange 41 and a male web 42 perpendicular to its plate surface, and the two side plates of the male web 42 have transverse outward protrusions 43.

[0040] The female T-shaped steel 30 has a female flange 31 and a pair of female webs 32 perpendicular to the plate surface. The inner plate surface of the pair of female webs 32 has a groove 33 formed by a transverse outward protrusion. The female web 32, the groove 33, the male web 42, and the protrusion 43 constitute the plug connection structure. The male flange 41, the male web 42, and the female web 32 are solid steel plates, and the female web 32 is a thin shell steel plate. The distance between the pair of female webs 32 is adapted to the thickness of the male web 42, and the depth and height of the groove 33 should not exceed 1 cm.

[0041] Reference Figure 8In the support structure system of the first stiffness level, the spacing of the female plug T-shaped steel 30 is 0.4m / frame, the female plug flange 31 plate surface is closely attached to the primary sprayed concrete layer 21, and a blocking strip 34 for closing its port is detachably provided at the outer end of the female plug web 32. The sprayed concrete layer includes a first re-sprayed concrete layer 22 sprayed from the primary sprayed concrete layer 21 to the outer end of the female plug flange 31.

[0042] The support structure system of the second level of stiffness is subdivided into the support structure system of the second level of stiffness, the support structure system of the second level of stiffness, and the support structure system of the second level of stiffness. Fig. 9 The support structure system of the second stiffness level is based on the support structure system of the first stiffness level. If the deformation rate of the tunnel exceeds 5mm / d, 40 male T-shaped steels are installed in the larger deformation section to form a steel frame layout of "1 frame of I-shaped steel + 2 frames of female T-shaped steel 30 + 1 frame of I-shaped steel", that is, the spacing between I-shaped steels is 1.2m / frame. Fig.10 The support structure system with the second b stiffness level is based on the support structure system with the second a stiffness level. If the tunnel deformation rate still exceeds 5 mm / d, one of the remaining two female T-shaped steels 30 without male T-shaped steels 40 installed is selected to install male T-shaped steel 40, forming a steel frame layout of "2 I-shaped steels + 1 female T-shaped steel 30 + 2 I-shaped steels", that is, the spacing between a group of 2 I-shaped steels is 0.8 m / frame. Fig.11 The support structure system with the IIc stiffness level is based on the support structure system with the IIb stiffness level. If the tunnel deformation rate still exceeds 5mm / d, the male T-shaped steel 40 will continue to be installed to form an I-shaped steel layout with a spacing of 0.4m / frame.

[0043] Reference Fig.12 The support structure system of the third stiffness level is based on the support structure system of the second c stiffness level. If the deformation rate of the tunnel still exceeds 5 mm / d, the male plug flanges 41 of the adjacent I-shaped steel are welded to form a constraint panel 50 that connects them into one body. The sprayed concrete layer includes a first sprayed concrete layer 22 to a second sprayed concrete layer 23 on the inner surface of the constraint panel 50 between the two adjacent male plug flanges 41. The constraint panel 50 is a solid steel plate, and its longitudinal dimension matches the spacing of the I-shaped steel. The dimension parameters are 0.4m along the longitudinal direction of the tunnel and 0.1m along the circumferential direction of the tunnel.

[0044] Reference Figures 8 to 12 The present invention provides a construction method for a variable stiffness high bearing capacity sprayed concrete-steel frame support structure, comprising the following steps:

[0045] Step 1: The primary sprayed concrete layer 21 covers the surrounding rock 10 to form a flat surface, and the female plug T-shaped steel 30 is installed along the longitudinal direction of the tunnel;

[0046] Step 2: spraying the first composite sprayed concrete layer 22 to the height of the mother insert web plate 32, at which time a support structure system with the first stiffness level is formed;

[0047] Step 3: Conduct deformation monitoring regression analysis on the tunnel. If the deformation rate exceeds 5 mm / d, install 40 male T-shaped steels in the larger deformation section to form a steel frame layout of "1 frame of I-shaped steel + 2 frames of female T-shaped steel 30 + 1 frame of I-shaped steel", that is, the spacing between I-shaped steels is 1.2 m / frame, and a support structure system with the second-level stiffness level is formed;

[0048] Step 4: Continue to conduct deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5mm / d, continue to install male T-shaped steel 40 in the section where the deformation is still large. Among the remaining 2 female T-shaped steels 30 without male T-shaped steel 40, select one to install male T-shaped steel 40, forming a steel frame layout of "2 I-shaped steels + 1 female T-shaped steel 30 + 2 I-shaped steels", that is, the spacing between a group of 2 I-shaped steels is 0.8m / frame. At this time, the stiffness of the support structure is one level higher than the stiffness level of the Ⅱa, that is, the support structure system of the Ⅱb stiffness level;

[0049] Step 5: Continue to conduct deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5 mm / d, continue to install male T-shaped steel 40 in the section where the deformation is still large, forming a layout of I-shaped steel with a spacing of 0.4 m / frame. At this time, the stiffness of the support structure is one level higher than the stiffness level of the Ⅱb, that is, the support structure system of the stiffness level of the Ⅱc;

[0050] Step 6: Continue to perform deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5 mm / d, install the constraint panel 50 in the section where the deformation is still large. At this time, first fill the area where the constraint panel 50 needs to be installed with the second composite sprayed concrete layer 23 to the height of the male plug flange 41, then install the constraint panel 50 and weld both sides to the male plug flange 41 of the I-shaped steel to limit the deformation of the sprayed concrete between the steels. At this time, a support structure system with the third stiffness level is formed;

[0051] Step 7: After forming a support structure system with a new stage of stiffness level, if the monitored tunnel deformation rate does not exceed 3 mm / d, spray the third re-sprayed concrete layer 24 to cover the female T-shaped steel 30, the male T-shaped steel 40 or the restraining panel 50, and then carry out waterproofing layer construction after the re-spraying is completed.

[0052] After the construction is completed, the variable rigidity high bearing capacity sprayed concrete-steel frame support structure system is arranged in the following cross section: Figure 1 shown.

[0053] In the above step 2, the height error between the surface of the first composite sprayed concrete layer 22 and the female insert web 32 does not exceed ±5 mm. During spraying, the nozzle should not be aimed at the female insert web 32 to avoid covering the sealing strip 34 on the port of the female insert web 32.

[0054] In the above steps three to four, when installing the male T-shaped steel 40, first remove the sealing strip 34 in the port of the female insert web 32, clear the space of the female insert web 32, align the male T-shaped steel 40, and use the pushing device to squeeze the male insert web 42 into the groove cavity of the female insert web 32, so that the protrusions 43 and grooves 33 of the two are locked together to form a quasi-I-shaped steel assembly.

[0055] The above description is only to illustrate some principles of the variable stiffness high bearing capacity sprayed concrete-steel frame support structure and its construction method of the present invention, and is not intended to limit the present invention to the specific structure and applicable scope shown and described. Therefore, all corresponding modifications and equivalents that may be used are within the scope of the patent applied for by the present invention.

Claims

1. A variable stiffness high bearing capacity sprayed concrete-steel frame support structure, comprising a sprayed concrete layer and a steel member, the sprayed concrete layer comprising a primary sprayed concrete layer (21) and a secondary sprayed concrete layer, the primary sprayed concrete layer (21) covering the surrounding rock (10), the steel members being arranged at intervals on the surface of the primary sprayed concrete layer (21) along the tunnel extension direction, and the secondary sprayed concrete layer covering the steel members, wherein: The steel structure comprises a female T-shaped steel (30), a male T-shaped steel (40) and a restraining panel (50), wherein the female T-shaped steel (30) and the male T-shaped steel (40) are connected to each other by a plug-in connection structure; in the initial stage of tunnel construction, the female T-shaped steel (30) and the sprayed concrete layer arranged at intervals along the tunnel extension direction form a support structure system with a first stiffness level; According to the longitudinal spatial deformation of the tunnel, male T-shaped steel (40) is installed in a targeted manner in the section with larger deformation, and is combined with the corresponding female T-shaped steel (3) to form a quasi-I-shaped steel, and the female T-shaped steel (30), the quasi-I-shaped steel and the sprayed concrete layer form a support structure system with a second level of stiffness, or a constraint panel (50) is arranged outside the male T-shaped steel (40) of the adjacent quasi-I-shaped steel to connect the two into one, and the quasi-I-shaped steel, the constraint panel (50) and the sprayed concrete layer form a support structure system with a third level of stiffness; the male T-shaped steel (40) and the constraint panel (50) are locally installed in the part of the tunnel with larger deformation.

2. A variable stiffness high bearing capacity sprayed concrete-steel frame support structure as claimed in claim 1, characterized in that: The male T-shaped steel (40) comprises a male flange (41) and a male web (42) perpendicular to its plate surface, and the two side plate surfaces of the male web (42) are provided with transverse outward protrusions (43); the female T-shaped steel (30) comprises a female flange (31) and a pair of female webs (32) perpendicular to its plate surface, and the inner plate surfaces of the pair of female webs (32) are provided with grooves (33) formed by transverse outward protrusions; the female webs (32), the grooves (33) and the male webs (42) and the protrusions (43) constitute the plug-in connection structure.

3. A variable stiffness high bearing capacity sprayed concrete-steel frame support structure as claimed in claim 2, characterized in that: In the support structure system of the first stiffness level, the installation spacing of the female plug T-shaped steel (30) is 0.4 m / frame, the female plug flange (31) plate surface is closely attached to the primary sprayed concrete layer (21), and a sealing strip (34) for closing its port is detachably provided at the outer end of the female plug web (32); the sprayed concrete layer includes a first re-sprayed concrete layer (22) sprayed from the primary sprayed concrete layer (21) to the outer end of the female plug flange (31).

4. The variable stiffness high bearing capacity sprayed concrete-steel frame support structure as claimed in claim 2, characterized in that: The support structure system of the second stiffness level is subdivided into a support structure system of the second stiffness level, a support structure system of the second stiffness level, and a support structure system of the second stiffness level; The support structure system of the second stiffness level IIa is based on the support structure system of the first stiffness level. If the deformation speed of the tunnel exceeds 5 mm / d, male T-shaped steel (40) is installed in the section with larger deformation, forming a steel frame arrangement of "1 frame of I-shaped steel + 2 frames of female T-shaped steel (30) + 1 frame of I-shaped steel", that is, the spacing between I-shaped steels is 1.2 m / frame; the support structure system of the second stiffness level IIb is based on the support structure system of the second stiffness level IIa. If the deformation speed of the tunnel still exceeds 5 mm / d, male T-shaped steel (40) is installed in the remaining sections where male T-shaped steel is not installed. Among the two female T-shaped steels (30) of the steel (40), one is selected to install the male T-shaped steel (40), forming a steel frame arrangement of "two I-shaped steels + one female T-shaped steel (30) + two I-shaped steels", that is, the spacing between a group of two I-shaped steels is 0.8 m / frame; the support structure system of the second c stiffness level is based on the support structure system of the second b stiffness level, and if the deformation speed of the tunnel still exceeds 5 mm / d, the male T-shaped steel (40) is continued to be installed to form an arrangement of I-shaped steels with a spacing of 0.4 m / frame.

5. The variable stiffness high bearing capacity sprayed concrete-steel frame support structure as claimed in claim 4, characterized in that: The support structure system with the third stiffness level is based on the support structure system with the second stiffness level. If the deformation speed of the tunnel still exceeds 5 mm / d, the male plug flanges (41) of adjacent I-shaped steel sections are welded to form an integral restraining panel (50), and the sprayed concrete layer includes a second sprayed concrete layer (23) from the first sprayed concrete layer (22) to the inner surface of the restraining panel (50) between the two adjacent male plug flanges (41); the restraining panel (50) is a solid steel plate, and its longitudinal dimension matches the spacing of the I-shaped steel sections, and the dimension parameters are 0.4 m along the longitudinal direction of the tunnel and 0.1 m along the circumferential direction of the tunnel.

6. A variable stiffness high bearing capacity sprayed concrete-steel frame support structure as claimed in claim 3, 4 or 5, characterized in that: The sprayed concrete layer further comprises a third sprayed concrete layer (24), the third sprayed concrete layer (24) covering the female T-shaped steel (30), the male T-shaped steel (40) or the restraining panel (50), with a covering thickness of not less than 3 mm.

7. A construction method for a variable stiffness high bearing capacity sprayed concrete-steel frame support structure according to any one of claims 1 to 6, comprising the following steps: Step 1: The surrounding rock (10) is covered with a primary sprayed concrete layer (21) to form a flat surface, and female T-shaped steel (30) is installed along the longitudinal direction of the tunnel; Step 2: spraying the first composite sprayed concrete layer (22) to the height of the mother insert web plate (32), at which time a support structure system with the first stiffness level is formed; Step 3: Perform deformation monitoring regression analysis on the tunnel. If the deformation rate exceeds 5 mm / d, install male T-shaped steel (40) in the section with larger deformation, forming a steel frame layout of "1 frame of I-shaped steel + 2 frames of female T-shaped steel (30) + 1 frame of I-shaped steel", that is, the spacing between I-shaped steel is 1.2 m / frame, and a support structure system with the second a stiffness level is formed; Step 4: Continue to perform deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5 mm / d, continue to install male plug T-shaped steel (40) in the section where the deformation is still large. Among the remaining two female plug T-shaped steels (30) that have not been installed with male plug T-shaped steel (40), select one of them to install male plug T-shaped steel (40), forming a steel frame layout of "2 frames of I-shaped steel + 1 frame of female plug T-shaped steel (30) + 2 frames of I-shaped steel", that is, the spacing between a group of 2 frames of I-shaped steel is 0.8 m / frame. At this time, the stiffness of the support structure is one level higher than the stiffness level of the second a, that is, the support structure system of the second b stiffness level; Step 5: Continue to perform deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5 mm / d, continue to install male T-shaped steel (40) in the section where the deformation is still large, forming a layout of I-shaped steel with a spacing of 0.4 m / frame. At this time, the stiffness of the support structure is one level higher than the stiffness level of the Ⅱb, that is, the support structure system of the stiffness level of the Ⅱc; Step 6: Continue to perform deformation monitoring regression analysis on the tunnel. If the deformation rate still exceeds 5 mm / d, then install the restraining panel (50) in the section where the deformation is still large. At this time, first fill the area where the restraining panel (50) needs to be installed with the second composite sprayed concrete layer (23) to the height of the male plug flange (41), then install the restraining panel (50) and weld both sides to the male plug flange (41) of the I-shaped steel to limit the deformation of the sprayed concrete between the steels. At this time, a support structure system with the third stiffness level is formed; Step 7: After forming a support structure system with a new stage of stiffness level, if the monitored tunnel deformation rate does not exceed 3 mm / d, spray a third re-sprayed concrete layer (24) to cover the female T-shaped steel (30), the male T-shaped steel (40) or the restraining panel (50), and then carry out waterproofing construction after the re-spraying is completed.

8. The construction method of a variable stiffness high bearing capacity sprayed concrete-steel frame support structure as claimed in claim 7, characterized in that: The height error between the surface of the first composite sprayed concrete layer (22) and the female insert web (32) does not exceed ±5 mm, and the nozzle should not be aimed at the female insert web (32) during spraying to avoid covering the sealing strip (34) on the port of the female insert web (32).

9. The construction method of a variable stiffness high bearing capacity sprayed concrete-steel frame support structure as claimed in claim 7, characterized in that: When installing the male T-shaped steel (40), first remove the sealing strip (34) in the port of the female insert web (32), clear the space of the female insert web (32), align the male T-shaped steel (40), and use a pushing device to squeeze the male insert web (42) into the groove cavity of the female insert web (32) so that the protrusions (43) and the grooves (33) of the two are locked together to form a quasi-I-shaped steel assembly.

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