Supporting design and roof picking construction method of three-way junction of inclined shaft turning into vertical tunnel

Abstract

The present application relates to a kind of tunnel's inclined shaft turns normal hole three-way junction support design and its roof picking construction method, belong to the method technical field of tunneling design arrangement.This method is designed in advance three-way junction support structure uses double-spliced I-beam arch, the finite element calculation model of double-spliced I-beam arch and normal hole arch is established in finite element software, after judging three-way junction belongs to shallow or deep, the structural parameters of double-spliced I-beam arch are calculated, and the strength of double-spliced I-beam arch is calculated after being substituted into the finite element calculation model of double-spliced I-beam arch, whether double-spliced I-beam arch is reliable is judged, if not reliable, then using increase arch type or three-spliced arch is redesigned and calculated;If reliable, then tunnel roof picking construction is implemented.This method is designed in advance three-way junction support uses double-spliced I-beam arch and calculates its strength whether reliable before tunnel construction, on the basis of reliable, then tunnel roof picking construction is completed, so that the stability of three-way junction support structure is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to a construction method for supporting and roof picking at a three-way junction of a change from an inclined shaft to a main tunnel in tunnel excavation, and belongs to the technical field of methods for tunnel excavation design and arrangement. BACKGROUND

[0002] Long tunnels often need to add auxiliary tunnels such as inclined shafts to increase the working face and speed up the construction progress. Meanwhile, the inclined shafts can also serve as maintenance and transportation passages for the main tunnel. The three-way junction of the intersection between the inclined shaft and the main tunnel has a complex spatial structure and is prone to stress concentration. Therefore, the supporting structure at this position needs to be designed and constructed with emphasis. The existing design and construction methods mostly rely on existing experience, and the supporting structure form of bracket + arch is mostly used. This supporting structure form cannot fully utilize the natural arch effect of the surrounding rock, and has large excavation volume and many construction procedures. A short column needs to be welded between the bracket and the arch to effectively transfer the load on the bracket to the arch. However, the welding quality and perpendicularity cannot be guaranteed during on-site installation. Moreover, a large amount of concrete needs to be sprayed to fill the cavity between the bracket and the arch, which increases the load burden on the arch and is not conducive to the stability of the structure.

[0003] In addition, the initial support of the main tunnel is performed after the pilot tunnel is excavated to the side of the main tunnel, and the main tunnel is excavated from the large to the small mileage after the working face is formed. This process takes a long time, and the main tunnel cannot be supported in time, which poses a safety hazard to the tunnel roof picking construction. Therefore, it is necessary to specially design the supporting structure at the three-way junction and optimize the roof picking construction method at the three-way junction to reduce the exposure time of the main tunnel excavation and the safety risk of the roof picking construction procedure conversion, which has important practical significance for tunnel construction safety. SUMMARY

[0004] The technical problem to be solved by the present application is to stabilize the stress of the supporting structure at the three-way junction of the intersection between the inclined shaft and the main tunnel and optimize the roof picking construction process at the three-way junction.

[0005] The technical solution proposed by the present application to solve the above technical problem is a supporting design and roof picking construction method for a three-way junction of a change from an inclined shaft to a main tunnel, comprising the following steps:

[0006] Step 1: design the supporting structure of the three-way junction, and the specific design and calculation are as follows,

[0007] Step 1.1: preliminarily design the supporting structure of the three-way junction using a double-spliced I-steel arch, and establish a finite element calculation model of the double-spliced I-steel arch in the finite element software,

[0008] Step 1.2: the supporting structure of the main tunnel uses an arch to form a main tunnel arch, one side of the main tunnel arch is entirely arranged on the double-spliced I-steel arch, and the main tunnel arch is taken as a calculation unit according to the supporting interval. A finite element calculation model of the main tunnel arch is established in the finite element software;

[0009] Step 1.3.1 judging whether the three-forked intersection is shallow or deep buried

[0010] Step 1.3.1 judging whether the three-forked intersection is shallow or deep buried

[0011] The tunnel deep-shallow buried demarcation depth H is calculated according to the following formula (1) p

[0012] H p = 1.125 x 2 S-1 w (1)

[0013] In formula (1), S is the surrounding rock grade number; w is the width influence coefficient, which is calculated according to the following formula (2),

[0014] w = 1 + i (B - 5) (2)

[0015] In formula (2), B is the tunnel width (unit: m); i is the surrounding rock pressure increase and decrease rate, when B < 5m, i = 0.2, when B > 5m, i = 0.1;

[0016] When the tunnel buried depth h < Hp, it is judged as shallow buried, when the tunnel buried depth h ≥ Hp, it is judged as deep buried;

[0017] Step 1.3.2 The structure parameters of double-pasted I-shaped steel arch include the self-weight of supporting structure, surrounding rock vertical pressure q, surrounding rock horizontal pressure e and surrounding rock elastic resistance K, which are checked as follows;

[0018] A. When shallow buried

[0019] A1. The surrounding rock vertical pressure q is calculated according to the following formula (3)

[0020]

[0021] In formula (3), γ is the specific gravity of surrounding rock, 27kN / m 3 for grade II surrounding rock, 25kN / m 3 for grade III surrounding rock, 23kN / m 3 for grade IV surrounding rock, and 20kN / m 3 for grade V surrounding rock;

[0022] θ is the friction angle on both sides of the supporting structure roof soil column, when the surrounding rock grade is grade III, when the surrounding rock grade is grade IV, when the surrounding rock grade is grade V, is the calculated friction angle of surrounding rock; λ is the lateral pressure coefficient, which is calculated according to the following formula (4),

[0023]

[0024] In formula (4), β is a rupture angle when the supporting structure generates the maximum thrust;

[0025] A2. Take the horizontal pressure e of the surrounding rock at the top and bottom of the tunnel section of the supporting structure, respectively, and calculate the horizontal pressure e of the surrounding rock by linear interpolation according to formula (5),

[0026] e = γhλ (5);

[0027] B. When deep buried

[0028] B1. Calculate the vertical pressure q of the surrounding rock according to the following formula (6)

[0029] q = γ (0.45 × 2 S-1 w) (6)

[0030] B.2 The horizontal pressure e of the surrounding rock is determined according to the surrounding rock grade, when the surrounding rock grade is I- II grade, the horizontal pressure is not considered; when the surrounding rock grade is III grade, e = 0.15q; when the surrounding rock grade is IV grade, e = 0.30q; when the surrounding rock grade is V grade, e = 0.50q;

[0031] C. Determine the elastic resistance K of the surrounding rock

[0032] According to the “Code for Design of Railway Tunnels” (TB10003-2016), when the surrounding rock is II grade, K is taken as 1800MPa / m, when the surrounding rock is III grade, K is taken as 1200MPa / m, when the surrounding rock is IV grade, K is taken as 500MPa / m, and when the surrounding rock is V grade, K is taken as 200MPa / m;

[0033] Step 1.4 Substitute the self-weight of the supporting structure, the vertical pressure q of the surrounding rock, the horizontal pressure e of the surrounding rock and the elastic resistance K of the surrounding rock into the finite element calculation model of the main arch of the positive tunnel, wherein the elastic resistance K of the surrounding rock is simulated by a curved surface spring constraint only under pressure, and the concentrated force Q of each positive tunnel arch on the double-spliced arch is calculated;

[0034] Step 1.5 Substitute the concentrated force Q into the finite element calculation model of the double-spliced I-beam arch, and calculate the strength σ of the double-spliced I-beam arch, when σ satisfies the following formula (7), it can be verified that the double-spliced I-beam arch is reliable, otherwise increase the I-beam type or use a three-spliced I-beam arch to repeat the above steps for redesign and calculation;

[0035] 1.1σ≤f (7)

[0036] In formula (7), 1.1 is a safety factor, and f is the design value of the bending and compressive strength of the double-spliced I-beam arch;

[0037] Step 2 After the supporting structure design is verified, the tunnel roof picking construction is implemented according to the following steps;

[0038] Step 2.1. When the inclined shaft is excavated to a distance of about 10m from the side of the main tunnel, the benching is excavated to the three-way intersection of the inclined shaft and the main tunnel with a slope of about 20% to ensure that the mechanical equipment such as excavators and wet spraying mechanical arms can smoothly climb the slope for out of the pit and shotcrete support;

[0039] Step 2.2. The three-way intersection is first installed with a three-way intersection arch, and the arch top range of the three-way intersection arch is pre-welded with a vertical column type landing platform and a cantilever type landing platform to provide support for the main tunnel arch, the landing platform spacing is consistent with the main tunnel arch support spacing, the arch foot of the three-way intersection arch is provided with three groups of locking anchor pipes and cement slurry for reinforcement, and the arch foot of the three-way intersection arch is provided with temporary transverse support connection to form a whole.

[0040] Step 2.3. The guide hole is excavated vertically to the main tunnel, the guide hole is first excavated in a zigzag manner and then excavated in a flat slope after a distance, the guide hole is supported by a temporary portal, the arch foot of the temporary portal is provided with locking anchor pipes for grouting and reinforcement and shotcrete support; at the same time, the vertical column type landing platform and the cantilever type landing platform of the main tunnel arch are connected with the three-way intersection arch, the guide hole is excavated while the temporary portal and the main tunnel arch are installed until the side of the main tunnel;

[0041] Step 2.4. After the guide hole is excavated, the temporary portal is removed, and the benching is excavated and supported towards the large or small distance of the main tunnel, forming a large working face and reaching the safe excavation step distance, then excavating other steps of the main tunnel; when the main tunnel is excavated to the bottom of the lower step, the inclined shaft top segment starts to excavate to the three-way intersection of the main tunnel pit bottom elevation; the arch foot of the three-way intersection arch of the lower step is expanded by a type steel expansion plate and buried underground, and then poured with concrete to make it dense, at this time the arch foot of the three-way intersection arch is provided with a permanent I-beam transverse support;

[0042] Step 2.5. Continue to excavate the main tunnel according to the benching method towards both ends of the main tunnel, and after the three-way intersection arch landing platform range of the main tunnel is fully enclosed into a ring, the construction is completed.

[0043] Further, in step 2.1, the arch spacing of the inclined shaft of the top segment is smaller than the standard segment arch spacing, the support is densified along the circular curve to the side of the main tunnel, and the shotcrete support is reinforced; the benching height is not less than 4.5m.

[0044] Further, in step 2.2, the locking anchor pipe is 42mm. 42mm.

[0045] Further, in step 2.3, the guide hole is 4m wide and 4.5m high, and the guide hole is supported by a I16 type steel temporary portal with a spacing of 1m.

[0046] Further, in step 2.4, the size of the type steel expansion plate is 400mm×400mm×16mm, and it is buried underground for 50cm.

[0047] Further, in step 2.5, the I-shaped steel of the permanent cross brace adopts double-spliced I22a I-shaped steel.

[0048] The beneficial effects of the present application are:

[0049] (1) The present application first tries to design a three-way junction support structure using double-spliced I-shaped steel arches before tunnel construction, and calculates whether the strength of the double-spliced I-shaped steel arches is reliable. If it is not reliable, then redesign the three-spliced I-shaped steel arches or increase the I-shaped steel type of the double-spliced I-shaped steel arches and calculate the strength of the arches. If it is reliable, then implement the tunnel roof picking construction, which ensures the stability and reliability of the support structure at the three-way junction of the inclined shaft to the straight tunnel.

[0050] (2) The present application designs the three-way junction support structure by load structure method, the double-spliced I-shaped steel arches are connected with the straight tunnel arches by setting horizontal cantilever type and vertical column type landing platforms on the arch top, the structural load is symmetrical, the stress is more reasonable, and a closed loop support system is formed by the temporary cross brace at the arch foot, without the need to construct a sleeve arch, which improves the overall stability of the support structure at the three-way junction.

[0051] (3) The temporary portal of the present application is installed synchronously with the straight tunnel arch unit through temporary brackets, after the pilot tunnel is completed, the straight tunnel arch is simultaneously supported, which greatly shortens the construction period and can quickly complete the support system conversion. BRIEF DESCRIPTION OF DRAWINGS

[0052] The tunnel inclined shaft to straight tunnel three-way junction support design and roof picking construction method of the present application will be further described below in conjunction with the drawings.

[0053] Figure 1 It is a double-spliced arch structure diagram of the embodiment of the present application.

[0054] Figure 2 It is a deep buried tunnel structure load calculation diagram of the embodiment of the present application.

[0055] Figure 3 It is a shallow buried tunnel structure load calculation diagram of the embodiment of the present application.

[0056] Figure 4 It is an embodiment of the present application Figure 1 It is a local detail view of node A.

[0057] Figure 5 It is an embodiment of the present application Figure 1 It is a local detail view of node B.

[0058] Figure 6 It is an I-type joint connection diagram of the embodiment of the present application.

[0059] Figure 7 It is a longitudinal section view of the inclined shaft to straight tunnel construction of the embodiment of the present application.

[0060] Figure 8 The plan view of the construction of the inclined shaft into the regular tunnel for the embodiment of the present application;

[0061] Figure 9 The schematic view of the portal structure for the embodiment of the present application.

[0062] The marks in the figure: 1. double-spliced arch, 2. cantilevered footing platform, 3. columnar footing platform, 4. connecting plate, 5. enlarged connecting plate, 6. cross brace, 7. first anchoring pipe with locking foot, 8. regular tunnel arch, 10. inclined shaft arch, 11. portal, 12. second anchoring pipe with locking foot. DETAILED DESCRIPTION

[0063] Embodiment one

[0064] The inclined shaft into the regular tunnel three-way junction support design and the roof picking construction method of the tunnel of the present embodiment, wherein the total length of the tunnel is 5100m, the cross-sectional size is 14m (wide) x 12m (high), and all of them are IV-class surrounding rock, the tunnel is provided with one inclined shaft, the length of the inclined shaft is 200m, the cross-sectional size is 6m (wide) x 7.5m (high), and all of them are IV-class surrounding rock, the intersection of the inclined shaft and the regular tunnel is buried at a depth of 35m; comprising the following steps:

[0065] Step 1. design the support structure of the three-way junction, the specific design and calculation are as follows,

[0066] Step 1.1. pre-design the support structure of the three-way junction with double-spliced I-beam arch 1, as shown in Figure 1 , the arch 1 is made of Q235 steel material with a yield strength of 215MPa. The calculation model of the double-spliced I-beam arch 1 is established in the finite element software. As shown in Figure 4 and Figure 5 , the arch top of the double-spliced I-beam arch 1 is provided with a cantilevered footing platform 2 and a columnar footing platform 3; as shown in Figure 6 , the arch 1 is welded together in units and connected as a whole through the connecting plate 4, and the arch foot of the double-spliced I-beam arch 1 is fixed through the enlarged connecting plate 5.

[0067] Step 1.2. the support structure of the regular tunnel adopts arch to form a regular tunnel arch, one side of the regular tunnel arch is entirely arranged on the double-spliced I-beam arch, and the regular tunnel arch is calculated as a unit according to the support spacing, and the finite element calculation model of the regular tunnel arch is established in the finite element software;

[0068] Step 1.3. determine the structure parameters of the double-spliced I-beam arch by calculation

[0069] Step 1.3.11. judge whether the three-way junction belongs to shallow or deep buried

[0070] The depth H of the shallow and deep buried division of the tunnel is calculated according to the following formula (1) p

[0071] Hp = 1.125 x 2 S-1 w (1)

[0072] In formula (1), S is the number of surrounding rock grade; w is the width influence coefficient, which is calculated according to the following formula (2),

[0073] w = 1 + i (B - 5) (2)

[0074] In formula (2), B is the tunnel width (unit: m); i is the surrounding rock pressure increase or decrease rate, when B < 5m, i = 0.2, when B > 5m, i = 0.1;

[0075] When the tunnel depth h < Hp, it is judged as shallow, when the tunnel depth h ≥ Hp, it is judged as deep.

[0076] In this embodiment, the above data is substituted to calculate:

[0077] The width influence coefficient w = 1 + i (B - 5) = 1 + 0.1 x (6 - 5) = 1.1, the critical depth Hp = 1.125 x 24 - 1 x 1.1 = 9.9m,

[0078] Since the tunnel depth h = 35m > Hp = 9.9m at the three-way intersection, the tunnel in this embodiment is judged as deep.

[0079] Step 1.3.2 The structural parameters of the double-spliced H-shaped steel arch include the self-weight of the supporting structure, the vertical pressure of surrounding rock q, the horizontal pressure of surrounding rock e and the elastic resistance of surrounding rock K, which are calculated as follows:

[0080] B. The tunnel in this embodiment is deep,

[0081] B1. Therefore, the vertical pressure of surrounding rock q of the tunnel is calculated according to the following formula (6)

[0082] q = γ (0.45 x 2 S-1 w) (6)

[0083] In formula (6), γ is the specific gravity of surrounding rock (unit: kN / m 3 , the specific gravity of grade II surrounding rock is 27kN / m 3 , the specific gravity of grade III surrounding rock is 25kN / m 3 , the specific gravity of grade IV is 23kN / m 3 , and the specific gravity of grade V is 20kN / m 3 ;

[0084] In this embodiment, the surrounding rock is grade IV, so the specific gravity of surrounding rock γ is 23kN / m 3 , the number of surrounding rock grade S = 4, then

[0085] q = γ (0.45 x 2 S-1 w) = 23 x (0.45 x 2 4-1x1.1) x 0.6 = 91.08 kPa.

[0086] B2. When the tunnel is deeply buried, the horizontal pressure e of the surrounding rock does not consider the influence of the tunnel burial depth due to the natural arch effect, so the horizontal pressure e of the surrounding rock is determined according to the surrounding rock grade. When the surrounding rock grade is I-II grade, the horizontal pressure is not considered; when the surrounding rock grade is III grade, e = 0.15q; when the surrounding rock grade is IV grade, e = 0.30q; and when the surrounding rock grade is V grade, e = 0.50q. Since the tunnel of the embodiment is IV grade surrounding rock, the horizontal pressure e of the surrounding rock is e = 0.3q = 0.3 x 91.08 = 27.32 kPa.

[0087] C. Determine the elastic resistance K of the surrounding rock

[0088] According to the Railway Tunnel Design Specification (TB10003-2016), when the surrounding rock is II grade, K is 1800 MPa / m, when the surrounding rock is III grade, K is 1200 MPa / m, when the surrounding rock is IV grade, K is 500 MPa / m, and when the surrounding rock is V grade, K is 200 MPa / m.

[0089] Since the tunnel of the embodiment is IV grade surrounding rock, the elastic resistance K of the tunnel surrounding rock of the embodiment is K = 500 MPa / m.

[0090] Step 1.4 as shown in Figure 2 and Figure 3 The positive hole arch of the embodiment is located on the double-spliced I-shaped steel arch, and there are 15 arches in total. According to the symmetry, 8 finite element calculation models of the positive hole arch are established. The self-weight of the supporting structure (double-spliced I-shaped steel arch), the vertical pressure q of the surrounding rock, the horizontal pressure e of the surrounding rock and the elastic resistance K of the surrounding rock are substituted into the finite element calculation model of the 8 positive hole arches. The elastic resistance K of the surrounding rock is simulated by a curved surface spring constraint only under pressure. The concentrated force (i.e. support reaction) Q of each positive hole arch 8 on the landing platform is calculated, which is 385.5 kN, 385.6 kN, 385.6 kN, 386 kN, 386.3 kN, 386.5 kN, 386.8 kN and 387.2 kN from the arch top to the arch foot direction respectively.

[0091] Step 1.5 according to the relationship between the force and the reaction, the concentrated force Q is substituted into the finite element calculation model of the double-spliced I-shaped steel arch, and the strength σ of the double-spliced I-shaped steel arch of the embodiment is calculated. When σ satisfies the following formula (7), it can be verified that the double-spliced I-shaped steel arch is reliable, otherwise the I-shaped steel type of the double-spliced I-shaped steel arch is increased or the three-spliced I-shaped steel arch is used to repeat the above steps for redesign and calculation;

[0092] 1.1σ≤f (7)

[0093] In formula (7), 1.1 is a safety factor, and f is the design value of the material bending and compression strength of the double I-beam arch.

[0094] In this embodiment, since 1.1σ=187.66 MPa≤f=215 MPa, it is verified that the double I-beam arch designed in advance is reliable as the supporting structure of the three-way junction.

[0095] After the structure design is verified, the tunnel roof picking construction is implemented according to the following steps.

[0096] As shown in Figure 7 , when the inclined shaft is excavated to a distance of about 10 m from the side of the main tunnel, the upper step is excavated to the three-way junction between the inclined shaft and the main tunnel at a slope of about 20%. The height of the upper step is not less than 4.5 m, which ensures that the mechanical equipment such as excavators and wet spraying mechanical hands can smoothly climb the slope for spoil removal and shotcrete support. The spacing of the inclined shaft arch 10 of the roof picking section is less than the spacing of the standard section arch, and the support is densified along the circular curve to the side of the main tunnel, and the shotcrete support is implemented.

[0097] As shown in Figure 1 and 7 , the double I-beam arch 1 is first installed on the upper step at the three-way junction, the arch top range of the double I-beam arch 1 is pre-welded with a vertical column type landing platform 2 and a cantilever type landing platform 3 to provide support for the main tunnel arch 8, the spacing of the landing platform 2 is consistent with the support spacing of the main tunnel arch 8, and the arch foot 7 of the double I-beam arch 1 is provided with three groups of 42 mm first locking foot anchor pipes 7 and cement grout is injected for reinforcement, and the arch foot of the double I-beam arch 1 is provided with temporary transverse supports 6 connected to form a whole.

[0098] As shown in Figure 8 , a pilot tunnel is excavated vertically to the main tunnel, the pilot tunnel has a width of 4 m and a height of 4.5 m; the pilot tunnel is first excavated in a zigzag manner for a distance and then excavated in a flat slope, and the pilot tunnel is supported by a temporary portal 11 made of I16 type steel, as shown in Figure 9 , with a spacing of 1 m, the arch foot of the temporary portal 11 is provided with a second locking foot anchor pipe 12 for grouting reinforcement and shotcrete support; as shown in Figure 8 , the main tunnel arch 8 is connected to the vertical column type landing platform 2 and the cantilever type landing platform 3 of the three-way junction arch at the same time, and the pilot tunnel is excavated while the temporary portal 11 and the main tunnel arch 8 are installed until the side of the main tunnel;

[0099] As shown in Figure 8As shown, after the pilot hole excavation is completed, the temporary portal 11 is removed, and the upper bench excavation and support are performed towards the large or small distance of the main hole, a large working face is formed and the safe excavation step distance is reached, and then the other bench excavation of the main hole is performed; when the main hole is excavated to the lower bench floor elevation, the inclined shaft roof segment lower bench is excavated synchronously to the three-way junction and connected with the main hole bottom elevation; the arch foot of the three-way junction arch is expanded using a steel expanded connecting plate 5 (400mm x 400mm x 16mm) and buried underground for 50cm, and then poured with concrete to be dense, at this time, the arch foot of the three-way junction arch is provided with a double-spliced I22a permanent cross brace.

[0100] Step 2.5 continues to construct the main hole in steps towards both ends of the main hole, and after the initial support of the main hole within the range of the foot platform of the three-way junction arch is completely closed in a ring, the construction is completed.

[0101] Example Two

[0102] This example is a variation based on Example One, except that it is different from Example One in that:

[0103] (1) The intersection of the inclined shaft and the main tunnel is buried at a depth of 9m.

[0104] (2) Since the tunnel at the three-way junction is buried at a depth h = 35m > Hp = 9.9m, the tunnel in this example is determined to be shallowly buried.

[0105] As shown, the calculated friction angle of the surrounding rock of the shallowly buried tunnel is Figure 3 θ = 0.7 .

[0106]

[0107] The lateral pressure coefficient λ is calculated according to the following formula (4)

[0108]

[0109] A1. The vertical pressure of the surrounding rock q is calculated according to the following formula (3)

[0110]

[0111] In formula (3), γ is the unit weight of the surrounding rock (unit kN / m 3 ), 27kN / m 3 for grade II surrounding rock, 25kN / m 3 for grade III surrounding rock, 23kN / m 3 for grade IV, and 20kN / m 3 for grade V; in this example, the surrounding rock is grade IV, so the unit weight of the surrounding rock γ is taken as 23kN / m 3 .

[0112] ​The calculated q = 161.7 kPa.

[0113] A2. When the tunnel is shallowly buried, the horizontal pressure of the surrounding rock at the top and bottom of the tunnel in the supporting structure section is calculated considering the influence of the stratum burial depth, and the horizontal pressure of the surrounding rock e is calculated by linear interpolation according to formula (5).

[0114] e = γhλ (5),

[0115] In this embodiment, the specific gravity γ of the surrounding rock of the IV-grade surrounding rock is 23 kN / m, the height of the supporting structure (double-spliced I-shaped steel arch 1) is equal to the height of the inclined shaft section 7.5 m, the height h of the top of the supporting structure is equal to the burial depth of the tunnel 9 m, and the height h of the bottom of the supporting structure is equal to the burial depth of the tunnel 9 m + the height of the supporting structure 7.5 m, so that

[0116] The horizontal pressure e of the surrounding rock at the top of the tunnel in the supporting structure section is 0.24 * 9 * 23 = 49.68 kPa,

[0117] The horizontal pressure e of the surrounding rock at the bottom of the tunnel in the supporting structure section is 0.24 * (9 + 7.5) * 23 = 91.08 kPa.

[0118] (3) Refer to the steps of Embodiment One, the strength σ of the double-spliced arch 1 at the three-way junction is calculated to be 241.2 MPa,

[0119] In this embodiment, since 1.1σ = 187.66 MPa ≤ f = 215 MPa, the structure design of the three-way junction I22a double-spliced arch 1 does not meet the requirements, and the above steps are repeated for redesign and calculation using a triple-spliced I22a I-shaped steel arch, and the specific process is not repeated.

[0120] The calculation strength σ of the triple-spliced I22a arch is recalculated to be 192.96 MPa,

[0121] Since 1.1σ = 212.26 MPa ≤ f = 215 MPa, the triple-spliced I22a I-shaped steel arch supporting structure of the three-way junction is safe and reliable.

[0122] The subsequent tunnel roof construction is the same as Embodiment One, and is not repeated.

[0123] The above only describes the preferred embodiments of the present application, but the present application is not limited thereto, all equivalent replacements or equivalent changes according to the concept and technical solutions of the present application should be covered within the protection scope of the present application.

Claims

1. A design of a three-way junction support of an inclined shaft to a regular tunnel of a tunnel and a roof picking construction method thereof, characterized in that The method comprises the following steps: Step 1, design the support structure of the three-way intersection, the specific design and calculation are as follows, Step 1.1, pre-design the support structure of the three-way intersection adopts double-spliced I-beam arch, a finite element calculation model of the double-spliced I-beam arch is established in the finite element software, Step 1.2, the support structure of the main tunnel adopts arches to form main tunnel arches, one side of the main tunnel arches is arranged on the double-spliced I-beam arch, the main tunnel arches are calculated as calculation units according to the support spacing, and a finite element calculation model of the main tunnel arches is established in the finite element software; Step 1.3, calculate and determine the structure parameters of the double-spliced I-beam arch Step 1.3.1, judge whether the three-way intersection is shallow or deep The tunnel depth and the depth of the shallow and deep buried interface H are calculated according to the following formula (1) p H p = 1.125 x 2 S-1 w (1) In formula (1), S is the surrounding rock grade number; w is the width influence coefficient, which is calculated according to formula (2) as follows, w = 1 + i (B-5) (2) In formula (2), B is the tunnel width (unit: m); i is the surrounding rock pressure increase / decrease rate, when B < 5 m, i = 0.2 is taken, and when B > 5 m, i = 0.1 is taken; When the tunnel depth h < Hp, it is judged as shallow, and when the tunnel depth h ≥ Hp, it is judged as deep; Step 1.3.2, the structure parameters of the double-spliced I-beam arch include the self-weight of the support structure, the vertical pressure q of the surrounding rock, the horizontal pressure e of the surrounding rock and the elastic resistance K of the surrounding rock, and the calculation is as follows; A. When shallow A1. calculate the vertical pressure q of the surrounding rock according to formula (3) as follows In formula (3), γ is the specific weight of the surrounding rock, 27 kN / m is taken for the second grade surrounding rock 3 , 25 kN / m is taken for the third grade surrounding rock 3 , 23 kN / m is taken for the fourth grade 3 , and 20 kN / m is taken for the fifth grade 3 ; θ is the friction angle on both sides of the roof soil column of the support structure, when the surrounding rock level is grade III, when the surrounding rock level is grade IV, when the surrounding rock level is grade V, is the calculated friction angle of the surrounding rock; λ is the lateral pressure coefficient, which is calculated according to the following formula (4), In formula (4), β is the rupture angle when the support structure generates the maximum thrust; A2. respectively take the horizontal pressure e of the surrounding rock at the top and bottom of the tunnel in the support structure interval, and calculate the horizontal pressure e of the surrounding rock by linear interpolation according to formula (5), e = γhλ (5); B. When deep B1. calculate the vertical pressure q of the surrounding rock according to formula (6) as follows q = y (0.45 x 2 S-1 w) (6) B.2 The horizontal pressure e of the surrounding rock is determined according to the surrounding rock grade, when the surrounding rock grade is I- II grade, the horizontal pressure is not considered; when the surrounding rock grade is III grade, e = 0.15q; when the surrounding rock grade is IV grade, e = 0.30q; when the surrounding rock grade is V grade, e = 0.50q; C. Determine the elastic resistance K of the surrounding rock When the surrounding rock is II grade, K is taken as 1800 MPa / m, when the surrounding rock is III grade, K is taken as 1200 MPa / m, when the surrounding rock is IV grade, K is taken as 500 MPa / m, and when the surrounding rock is V grade, K is taken as 200 MPa / m; Step 1.4, the self-weight of the support structure, the vertical pressure q of the surrounding rock, the horizontal pressure e of the surrounding rock and the elastic resistance K of the surrounding rock are substituted into the finite element calculation model of the main tunnel arches, wherein the elastic resistance K of the surrounding rock is simulated by using only the pressure curved surface spring constraint, and the concentrated force Q of each main tunnel arch on the double-spliced arch is calculated; Step 1.5, the concentrated force Q is substituted into the finite element calculation model of the double-spliced I-beam arch, and the strength σ of the double-spliced I-beam arch is calculated, when σ satisfies formula (7) as follows, it is verified that the double-spliced I-beam arch is reliable, otherwise, the I-beam type is increased or the three-spliced I-beam arch is used to repeat the above steps for redesign and calculation; 1.1σ≤f (7) In formula (7), 1.1 is the safety factor, and f is the material bending and compression strength design value of the double-spliced I-beam arch; Step 2, after the support structure design verification, the tunnel roof picking construction is implemented according to the following steps; Step 2.

1. When the inclined shaft is excavated to a distance of about 10 m from the side of the main tunnel, the top step is excavated with a slope of about 20% to the three-way intersection of the inclined shaft and the main tunnel, to ensure that the mechanical equipment such as excavators and wet spraying mechanical hands can smoothly climb the slope to carry out the out of the pit and the shotcrete support; Step 2.

2. The three-way intersection is first installed on the top step, and the three-way intersection arch is provided with a pre-welded column type foot platform and a cantilever type foot platform to support the main tunnel arch, the distance between the foot platforms is consistent with the support distance of the main tunnel arch, the arch foot of the three-way intersection arch is provided with three groups of locking anchor pipes and cement slurry for reinforcement, and the arch foot of the three-way intersection arch is provided with temporary transverse support connection to form a whole; Step 2.

3. The vertical main tunnel is excavated as a pilot tunnel, the pilot tunnel is excavated in a line first and then in a flat slope, the pilot tunnel is supported by a temporary portal, the arch foot of the temporary portal is provided with a locking anchor pipe for grouting reinforcement and shotcrete support; at the same time, the column type foot platform and the cantilever type foot platform of the main tunnel arch are connected to the three-way intersection arch, the temporary portal and the main tunnel arch are installed while the pilot tunnel is excavated until the side of the main tunnel; Step 2.

4. After the pilot tunnel is excavated, the temporary portal is removed, and the main tunnel is excavated and supported in the direction of the large or small distance, a large working face is formed, and the safe excavation step distance is reached, then the other steps of the main tunnel are excavated; when the main tunnel is excavated to the bottom of the lower step, the lower step of the inclined shaft top excavation is excavated to the three-way intersection of the main tunnel pit bottom elevation; the arch foot of the three-way intersection arch of the lower step is expanded by a steel plate and buried underground, and then poured with concrete to make it dense, at this time, the arch foot of the three-way intersection arch is provided with a permanent I-shaped steel cross brace; Step 2.

5. Continue to excavate the main tunnel in the direction of the two ends of the main tunnel according to the step method, and after the main tunnel is initially supported in the range of the foot platform of the three-way intersection arch, the whole construction is completed.

2. The method of claim 1, wherein: In step 2.1, the arch spacing of the inclined shaft of the top excavation section is smaller than the standard arch spacing, the support is densified along the circular curve to the side of the main tunnel, and the shotcrete support is reinforced according to the shotcrete support; the height of the top step is not less than 4.5 m.

3. The method of claim 1, wherein: In step 2.2, the lock foot anchor tube is adopted 4. The method of claim 1, wherein: In step 2.3, the pilot tunnel has a width of 4 m and a height of 4.5 m, and is supported by a I16 type steel temporary portal with an interval of 1 m.

5. The method of claim 1, wherein: In step 2.4, the size of the steel expanded connecting plate is 400mm×400mm×16mm, and it is buried underground for 50 cm.

6. The method of claim 1, wherein: In step 2.5, the permanent cross brace is made of double-pinned I22a I-shaped steel.

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