Construction method for underground excavation tunnel to penetrate through water-rich backfill unstable stratum and overpass existing lines

Abstract

The invention provides a construction method for a subsurface tunnel to penetrate through a water-rich backfill unstable stratum and to cross an existing line, and relates to the technical field of tunnel construction.The construction method comprises the following steps that firstly, after a tunnel is excavated, advanced curtain grouting is conducted in the tunnel; secondly, ground surface filling grouting is adopted in the range of the tunnel and the existing cross road; thirdly, advanced small guide pipes are arranged for advanced supporting; fourthly, the backfill soil section is mechanically excavated through an annular core soil reserving method, and blasting construction is conducted on other sections through a full-section method; fifthly, the bottom of the tunnel is reinforced through steel floral tube grouting; sixthly, a tunnel bottom cushion layer and an inverted arch second lining are constructed; and seventhly, lining and backfill grouting are conducted. The problems that traffic of a conventional road is interrupted, a temporary supporting and reinforcing measure is adopted in an existing line, the construction period is long, efficiency is low, and collapse risks exist are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and particularly relates to a construction method for a mined tunnel passing through a water-rich backfill unstable stratum and spanning an existing line. Background Art

[0002] With the booming development of urban rail transit, more and more urban subway constructions are moving towards the era of large-scale network operation. Inevitably, during the construction process, there are situations where newly built tunnels pass through water-rich backfill unstable geology and span existing lines. The water-rich backfill unstable stratum has complex backfill components, loose structure, large porosity, poor self-stability, strong water permeability, and is vulnerable to abundant groundwater, which may cause problems such as quicksand and leakage. The risk of uneven settlement is high, and it is prone to collapse. When a conventional mined tunnel passes through a water-rich backfill unstable stratum, traffic is usually interrupted temporarily, and traffic is reopened after the secondary lining structure of the tunnel is constructed. However, when the tunnel in the backfill layer is located below the existing main road, traffic cannot be interrupted, and when spanning an existing line that is under construction, measures such as temporary support inside the existing line tunnel are usually adopted, resulting in a long construction period, and the temporary interruption of traffic and the temporary support process inside the existing line tunnel are not practical. Summary of the Invention

[0003] Aiming at the deficiencies in the prior art, the present invention provides a construction method for a mined tunnel passing through a water-rich backfill unstable stratum and spanning an existing line, which solves the problems of conventional road traffic interruption, long construction period, low efficiency, and collapse risk in the construction of using temporary support reinforcement measures inside the existing line.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A construction method for a mined tunnel passing through a water-rich backfill unstable stratum and spanning an existing line, comprising the following steps:

[0006] Step 1: After the tunnel is excavated, advanced curtain grouting is carried out inside the tunnel;

[0007] Step 2: Surface filling grouting is carried out in the range of the tunnel and the existing intersecting road;

[0008] Step 3: Advance small pipes are set for advance support;

[0009] Step 4: In the backfill section, mechanical excavation is carried out using the ring-shaped reserved core soil method, and full-section blasting construction is carried out for the remaining sections;

[0010] Step 5: The bottom of the tunnel is grouted and reinforced with steel flower pipes;

[0011] Step 6: Construction of the tunnel bottom cushion and inverted arch secondary lining;

[0012] Step 7: Lining and backfill grouting.

[0013] Furthermore, construction preparations are carried out before tunnel excavation, and advanced geological forecasts are used to explore the surrounding rock characteristics, weak stratum sections, structures, etc. in front of the excavation face.

[0014] Furthermore, in step one, the length of each grouting cycle is 15m, 12m is excavated, and a 3m grouting stop plate is retained. The grouting range is 3m from the tunnel excavation contour line. A total of five rings of grouting holes are set up, and the effective diffusion radius of the grouting holes in the first, second, third and fourth rings is 1m, and the effective diffusion radius of the fifth ring is 1.5m.

[0015] Furthermore, during grouting, the grouting sequence is from outside to inside, and the same circle of holes is constructed at intervals.

[0016] Furthermore, in step 2, the grouting range is 3m outside the transverse tunnel, 3m above the arch to the upper half section of the tunnel, and 3m above the arch to the tunnel base.

[0017] Furthermore, in step three, the small advance conduit is made of hot-rolled seamless steel pipe with a wall thickness of 3.5 mm.

[0018] Furthermore, in step 4, when excavating the backfill section, the upper step is excavated first, then the core soil is excavated, and finally the lower step is excavated. Initial support should be applied in time during construction; the left-line tunnel is constructed first in the backfill section, and the right-line tunnel is excavated after the second lining of the left-line tunnel is completed. The two are staggered at least 30m apart in longitudinal distance.

[0019] Furthermore, in step five, after the initial support is completed by excavating the bottom of the invert arch, steel pipe grouting reinforcement is used.

[0020] Furthermore, in step six, the thickness of the cushion layer at the bottom of the tunnel is 20 cm, and the cushion layer is carried out immediately after excavation. In order to reduce its interference with the mucking transportation, the left and right lines of the transverse channel are converted for construction.

[0021] Furthermore, in step seven, before the arch wall lining is carried out, a steel pipe is first arranged on the arch top, and backfill grouting is performed behind the secondary lining.

[0022] The present invention has the following beneficial effects:

[0023] Through joint settlement control measures such as advanced curtain grouting in the tunnel, surface filling grouting, advanced small duct support, mechanical excavation of annular reserved core soil, steel flower pipe grouting and lining backfill grouting, the risk of collapse caused by construction disturbance is reduced, and the dark excavation tunnel under the condition of differential settlement deformation control is realized to pass through the unstable stratum of water-rich backfill soil and cross the existing line safely and quickly, thus ensuring the normal passage of existing roads and the normal construction and operation of existing lines.

[0024] Other advantages, objects and features of the present invention will be partly reflected by the following description, and partly will be understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the construction steps of the present invention;

[0026] Figure 2 It is a schematic diagram of the construction of the structural part of the present invention;

[0027] Figure 3 It is a longitudinal sectional view of the advanced support structure of the present invention;

[0028] Figure 4 It is a schematic diagram of the steel flower pipe structure of the present invention.

[0029] In the above-mentioned drawings: 1. Advanced small duct; 2. Steel flower pipe; 3. Locking foot anchor bolt. Detailed Embodiment

[0030] In order to make the technical means, creative features, achieved purposes and functions of the present invention clearer and easier to understand, the technical solutions in the present invention will be further described below with reference to the drawings and embodiments.

[0031] Please refer to Figures 1 to 4 As shown, a construction method for a mined tunnel to cross a water-rich backfill unstable stratum and span an existing line includes the following steps:

[0032] Step 1: After the tunnel is excavated, advanced curtain grouting is carried out in the tunnel;

[0033] Step 2: Surface filling grouting is adopted in the range of the tunnel and the existing cross road;

[0034] Step 3: Set the advanced small duct 1 for advanced support;

[0035] Step 4: The mechanical excavation of the backfill section is carried out by the method of circularly reserving the core soil, and the full-section method is adopted for blasting construction in the rest of the sections;

[0036] Step 5: The steel flower pipe 2 is grouted to reinforce the bottom of the tunnel;

[0037] Step 6: Construct the bottom cushion and inverted arch secondary lining of the tunnel;

[0038] Step 7: Lining and backfill grouting.

[0039] Before tunnel excavation, construction preparations are carried out and simulation calculations are performed on each process. For example, the MADIS GEN numerical simulation technology is used to find out the most unfavorable stage for uneven surface settlement and deformation control of existing line structures under various working conditions, and targeted measures are formulated; labor plans, tool and equipment configuration plans, and material plans are prepared according to the number of working faces. Before tunnel excavation, advanced geological prediction methods should be used to explore the surrounding rock characteristics, weak stratum sections, structures, etc. in front of the excavation face. According to the results obtained, information feedback is provided to provide a basis for the correct selection of construction methods, optimization of support, and adoption of special measures to guide construction. Specifically, the engineering geological method and advanced horizontal exploration are used to carry out advanced geological prediction work. Using geological sketches in the cave, a digital photo is taken of the left and right sides of the cave wall, the cave top, and the face every 10 meters. Multi-hole horizontal drilling and multi-hole CT are used. Here, 6 holes are used, and the drilling length is 30m; a single hole is drilled horizontally every 25 meters, and the length of a single hole is 10 meters; digital imaging is performed in the hole.

[0040] After tunnel excavation, the groundwater volume reached 25m 3 / hour, which will affect the self-stabilization of the tunnel face. In the tunnel, curtain grouting reinforcement and water stop are adopted. In step one, the length of each grouting cycle is 15m, the excavation is 12m, and a 3m stop plate is retained. The grouting range is 3m of the tunnel excavation contour line. The first cycle uses a 400mm thick plain shotcrete tunnel face as a stop wall; a total of five rings of grouting holes are set, and the effective diffusion radius of the grouting hole diffusion radius is 1m for the first, second, third, and fourth rings of single holes, and the effective diffusion radius of the fifth ring of single holes is 1.5m. The opening diameter of the 3m before the grouting hole is not less than 108mm, and the final hole diameter is not less than 90mm; the orifice pipe adopts a hot-rolled seamless steel pipe with a diameter of 108mm and a wall thickness of 5mm, and the pipe length is 3m. The orifice pipe should be firmly buried. The drilling and grouting sequence is from outside to inside, and the same circle of holes is constructed at intervals. Grouting generally uses cement slurry, and the water-cement ratio of cement slurry is 1:0.4~0.6. Single hole grouting end standard: grouting pressure gradually increases to the designed final pressure, then continue grouting for more than 10 minutes, the grouting volume is less than 1 / 4 of the initial grouting volume, and the water inflow of the inspection hole is less than 0.2L / min. Full section grouting end standard: all grouting holes meet the single hole end conditions, and the predicted water inflow of the tunnel after grouting is less than 1m 3 / (d·m).

[0041] Furthermore, to improve the consolidation of the surface layer at the top of the tunnel and reduce the risk of surface layer collapse caused by construction disturbance, surface filling grouting is adopted in the area of the tunnel and the existing intersecting road. In Step 2, the grouting range is 3m outside the transverse tunnel, from 3m above the arch crown to the upper half section of the tunnel, and from 3m above the arch crown to the tunnel base. The grouting holes are arranged in a plum blossom shape, with a layout spacing of 2.5m x 2.5m. During grouting, drilling is carried out first, and the drilling hole diameter is 90mm. Then, a steel flower pipe 2 with a diameter of 76×4mm is placed in the drilling hole. The grout used is cement slurry, and the water-cement ratio of the cement slurry is 1:1. The grouting is ended with the final grouting pressure, and the grouting stops when the grouting pressure reaches 0.2 - 0.4MPa. To reduce the impact of vehicle concentrated load on tunnel construction, a 2cm thick steel plate can also be laid in the area where the vehicle road intersects with the tunnel to reduce the load impact of vehicles on the tunnel.

[0042] Furthermore, to control the release of formation stress, special attention is paid to the support work during tunnel construction, and the construction is carried out strictly in accordance with the technical requirements of "advance pipe, strict grouting, strong support, block closure, and frequent measurement". In Step 3, the advanced small pipe 1 is processed from hot-rolled seamless steel pipe with a wall thickness of 3.5mm. The tunnel adopts an I-beam steel frame, and locking foot bolts 3 are set at the joints of the arch frames.

[0043] Furthermore, in Step 4, when excavating the backfill section, the upper bench is excavated first. The upper bench must be excavated manually, and the excavation footage per cycle is not greater than 1 steel frame. Then, the core soil is excavated, and finally the lower bench is excavated. During construction, the initial support should be applied in a timely manner. For the backfill soil section, the left-line tunnel is constructed first, and the right-line tunnel is excavated after the second lining of the left-line tunnel is completed. The longitudinal distance between the two should be at least 30m apart. The installation of the locking foot bolts 3 of the steel frame must be completed before the excavation of the invert. The excavation footage per cycle is not greater than 3m. The invert should be constructed ahead of the arch wall.

[0044] Furthermore, to enhance the bearing capacity of the tunnel foundation, in Step 5, after the initial support is completed for the excavation at the bottom of the invert, grouting reinforcement is carried out using the steel flower pipe 2. The front end of the steel flower pipe 2 is processed into a cone shape, and grouting holes with a diameter of φ10mm are drilled on the pipe body, with a spacing of 150mm. The single theoretical length of the pipe is 3.5m. The spacing of the grouting holes is 1.0m x 1.0m, arranged in a plum blossom shape, and the depth ranges from the base to 0.5m below the rock layer line. The grouting material selected is pure cement slurry. Inspection must be carried out after grouting reinforcement to ensure that the bearing capacity of the foundation after reinforcement is not less than 350KPa.

[0045] Furthermore, in order to bear and transfer the upper load, protect the foundation soil from disturbance, and reduce settlement, in Step 6, a C25 cushion concrete is provided at the bottom of the tunnel. The thickness of the tunnel bottom cushion is 20 cm. The cushion is constructed immediately after excavation. To reduce the interference with the muck transportation, the construction of the left and right lines of the transverse passage is converted. Manual bottom cleaning is required to remove soft soil, slurry, and floating slag; manual spreading is carried out, and a flat vibrator is used for tamping. After tamping, leveling and finishing are carried out. Sprinkler curing is carried out within 12 hours after the concrete pouring is completed.

[0046] Furthermore, in order to effectively control the settlement of the interval tunnel, the inverted arch and the arch wall lining are constructed in a timely manner after the initial support and the lower bearing pile foundation are completed, so as to connect the various stress-bearing systems of the tunnel into a whole. The tunnel lining is constructed by using a 10m hydraulic full-section trolley. Before lining, a φ42mm steel pipe is set at the crown of the tunnel, and backfill grouting is carried out behind the secondary lining to eliminate the cavities behind the arch wall lining, closely connect the tunnel lining system with the surrounding rock, achieve the purpose of common action, and effectively control the ground settlement.

[0047] Through a series of combined settlement control measures such as advanced curtain grouting in the tunnel, surface filling grouting, advanced small pipe 1 support, mechanical excavation with a circular reserved core soil, steel pipe 2 grouting, cushion construction, and lining backfill grouting, the risk of collapse caused by construction disturbance is reduced, and the safe and rapid construction of the mined tunnel passing through the water-rich backfill soil unstable formation and spanning the existing line under the condition of differential settlement deformation control is realized, ensuring the normal passage of the existing road and the normal construction operation of the existing line.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A construction method for a dark tunnel that passes through unstable strata of water-rich backfill soil and crosses over an existing line, characterized in that: The following steps are involved: Step 1: After tunnel excavation, advance curtain grouting is carried out in the tunnel; Step 2: Use surface filling grouting in the area between the tunnel and the existing intersection road; Step 3: Setting an advance small conduit 1 for advance support; Step 4: The backfill section is mechanically excavated using the annular reserved core soil method, and the remaining sections are blasted using the full section method; Step 5: Grouting steel pipe 2 to reinforce the bottom of the tunnel; Step 6: Construction of the tunnel bottom cushion and invert secondary lining; Step 7: Lining and backfill grouting.

2. A construction method for a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 1, characterized in that: Construction preparations are carried out before tunnel excavation, and advanced geological forecasts are used to explore the surrounding rock characteristics, weak stratum sections, and structures in front of the excavation face.

3. A construction method for a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 1, characterized in that: In step one, the length of each grouting cycle is 15m, the excavation is 12m, and a 3m grouting plate is retained. The grouting range is 3m from the tunnel excavation contour line. A total of five rings of grouting holes are set up. The effective diffusion radius of the grouting holes in the first, second, third and fourth rings is 1m, and the effective diffusion radius of the fifth ring is 1.5m.

4. A construction method for a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 3, characterized in that: When grouting, the grouting order is from outside to inside, and the holes in the same circle are constructed at intervals.

5. The construction method of a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 1, characterized in that: In step 2, the grouting range is 3m outside the transverse tunnel, 3m above the arch to the upper half section of the tunnel, and 3m above the arch to the tunnel base.

6. A construction method for a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 1, characterized in that: In step three, the small leading guide tube 1 is made of hot-rolled seamless steel pipe with a wall thickness of 3.5 mm.

7. A construction method for a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 1, characterized in that: In step 4, when excavating the backfill section, first excavate the upper step, then excavate the core soil, and finally excavate the lower step. Initial support should be applied in time during construction; the left-line tunnel is constructed first in the backfill section, and the right-line tunnel is excavated after the second lining of the left-line tunnel is completed. The two are staggered at least 30m apart in longitudinal distance.

8. The construction method of a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 1, characterized in that: In step 5, after the initial support is completed by excavating the bottom of the invert arch, the steel flower pipe 2 is used for grouting reinforcement.

9. A construction method for a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 1, characterized in that: In step six, the thickness of the cushion layer at the bottom of the tunnel is 20 cm. The cushion layer is carried out immediately after excavation. In order to reduce its interference with the mucking transportation, the left and right lines of the horizontal channel are converted into construction.

10. A construction method for a dark tunnel through unstable strata of water-rich backfill soil and over an existing line as claimed in claim 1, characterized in that: In step seven, before the arch wall lining, steel pipes are set in the arch top and backfill grouting is carried out behind the secondary lining.

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