CN110469345B - Sedimentation-control convergence construction method for high-water-level shallow-buried loess tunnel - Google Patents

Sedimentation-control convergence construction method for high-water-level shallow-buried loess tunnel Download PDF

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CN110469345B
CN110469345B CN201910746516.3A CN201910746516A CN110469345B CN 110469345 B CN110469345 B CN 110469345B CN 201910746516 A CN201910746516 A CN 201910746516A CN 110469345 B CN110469345 B CN 110469345B
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construction
tunnel
temporary
excavation
arch
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CN110469345A (en
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张岳
殷浩喜
王玉伟
申晋峰
曹永杰
王富强
张志恒
白雪鹏
胡肖肖
郑梦琦
王俊杰
刘晓欢
于守江
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China Railway Sixth Group Co Ltd
Taiyuan Railway Construction Co Ltd of China Railway Sixth Group Co Ltd
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China Railway Sixth Group Co Ltd
Taiyuan Railway Construction Co Ltd of China Railway Sixth Group Co Ltd
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    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21DSHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
    • E21D11/00Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
    • E21D11/04Lining with building materials
    • E21D11/10Lining with building materials with concrete cast in situ; Shuttering also lost shutterings, e.g. made of blocks, of metal plates or other equipment adapted therefor
    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21DSHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
    • E21D11/00Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
    • E21D11/14Lining predominantly with metal
    • E21D11/18Arch members ; Network made of arch members ; Ring elements; Polygon elements; Polygon elements inside arches
    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21DSHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
    • E21D21/00Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
    • E21D21/008Anchoring or tensioning means

Abstract

The invention discloses a settlement control convergence construction method for a high-water-level shallow loess tunnel, which comprises the following steps of: (1) dewatering by a dewatering well; (2) determining the reserved deformation; (3) determining the height of the step; (4) excavating an upper step and performing primary support; (5) constructing a temporary cross brace for the upper step; (6) excavating one side of the middle step and performing primary support; (7) constructing a middle step temporary transverse support; (8) excavating one side of the lower step and performing primary support; (9) performing primary support closed-loop construction; (10) pouring the second lining inverted arch; (11) and pouring the second lining arch wall. The method has reasonable design, obvious economic and social benefits, energy conservation and environmental protection which can meet the standard requirements, and better popularization and application value, and the technology reaches the domestic leading level.

Description

Sedimentation-control convergence construction method for high-water-level shallow-buried loess tunnel
Technical Field
The invention belongs to the field of tunnel building construction, and particularly relates to a settlement-control convergence construction method for a high-water-level shallow-buried loess tunnel, which is suitable for any form of primary arch construction of a subsurface excavated soil tunnel.
Background
The vigorous development of underground engineering relieves the problem of ground surface tension to a great extent. And with the continuous development of engineering, the research of people on underground engineering also enters a new stage. How to effectively control the settlement of tunnel construction is the difficult point of tunnel construction, especially for those high water level shallow-buried loess tunnels, if the settlement can not be effectively controlled, not only the construction quality can not be guaranteed, but also the risk of collapse at any time is faced, and the construction efficiency and the personal safety are influenced. Therefore, the control of the tunnel settlement is a problem for the cumin underground workers to search and study continuously. The method is successfully applied to practice by the aid of achievements of predecessors and self construction research, and has a good effect of improving the settlement of the tunnel.
Disclosure of Invention
The invention aims to provide a settlement-control convergence construction method for a high-water-level shallow-buried loess tunnel, which is used for improving the original design method in details on the basis of construction according to the original three-step temporary inverted arch method without increasing extra cost. Reserving core soil, and increasing the stability of the tunnel face by reducing the disturbance of an undisturbed soil body; back pressure is carried out on backfilled soil, and the outward radial supporting force of the soil body on the arch centering and the arch centering are utilized to jointly balance the internal pressure and the external pressure of the hole; standardize the height of each step, reasonable arrangement on-the-spot excavation mode. Therefore, convergence and vault settlement in the tunnel are effectively controlled, the good construction effect is achieved, the soil output during excavation in each construction process of the tunnel is reduced, and the construction time is saved.
The invention is realized by adopting the following technical scheme:
a settlement control convergence construction method for a high-water-level shallow loess tunnel comprises the following steps:
(1) dewatering well for dewatering
Because the underground water level is at the vault position, before tunnel construction, precipitation work is well done, and the water level is 1.5m below the inverted arch; the dewatering well is arranged 80m in front of the construction face and pre-pumps water in advance; a technician performs water level measurement work of the dewatering well and records the water level measurement work; and (4) observing whether water leakage exists in the tunnel by workers in the tunnel, and stopping tunnel face opening construction for treatment if the water leakage exists in the tunnel.
(2) Determining the reserved deformation
And during construction, the deformation is reserved according to design, and the deformation is adjusted in time according to the monitoring and measuring data result.
(3) Determining the step height
The excavation height of the upper step is more than or equal to 0.3 time of the excavation span of the upper step, and the excavation heights of the middle step and the lower step are the average distribution of the tunnel total excavation height minus the excavation height of the upper step.
(4) Excavating upper bench and preliminary bracing
The spacing between the construction arches is 0.65m, and the soil excavation spacing is controlled within 0.9 m; the construction is strictly carried out according to the design requirement during the initial construction, when the steel frame is subjected to the step-up re-spraying, the re-spraying thickness is 65mm, thin steel bars with the length of 65mm are welded on the steel frame, and the steel bars are arranged every 2m and used for controlling the re-spraying thickness;
the designed size of the arch center connecting plate is 225mm multiplied by 300mm multiplied by 16mm, and a large cushion block of 400mm multiplied by 100mm is adopted; grouting is carried out during construction of the lock leg anchor pipes, the rigidity of the lock leg anchor pipes is increased, 4 lock legs are designed at each position, and the number of the lock leg anchor pipes is increased for a soil loose section;
the length of the upper step is controlled to be 5-6 m, core soil is reserved, the length of the core soil is kept to be 3-4 m, and a temporary cross brace arranged on the core soil section is removed.
(5) And constructing temporary cross brace for upper step
The temporary transverse supports of the upper steps are constructed in time, the temporary steel frames are made of H175 steel, one position is longitudinally arranged at each 2 trusses and connected with the hole body steel frames through bolts, pre-embedded steel plates are welded at corresponding positions after the hole body steel frames are erected, bolts are preset so that the temporary steel frames can be connected, and the height of a welding seam at the joint of the connecting steel plates is more than or equal to 10 mm; the adjacent steel frames are connected by steel bars, and the circumferential distance is 1m, and the adjacent steel frames are welded at the inner flange of the steel frame; after the temporary cross arm is completely constructed, the upper step forms a closed loop, and the settlement is effectively controlled.
(6) Excavating one side of the bench and performing primary support
The middle step can not be excavated at two sides simultaneously, steps are staggered left and right, and the step staggering distance is 2-3 m; the core soil is reserved during the middle step excavation, the full-section excavation cannot be performed, and only one side needs to be excavated and enough construction space is provided; the middle step is excavated once within 2 trusses, and the excavation distance is controlled during excavation and is within 1.5 m; performing primary support after excavation is finished, and ensuring the re-spraying thickness;
after the re-spraying is finished, the middle step backfills earth to perform back pressure.
(7) Temporary step cross brace in construction
The intermediate step temporary transverse support is constructed in time to ensure construction quality, the temporary steel frame adopts H175 steel, one part is arranged at every 2 vertical trusses, and the temporary steel frame is connected with the hole body steel frame through bolts;
after the application is finished, back pressure is carried out on the backfilled soil in time;
and a closed loop is formed after the middle step cross brace is applied, so that the sedimentation is effectively controlled.
(8) Excavating one side of the lower step and performing primary support
Judging whether the lower step can be excavated according to the settlement and convergence values, and performing diagonal construction on the middle and lower steps only under the condition that the settlement and convergence control measurement is stable; when the lower step is excavated, the core soil is reserved, and only one side is excavated to form a construction space; performing primary support according to design requirements after excavation is finished;
and after the initial construction is finished, back-pressure backfilling is carried out in time, and the settlement amount is controlled.
(9) Initial support closed loop construction
Sealing and looping a primary support in time after tunnel excavation, controlling a full-section closed loop within 15 days, wherein the distance between the sealed and looping position and a tunnel face is less than or equal to 35 m; the footage of each cycle of the primary closed loop is less than or equal to 3 m; reserving soil bodies with the thickness of 60-70 cm at the arch springing and the corner springing of the wall, and manually excavating; meanwhile, C20 prefabricated cushion blocks are arranged at the bottom of the steel frame to keep the stability of the steel frame.
(10) Two-lining inverted arch pouring
The second lining inverted arch is constructed immediately following the primary closed loop in time, and the distance between the position of the second lining inverted arch and the tunnel face is less than or equal to 40 m; constructing a secondary-lining inverted arch in time, and forbidding the construction of a primary-support closed loop during the construction period of the inverted arch; the distance between the position of the primary support closed loop and the construction position of the secondary lining inverted arch is more than or equal to 2m so as to ensure the stability of the tunnel during the construction of the inverted arch.
(11) Two-lining arch wall pouring
Constructing two lining arch walls in time, wherein the distance between the position of the two lining arch walls and the tunnel face is less than or equal to 70 m; before the second-lining arch wall is constructed, necessary detection is carried out after the tunnel is primarily supported, and grouting and concrete pouring treatment are required to be carried out in time if a hole and a dark hole are found; measuring the section of the second lining by a measuring team, determining that the initial support does not invade the limit, and then constructing; when the second lining is poured, pouring is carried out window by window, and the falling height of concrete is less than or equal to 2 m; after pouring is finished, grouting is carried out on the vault in time, and cavities are prevented from being generated.
The key of the construction method for controlling settlement and convergence of the high-water-level shallow loess tunnel is as follows:
1. the length of the upper step is controlled to be 5-6 m, the core soil is required to be kept at 3-4 m, and the soil body on the tunnel face is stabilized. And removing the core soil and then installing a temporary cross brace.
The length of the middle step and the lower step is controlled to be 5-6 m, the core soil is required to be kept at 2-3 m, and the step soil body is stabilized. After the core soil is removed, the middle step is used as a temporary cross brace, and the lower step is closed in time to form a ring, so that the sedimentation is effectively controlled.
2. And the middle step and the lower step are constructed according to the design requirements, after the re-spraying is finished, back-pressure backfill is carried out on two sides, the backfill applies radial supporting force to the arch centering, resists the lateral pressure of an external soil body together with the arch centering, and reduces the settlement and convergence of the arch centering.
3. The middle step and the lower step require left-right staggered excavation, and the staggered distance is 2-3 m. Prevent two arch feet at the same step from being suspended at the same time, which causes the settlement at the same side to be increased.
The middle and lower steps can not be excavated at the same side, so that multiple arch springing at the same step can be prevented from being suspended, and the unilateral settlement is prevented from being overlarge.
The method of the invention has the following advantages:
1. the core soil is reserved on the upper step, the middle step and the lower step, so that the disturbance of the tunnel soil body is reduced.
2. The middle and lower steps back pressure backfill soil and the arch frame resist the lateral pressure of the external soil body together, and the settlement and convergence of the arch frame are reduced.
3. The middle step and the lower step are excavated in a left-right staggered mode, excavation at the same side is not needed, multiple parts of the single-side arch frame are prevented from being suspended, and single-side settlement is reduced.
4. The middle step and the lower step are not dug at the same step, and are staggered by 2-3 m from left to right, so that multiple suspension of arch springing of the same step is reduced, and disturbance of an arch center is reduced.
5. The tunnel has high water level, shallow buried depth, loose soil quality, unstable soil body and higher risk coefficient in construction. The convergence and the vault settlement are important reference values for tunnel construction, the construction cost does not need to be increased, and the convergence and the vault settlement of the tunnel can be effectively controlled by applying reverse pressure to two sides of the primary support.
6. In the implementation process of the technology, the soil output between construction processes can be reduced, the construction time is saved, the resource consumption is reduced, and the economic benefit maximization is achieved.
7. The method has strong pertinence and simple operation, and is easy to master by operators.
The method is applied to construction of a hidden excavation section of a newly-built southwest loop line project XNHS-1 standard section Dongjin tunnel of a Taiyuan railway junction. The built mileage is changed into DK6+ 127-DK 7+239.25 sections, and the length is 1112.25 m. The tunnel is a railway double-track tunnel, the surrounding rock grade is VI grade, the soil is silty clay, the maximum buried depth of the tunnel is 16.7m, the longitudinal slope is 3 per thousand, the water level is above the vault of the tunnel, the lining adopts composite lining, the arch structure form of a curved wall is adopted, the DK6+ 185-DK 7+205 sections are constructed by adopting a phi 42mm advanced small conduit and three-step temporary inverted arch method, HW175 profile steel is adopted, the spacing of steel frames is 65cm, one of two advanced small conduits is 3.5m, the angle is 10-15 ℃, the number is 42, 4 HW foot-contracting anchor pipes are arranged at each position, the length is 4m, and the angle is 45 ℃. The total length of the tunnel is 1112.5m, the buried depth is 9-16 m, the soil quality is loose, and the normal construction of the tunnel can be guaranteed only by effectively controlling sedimentation. Through practice, the construction method can solve the problems of short construction period, complicated construction and the like, effectively ensures the settlement amount of construction, ensures the safety and quality of normal construction, improves the construction progress, reduces the comprehensive construction cost of the project, has mature technology, obvious economic and social benefits and better popularization and application values.
Drawings
FIG. 1 shows a schematic process flow diagram of the present invention.
FIG. 2 shows the core soil reservation and back pressure backfill stress diagrams of the upper, middle and lower steps.
Fig. 3 shows a schematic cross-sectional view of a three-step temporary wale (inverted arch) process.
Fig. 4 is a schematic view showing a construction method of a three-step temporary wale (inverted arch) method.
In the figure: 1-upper step excavation, 2-middle step excavation, 3-lower step excavation and 4-inverted arch excavation; i-a small advanced conduit, II-an upper step primary support, III-an upper step temporary cross brace, IV-a middle step primary support, V-a middle step temporary cross brace, VI-a lower step primary support, VII-an inverted arch primary support, VIII-an inverted arch pouring, IX-an inverted arch filling concrete, X-arch wall concrete and XI-phi 42mm locking steel pipes.
Detailed Description
The detail of the VI-level shallow-buried loess tunnel at the underground excavation section of the Dongxin tunnel of the standard section of XNHS-1 newly built southwest loop line project on the original railway junction is described in detail below.
A settlement control convergence construction method for a high-water-level shallow loess tunnel comprises the following steps:
1. precipitation well precipitation
In the engineering of the section, the underground water level is positioned at the vault. Before tunnel construction, precipitation work needs to be done, and construction conditions are met only when the water level is 1.5m below an inverted arch. The dewatering well is arranged 80m in front of the construction face to pre-pump water in advance. And (4) making water level measurement work of the dewatering well by a technician and making a record. And (4) observing whether water leakage exists in the tunnel by workers in the tunnel, stopping tunnel face construction if the water leakage is abnormal, and timely processing.
2. Determining reserved deformation
During construction, deformation is reserved according to design files, and timely adjustment is needed according to monitoring and measuring data results to avoid limit invasion.
3. Determining step height
The upper step excavation height is not less than 0.3 time of the upper step excavation span and is generally 0.3-0.4 m; the excavation heights of the middle step and the lower step are equal to the total excavation height (without an inverted arch) of the tunnel minus the excavation height of the upper step.
4. Excavating upper steps and preliminary bracing
The spacing between the construction arch frames is 0.65m, manual cooperation with mechanical excavation is required during construction, the soil excavation spacing is controlled within 0.9m, and overexcavation is not required. Construction is strictly carried out according to design bottom-crossing requirements during initial construction, construction procedures cannot be reduced, and labor and materials cannot be stolen. When the re-spraying is carried out on the upper step, the re-spraying thickness must be ensured.
The thickness of the re-spraying is 65mm, thin steel bars with the length of 65mm are welded on the steel frame, and the number of the thin steel bars is set every 2m to control the thickness of the re-spraying.
The designed size of the arch connecting plate is 225mm multiplied by 300mm multiplied by 16mm, and the large cushion blocks of 400mm multiplied by 100mm are adopted, so that the stress applied by the arch to the soil body is reduced. The soil body below the cushion block must be compact. The lock leg anchor pipe is the most important link for planning settlement, and grouting is performed during construction of the lock leg anchor pipe, so that the rigidity of the lock leg anchor pipe is increased. 4 locking feet are designed at each position, and the number of the locking foot anchor pipes can be increased for soil loose sections.
The length of the upper step is controlled to be 5-6 m, core soil is reserved, the length of the core soil is kept to be 3-4 m, and a temporary cross brace arranged on the core soil section is removed.
5. Temporary cross brace for constructing upper step
The temporary transverse supports of the upper steps are constructed in time, the temporary steel frames are made of H175 steel, one position is longitudinally arranged at each 2 trusses and connected with the hole body steel frames through bolts, pre-embedded steel plates are welded at corresponding positions after the hole body steel frames are erected, bolts are preset so that the temporary steel frames can be connected, and the height of a welding seam at the joint of the connecting steel plates is not less than 10 mm; the adjacent steel frames are connected by adopting HRB phi 22mm steel bars, and the circumferential distance is 1m, and the steel frames are welded at the inner flange of the steel frame. After the temporary cross arm is completely constructed, the upper step forms a closed loop, and the settlement is effectively controlled.
6. Excavating one side of the middle step and performing preliminary bracing
The middle step can not be excavated on two sides simultaneously, steps are staggered left and right, and the step staggering distance is 2-3 m. The core soil is reserved during the middle step excavation, the full-section excavation cannot be performed, and only one side needs to be excavated and enough construction space is provided. The middle step is excavated at one time and does not exceed 2 trusses, and the excavation distance is controlled during excavation and does not exceed 1.5 m. And (5) performing primary support after excavation is finished, and ensuring the re-spraying thickness.
After the re-spraying is finished, the middle step backfills earth to perform back pressure.
7. Temporary step cross brace in construction
The temporary transverse supports of the middle step are constructed in time to ensure construction quality, the temporary steel frames are made of H175 section steel, one part is arranged at every 2 vertical frames, and the temporary steel frames are connected with the hole body steel frames through bolts.
After the construction is finished, the backfilling soil is timely and reversely pressed.
And a closed loop is formed after the middle step cross brace is applied, so that the sedimentation is effectively controlled.
8. Excavating one side of the lower step for preliminary bracing
And judging whether the lower step can be excavated according to the settlement and convergence values, wherein the middle and lower steps can be constructed diagonally and cannot be excavated on the same side as the middle step only under the condition that the settlement and convergence control measurement is stable. When the lower step is excavated, the core soil is reserved, the lower step cannot be excavated in a full-section manner, and only one side needs to be excavated and the construction space is provided. And performing primary support according to design requirements after excavation is finished.
And after the initial construction is finished, back-pressure backfilling is carried out in time, and the settlement amount is controlled.
9. Preliminary bracing closed loop construction
And (3) sealing the primary support into a ring in time after the tunnel is excavated, wherein the full-section closed ring is preferably controlled to be about 15d, and the distance between the sealed ring and the tunnel face is not more than 35 m. And the footage of the primary support closed loop in each cycle is not more than 3m, and all operations of the lower step are strictly forbidden when the primary support closed loop is excavated. The excavation adopts a mechanical and manual excavation mode, and the overexcavation cannot be carried out under any condition. Soil with the thickness of 60-70 cm is reserved at corners such as arch legs, wall corners and the like, and the soil is excavated manually. Meanwhile, C20 prefabricated cushion blocks are arranged at the bottom of the steel frame to keep the stability of the steel frame.
10. Two-lined inverted arch pouring
The two-lining inverted arch is constructed immediately following the primary closed loop, and the distance between the position of the two-lining inverted arch and the tunnel face is not more than 40 m. And when the construction of the second-lining inverted arch is provided, the inverted arch construction is carried out in time. And during the construction of the inverted arch, the construction of the primary support closed loop is forbidden. The distance between the position of the primary support closed loop and the construction position of the secondary lining inverted arch is not less than 2m, so that the stability of the tunnel during the construction of the inverted arch is ensured. And when the two-lining inverted arch has pouring conditions, pouring in time.
11. Two-lined arch wall pouring
And the two lining arch walls are constructed in time, and the distance between the positions of the two lining arch walls and the tunnel face is not more than 70 m. Before the second-lining arch wall is constructed, necessary detection needs to be carried out after the tunnel is initially supported, and grouting and concrete pouring treatment needs to be carried out in time if a hole or a dark hole is found. And measuring the section of the second lining by a measuring team, and determining that the initial support is not limited to construction. And when the two-lining pouring is carried out, the pouring is carried out window by window, and the falling height of the concrete is not more than 2 m. After pouring is finished, grouting is carried out on the vault in time, and cavities are prevented from being generated.
Under the premise that the original construction method is not changed, the tunnel can effectively control convergence and vault settlement by reasonably utilizing the on-site earthwork and adopting a reasonable excavation mode, the normal operation of construction is maintained, and no extra cost is generated. And when in site construction, the core soil is reserved at the upper part, the middle part and the lower part, and back pressure backfill construction is adopted, so that the dispersed soil yield among all construction procedures is reduced, finally, the primary support closed loop is used for uniformly and intensively soil production, and the soil production time of each cycle of excavation is saved. Before the construction method is not adopted, the unearthing time of each cycle is about 3 and a half hours. When the construction method is used for construction, the unearthing time of each cycle is only 2 and a half hours, time is saved by 1 hour for each cycle, the total length of the tunnel is 1112.5m, 1700 cycles are required for construction, 1700 hours are saved, the time is saved by 71 days, and the construction period is ensured.
For the VI-level surrounding rock high-water-level shallow-buried loess tunnel, how to control convergence and settlement in the tunnel ensures the safety of constructors, prevents the limit invasion of a primary support arch frame and is the important point in construction. The settlement convergence is too large, which not only affects the safety in construction, but also seriously hinders the construction progress. In the traditional construction method with design requirements, the stability of the soil body on the tunnel face is greatly influenced, and the settlement cannot be guaranteed within the standard range strictly according to the design construction. The method does not change the construction requirements of the traditional design method, and has good effect on improving the settlement of the tunnel by drilling and researching results of predecessors and self construction and successfully applying to practice. The engineering quality is ensured, good economic and social benefits are obtained, and the technology reaches the domestic leading level.
The method has reasonable design, obvious economic and social benefits, energy conservation and environmental protection and reaches the standard requirement, and the technology reaches the domestic leading level. The quick mounting and construction method is used for quick mounting and construction of the T-shaped steel box girder of the large-span railway swivel and has good popularization and application values.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the detailed description is made with reference to the embodiments of the present invention, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the protection scope of the claims of the present invention.

Claims (1)

1. A settlement control and convergence construction method for a high-water-level shallow loess tunnel is characterized by comprising the following steps: the method comprises the following steps:
(1) dewatering well for dewatering
Because the underground water level is at the vault position, before the tunnel construction, the precipitation work is done, so that the water level is 1.5m below the inverted arch; the dewatering well is arranged 80m in front of the construction face and pre-pumps water in advance; a technician works and records the water level measurement work of the dewatering well; the workers in the tunnel observe whether the water leakage condition exists in the tunnel, and if the water leakage condition exists in the tunnel, the tunnel face construction is stopped for processing;
(2) determining the reserved deformation
During construction, the deformation is reserved according to design, and adjustment is carried out according to the monitoring and measuring data result;
(3) determining the step height
The excavation height of the upper step is more than or equal to 0.3 time of the excavation span of the upper step, and the excavation heights of the middle step and the lower step are the average distribution of the tunnel total excavation height minus the excavation height of the upper step;
(4) excavating upper bench and preliminary bracing
The spacing between the construction arches is 0.65m, and the soil excavation spacing is controlled within 0.9 m; the construction is carried out according to the design requirement during the initial construction, when the steel frame is subjected to the step-up re-spraying, the re-spraying thickness is 65mm, thin steel bars with the length of 65mm are welded on the steel frame, and the steel bars are arranged every 2m and used for controlling the re-spraying thickness;
the designed size of the arch center connecting plate is 225mm multiplied by 300mm multiplied by 16mm, and a large cushion block of 400mm multiplied by 100mm is adopted; grouting is carried out during construction of the lock leg anchor pipes, the rigidity of the lock leg anchor pipes is increased, 4 lock legs are designed at each position, and the number of the lock leg anchor pipes is increased for a soil loose section;
the length of the upper step is controlled to be 5-6 m, core soil is reserved, the length of the core soil is kept to be 3-4 m, and a temporary cross brace arranged on the core soil section is removed;
(5) and constructing temporary cross brace for upper step
The temporary transverse supports of the upper steps are constructed in time, the temporary steel frames are made of H175 steel, one position is longitudinally arranged at each 2 trusses and connected with the hole body steel frames through bolts, the embedded steel plates are welded at corresponding positions after the hole body steel frames are erected, bolts are preset so that the temporary steel frames can be connected, and the height of a welding seam at the joints of the embedded steel plates is more than or equal to 10 mm; the adjacent temporary steel frames are connected by adopting steel bars, the circumferential distance is 1m, and the temporary steel frames are welded at the inner flange of each temporary steel frame; after the temporary transverse support is constructed, the upper step forms a closed loop;
(6) excavating one side of the bench and performing primary support
The middle step can not be excavated at two sides simultaneously, steps are staggered left and right, and the step staggering distance is 2-3 m; the core soil is reserved during the middle step excavation, only one side needs to be excavated, and the construction space is provided; the middle step is excavated once within 2 trusses, and the excavation distance is controlled during excavation and is within 1.5 m; performing primary support after excavation is finished, and ensuring the re-spraying thickness;
after the re-spraying is finished, back-pressing the middle step backfill earthwork;
(7) temporary step cross brace in construction
The intermediate step temporary transverse support is constructed in time to ensure construction quality, the temporary steel frame adopts H175 steel, one part is arranged at every 2 vertical trusses, and the temporary steel frame is connected with the hole body steel frame through bolts;
after the application is finished, back pressure is carried out on the backfilled soil in time;
forming a closed loop after the middle step cross brace is applied;
(8) excavating one side of the lower step and performing primary support
Judging whether the lower step can be excavated according to the settlement and convergence values, and performing diagonal construction on the middle and lower steps only under the condition that the settlement and convergence control measurement is stable; when the lower step is excavated, the core soil is reserved, and only one side is excavated to form a construction space; performing primary support according to design requirements after excavation is finished;
performing back pressure backfilling after the initial construction is finished;
(9) initial support closed loop construction
Sealing and looping the primary support in time after the tunnel is excavated, controlling the full-section closed loop at 15d, and keeping the distance between the sealed and looping position and the tunnel face to be less than or equal to 35 m; the footage of each cycle of the primary closed loop is less than or equal to 3 m; reserving soil bodies with the thickness of 60-70 cm at the arch springing and the corner springing of the wall, and manually excavating; meanwhile, C20 concrete prefabricated cushion blocks are arranged at the bottom of the steel frame to keep the stability of the steel frame;
(10) two-lining inverted arch pouring
The second lining inverted arch is constructed immediately following the primary closed loop in time, and the distance between the position of the second lining inverted arch and the tunnel face is less than or equal to 40 m; constructing a secondary-lining inverted arch in time, and forbidding the construction of a primary-support closed loop during the construction of the inverted arch; the distance between the position of the primary support closed loop and the construction position of the secondary lining inverted arch is more than or equal to 2m so as to ensure the stability of the tunnel during the construction of the inverted arch;
(11) two-lining arch wall pouring
Constructing two lining arch walls in time, wherein the distance between the position of the two lining arch walls and the tunnel face is less than or equal to 70 m; before the second lining arch wall is constructed, detecting the tunnel after the tunnel is primarily supported, and if a cavity and a dark hole are found, carrying out grouting and concrete pouring treatment; measuring the section of the second lining, determining that the initial support does not invade the limit, and then constructing; when the second lining is poured, pouring is carried out window by window, and the falling height of concrete is less than or equal to 2 m; after pouring is finished, vault grouting is carried out, and cavities are prevented from being generated.
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