CN111677530B - Safe construction method for three-step temporary inverted arch at tunnel through section - Google Patents
Safe construction method for three-step temporary inverted arch at tunnel through section Download PDFInfo
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- 238000000034 method Methods 0.000 claims abstract description 26
- 239000002689 soil Substances 0.000 claims abstract description 20
- 239000011435 rock Substances 0.000 claims abstract description 13
- 238000009412 basement excavation Methods 0.000 claims description 26
- 238000005507 spraying Methods 0.000 claims description 15
- 239000004567 concrete Substances 0.000 claims description 8
- 230000003014 reinforcing effect Effects 0.000 claims description 7
- 230000005641 tunneling Effects 0.000 claims description 7
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/04—Lining with building materials
- E21D11/10—Lining 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
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/04—Lining with building materials
- E21D11/10—Lining 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
- E21D11/105—Transport or application of concrete specially adapted for the lining of tunnels or galleries ; Backfilling the space between main building element and the surrounding rock, e.g. with concrete
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/14—Lining predominantly with metal
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/14—Lining predominantly with metal
- E21D11/15—Plate linings; Laggings, i.e. linings designed for holding back formation material or for transmitting the load to main supporting members
- E21D11/152—Laggings made of grids or nettings
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D20/00—Setting anchoring-bolts
- E21D20/02—Setting anchoring-bolts with provisions for grouting
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Abstract
The invention relates to a tunnel through construction technology, in particular to a safe construction method for a three-step temporary inverted arch at a tunnel through section. The technical problem that the construction efficiency is lower in the conventional CRD method or advanced pipe shed construction for tunnel through construction is solved. The invention is characterized in that: for VI-level surrounding rock through construction of shallow high water level, a three-step temporary inverted arch method and phi 42 advanced close-packed small guide pipes are adopted for through construction, and the overall construction efficiency is greatly improved. The tunnel face is reserved with core soil, and is drilled with an anchor pipe and is grouted, so that the stability of the tunnel face soil body is ensured. The number of foot-contracting anchor pipes is increased by the arch feet, the arch foot cushion blocks are increased, and each truss is provided with the temporary inverted arch, so that the stability and the bearing capacity of the primary support steel frame are improved. On the basis of the construction of the three-step temporary inverted arch method, the invention improves various support parameter requirements and improves the construction method of the three-step temporary inverted arch, so that the construction progress can be ensured and the safety coefficient of construction can be greatly improved in the through construction process of the tunnel.
Description
Technical Field
The invention relates to a tunnel through construction technology, in particular to a safe construction method for a three-step temporary inverted arch at a tunnel through section.
Background
With the rapid development of national economy, the rapid expansion of cities and the long-term planning of urban construction, the demand of human beings on underground space is more and more, the application is more and more extensive, and the technology is more and more mature, so that the research on underground engineering is developed rapidly. The vigorous development of the underground tunnel and the subway solves the problems of transportation. However, the construction of underground excavation tunnels is accompanied by various difficulties, among which the tunnel penetration construction is a great difficulty. How can the completion tunnel of safety and stability link up, can guarantee the tunnel construction progress again in, accomplish the tunnel and link up the construction, guarantee constructor's safety, become a difficult point place that link up the construction. The CRD method or the advanced pipe shed construction is usually adopted in the general tunnel through construction, although the construction safety can be guaranteed, the construction efficiency is influenced, various supporting parameters of construction are increased on the basis of the three-step temporary inverted arch method construction in the project department, the construction safety can be guaranteed, the normal construction efficiency is not influenced, and the smooth through of the tunnel is guaranteed.
Disclosure of Invention
The invention provides a safe construction method for a three-step temporary inverted arch at a tunnel through section, which aims to solve the technical problem of low construction efficiency in the conventional CRD (cross-linked concrete) method or advanced pipe shed construction for tunnel through construction.
The invention is realized by adopting the following technical scheme: a safe construction method for a three-step temporary inverted arch at a tunnel through section comprises the following steps: construction step before shutdown of inlet section
(1) Constructing the last upper step arch before the shutdown of the inlet section and arranging a small advanced duct: after the heading of the face is stopped, anchor pipes with the interval of 1m x 1m and the length of 18 m are arranged on the face of the upper step, the pipe heads are made into a pointed cone shape, and the pipe bodies are drilled at intervals of 30cm in a quincunx arrangement mode and are grouted; after grouting, hanging a net and spraying anchors, wherein the spraying thickness is 10 cm;
(2) the upper and middle step non-closed loop arches (except the core soil reserved influence range) of the inlet section are constructed as temporary inverted arches in time, the primary support closed loop construction is flush with the lower step, and the steel frame is ensured to form loop stress;
(3) then carrying out soil piling and back pressure on the face of the tunnel, wherein the filling height is required to be not less than 4m, the face of the tunnel is backfilled to the vault position as much as possible, and the other end of the face of the tunnel is backfilled to the primary support to seal the ring-shaped end head;
(II) construction step of through stage
(1) Excavating: after the construction of the inlet section is stopped, performing one-way tunneling on the outlet section, excavating by adopting a three-step temporary inverted arch method, wherein the distance between steel frames is 1 per cycle of the upper step, the middle step and the lower step are excavated in a staggered mode, the step distance between adjacent steps is not more than 5 meters, and core soil of 2-3 meters is reserved in the upper step;
(2) steel frame construction: digging grooves in place when steel frames are erected, enlarging cushion blocks at the bottom of the steel frames to 40cm by 40cm, connecting the steel frames by longitudinal steel bars, connecting the steel frames into a whole, and applying force together, wherein the longitudinal connecting steel bars are arranged at an annular interval of 1.0 meter;
(3) and (3) anchor pipe construction: firstly, adopting phi 42 advanced densely-arranged small ducts in the range of 140 degrees of an upper step arch part, wherein the annular distance is 3 pieces/m, the length is 4m, and each roof truss is constructed with the advanced small ducts; two sides of the upper, middle and lower step arch springing are provided with six phi 42 locking anchor pipes, and the anchor pipes are 4m long; thirdly, arranging phi 42 side wall anchor pipes with the length of 4m on the middle and lower steps at intervals of 1.5 x 1.5 m; grouting all anchor pipes;
(4) and (3) construction of a reinforcing mesh: phi 8 reinforcing mesh sheets are adopted, the space between the meshes is 20 multiplied by 20cm, the mesh sheets are arranged in a single layer, and the overlapping length of the mesh sheets is not less than one mesh;
(5) concrete spraying construction;
(6) constructing a temporary inverted arch: the outlet is provided with a temporary inverted arch penetrating through the upper and middle steps of the front 5m section and is designed to be constructed one truss at a distance.
The characteristic of the method of the invention
1. For VI-level surrounding rock through construction of shallow high water level, a three-step temporary inverted arch method and phi 42 advanced close-packed small guide pipes are adopted for through construction, and the overall construction efficiency is greatly improved.
2. The tunnel face is reserved with core soil, and is drilled with an anchor pipe and is grouted, so that the stability of the tunnel face soil body is ensured.
3. The number of foot-contracting anchor pipes is increased by the arch feet, the arch foot cushion blocks are increased, and each truss is provided with the temporary inverted arch, so that the stability and the bearing capacity of the primary support steel frame are improved.
4. The invention creatively adopts the technical means of digging an anchor pipe on the face of the upper step and piling soil for back pressure at the inlet section, thereby effectively improving the construction safety.
Application scope of the invention
The method is suitable for soil tunnels of V-level and VI-level surrounding rocks and the like.
The invention's process principle
On the basis of the construction of the three-step temporary inverted arch method, various support parameter requirements are improved, and the construction method of the three-step temporary inverted arch is improved, so that the construction progress can be guaranteed and the safety coefficient of construction can be greatly improved in the process of penetrating through the tunnel.
Benefit analysis of the invention
The traditional large pipe shed construction is adopted, a drilling platform needs to be installed and erected, a large-scale pipe shed drilling machine is introduced, and the manpower input is not less than 35 persons. By adopting the construction method, the introduction and installation of a drilling platform frame and a large-scale pipe shed drilling machine are reduced, only equipment for normal construction is needed, and a constructor only needs 15 persons, so that material resources and manpower are greatly saved, and the cost is saved by 40 ten thousand yuan. Meanwhile, the construction method is adopted for construction, and the tunnel is successfully communicated only in 8 days. Compared with the traditional large pipe shed construction, the construction period is saved by about 12 days, and good economic and social benefits are obtained.
Drawings
FIG. 1 is a flow chart of the construction process of the present invention.
Fig. 2 is a schematic construction diagram before shutdown of an inlet section.
FIG. 3 is a schematic view of a leading closely-spaced conduit arrangement.
Fig. 4 is a schematic view of an entrance tunnel face net hanging anchor pipe laying site.
Fig. 5 is a schematic view of the field for the completion of the anchoring of the tunnel face of the inlet section.
FIG. 6 is one of the schematic drawings of the construction of three steps on site.
Fig. 7 is a second schematic view of the construction of three steps on site.
FIG. 8 is a schematic view of the construction of the anchor pipe with the locking feet on site.
FIG. 9 is a schematic view of the construction of the step-up construction on site.
Detailed Description
The construction process flow and the operation key points of the invention
Firstly, a construction process flow is shown in figure 1.
Second, the construction operation key points
1. Preparation phase
Collecting the measurement data of the surrounding rock. And (4) carefully surveying the earth surface, setting settlement observation points on the earth surface in an encrypted manner, and measuring the subsidence of the earth surface.
(1) The monitoring measurement is enhanced for the inside and the surface of the hole, and the monitoring measurement must be carried out according to the following measurement items: observation inside and outside the tunnel, measurement of clearance level convergence, measurement of vault crown subsidence and measurement of ground surface subsidence.
(2) The step pitch is adjusted, the principle of 'pipe advance, measurement in duty, early sealing and strong support' is adhered to in construction, the step pitch of each step is strictly controlled, the construction of the entrance section is carried out until the penetrating mileage is reached, the distance between the two lining faces is not more than 50m, and the safety and the order of the tunnel penetrating process are ensured.
2. Construction step before shutdown of inlet section
The last upper step arch frame constructed before the shutdown of the entrance section is provided with a leading small guide pipe, after the tunneling of the tunnel face is stopped, anchor pipes (the leading small guide pipes) with the distance of 1m x 1m and the length of 18 m are drilled on the tunnel face of the upper step, the pipe heads are made into taper shapes, the pipe bodies are drilled at intervals of 30cm, after the grouting is finished, net hanging and anchor spraying are carried out, the spraying thickness is 10cm (shown in figures 4 and 5), in order to further ensure the stability of the tunnel face, the soil piling back pressure is carried out on the tunnel face, when the last two molds are constructed, excavated earthwork is piled on the tunnel face, when the earthwork is insufficient, soil is transported from the hole, a digger is used for carrying out anchor spraying to tamp the soil, the filling height is required to be not less than 4m, the tunnel face is backfilled to the arch crown part as far as possible, and the other end is backfilled to the primary closed ring end as far as possible. Fill back pressure is shown in figure 2.
3. Construction step of run-through stage
(1) Excavating: and after the construction of the inlet section is stopped, the outlet section is tunneled in one way, the three-step temporary inverted arch method is adopted for excavation, the distance between two steel frames is 1 in each circulation of the upper step, the disturbance to the surrounding rock is reduced by adopting a manual matching mechanical excavation mode, 50cm soil is reserved and is maintained by adopting manual excavation, the middle step and the lower step are excavated in a staggered mode, the step distance between adjacent steps is not more than 5m, 2-3 m core soil is reserved on the upper step, a special person is arranged in the excavation process to observe the surrounding rock and the change of the adjacent primary support, and the geological sketch work is well done. The site construction of the three-step temporary inverted arch method is shown in figures 6 and 7, and three temporary steps can be seen from the figures (pictures).
(2) Steel frame construction: the steel frames are excavated and positioned when being erected, the virtual slag and sundries below the bottom feet are removed before installation, cushion blocks at the bottoms of the steel frames are enlarged to 40cm by 40cm (designed to 25cm by 25 cm), the steel frames are connected by longitudinal steel bars, so that the steel frames are connected into a whole to bear force together, and the longitudinal connecting steel bars are arranged at an annular interval of 1.0 meter.
(3) Construction of a small advanced guide pipe: firstly, as shown in FIG. 3, the 140-degree range of the upper step arch part adopts phi 42 (mm) advanced densely-arranged small ducts, the annular space is 3 pieces/m, the length is 4m (design 3.5 m), and each steel frame is provided with a cycle (design for constructing one frame at every other frame); two sides of the arch springing of the upper, middle and lower steps are provided with six phi 42 (mm) locking anchor pipes, and the length of the anchor pipe is 4m (the picture on site is shown in figure 8); thirdly, anchor pipes with phi 42 side walls are arranged on the middle and lower steps at intervals of 1.5 x 1.5m, and the length of each anchor pipe is 4 m. All anchor pipes are grouted.
(4) And (3) construction of a reinforcing mesh: the mesh is characterized in that phi 8 x (mm) steel bar meshes are adopted, the mesh spacing is 20 x 20cm, the mesh is arranged in a single layer mode, and the overlapping length of the meshes is not less than one mesh. The reinforcing mesh is arranged by adhering to the steel support outer arc, and the reinforcing mesh must be firmly welded with the I-shaped steel.
(5) And (3) concrete spraying construction: the spraying operation is segmented, sliced and layered, and spirally ascends from bottom to top in sequence.
(6) Constructing a temporary inverted arch: the outlet penetrates through the upper 5m section and the middle step, and a temporary inverted arch (constructed by one truss at intervals) is arranged for each truss.
Materials and apparatus
Quality control
First, measure technical guarantee measure of monitoring and measuring
1. Observation inside and outside the hole
(1) The hole appearance observation comprises observation of surface condition, surface subsidence and surface water penetration.
(2) The observation in the hole comprises the observation of the tunnel face and the observation of the supporting structure.
(3) Visual observation is carried out after excavation and before concrete is sprayed for the first time, and a geological sketch map is drawn after each excavation for checking the grade of surrounding rocks and judging the support stability; whether the sprayed concrete cracks and develops or not and whether the anchor rod looses or not are checked, relevant records are made, and visual and necessary information is provided for safe construction.
2. In-hole monitoring and measuring
(1) Monitoring and measuring section and measuring point design: the items to be measured, such as clearance change, vault subsidence and the like, are arranged on the same section, and a measuring section is arranged every 5m of tunneling and comprises 3 clearance change baselines and 1 vault subsidence measuring point.
(2) Main monitoring project measuring point arrangement
Horizontally converging: and 1 group of measuring piles are buried at the position 2m above the maximum width of the tunnel within 2 hours after the excavation and support of the measured section are determined, and initial reading is carried out. The measuring method adopts a total station instrument for measuring.
Vault sinking: and (3) burying 1 measuring pile at the vault position of the tunnel within 2 hours after excavation and support of the measured section, and performing initial reading. The monitoring instrument adopts a total station.
3. Observation of surface subsidence
(1) Observation point setting
1 monitoring measuring section is respectively arranged in the range of the through mileage and the distance between the two sides of the through mileage and ten meters, each section is provided with 13 measuring points, and the distance between the measuring points is 2 m. The monitoring point sets requirements: firm in point setting, correct in position and good in visibility.
(2) Observation mode
And (3) beginning observation when the tunnel excavation construction is 20m away from the through point, adjusting the measuring frequency to the monitoring measuring point in the tunnel once every 4h and once every 12h on the earth surface according to the surrounding rock variation, and forming a monitoring measuring daily report. And after the tunnel is communicated, finishing secondary lining and stopping measuring after the settlement is stable.
4. Measurement data sorting, analyzing and feeding back
And after each measurement, data sorting is carried out in time, a measured data time-state curve and an excavation surface geological sketch map are drawn, the audit of a project general engineer 20:00 in the day is reported, regression analysis is carried out on the initial time-state curve, and the maximum value and the change speed which are possible to occur are predicted. And when the vault is sunk, the horizontal convergence rate reaches 5mm/d or the displacement is accumulated to reach 100mm, the tunneling is suspended, the reason is analyzed, and reinforcement measures such as thickening a spray layer, encrypting or strengthening advanced support, increasing a steel frame and the like are taken in time according to specific conditions.
Second, excavation construction technology guarantee measure
The tunnel excavation is strictly carried out, the excavation length of each cycle of the upper step is not more than 1 steel frame space, a manual cooperation mechanical excavation mode is adopted, the disturbance to surrounding rock is reduced, and the part close to the outer contour is trimmed by manual excavation. And for the part which cannot be directly excavated by using the machine, chiseling by using an air pick. And (3) strictly controlling overbreak and underbreak, immediately carrying out primary support after excavation is finished, observing the face by a professional safety worker before excavation, and carrying out excavation operation after no potential safety hazard is found.
Safety measures
1. Excavation and support personnel must carry out pre-post training, and can enter a construction site to work after examination is qualified.
2. All personnel participating in construction must wear safety protection articles according to the regulation, and the personnel must concentrate on in the work because drinking is forbidden before going to work. All constructors must wear safety helmets when entering a construction site, and the safety belts are tied and safety nets are hung during high-altitude operation.
3. All construction machines and tools need to be operated by certified persons who are qualified in training and examination on duty, safety operation of the hang tag is carried out, the operation is strictly forbidden to persons without certification or unfamiliar performance, drunk driving and fatigue driving are strictly forbidden. The construction equipment needs to confirm that the technical state is good and the spare parts are complete and effective.
4. When electric and gas welding is carried out, fire prevention measures and special guard must be provided, and the distance between oxygen and acetylene must be controlled to be more than 5 m.
5. The concrete spraying operator needs protective tools such as a dust mask, protective glasses and the like, and avoids directly contacting with the liquid accelerator, and the operator needs to immediately wash with clean water after careless contact.
Environmental protection measure
1. When the dust-free working environment is used for working, working personnel must be equipped with labor protection articles.
2. When the earth surface is unearthed, the water is sprayed on the field and the unearthed traffic road, so that dust is prevented from flying and polluting the surrounding environment. A fog gun machine is arranged in the hole to reduce dust in the hole.
3. The concrete delivery pump cleaning sewage needs to be discharged through a professional pipeline.
4. And the method complies with the national or industry-related environmental protection requirements and standards.
Examples of the applications
The construction method is applied to construction of VI-level surrounding rocks with high water level in underground excavation and shallow burying of Dongxin tunnels in standard sections of XNH-1S for newly-built southwest loop projects of Taiyuan railway hubs. The tunnel has the beginning-to-end mileage of from DK6+127 to DK7+239.25, and the length of 1112.25 m. The tunnel is a railway double-track tunnel, the grade of surrounding rock 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 a composite lining and a curved wall arch structure, wherein the DK6+ 127-DK 6+185 sections adopt phi 42 advanced closely-spaced small ducts and a CRD method for excavation construction, the DK6+ 185-DK 7+205 sections adopt phi 42 advanced small ducts and a three-step seven-step excavation construction, and the DK7+ 205-DK 7+239.25 sections adopt phi 42 advanced closely-spaced small ducts and a CRD method for excavation construction. The planned through mileage of the tunnel is DK6+640, the grade of surrounding rock is VI grade, and the buried depth is 10 m. The entry section is tunneled to a through mileage and then the tunneling is stopped, and the second lining is constructed to be 40m away from the tunnel face; excavating the outlet section according to the daily schedule of 1.5m, and excavating the upper step to a through point in 20 days in 5 months in 2019, wherein the distance between the two linings and the tunnel face is 50 m; and lining construction is carried out for two days in 5 months and 30 days to form a lining closed loop.
Claims (3)
1. A safe construction method for a three-step temporary inverted arch at a tunnel through section is characterized by comprising the following steps: construction step before shutdown of inlet section
(1) Constructing the last upper step arch before the shutdown of the inlet section and arranging a small advanced duct: after the heading of the face is stopped, anchor pipes with the interval of 1m x 1m and the length of 18 m are arranged on the face of the upper step, the pipe heads are made into a pointed cone shape, and the pipe bodies are drilled at intervals of 30cm in a quincunx arrangement mode and are grouted; after grouting, hanging a net and spraying anchors, wherein the spraying thickness is 10 cm;
(2) the upper and middle step non-closed loop arches at the inlet section are constructed as temporary inverted arches in time, the primary support closed loop construction is parallel to the lower step, and the steel frame is ensured to form loop stress; after the tunnel face stops tunneling, when the non-closed-loop arches on the upper and middle steps of the inlet section are used as temporary inverted arches, the non-closed-loop arches are used except the reserved influence range of the core soil, and the ring-forming stress of the steel frame is ensured;
(3) then carrying out soil piling and back pressure on the face of the tunnel, wherein the filling height is required to be not less than 4m, the face of the tunnel is backfilled to the vault position as much as possible, and the other end of the face of the tunnel is backfilled to the primary support to seal the ring-shaped end head; after the last two inverted arches are constructed, when the tunnel face is piled up, the excavated earthwork is piled up on the tunnel face, when the earthwork is insufficient, the earthwork is transported from the outside of the hole, and the soil body is compacted by an excavator to carry out anchor spraying;
(II) construction step of through stage
(1) Excavating: after the construction of the inlet section is stopped, performing one-way tunneling on the outlet section, excavating by adopting a three-step temporary inverted arch method, wherein the distance between steel frames is 1 per cycle of the upper step, the middle step and the lower step are excavated in a staggered mode, the step distance between adjacent steps is not more than 5 meters, and core soil of 2-3 meters is reserved in the upper step; the distance between two steel frames is 1 per cycle of footage of the upper step, a manual matching mechanical excavation mode is adopted, disturbance to surrounding rocks is reduced, and a soil body of 50cm is reserved and is trimmed by manual excavation;
(2) steel frame construction: digging grooves in place when steel frames are erected, enlarging cushion blocks at the bottom of the steel frames to 40cm by 40cm, connecting the steel frames by longitudinal steel bars, connecting the steel frames into a whole, and applying force together, wherein the longitudinal connecting steel bars are arranged at an annular interval of 1.0 meter;
(3) and (3) anchor pipe construction: firstly, adopting phi 42 advanced densely-arranged small ducts in the range of 140 degrees of an upper step arch part, wherein the annular distance is 3 pieces/m, the length is 4m, and each roof truss is constructed with the advanced small ducts; two sides of the upper, middle and lower step arch springing are provided with six phi 42 locking anchor pipes, and the anchor pipes are 4m long; thirdly, arranging phi 42 side wall anchor pipes with the length of 4m on the middle and lower steps in a quincunx shape at intervals of 1.5 x 1.5 m; grouting all anchor pipes;
(4) and (3) construction of a reinforcing mesh: phi 8 reinforcing mesh sheets are adopted, the space between the meshes is 20 multiplied by 20cm, the mesh sheets are arranged in a single layer, and the overlapping length of the mesh sheets is not less than one mesh;
(5) concrete spraying construction;
(6) constructing a temporary inverted arch: temporary inverted arches are arranged on the upper and middle stages of the outlet penetrating through the front 5m section for each roof truss, and the outlet is designed to be constructed for one roof truss at intervals.
2. The safe construction method of the three-step temporary inverted arch at the through section of the tunnel according to claim 1, wherein the bottom cushion blocks of the steel frame are increased from 25 × 25cm to 40 × 40cm, the number of the foot-reducing anchor pipes of the steel frame is increased, and each frame is provided with the temporary inverted arch, so that the stability and the bearing capacity of the primary support steel frame are greatly improved.
3. The safe construction method of the three-step temporary inverted arch of the tunnel penetration section according to claim 1, characterized in that (5) concrete spraying construction: the spraying operation is segmented, sliced and layered, and spirally ascends from bottom to top in sequence.
Priority Applications (1)
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