Construction method for railway tunnel portal in steep severe bias creep terrain

Abstract

The invention discloses a construction method for a railway tunnel portal in steep and severe bias creep terrain, and relates to the technical field of tunnel engineering construction, and the construction method comprises the following steps: building a tunnel portal construction full-process model based on a BIM technology, simulating the construction sequence and stress state of slide-resistant piles, open cut tunnels and protective nets, and optimizing construction steps. Construction site arrangement optimization is carried out; hole positions of the anti-slide piles, the pre-reinforcing piles and the surface jet grouting piles are accurately measured and lofted, then holes are dug in the anti-slide piles, and the pre-reinforcing piles and the surface jet grouting piles are cast-in-situ bored piles; pile foundation joists and joist bored piles are sequentially arranged at the bottoms of the two sides of the double-lug wall open cut tunnel; first-time cement backfill layered construction is conducted on the two sides of the double-lug wall open cut tunnel, and construction of the double-lug wall open cut tunnel is completed; and for the side, close to the mountain, of the double-lug-wall open cut tunnel, ramming and filling soil stone is arranged between the double-lug-wall open cut tunnel and the slope, and for the side, away from the mountain, of the double-lug-wall open cut tunnel, secondary cement backfill soil layered construction is conducted.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel engineering construction, in particular to a construction method for a railway tunnel portal in steep and severe eccentric pressure creep terrain. Background Art

[0002] Railway tunnel construction faces numerous complex geological and topographical conditions. Tunnel portal construction in steep terrain with severe eccentric pressure and creep is particularly challenging. This terrain often includes high slopes, unstable rock and soil, and abundant groundwater. These conditions can easily lead to severe rock deformation, landslides, or collapses during tunnel excavation, impacting construction safety, progress, and the long-term stability of the tunnel. Traditional tunnel construction methods often face numerous limitations when faced with steep, eccentric pressure and creep conditions. First, the complex forces acting on the rock during construction make it difficult to detect and address creep deformation in a timely manner, increasing construction complexity. Second, conventional tunnel lining designs cannot effectively address the stress concentration and deformation caused by ground slip or eccentric pressure, easily leading to lining damage or instability. Furthermore, the influence of groundwater can make the ground more loose, making collapse and water seepage more likely during construction. In severe cases, this can impact the construction and operation of the entire tunnel. Therefore, developing an effective tunnel construction method for these complex geological conditions is crucial. Summary of the Invention

[0003] In response to the above technical problems in the related art, the present invention provides a construction method for a railway tunnel portal in steep and severely biased creep terrain, which can solve the above problems.

[0004] To achieve the above technical objectives, the technical solution of the present invention is implemented as follows: A construction method for a railway tunnel portal in steep and severely eccentric creep terrain comprises the following steps: S1. Build a full-process model of tunnel portal construction based on BIM technology, simulate the construction sequence and stress state of anti-slip piles, open holes, and protective nets, optimize construction steps, and optimize construction site layout; S2. Accurately measure and stake out the hole positions for anti-sliding piles, pre-reinforced piles, and surface jet grouting piles. Then, dig holes for the anti-sliding piles and use bored cast-in-place piles for the pre-reinforced piles and surface jet grouting piles. S3. Arrange pile foundation joists and joist bored piles at the bottom of both sides of the open hole in the double-ear wall. Backfill the space between the joist bored piles on both sides with group AB filler. Lay a layer of crushed stone cushion at the bottom of group AB filler. S4. Carry out the first layer of cement backfill on both sides of the double-ear wall open hole, backfilling to the roadbed surface. Then, use the tunnel lining trolley as the inner formwork and the steel formwork fixed by the scaffolding as the outer formwork. Pour concrete in multiple sections according to the length of the double-ear wall open hole to complete the construction of the double-ear wall open hole. S5. For the side of the double-ear wall opening close to the mountain, rammed earth and rock are installed between the double-ear wall opening and the slope, and a clay waterproof layer is installed on top of the rammed earth and rock. For the side of the double-ear wall opening away from the mountain, a second layer of cement backfill is carried out in layers. At the same time, a herringbone water-blocking skeleton is installed on the outside of the rammed earth and rock and cement backfill. S6. Set up a passive flexible protection net along the contour line on the steep slope.

[0005] Furthermore, the anti-slip piles are rectangular square piles, the pre-reinforcement piles are circular bored piles, the surface jet grouting piles are circular bored piles, and the joist bored piles are circular bored piles.

[0006] Furthermore, the crushed stone cushion layer includes polypropylene bidirectional geogrid and unweathered, clean and well-graded sand and gravel or crushed stone, the maximum particle size of the sand and gravel or crushed stone is not greater than 20 mm, and the mud content is not greater than 5%.

[0007] Furthermore, the AB group filler is located above the ground surface and below the roadbed surface, the particle size of the AB group filler is not greater than 15 cm, and when the AB group filler is compacted in layers, the maximum compaction thickness of the layers is not greater than 30 cm, the compaction standard foundation coefficient is ≥110 MPa / m, static pressure is applied first and then weak vibration, the compaction overlap between rows along the longitudinal direction of the line is not less than 40 cm, and the backfill is rolled and densely packed to the top surface of the pile foundation support beam pedestal.

[0008] Furthermore, a number of acoustic detection steel pipes are arranged at equal intervals along the periphery of the anti-slip piles, pre-reinforced piles, and bored piles of beam support and bored piles.

[0009] Furthermore, the pile foundation support beam is evenly provided with a plurality of deformation joints along the tunnel direction.

[0010] Furthermore, when the cement backfill soil is backfilled for the first time in layers, the height of each layer shall not exceed 1m, and geogrids shall be laid on the layer surface. The backfill height shall be up to the roadbed surface, and staggered steps shall be set along the interface of the bottom part of the stratum and geogrids shall be buried.

[0011] Furthermore, the double-ear wall open hole is made of reinforced concrete, and deformation joints are set during segmented pouring. The caulking material is polysulfide sealing paste, and the leaking parts between the arch of the double-ear wall open hole and the outer wall are filled with concrete.

[0012] Furthermore, the rammed earth and rocks are compacted layer by layer, with each layer not exceeding 30 cm in thickness. A 50 cm thick clay waterproof layer is laid on top of the rammed earth and rocks for sealing, and a drainage slope is set to introduce a rectangular intercepting ditch.

[0013] Furthermore, the passive flexible protection net includes a steel column, which is welded by an I-beam and an arched channel steel. A wire rope net is overlapped on the outer surface of the steel column and tightened with steel fasteners. The steel column is connected to an anchor bolt embedded in the bedrock through an anchor rope.

[0014] Beneficial effects of the invention: This application effectively solves the construction problems of dangerous rock falls at the entrance of railway tunnels in steep and severely biased creep terrain, stratum structural displacement, slope collapse, uneven foundation settlement, lining structure cracking and damage, etc. It has the advantages of improving the train operating environment, ensuring the smooth progress of the project, and significantly improving the safety and quality of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] The present invention will be described in further detail below with reference to the accompanying drawings.

[0017] Figure 1 This is a schematic diagram of the plan layout of the steep tunnel entrance protection according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the longitudinal arrangement of steep tunnel entrance protection according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the front layout of the steep tunnel entrance protection according to an embodiment of the present invention; Figure 4 1 is a schematic diagram of the longitudinal section arrangement of the pile foundation joist according to an embodiment of the present invention; Figure 5 Schematic diagram of the plane layout of surface jet grouting piles according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the front layout of the herringbone water-cutting frame according to an embodiment of the present invention; Figure 7 Schematic diagram of the cross-sectional arrangement of the herringbone water-cutting frame according to an embodiment of the present invention; Figure 8 It is a schematic diagram of the facade layout of the passive flexible protection net described in an embodiment of the present invention.

[0018] In the figure: 1. Anti-slip piles; 2. Pre-reinforced piles; 3. Surface jet grouting piles; 4. AB group filler; 5. Bored piles with joists; 6. Ground surface; 7. Roadbed surface; 8. Pile foundation joists; 9. Cement backfill; 10. Double-ear wall opening; 11. Gravel cushion layer; 12. Rammed earth and stone; 13. Clay water barrier; 14. Herringbone water-blocking skeleton; 15. Passive flexible protective net; 16. Expansion joint 1; 17. Rectangular water-blocking ditch; 18. Steel column; 19. Wire rope net; 20. Anchor bolt; 21. Expansion joint 2; 22. Concrete platform; 23. Step ladder; 24. Anchor rope. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0020] like Figure 1-8 As shown, according to the present invention, a construction method for a railway tunnel portal in a steep and severely biased creep terrain is disclosed, which is characterized by comprising the following steps: S1. Build a full-process model of tunnel portal construction based on BIM technology to simulate the construction sequence and stress conditions of anti-slip piles, open-cut holes, and protective nets. This optimizes construction steps (e.g., adjusting the time interval between bored piles and open-cut hole pouring) to reduce process conflicts and the cumulative effect of bias pressure. Furthermore, optimize the construction site layout to avoid interference between jet grouting (mechanical movement is prohibited within 28 days) and other processes, thereby improving construction efficiency. S2. Accurately measure and stake out the hole positions for anti-slip piles 1, pre-reinforced piles 2, and surface jet grouting piles 3. Then, dig holes for anti-slip piles 1. Use bored cast-in-place piles for pre-reinforced piles 2 and surface jet grouting piles 3. During construction, focus on controlling pile position deviation, hole depth, sediment thickness, and pile casting quality. The piles penetrate the potential sliding surface and penetrate deep into the stable rock strata, providing retaining force and enhancing foundation stability. S3. Pile foundation joists 8 and joist bored piles 5 are sequentially arranged at the bottom of both sides of the double-ear wall open hole 10 to bear the structural load of the double-ear wall open hole 10, realizing a load-bearing form in which the train load and the lining structure load are separated. AB group filler 4 is backfilled between the joist bored piles 5 on both sides. A layer of crushed stone cushion 11 is laid at the bottom of the AB group filler 4. The construction focus is on ensuring the uniformity and density of the filler to prevent settlement or damage due to insufficient bearing capacity; S4. Carry out the first layer of cement backfill 9 on both sides of the open-ended wall opening 10, up to the roadbed surface 7, to prevent extrusion deformation and shear failure caused by asymmetric eccentric pressure in the tunnel. Then, use the tunnel lining trolley as the inner formwork and the steel formwork fixed by the scaffolding as the outer formwork. Pour concrete in multiple sections according to the length of the open-ended wall opening 10 to complete the construction of the open-ended wall opening 10. S5. On the side of the double-ear wall open hole 10 close to the mountain, rammed earth and rock 12 is installed between the double-ear wall open hole 10 and the slope, and a clay waterproof layer 13 is installed on top of the rammed earth and rock 12. On the side of the double-ear wall open hole 10 away from the mountain, a second layer of cement backfill 9 is constructed in layers. At the same time, a herringbone water-blocking frame 14 is constructed on the outer sides of the rammed earth and rock 12 and the cement backfill 9 for protection. S6. A passive flexible protection net 15 is set up along the contour line on the steep slope to prevent dangerous rocks, falling rocks and foreign objects from invading the construction limits of the railway.

[0021] In a specific embodiment of the present invention, ten anti-slip piles (1) are constructed using C35 rectangular square piles, which provide enhanced anti-slip performance. Pile formation is achieved through manual excavation to enhance underground drainage and ventilation. The pile cross-section measures 3.5m high by 2.5m wide, with a length of 12 to 20m. The pile spacing is 5m from center to center. The upper 2m of the wellhead is a locking mouth, with retaining walls every 2m below. Locking mouths should be constructed immediately after 2m of excavation, and retaining walls should be constructed every 2m. The main reinforcement is 12mm diameter, and the distribution reinforcement is 8mm diameter. C20 concrete is used for both the locking mouth and retaining walls. If the ground slope at the pile top is steep, the top surface of the locking mouth can be sloped to conform to the terrain. The cantilever section of the anti-slip pile (1) is approximately one-third of the pile length, and the anchoring section is approximately two-thirds of the pile length.

[0022] In a specific embodiment of the present invention, the number of pre-reinforced piles 2 is 11. These are C35 circular bored cast-in-place piles with a diameter of 2m and a length of 19m. The piles are spaced 4m apart from each other, with main reinforcement of 25mm diameter and 15cm spacing, and distribution reinforcement of 16mm diameter and 40cm spacing. These piles are placed on the mountain side and equipped with double-legged reinforcement. If the backfill is soft and permeable, the pre-reinforced piles 2 are constructed using steel casings. Each section is 2m long, and the top of the casing is 0.3m above the construction surface to prevent mud loss, diameter shrinkage, and hole collapse.

[0023] In a specific embodiment of the present invention, the surface jet grouting pile 3 adopts a circular bored pile with a pile diameter of 0.6m. The pile length is 7 to 10m according to the trend of the ground surface 6, the spacing of the plum blossom arrangement is 1.2*1.2m, and the compressive strength is not less than 3.3MPa. The construction sequence of the high-pressure jet grouting pile should be from the middle to the periphery, or from one side to the other. The water-cement ratio of the cement slurry should be 1.0 to 1.2. The mixed cement slurry shall not be used for more than 2 hours. The pressure of the high-pressure cement slurry of the jet grouting pile should be greater than 20MPa. The construction steps of the high-pressure jet grouting pile include drilling rig positioning, drilling, intubation, high-pressure jet grouting, pipe pulling, and cleaning. The deviation between the drilling position and the design shall not be greater than 50mm, and the overlap length of the segmented jet grouting shall not be less than 300mm. When the rotary jet pipe is lifted close to the pile top, it should be lifted slowly from 1m below the pile top, and the rotary jet should be sprayed for a few seconds, and then slowly lifted upward by 0.5m until the grouting surface stops. If the grouting is stopped for some reason during construction, the grouting rotary jet construction should be repeated with an overlap of 0.5m above and below the broken grouting surface when the grouting supply is resumed. The grouting surface of the high-pressure rotary jet pile should be 30 to 50cm higher than the design elevation of the pile top. After the construction is completed, the pile section with poor construction quality at the top of the rotary jet pile should be manually excavated.

[0024] In a specific embodiment of the present invention, the crushed stone cushion layer 11 uses unweathered clean and well-graded gravel or crushed stone, the maximum particle size of which shall not be greater than 20 mm, and the mud content shall not be greater than 5%. A polypropylene bidirectional geogrid is also used, with a width of not less than 4 m and a longitudinal and transverse ultimate tensile strength of not less than 80 KN / m. When installing the geogrid, it must be straightened and flattened, and the widths must be aligned and overlapped. The geogrid must be resistant to crushed stone extrusion and must not break when filling and compacting the cushion layer.

[0025] In a specific embodiment of the present invention, the particle size of the AB group filler 4 is no greater than 15 cm. Silt sand or fine sand should not be used as filler. The maximum layered compaction thickness is no greater than 30 cm, and the standard foundation coefficient for compaction is ≥110 MPa / m. Static compaction is performed first, followed by weak vibration. The overlap between rows along the longitudinal direction of the route is no less than 40 cm, and the backfill is compacted and densely rolled to the top surface of the pile foundation joist 8 cap. A bulldozer is used for initial leveling of the filler, a motor grader for fine leveling, and a roller for rolling, following the principle of light first, heavy later, and slow later. Small compaction equipment is used for supplementary compaction in corners. Compaction testing points are established and tested at a prescribed frequency.

[0026] In a specific embodiment of the present invention, two rows of 44 joist bored piles 5 are C35 circular bored cast-in-place piles with a pile diameter of 1.25m and a pile length of 19 to 29m. The pile spacing along the line direction under the pile foundation joist 8 is 2.8m, and the pile spacing in the vertical line direction is 3.7m. The main reinforcement is φ25 with a spacing of 10cm, the distribution reinforcement is φ16 with a spacing of 30cm, and a straight bent hook is set at the top to extend into the top surface of the pile foundation joist 8 25cm away.

[0027] In a specific embodiment of the present invention, three acoustic detection steel pipes are equidistantly arranged along the perimeter of the anti-slip pile 1, pre-reinforced pile 2, and bored pile 5 bored piles. The inner diameter is not less than 40 mm, and the wall thickness is not less than 3 mm. The acoustic detection pipe is sealed at the lower end and covered at the upper end. There should be no foreign matter inside the pipe. The connection should be smooth and leak-proof. The pipe mouth should be more than 100 mm above the pile top, and the height of each acoustic detection pipe mouth should be consistent. The acoustic detection pipe must be fixed vertically, parallel, and accurately positioned to avoid distortion. The low-strain method is used to test the integrity of the pile body. Clean water is added to the pipe. The propagation time, amplitude, frequency, and other parameters of the sound wave in the concrete are measured point by point at a certain interval of 200 mm to 500 mm to determine whether there are defects such as voids, cracks, mud inclusions, etc. inside the concrete, and to determine the location and size of the defects.

[0028] In a specific embodiment of the present invention, a pile foundation joist 8 is installed at the base of each exterior wall on either side of the open-ended wall opening 10. This joist is cast in-situ, C35, has a span of 30 meters, and a beam cross-section of 6.0 meters wide by 2.5 meters high. The longitudinal reinforcement is 25 mm diameter, spaced 14 cm apart, and the horizontal and vertical reinforcement is 16 mm diameter, spaced 20 cm apart. A 1 cm wide expansion joint 16 is provided in the center of the pile foundation joist 8. The longitudinal reinforcement joints are connected using flash butt welding or steel casing in accordance with relevant construction specifications. Within 35d of the joint, the area of ​​the reinforcement exposed to the joint must not exceed 50% of the area of ​​the reinforcement in that cross-section. The thickness of the reinforcement cover must be no less than 55 mm.

[0029] In a specific embodiment of the present invention, before paving the filler with cement backfill 9, the cultivated soil and soft soil layer below the bottom of the fill layer in the site should be removed or processed, and the first layered backfill height should be up to the roadbed surface 7, with each layer height not exceeding 1m, and geogrids should be laid on the layer surface. Staggered steps should be set along the interface of the bottom of the stratum and geogrids should be buried. The specific size of the steps is determined according to the topographic and geological conditions, but the longitudinal distance of each step is not less than 1m, the water-cement ratio is 0.5, the cement admixture ratio is 15%, the compaction coefficient of the cement backfill 9 should be >0.97, and its foundation bearing capacity characteristic value should be >150KPa.

[0030] In a specific embodiment of the present invention, the double-ear wall open hole 10 uses a tunnel lining trolley as an inner mold and a steel formwork fixed by a scaffolding as an outer mold. It adopts C35 reinforced concrete, reserves exhaust holes and pre-buried grouting pipes, longitudinal steel bars φ25, spacing 20cm, distributed steel bars φ14, spacing 25cm, stirrups φ10, spacing 20*25cm, and C30 concrete is used for the outer walls on both sides with an inclination slope of 1:0.2. The expansion joints of 2cm are set in segments. The caulking material is polysulfide sealing paste. The leakage hole between the arch of the double-ear wall open hole 10 and the outer wall is filled with C20 concrete pumping.

[0031] In a specific embodiment of the present invention, the gap between the double-ear wall open hole 10 and the mountain is compacted layer by layer with rammed earth and stone 12, and the thickness of each layer shall not be greater than 30 cm. Artificial backfilling is adopted to avoid damage to the waterproof membrane and geotextile behind the open hole structure; a 50 cm thick clay waterproof layer 13 is laid on the top of the rammed earth and stone 12 to seal it, and a 2% drainage slope is set to introduce a rectangular intercepting ditch to prevent or limit water infiltration. The waterproof layer should overlap smoothly with the side slope and be tightly sealed to prevent surface water from seeping in.

[0032] In a specific embodiment of the present invention, the cement backfill 9 is backfilled to the design elevation for the second time in layers, and the rammed earth and stone 12 and the cement backfill 9 are protected by a C25 herringbone water-blocking frame 14. The main frame has a net distance of 6m, a width of 0.6m and a thickness of 0.6m. The support frame has a net distance of 3m, a width of 0.5m and a thickness of 0.6m. The support frame and the main frame are at a 45° angle. Concrete edging reinforcement is set within a width of 0.5m at each starting and ending point of the slope protection, with a thickness of 0.5m and a spacing of about 50m. A step is set at the main frame position along the slope, with a width of 0.6m and a slope gradient of 1:1.5. A 10*10cm water retaining edge is set, the protection height of each level is 8m, and a platform ditch with a width of 2m is set. Grass is sprayed and planted in the frame in appropriate seasons. A concrete platform 22 is set at the end of the herringbone water-blocking frame 14, and a step ladder 23 is set in the middle of the herringbone water-blocking frame 14 to facilitate pedestrian walking.

[0033] In a specific embodiment of the present invention, the passive flexible protective net 15 is 6m high and 50m long. The foundation is made of C20 concrete. The anchor bolt 20 is made of φ32 threaded steel bars with a total length of 1.0m, a top thread of M28*100, and is equipped with corresponding gaskets and nuts. The steel column 18 is welded by I-beams and arched channel steels, the surface is hot-dip galvanized, the height is 5m, the column spacing is 10m, the upper and lower support ropes are 2φ16 double ropes, and an intermediate reinforcement anchor rope is set every 25m. The φ28 threaded steel anchor is embedded in the bedrock to a depth of ≥5m, the pressure relief ring has a diameter of 448mm, and the wire rope net 19 is woven with anti-displacement and anti-falling cross buckles. The end overlap length is not less than 10cm and is tightened with steel fasteners at least three places. The breaking tension of the wire rope, the mechanical properties of the pressure relief ring, the length of the threaded anchor and the pull-out resistance are tested and inspected according to the standard. Furthermore, the passive flexible protection net (6m high, 50m long) can be integrated with a sensor network. For example, strain sensors and inclination sensors can be installed on steel columns, support ropes and decompression rings to monitor the impact load of falling rocks and the deformation of the protection net in real time. The data can be transmitted to the monitoring center through the Internet of Things technology to achieve early warning and active protection against dangerous rockfalls.

[0034] In a specific embodiment of the present invention, fiber optic sensors are embedded in slopes, anti-slip piles, and open-cut structures to monitor surface displacement, pile stress, and open-cut settlement in real time (with an accuracy of up to 0.1 mm). Combined with AI algorithms, deformation trends are predicted, and reinforcement measures are taken in advance, replacing traditional manual inspections and improving construction safety levels.

[0035] In a specific embodiment of the present invention, construction is conducted in an environment with significant temperature fluctuations. The impact of these fluctuations on the rock mass is primarily due to thermal expansion and contraction of the rock surface caused by diurnal temperature differences or seasonal changes. This can lead to problems such as cracks and displacement in the rock mass, increasing the risks of construction and subsequent operations. Therefore, a tunnel temperature control device can be installed in this environment. Specifically, temperature control pipes can be installed in the tunnel's surrounding rock mass or within the tunnel structure, transporting a cooling or heating medium. Temperature sensors can be installed inside and outside the tunnel, and a controller can be used to adjust and control the temperature difference between the inside and outside of the tunnel.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A construction method for a railway tunnel portal in a steep and severely eccentric creep terrain, characterized by: The steps include: S1. Build a full-process model of tunnel portal construction based on BIM technology, simulate the construction sequence and stress state of anti-slip piles, open holes, and protective nets, optimize construction steps, and optimize construction site layout; S2, accurately measure and stake out the hole positions of the anti-sliding piles (1), pre-reinforced piles (2), and surface jet grouting piles (3), then dig holes for the anti-sliding piles (1), and use bored cast-in-place piles for the pre-reinforced piles (2) and surface jet grouting piles (3); S3, arranging pile foundation joists (8) and joist bored piles (5) on both sides of the double-ear wall open hole (10) in sequence, backfilling the AB group filler (4) between the joist bored piles (5) on both sides, and laying a layer of crushed stone cushion (11) on the bottom of the AB group filler (4); S4, the first cement backfill (9) is constructed in layers on both sides of the double-ear wall open hole (10), and the backfill height is up to the roadbed surface (7). Then, a tunnel lining trolley is used as an inner formwork, and a steel formwork fixed by a scaffolding is used as an outer formwork. Concrete is poured in multiple sections according to the length of the double-ear wall open hole (10), and the construction of the double-ear wall open hole (10) is completed; S5. For the side of the double-ear wall open hole (10) close to the mountain, rammed earth and stone (12) is set between the double-ear wall open hole (10) and the slope, and a layer of clay waterproof layer (13) is set on the top of the rammed earth and stone (12). For the side of the double-ear wall open hole (10) away from the mountain, a second layer of cement backfill (9) is constructed in layers, and at the same time, a herringbone water-blocking skeleton (14) is constructed on the outer sides of the rammed earth and stone (12) and the cement backfill (9); S6. Install a passive flexible protection net (15) along the contour line on the steep slope.

2. The method for constructing a railway tunnel portal in a steep and severely eccentric creep terrain according to claim 1 is characterized in that: The anti-slide pile (1) adopts a rectangular square pile, the pre-reinforced pile (2) adopts a circular bored pile, the surface jet grouting pile (3) adopts a circular bored pile, and the beam bored pile (5) adopts a circular bored pile.

3. The method for constructing a railway tunnel portal in a steep and severely eccentric creep terrain according to claim 1, characterized in that: The crushed stone cushion layer (11) comprises polypropylene bidirectional geogrid and unweathered clean and well-graded sand gravel or crushed stone, wherein the maximum particle size of the sand gravel or crushed stone is not greater than 20 mm and the mud content is not greater than 5%.

4. The method for constructing a railway tunnel portal in a steep and severely eccentric creep terrain according to claim 1 is characterized in that: The AB group filler (4) is located above the ground surface (6) and below the roadbed surface (7). The filler particle size of the AB group filler (4) is not greater than 15 cm. When the AB group filler (4) is compacted in layers, the maximum compacted thickness of each layer is not greater than 30 cm. The standard foundation coefficient of compaction is ≥110 MPa / m. Static pressure is applied first and then weak vibration is applied. The compaction overlap between rows along the longitudinal direction of the line is not less than 40 cm. The backfill is rolled and densely backfilled to the top surface of the pile foundation support beam (8).

5. The method for constructing a railway tunnel portal in a steep and severely eccentric creep terrain according to claim 1 is characterized in that: A plurality of acoustic detection steel pipes are arranged at equal intervals along the periphery of the anti-slip pile (1), the pre-reinforced pile (2), the beam bored pile (5) and the bored pile body.

6. The method for constructing a railway tunnel portal in a steep and severely eccentric creep terrain according to claim 1, characterized in that: The pile foundation support beam (8) is evenly provided with a plurality of deformation joints (16) along the tunnel direction.

7. The method for constructing a railway tunnel portal in a steep and severely eccentric creeping terrain according to claim 1, characterized in that: When the cement backfill soil (9) is backfilled for the first time in layers, the height of each layer shall not exceed 1m, and geogrids shall be laid on the layers. The backfill height shall be up to the roadbed surface (7), and staggered steps shall be set along the interface of the bottom part of the stratum and geogrids shall be buried.

8. The method for constructing a railway tunnel portal in a steep and severely eccentric creep terrain according to claim 1, characterized in that: The double-ear wall open hole (10) is made of reinforced concrete. When the double-ear wall open hole (10) is cast in sections, a second deformation joint (21) is set. The caulking material is polysulfide sealing paste. The leaking hole between the arch of the double-ear wall open hole (10) and the outer wall is filled with concrete.

9. The method for constructing a railway tunnel portal in a steep and severely eccentric creeping terrain according to claim 1, characterized in that: The rammed earth and stone (12) is compacted layer by layer, and the thickness of each layer shall not be greater than 30 cm. A 50 cm thick clay waterproof layer (13) is laid on the top of the rammed earth and stone (12) to seal it, and a drainage slope is set to introduce a rectangular intercepting ditch (17).

10. The method for constructing a railway tunnel portal in a steep and severely eccentric creep terrain according to claim 1, characterized in that: The passive flexible protection net (15) includes a steel column (18), which is welded from an I-steel and an arched channel steel. A steel wire rope net (19) is overlapped on the outer surface of the steel column (18) and is tightened with steel fasteners. The steel column (18) is connected to an anchor bolt (20) embedded in the bedrock through an anchor rope (24).

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