A steep fold rock wall cutting single side bridge road method excavation construction method

Abstract

This invention belongs to the field of water conservancy and hydropower construction technology, specifically providing a construction method for excavating a single-sided bridge across a steep folded rock face road cut. The method includes the following steps: measuring and setting out according to design drawings; fabricating steel beams and installing them at the target location in the ditch; using machinery to excavate the slope along the designed route; excavating the slope overburden and upper strongly weathered rock; excavating the lower weakly weathered rock of the pre-splitted slope, using stepped blasting for rock excavation in stages; and completing the excavation of the single-sided bridge across a steep folded rock face road cut after inspection and acceptance. This invention solves the problems of large excavation volume, difficulty for machinery to cross gullies, collapse of upper deposits, and significant construction hazards associated with existing mechanical + blasting methods for excavating steep folded rock faces. This invention features minimal over-excavation, shorter construction period, guaranteed quality, safety and reliability, and reduced ecological impact.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and hydropower construction technology, specifically relating to a construction method for excavating and building a single-sided bridge across steep folded rock face road cuts. Background Technology

[0002] Pumped-storage power stations are mostly built in mountainous areas, and the connecting roads between the upper and lower reservoirs are the main transportation routes connecting the power station's key facilities. The roads begin at the access road and end at the ring road around the upper reservoir. Because the straight-line distance between the upper and lower reservoirs is generally short and the elevation difference is significant, with steep terrain, well-developed gullies, and complex topography, the connecting roads are typically laid out in a zigzag pattern along the mountainside, with multiple hairpin bends. The roadbed excavation methods vary depending on the geological structure of the strata along the road, the type of surrounding rock, the distribution of gullies, and the thickness of the overburden layer at the opening line. Generally, soft rock and strongly weathered rock layers are excavated mechanically, while medium-hard rock and hard rock are excavated using drill-and-blast methods. Sections with high opening lines, high gully density, and thick overburden layers are constructed using a combination of mechanical excavation and blasting.

[0003] The connecting road between the upper and lower reservoirs of the Fukang Pumped Storage Power Station in Xinjiang is approximately 12.13 km long, with an elevation difference of 565 m and an average longitudinal slope of 4.6%. It is designed to the standards of a Class III hydropower highway, with a design speed of 20 km / h and a roadbed width of 8.5 m. The road traverses steep slopes and deep gullies, with some sections having high opening lines. The slopes are characterized by alternating exposed mountain ridges and gullies, forming a folded appearance. Using a combination of mechanical excavation and blasting presents numerous challenges, including large excavation volumes, difficulties in crossing gullies with machinery, potential collapse of the superstructure, and exceeding the permitted red line, posing significant safety hazards during construction.

[0004] Chinese patent document CN110306571B, published on November 24, 2020, discloses a method for excavating road cuts. The method comprises the following steps: Step S1: excavating intercepting and drainage ditches; Step S2: clearing the surface; Step S3: surveying and setting out; Step S4: road cut excavation and slope protection construction. This document addresses the shortcomings of existing excavation methods by employing a top-down, inside-out, step-by-step excavation approach; and by adopting a new multi-level protection structure, it solves the problem of inadequate protection against falling rocks. However, this document does not address the problems encountered with existing steep, folded rock face excavation methods using mechanical and blasting techniques, such as large excavation volumes, difficulty in mechanical crossing of gullies, collapse of the upper deposits, and significant construction hazards. Summary of the Invention

[0005] The purpose of this invention is to provide a construction method for excavating a single-sided bridge across a steep folded rock face road cut, which overcomes the problems of large excavation volume, difficulty of mechanical crossing of gullies, collapse of the upper deposits, and exceeding the red line in the existing mechanical + blasting method for excavating steep folded rock faces, and also poses a great hidden danger to safe construction.

[0006] Therefore, the present invention provides a construction method for excavating and constructing a single-sided bridge crossing in steep, folded rock face road cuts, comprising the following steps:

[0007] 1) Measure and lay out the lines according to the design drawings;

[0008] 2) Fabricate steel beams and install them at the target locations in the trench;

[0009] 3) Machinery excavates and clears the slope according to the designed route;

[0010] 4) Excavate the slope overburden and upper strongly weathered rock;

[0011] 5) For the weakly weathered rock in the lower layer of the pre-splitting slope, the rock excavation is carried out by step-by-step blasting in stages. After inspection and acceptance, the single-sided bridge crossing method is used to excavate the steep folded rock wall road cut.

[0012] Preferably, slope protection is used during excavation in both steps 4) and 5).

[0013] Preferably, the steel beam includes multiple crossbeams and multiple connecting bars. The multiple crossbeams are distributed in parallel from front to back and are all arranged laterally. The multiple crossbeams are connected from left to right by multiple connecting bars and are all arranged longitudinally.

[0014] Preferably, the crossbeam is made of I-beam.

[0015] Preferably, the method for installing the steel beam at the target position in the ditch in step 2) includes the following steps: first, remove the slag from the rock mass on both sides of the ditch, then drill holes at the target position to support the steel beam, insert reinforcing bars into the holes and expose the reinforcing bars, place the steel beam at the target position, and finally connect the exposed reinforcing bars to the steel beam to complete the installation of the steel beam.

[0016] Preferably, after excavation in step 3), the excavated soil and rock are covered on the surface of the steel beam until the covering thickness reaches the target thickness; when passing through, one side of the machine's track rests on the steel beam and the other side rests on the slope entity.

[0017] Preferably, step 4) excavating the slope overburden and upper strongly weathered rock includes the following steps:

[0018] 4.1) First, measure and lay out the lines according to the design drawings, mark the excavation boundary line at the top of the slope, and calculate the excavation boundary of each step based on the design excavation depth and slope inclination.

[0019] 4.2) Before excavation, according to the survey and layout, dig the intercepting and drainage ditch according to the design drawings, and then clean the topsoil from high to low and from the outside to the inside, and clean the covering soil layer of the excavation area.

[0020] 4.3) For soft rock and strongly weathered rock on slopes, mechanical excavation shall be carried out in layers from top to bottom until the excavation is completed.

[0021] Preferably, the slope is constructed using a method of excavation followed by protection.

[0022] Preferably, in step 5), the excavation is carried out step by step from top to bottom until the last step is excavated.

[0023] Preferably, the slope protection adopts a support form of anchor bolts + steel mesh + shotcrete.

[0024] The beneficial effects of this invention are:

[0025] 1. The single-sided bridge crossing method for steep folded rock face road cuts provided by this invention, based on the analysis and research of the geological and topographical conditions of the excavation section and the lithology at both ends of the folded gully, utilizes I-beams to process steel beams. Through theoretical calculations of bearing capacity and repeated tests, the steel beams are erected on the road cut gully and close to one side of the slope. The bearing capacity of the steel beams and the underlying rock mass ensures the safe passage of excavating machinery through the gully obstacle, achieving the goal of excavating the road cut slope from top to bottom according to the design scheme. This reduces the over-excavation of slope rock, allows machinery to quickly pass through gully sections, and reaches the road cut opening line, shortening the process time.

[0026] 2. The single-sided bridge crossing method for steep folded rock face road cuts provided by this invention involves mechanically excavating the slope cover layer and the upper layer of strongly weathered rock layer from top to bottom. This method enables mechanical excavation of the strongly weathered rock layer and gully deposits for single-sided bridge crossings, which can better ensure the design cross-sectional dimensions of the road cut, avoid damage to the open face of the slope caused by blasting excavation, and facilitate subsequent construction of intercepting and drainage ditches and slope protection.

[0027] 3. The single-sided bridge crossing method for steep folded rock face road cuts provided by this invention is a construction method that uses a single-sided bridge to cross the ditch when excavation machinery cannot reach the working face in steep folded rock face road cuts. Compared with non-mechanical excavation, which involves manually clearing the thick deposits on the slope before blasting, it has significant advantages and high efficiency in terms of safety, excavation quality, and construction efficiency.

[0028] 4. The single-sided bridge crossing method for steep folded rock face road cuts provided by this invention involves mechanically excavating the slope overburden and upper strongly weathered rock, and the lower weakly weathered rock of the pre-splitted slope. Step-by-step blasting is then used to excavate the rock in stages, completing the single-sided bridge crossing method for steep folded rock face road cuts. The upper accumulation is less prone to collapse and will not exceed the red line; it significantly reduces the amount of mountain excavation, minimizing damage to surface vegetation and reducing waste, thus protecting the natural ecological environment; it also significantly reduces over-excavation, avoiding and reducing the permanent land occupation area of ​​the project, and lowering construction costs. Attached Figure Description

[0029] The present invention will now be described in further detail with reference to the accompanying drawings.

[0030] Figure 1 This is a flowchart of the present invention;

[0031] Figure 2 This is a structural diagram of a steel beam.

[0032] Figure 3 This is a structural diagram of the steel beam under stress.

[0033] Explanation of reference numerals in the attached diagram: 1. Horizontal beam; 2. Connecting reinforcement. Detailed Implementation

[0034] Example 1:

[0035] like Figure 1 As shown, a construction method for excavating and building a single-sided bridge across a steep, folded rock face road cut includes the following steps:

[0036] 1) Measure and lay out the lines according to the design drawings;

[0037] In practice, the excavation lines are measured and laid out according to the design drawings. The excavation boundary is marked with lime or other markers. The excavation boundary is calculated based on the design excavation depth and slope gradient. Safety protection measures are implemented with wooden stakes and warning tape 5 meters away from the excavation boundary, and clear warning signs are placed at major access points to ensure construction safety during the excavation process. Simultaneously, the width of each trench along the planned machinery travel route is measured or calculated to provide a basis for designing the steel beam span.

[0038] 2) Fabricate steel beams and install them at the target locations in the trench;

[0039] 3) Machinery excavates and clears the slope according to the designed route;

[0040] 4) Excavate the slope overburden and upper strongly weathered rock;

[0041] 5) For the weakly weathered rock in the lower layer of the pre-splitting slope, the rock excavation is carried out by step-by-step blasting in stages. After inspection and acceptance, the single-sided bridge crossing method is used to excavate the steep folded rock wall road cut.

[0042] This invention provides a method for excavating and constructing a single-sided bridge across steep, folded rock face road cuts. By fabricating steel beams and installing them at the target location in the ditch, machinery excavates the slope according to the designed route, reducing over-excavation of the slope rock. The machinery can quickly traverse gully areas to reach the road cut opening line, shortening the construction time. Through mechanical excavation of the slope overburden and upper strongly weathered rock, and the lower weakly weathered rock of the pre-splitted slope, step-by-step blasting is used for rock excavation in stages, completing the single-sided bridge crossing construction method for steep, folded rock face road cuts. The upper accumulation is less prone to collapse and does not exceed the red line; it significantly reduces the amount of mountain excavation, minimizing damage to surface vegetation and reducing waste, thus protecting the natural ecological environment; it also significantly reduces over-excavation, avoiding and reducing the permanent land occupation of the project, and lowering construction costs.

[0043] Example 2:

[0044] Fabricate the steel beams and install them at the target locations in the trench:

[0045] Based on Example 1, such as Figure 2 As shown, the steel beam includes multiple crossbeams 1 and multiple connecting bars 2. The multiple crossbeams 1 are distributed in parallel from front to back and are all arranged laterally. The multiple crossbeams 1 are connected from left to right by multiple connecting bars 2 and are all arranged longitudinally.

[0046] In terms of structural selection, considering the narrowness of the ditch and the fact that only excavation machinery can pass through, a plate structure, namely the steel plate beam, is adopted.

[0047] Preferably, there are four crossbeams 1 and three to four connecting ribs 2, and the crossbeams 1 and connecting ribs 2 are welded together. The welding method is simple, the structure is stable, and the load-bearing capacity is good.

[0048] Preferably, the bottom of the plurality of crossbeams 1 is connected by reinforcing beams to improve the stability of the overall structure. The connecting reinforcement is made of steel bars.

[0049] Preferably, the crossbeam 1 is made of I-beam.

[0050] Regarding the selection of single-sided bridge structure, based on a comparison of rigid frame structures, truss structures, beam-truss combinations, and Bailey structures, and considering that the width of the ditch in the construction area is generally 2-5m (for widths greater than 5m, excavated slopes are used to shorten the span), in terms of material selection, through a comparison of the mechanical characteristics and ease of fabrication and installation of conventional I-beams and channel steel, I-beams were selected as the main material for single-sided bridges because of their wide flanges, high lateral stiffness, strong bending resistance, and the fact that the two flange surfaces are parallel to each other, making connection, processing, and installation simple.

[0051] Based on the analysis and study of the geological and topographical conditions of the excavation section and the lithology at both ends of the folds and gullies, steel beams were fabricated using I-beams, and the bearing capacity was calculated using load-bearing capacity theory (see Table 1 and...). Figure 2 and Figure 3 Through repeated testing, steel beams were erected on the road cut gullies and close to the slope side. The bearing capacity of the steel beams and the underlying rock mass ensured the safe passage of excavating machinery through the gully obstacles, achieving the goal of excavating the road cut slope from top to bottom according to the design plan. This reduced the amount of over-excavation of the slope rock, allowed machinery to quickly pass through gully areas and reach the road cut opening line, and shortened the process time.

[0052] Table 1. Formulas for Calculating the Mechanical Properties of Steel Beams

[0053]

[0054]

[0055]

[0056] Load analysis:

[0057] Since the single-sided steel beam bridge is only a temporary construction measure and is located close to the mountain, wind load, seismic load, and other loads are not considered here; only the self-weight of the machinery and the weight of the soil and rock cushion layer are considered. The machinery used in this method is a PC-320 excavator with a working weight of 34.916T (dynamic load). The soil and rock cushion layer has a unit weight of 1650kg / m3 and a layer thickness of 0.5m. The cushion layer is considered as a uniformly distributed dead load.

[0058] Steel beam fabrication:

[0059] The fabrication of steel beams consists of four steps: component processing, transportation, on-site welding, and weld inspection.

[0060] 1) Cut the I-beams to the design dimensions at the steel bar processing yard, and then transport the finished components to the site using transport machinery;

[0061] 2) Place multiple (4) processed I-beams in parallel and weld them laterally with connecting bars (reinforcing bars) to form a steel beam;

[0062] 3) When the span is large or the steel beam is wide, I-beams are welded laterally at the bottom of the steel beam to ensure the overall stability and balanced stress of the steel beam;

[0063] 4) After welding is completed, the welding quality is inspected to ensure that the connection is safe and reliable.

[0064] Preferably, the method for installing the steel beam at the target position in the ditch in step 2) includes the following steps: first, remove the slag from the rock mass on both sides of the ditch, then drill holes at the target position to support the steel beam, insert reinforcing bars into the holes and expose the reinforcing bars, place the steel beam at the target position, and finally connect the exposed reinforcing bars to the steel beam to complete the installation of the steel beam.

[0065] When drilling, the hole depth is 0.3 to 0.5 m, and the exposed reinforcing bars are used to connect the steel beams. The exposed reinforcing bars are welded to the steel beams.

[0066] Example 3:

[0067] The machinery excavated and cleared the slope according to the designed route:

[0068] Based on Example 2, in step 3), after excavation, the excavated soil and rock are covered on the surface of the steel beam until the thickness of the cover reaches the target thickness; when passing through, one side of the machine's track rests on the steel beam and the other side rests on the slope entity.

[0069] After the steel beams are installed, the machinery will excavate the slope according to the designed route. Excavation of earth and strongly weathered rock layers should be carried out in layers from top to bottom, with each layer ideally 3 meters thick. Over-excavation and haphazard excavation are strictly prohibited, and bottom excavation is strictly forbidden to prevent the collapse of the upper accumulation. After excavation, some soil and rock will be placed on the surface of the steel beams, with a thickness controlled at approximately 0.5 meters, as a protective layer for machinery crossing the steel beams. When machinery passes over the steel beam structure, the tracks should rest on both the beam and the slope structure to minimize stress on the steel beams and ensure construction safety. The machinery passageway should be at least 3.5 meters wide in the steel beam section (from the outer side of the beam to the toe of the slope). After machinery has excavated and passed over the single-sided bridge, guardrails or other warning signs should be promptly installed on the outer side.

[0070] Example 4:

[0071] Based on Example 3, step 4) excavating the slope overburden and upper strongly weathered rock includes the following steps:

[0072] 4.1) First, measure and lay out the lines according to the design drawings, mark the excavation boundary line at the top of the slope, and calculate the excavation boundary of each step based on the design excavation depth and slope inclination.

[0073] 4.2) Before excavation, according to the survey and layout, dig the intercepting and drainage ditch according to the design drawings, and then clean the topsoil from high to low and from the outside to the inside, and clean the cover soil layer of the excavation area; the cover soil layer includes surface vegetation, humus and other slope deposits.

[0074] 4.3) For soft rock and strongly weathered rock on slopes, mechanical excavation shall be carried out in layers from top to bottom until the excavation is completed.

[0075] The layer thickness should be controlled between 3.0m and 4.0m. During excavation, the standard cross-section and slope should be formed strictly according to the design. Over-excavation is prohibited. Undercutting or creating a reverse slope is strictly prohibited to avoid collapse.

[0076] The excavation of the slope overburden and the upper layer of strongly weathered rock was carried out using transport vehicles (backhoe excavators and transport vehicles) to transport the waste to the designated waste disposal site.

[0077] Preferably, the slope is constructed using a method of excavation followed by protection.

[0078] When the height of the overburden and upper layer of strongly weathered rock slope is greater than the designed height of the first step (generally 8m), the slope is excavated and protected one step at a time. Excavation of the next slope level can only proceed after the previous level of slope protection (slope support) has been fully implemented and is functioning properly, ensuring slope stability and structural safety. When the height of the overburden and upper layer of strongly weathered rock slope is less than the designed height of the first step, slope protection (slope support) should be implemented promptly after excavation and ensure its effectiveness before proceeding with blasting of the lower hard rock to prevent vibration damage to the already formed slope.

[0079] Preferably, temporary drainage measures are taken during the excavation process to ensure that water does not accumulate on the construction work surface.

[0080] Example 5:

[0081] The weakly weathered rock in the lower layer of the pre-splitting slope was excavated by step-by-step blasting. After inspection and acceptance, the single-sided bridge crossing method was completed for the steep folded rock wall road cut.

[0082] Since the weakly weathered rock in the lower layer of the slope cannot be directly removed by machinery, blasting is used for excavation. To reduce the disturbance and damage to the surrounding rock caused by blasting vibration, pre-splitting blasting is used for the surrounding rock; for localized small areas (where pre-splitting blasting is not suitable), smooth blasting is used.

[0083] Rock excavation is carried out in steps using stepped blasting, with each step height set at 3 to 6 meters. After each level of slope excavation is completed, slope support is carried out promptly. The slope support before the excavation is completed must not exceed two levels.

[0084] The bottom 2-3m of the excavated slope adjacent to the road cut is a protective layer for rock excavation. Horizontal drilling is performed using a YT-28 pneumatic drill. Smooth blasting is used at the roadbed excavation face. Hydraulic drilling is primarily used for drilling; however, YT-28 pneumatic drills are used for corners and thin slope layers where hydraulic drilling is not feasible. Pre-splitting holes are drilled using either a hydraulic drill or a QZJ-100B down-the-hole drill, depending on the slope. Smooth blasting is performed using YT-28 pneumatic drills.

[0085] Based on the results of the pre-construction blasting test, the pre-splitting and stepped blasting parameters are as follows:

[0086] The pre-splitting blasting holes and stepped blasting holes have a diameter of 90mm, and are inclined at 75°–80° to the blasting free face or consistent with the design slope ratio. The spacing between blasting holes is 1.5–2.0m, and the depth exceeds the blasting height by 50cm. Expanded nitramine explosive is used with coupled charging, and the hole plugging depth is 0.5–1.0m. The initial unit explosive consumption is set at 420–500g / m³. The explosive charge in the buffer holes near the bedrock surface is controlled at 2 / 3 of the blasting hole charge to prevent slope damage to the bedrock surface. The spacing between pre-splitting holes is 75–90cm, and the hole depth exceeds the design slope length by 50cm. φ70 emulsion explosive is used with uncoupled interval charging, and the linear charge density is initially set at 350–450g / m³. All blasting uses non-electric millisecond detonating cord detonators.

[0087] The excavation of slopes should be followed by the removal of blasted material, with sections trimmed from top to bottom. At the same time, dangerous rocks and loose stones on the slope should be cleared. Excavated material should be promptly transported to the nearest embankment section, and any excess should be transported to a designated spoil disposal site using 20-ton dump trucks.

[0088] Based on Example 4, in step 5), excavation should proceed from top to bottom, step by step, until the last step is completed. Any under-excavated portions of the roadbed must be removed, and the side ditches should be constructed simultaneously with the roadbed.

[0089] Example 6:

[0090] Preferably, slope protection is used during excavation in both steps 4) and 5).

[0091] Preferably, the slope protection adopts a support form of anchor bolts + steel mesh + shotcrete.

[0092] The slope protection includes the following construction steps: drilling → inserting anchor rods into the drilled holes and grouting → hanging steel mesh → setting drainage holes → spraying concrete → finishing the slope surface and applying additional spray.

[0093] 1) Drill holes and insert anchor bolts into the drilled holes and grout:

[0094] For anchor bolts with a drilling depth of less than 5m, the process of grouting before bolt insertion is adopted; for anchor bolts with a rock penetration depth of 5m or more, the process of bolt insertion before grouting is adopted.

[0095] The construction steps of the grouting-then-insertion process are as follows: hole layout → drilling rig positioning → drilling anchor holes → cleaning anchor holes → grouting into anchor holes → placing anchors in the grouted anchor holes → sealing the anchor holes where anchors are placed.

[0096] The construction steps of the pre-insertion and post-grouting process are as follows: hole location layout → drilling rig positioning → drilling anchor holes → cleaning anchor holes → binding grouting pipes, vent pipes, etc. to the anchor rod body → inserting the bound anchor rod into the anchor hole → fixing the anchor hole opening → grouting into the anchor hole → tying the grouting pipes and vent pipes.

[0097] ① Drilling

[0098] In the process of grouting before inserting anchor rods, the drilling of anchor rod holes and the drilling of self-drilling anchor rods are carried out using a YT-28 pneumatic leg drill, with an anchor rod hole diameter of 48mm.

[0099] In the aforementioned process of inserting anchor rods before grouting, the anchor rod holes are drilled using a QZJ-100B down-the-hole drill with a diameter of 75mm. Before drilling, the hole positions are measured and marked according to the design requirements in the drawings.

[0100] During the drilling process, pay attention to controlling the drilling angle and direction. For mortar anchors, the anchor hole should be perpendicular to the excavated slope; for self-drilling anchors, the hole should be tilted downwards at 15° as designed. A construction platform should be erected for slope anchor drilling operations. After the mortar anchor holes are completed, they should be cleaned promptly with a combination of high-pressure air and water. After cleaning, the hole opening should be protected to prevent falling rocks and debris.

[0101] ② Insert anchor bolts into the drilled hole and grout.

[0102] In the pre-grouting and post-installation process, pure cement grout is used for grouting into the anchor holes, with a water-cement ratio of 1:0.5 and a grouting pressure between 0.4 and 1.0 MPa, adjusted according to the slope geological conditions. M7.5 cement mortar is then poured (specifically according to design requirements), and the grout is injected evenly into the holes. When inserting the anchor rod, the reinforcing bar is slowly pulled out to ensure the anchor holes are unobstructed and the cement mortar is fully filled.

[0103] In the pre-insertion and post-grouting process, an HJB-25 grouting machine is used to inject grout into the anchor bolt hole, preparing the grout on the slope walkway (or roadbed). Before inserting the bolt, the grouting pipe and vent pipe should be fixed to the anchor bolt body, with the end of the grouting pipe approximately 5cm away from the end of the bolt body. After the bolt is inserted, the hole opening is wedge-locked to prevent damage.

[0104] 2) Install steel mesh:

[0105] The reinforcing mesh uses φ6.5@200×200mm and is installed manually. The mesh should be 3-5cm above the slope surface and securely tied to anchor bolts or other anchor points. Lap joints should meet relevant specifications, with a lap length of at least 30d and adjacent joints staggered by at least 50cm. Lap sections should be securely tied, with at least two ties. Longitudinal and transverse reinforcing bars can be tied in a staggered pattern, but the number of connection points should not be less than 50% of the mesh nodes.

[0106] 3) Install drainage holes:

[0107] Drainage holes are located at the anchor spraying points where the reinforcing mesh is attached. The holes are 3m deep, 42mm in diameter, and spaced 3m apart. The drainage holes are constructed after the shotcrete is applied. Drilling is done using a YT-28 pneumatic leg drill. During construction, the holes are tilted upwards as required by the design to facilitate drainage after drilling. They should also be staggered from the anchor bolts in a staggered pattern.

[0108] 4) Shotcrete application, slope finishing, and touch-up spraying:

[0109] Shotcrete work is carried out according to the section division and overall construction sequence. For the slopes, the scaffolding is erected and the reinforcing mesh is installed, generally following a bottom-up, right-to-left construction procedure. HPZ-9 shotcrete machines are used for shotcreting. Plain shotcrete is applied to the designed thickness in one pass. For shotcrete with reinforcing mesh, each section is sprayed twice to the designed thickness. The first application is an initial spray to seal the surrounding rock, with a thickness of 3cm, carried out promptly after slope cleaning and scaffolding erection. The second application is a final spray to the designed thickness, applied after the reinforcing mesh is installed.

[0110] Before spraying concrete, the slope surface is first cleaned manually using high-pressure air, and spray thickness marks are set on the work surface before spraying. Spraying proceeds from bottom to top. In the initial spraying, depressions are filled first, followed by leveling. The nozzle should be as perpendicular as possible to the sprayed surface, generally maintaining a distance of 0.6 to 1.0 meters. Before the second spraying operation, the surface of the first sprayed concrete is moistened with water, and the surface film and dust are washed away. When spraying in layers, the interval between each spray layer should comply with relevant regulations. If the interval exceeds 2 hours, the concrete surface should be moistened with water before re-spraying to ensure good adhesion between concrete layers.

[0111] In the description of this invention, it should be understood that if terms such as "front" or "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, it does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are for illustrative purposes only and should not be construed as limiting the invention.

[0112] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A construction method for excavating and constructing a single-sided bridge crossing in a steep, folded rock face road cut, characterized in that: Includes the following steps: 1) Measure and lay out the lines according to the design drawings; 2) Fabricate steel beams and install them at the target location in the ditch; the steel beams include multiple crossbeams (1) and multiple connecting bars (2), the multiple crossbeams (1) are distributed parallel to each other from front to back and the multiple crossbeams (1) are all arranged laterally, the multiple crossbeams (1) are connected from left to right by multiple connecting bars (2) and the multiple connecting bars (2) are all arranged longitudinally; when the span is large or the steel beam is wide, I-beams are welded laterally at the bottom of the steel beam; 3) The machinery excavates and passes through the slope according to the designed route; when passing through, one side of the machinery's tracks rests on the steel beams, and the other side rests on the slope structure. 4) Excavate the slope overburden and upper strongly weathered rock; 5) For the weakly weathered rock beneath the pre-splitting slope, step-by-step blasting is used for rock excavation in stages. To reduce the disturbance and damage to the surrounding rock caused by blasting vibrations, pre-splitting blasting is used for the surrounding rock. For areas where pre-splitting blasting is not suitable, smooth blasting is used. The bottom of the excavated slope, 2-3m away from the road cut, serves as a protective layer for rock excavation. Smooth blasting is used at the roadbed excavation surface. After inspection and acceptance, the single-sided bridge crossing method for steep folded rock wall road cuts is completed. Slope support is used during excavation in steps 4) and 5). The slope support adopts the support form of anchor bolts + steel mesh + shotcrete. The slope support includes the following construction steps: drilling, inserting anchor bolts into the drilled holes and grouting, hanging steel mesh, setting drainage holes, shotcreting, sizing the slope, and supplementing shotcreting.

2. The excavation and construction method for a single-sided bridge crossing in a steep, folded rock face road cut as described in claim 1, characterized in that: The crossbeam (1) is made of I-beam.

3. The excavation and construction method for a single-sided bridge crossing in a steep, folded rock face road cut, as described in claim 1, is characterized in that: The method for installing the steel beam at the target location in the ditch in step 2) includes the following steps: first, remove the slag from the rock mass on both sides of the ditch, then drill holes at the target location to support the steel beam, insert reinforcing bars into the holes and expose the reinforcing bars, place the steel beam at the target location, and finally connect the exposed reinforcing bars to the steel beam to complete the installation of the steel beam.

4. The excavation and construction method for a single-sided bridge crossing in a steep, folded rock face road cut as described in claim 1, characterized in that: After excavation in step 3), the excavated soil and rock are covered on the surface of the steel beam until the thickness of the cover reaches the target thickness.

5. The excavation and construction method for a single-sided bridge crossing in a steep, folded rock face road cut as described in claim 1, characterized in that: Step 4) excavating the slope overburden and upper strongly weathered rock includes the following steps: 4.1) First, measure and lay out the lines according to the design drawings, mark the excavation boundary line at the top of the slope, and calculate the excavation boundary of each step based on the design excavation depth and slope inclination. 4.2) Before excavation, according to the survey and layout, dig the intercepting and drainage ditch according to the design drawings, and then clean the topsoil from high to low and from the outside to the inside, and clean the covering soil layer of the excavation area. 4.3) For soft rock and strongly weathered rock on slopes, mechanical excavation shall be carried out in layers from top to bottom until the excavation is completed.

6. The excavation and construction method for a single-sided bridge crossing in a steep, folded rock face road cut, as described in claim 5, is characterized in that: The slope was constructed using a first-stage excavation and second-stage protection method.

7. The excavation and construction method for a single-sided bridge crossing in a steep, folded rock face road cut as described in claim 1, characterized in that: In step 5), the excavation is carried out step by step from top to bottom until the last step is excavated.

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