Forward tunneling construction method for iron ore ramp under water-containing composite stratum condition

Abstract

The invention discloses an iron ore slope ramp forward tunneling construction method under the condition of a water-containing composite stratum, which comprises the following steps: firstly, aiming at a water-containing stratum in a construction area, drilling holes from the earth surface to implement curtain grouting, using cement single-liquid slurry and cement-water glass double-liquid slurry, and coring and detecting the effect after grouting; advanced water detection is conducted before roadway excavation, and secondary grouting is conducted through double-liquid slurry if the water control effect does not reach the expectation; advanced small guide pipe supporting is conducted firstly, then main steps are excavated step by step and in sequence, the whole section is divided into upper and lower steps, and the lower steps are constructed in a left-right staggered mode; the primary support is closed into a ring by an I-shaped steel arch frame, and the permanent support is double-layer reinforced concrete; a broken and collapsed area is rapidly supported by combining advanced grouting and pre-supporting of a small guide pipe or a pipe shed with short footage. According to the method, aiming at different water-containing geological conditions, curtain grouting is combined with advance support, grading excavation is carried out, and targeted treatment of the whole road section is achieved.

Description

Technical Field

[0001] This invention relates to the field of mine shaft and tunnel engineering technology, specifically to a method for forward excavation of iron ore inclined ramps under water-bearing composite strata conditions. Background Technology

[0002] Iron ore ramps serve as crucial passageways between the underground and surface, functioning as transportation hubs for equipment and personnel, as well as safety exits. However, in aquifer and complex geological conditions, ramp excavation faces multiple challenges: Quaternary loose aquifers exhibit poor self-stability and are prone to collapse; gravel weathering layers are highly water-bearing, posing a risk of water inrush. Traditional construction methods suffer from uneven grouting effects, poor coordination between support and excavation, and weak adaptability to geological formations, resulting in low construction efficiency and high safety risks.

[0003] Existing technologies, tunneling methods for single strata (such as pure bedrock blasting or loose layer shield tunneling) are difficult to adapt to the complex conditions of composite strata. Therefore, it is necessary to develop an integrated construction method that combines advanced detection, graded reinforcement, and dynamic support to achieve safe and efficient tunneling in different strata. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for forward tunneling of iron ore inclined ramps under water-bearing composite strata conditions.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions, comprising the following steps:

[0006] (1) Grouting construction: Based on the distribution range of the aquifer in the construction area, boreholes are drilled from the ground surface and curtain grouting is implemented. The grouting materials are single-liquid cement grout and two-liquid cement grout mixed with water glass. After the grouting is completed, core samples are taken to verify the grouting effect by testing the integrity and permeability of the core samples.

[0007] (2) Advance water exploration: Before the tunnel excavation, advance water exploration is carried out. Water exploration boreholes are laid out to find out the water content and the effect of grouting to control water. If the effect of grouting to control water does not meet expectations, the working face pre-grouting construction process is adopted for secondary grouting. The secondary grouting material is a two-liquid grout mixed with cement grout and water glass.

[0008] (3) Segmented excavation: First, advance small pipe support is carried out, and then the step-by-step method is adopted to divide the entire cross section into two steps, the lower step is further divided into left and right parts, and the left and right parts are constructed alternately on site.

[0009] (4) Support: The initial support adopts I-beam steel arch frame to form a closed ring with steel bars for circumferential and longitudinal connection; 16 seamless steel pipe anchor rods are installed on the arch and both sides of each steel arch frame, and the anchor rods are welded and fixed to the steel arch frame; then steel mesh is laid and shotcrete is sprayed to form the initial support layer; the permanent support adopts a double-layer reinforced concrete structure.

[0010] (5) Special conditions treatment: For the broken and collapsed area, the pre-support of small pipe grouting or pipe roof grouting is combined with the short advance rapid support technology.

[0011] Preferably, the curtain grouting in step (1) adopts a plum blossom pattern of holes with a hole spacing of 3.5-4m; the grouting material is P.O42.5 grade cement and water glass, and the grouting liquid is divided into ordinary cement single liquid grout and cement-water glass double liquid grout, with a final grouting pressure of 1.5-2.0MPa.

[0012] Preferably, the principle of water exploration borehole arrangement in step (2) is as follows: no less than 4 water exploration boreholes distributed in a fan shape are arranged at the working face, wherein the middle hole is arranged along the roadway direction, the bottom hole is opened at an angle to the roadway direction downward, the side hole is inclined to the outside of the roadway, and the final hole of all water exploration boreholes is not less than 5m away from the roadway outline.

[0013] Preferably, the pre-grouting of the working face in step (2) adopts the forward segmented grouting method. First, a grout stop wall is constructed on the working face. A core is drilled on the grout stop wall using an alloy steel drill. The drilling and grouting operations are completed simultaneously using a forward drilling and grouting integrated machine. The advance of each cycle is generally controlled at 1 to 2 meters. When the drill rod is drilled to a depth of 1 to 2 meters, grout is injected until the grout is saturated. Drill rods are added to repeat the drilling-grouting process. This cycle is repeated until the first 20-meter grouting section is completed. After water exploration and inspection to confirm that the water control effect meets the standards, the tunnel body is excavated.

[0014] Preferably, the pre-grouting method of the working face in step (2) is to use a pre-drilled small guide pipe. The pre-drilled small guide pipe is made of hot-rolled seamless steel pipe with a length of 3-6m. Its top is conical and grouting holes are opened in the pipe wall with a circumferential spacing of 350mm and an external insertion angle of 5-15°. After drilling, the small guide pipe is inserted into the hole with an exposed end length of 20cm. The exposed end is supported on the steel arch frame behind the excavation face and together with the steel arch frame, it forms a pre-support system.

[0015] Preferably, the construction sequence of step (3) is as follows: first, the upper half of the tunnel body is excavated, and after the top temporary support is completed, the lower half is excavated; the staggered distance between the upper and lower steps is controlled within 20m, and the changes in the properties of the surrounding rock with the advance are observed in real time during the excavation process, and the staggered distance is adjusted in a timely manner.

[0016] Preferably, in the double-layer reinforced concrete structure described in step (4), the longitudinal reinforcement is Φ16mm HRB400 steel bar, the ring reinforcement is Φ22-25mm HRB400 steel bar, and the concrete is C40 waterproof concrete.

[0017] Preferably, the pipe shed in step (5) is made of Φ108×6mm seamless steel pipe with a length of 20m, a circumferential spacing of 40cm, and a longitudinal overlap length of ≥3m. The pipe shed is arranged within a 150° range of the arch and is welded to the steel arch frame after grouting to form a pipe shed-steel arch frame joint support system.

[0018] Preferably, during the grouting of the small guide tube in step (3), grouting holes are made with a five-hole arrangement, a circumferential spacing of 350mm, an external insertion angle of 5-15°, an initial grouting pressure of 0.5-1.0MPa, and a final pressure of 2.0MPa.

[0019] Preferably, each construction section is equipped with a monitoring and measurement system to monitor the surrounding rock convergence and settlement data in real time. When the deformation rate exceeds 5 mm / d, the support parameters are adjusted or construction is suspended.

[0020] Compared with the prior art, the present invention provides a method for forward tunneling of iron ore inclined ramps under water-bearing composite strata conditions, which has the following beneficial effects:

[0021] 1. This invention employs a construction strategy that combines curtain grouting with advanced support and staged excavation for different water-bearing geological conditions, achieving targeted treatment for the entire road section;

[0022] 2. The innovative integrated process of "curtain grouting - advanced support - staged excavation" effectively controls the risks of water inrush and collapse, improving construction efficiency by 30% and reducing the accident rate by 80% compared with traditional methods;

[0023] 3. The support structure adopts a composite system combining steel arch frames and reinforced concrete, which can adapt to the deformation characteristics of complex strata, increase the support strength by 40%, and reduce the later maintenance costs.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Specific embodiments of the present invention are given in detail below with reference to the accompanying drawings. Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0026] Figure 1 This is a plan view of the ramp layout;

[0027] Figure 2 This is a cross-sectional view of the ramp;

[0028] Figure 3 Schematic diagram of the arrangement of small guide tubes with cross-section advance;

[0029] Figure 4 This is a schematic diagram of the advanced pipe shed layout;

[0030] Figure 5 This is a schematic diagram of the drilling operation for water exploration in the Quaternary aquifer.

[0031] Figure 6 Schematic diagram of aquifer exploration borehole construction Figure 1 ;

[0032] Figure 7 Schematic diagram of aquifer exploration borehole construction Figure 2 ;

[0033] Figure 8 Schematic diagram of aquifer exploration borehole construction Figure 3 ;

[0034] Figure 9 This is a schematic diagram of the grouting hole layout;

[0035] Figure 10 Schematic diagram of grouting with pre-conduit pipes in aquifer;

[0036] Figure 11 A schematic diagram of the cross-section blast hole layout;

[0037] Figure 12 Cross-sectional view of the grouting borehole for the curtain wall;

[0038] Figure 13 This is a schematic diagram of segmented downward grouting.

[0039] Figure 14 This is a flowchart of the construction process. Detailed Implementation

[0040] I. Preparations before construction:

[0041] 1. Geological Exploration: The strata were exposed through boreholes SW01, SW02, and SW03, clarifying the geological characteristics of each section. The Quaternary strata are mainly clay and silty clay, with a thickness of 43.16–101.76 m, and contain a gravel layer at the bottom; the gravel weathering layer is fractured and has strong water-bearing capacity; the bedrock section is mainly composed of dolomite marble, with local fracture zones.

[0042] II. Specific Construction Steps

[0043] (I) Grouting Construction

[0044] Based on the aquifer distribution range determined by the survey, boreholes were drilled from the surface using a drilling rig. During drilling, the verticality and depth of the boreholes were strictly controlled to ensure accurate penetration of the aquifer. Subsequently, curtain grouting was implemented, using P.O42.5 grade cement and water glass as the grouting materials. Depending on the aquifer's inflow and permeability coefficient, either ordinary cement single-component grout or cement-water glass double-component grout was selected: ordinary cement single-component grout was used when the aquifer's inflow was small and the permeability coefficient was low; when the aquifer's inflow was large and the permeability coefficient was high, cement-water glass double-component grout was used to improve the grouting and water-blocking effect. During grouting, the grouting pressure was controlled by a grouting pump, with the final grouting pressure controlled at 1.5-2.0 MPa. A staggered borehole pattern was used, with a borehole spacing of 3.5-4 m, to ensure the formation of a continuous curtain of grout.

[0045] After grouting is completed, core sampling verification holes are constructed in the curtain grouting area. The number of core samples is determined based on the curtain area, generally one verification hole is placed every 50-100 square meters. Core samples are obtained using a core drilling rig, and their integrity is observed. If the core sample is continuous and has no obvious voids, it indicates a good grouting effect. Simultaneously, the permeability coefficient of the core sample is tested using pumping or pressure testing methods. If the permeability coefficient is less than 1×10⁻⁻⁻⁶, the grouting effect is considered good. 6 If the core sample density is 1 cm / s, the grouting effect is considered to be up to standard, and the next construction stage can be carried out; if the core sample integrity is poor or the permeability coefficient does not meet the standard, the grouting construction needs to be repeated.

[0046] (II) Advance water exploration

[0047] Before the tunnel excavation, drilling rigs are used to lay water-exploratory boreholes at the working face. The arrangement of the water-exploratory boreholes follows these principles: at least four water-exploratory boreholes are laid out in a fan shape. The central borehole is arranged along the design axis of the tunnel and is used to detect the water content directly in front of the tunnel. The bottom borehole is opened at a 10-15° angle downwards with respect to the tunnel direction and is used to detect the water content below the bottom of the tunnel. The side boreholes are inclined to the outside of the tunnel at an angle of 15-20° and are used to detect the water content on both sides of the tunnel. The final borehole of all water-exploratory boreholes is no less than 5m from the tunnel outline to ensure that the water content around the tunnel can be fully explored and the grouting water control effect can be achieved.

[0048] During drilling, observe the water inflow and pressure. If the inflow is less than 0.5 m³ / h and there is no significant water pressure, the grouting water control effect is satisfactory. If the inflow is greater than 0.5 m³ / h or there is significant water pressure, the grouting water control effect has not met expectations, and secondary grouting using a pre-grouting process at the working face is required. The secondary grouting material is a two-component grout mixture of cement grout and water glass. The specific construction process is as follows:

[0049] First, a grout-stopping wall is constructed at the working face using shotcrete. The thickness of the grout-stopping wall is not less than 1.5m to ensure that the grout-stopping wall has sufficient strength and sealing to prevent grout leakage during the grouting process.

[0050] Cores are taken from the grout-stopping wall using an alloy steel drill. The diameter of the drill hole is determined according to the specifications of the grouting pipe, and is generally 5-10 mm larger than the diameter of the grouting pipe.

[0051] The drilling and grouting operation is completed simultaneously using a forward-type drilling and grouting machine. The advance of each cycle is controlled at 1 to 2 meters. When the drill rod is drilled to a depth of 1 to 2 meters, the drilling is stopped and the grouting pump is turned on to inject grout into the hole until the grout is saturated (that is, the grouting pressure reaches the design final pressure and the grout no longer needs to be injected). Then, the drill rod is added and the drilling-grouting process is repeated. This cycle is repeated until the first 20-meter grouting section is completed.

[0052] After grouting is completed, a water exploration check is conducted again. If the water flow and water pressure meet the standards, the tunnel can be excavated. If they still do not meet the standards, grouting needs to continue.

[0053] In addition, pre-grouting at the working face can also be achieved using pre-grouted guide pipes. These guide pipes are made of hot-rolled seamless steel pipes, with a length of 3-6m, selected according to the degree of rock fragmentation: 3-4m long guide pipes are used when the surrounding rock is relatively intact; 5-6m long guide pipes are used when the surrounding rock is more fragmented. The top of the guide pipe is tapered for easy insertion into the borehole. Grouting holes are opened in the pipe wall, with a circumferential spacing of 350mm and an external insertion angle controlled at 5-15°. After drilling is completed, the guide pipe is inserted into the hole, with the exposed end of the guide pipe being 20cm long. The exposed end is supported on the steel arch frame behind the excavation face, forming a pre-support system together with the steel arch frame. Grout is then injected into the surrounding rock through the guide pipe to further reinforce the surrounding rock and block water.

[0054] (III) Segmented Excavation

[0055] Before segmented excavation, advance small pipe support is carried out. The construction parameters of the advance small pipe are the same as those of the advance small pipe in the pre-grouting of the working face. When grouting the small pipe, grouting holes are opened in the pipe wall. The holes are arranged in a five-point pattern with a circumferential spacing of 350mm and an external insertion angle of 5-15°. The initial grouting pressure is controlled at 0.5-1.0MPa, and the pressure is gradually increased to a final pressure of 2.0MPa to ensure that the grout is evenly diffused into the surrounding rock fissures.

[0056] After the pre-excavation small guide pipe support is completed, the step-by-step excavation method is adopted to divide the entire cross-section of the tunnel into upper and lower steps. The lower step is further divided into left and right sections. The construction sequence is as follows: First, the upper part of the tunnel is excavated using excavators or blasting. The excavation height is determined according to the designed tunnel height, generally 1 / 2 to 2 / 3 of the total tunnel height. After the upper part is excavated, shotcrete is immediately used for temporary roof support, with a shotcrete thickness of 50-100mm, to prevent the surrounding rock from collapsing. Then, the lower part is excavated. The left and right sections of the lower step are constructed in an alternating manner, that is, the left section is excavated first, with an excavation length of 3-5m, and then the right section is excavated to avoid stress concentration in the surrounding rock caused by simultaneous excavation. The staggered distance between the upper and lower step excavation faces is controlled within 20m. During the excavation process, a dedicated person is assigned to observe the changes in the surrounding rock properties with the advance. If the surrounding rock is found to become fractured or signs of water inrush are found, the staggered distance is reduced in time, and the excavation cycle advance is shortened.

[0057] (iv) Support

[0058] 1. Initial support

[0059] After the upper section is excavated and the temporary top support is completed, the initial support construction begins immediately: I-beam steel arch frames are used to form a closed ring across the entire cross-section. The type of I-beam is determined based on the tunnel span and surrounding rock pressure, generally I16-I22 I-beams are selected, and the spacing between the steel arch frames is 0.8-1.2m. After the steel arch frames are installed, Φ22mm HRB400 steel bars are used for circumferential and longitudinal connections between the steel arch frames. The circumferential bar spacing is 500mm, and the longitudinal bar spacing is 1000mm, forming an integral support frame. Sixteen seamless steel pipe anchor bolts are installed at the arch and both sides of each steel arch frame. The anchor bolts are made of Φ42mm seamless steel pipe, 2-3m in length, and are welded to the steel arch frame with a weld length of not less than 100mm to enhance the stability of the steel arch frame. Subsequently, a Φ6mm steel mesh is laid with a mesh size of 200×200mm. The steel mesh is tightly fitted to the steel arch frame. Finally, C25 concrete is sprayed using a shotcrete machine to form the initial support layer with a thickness of 150-200mm.

[0060] 2. Permanent support

[0061] After the initial support is completed and the surrounding rock deformation stabilizes (determined by monitoring and measurement; when the surrounding rock convergence rate is less than 0.5 mm / d, the surrounding rock deformation is considered stable), permanent support construction begins. The permanent support adopts a double-layer reinforced concrete structure. Longitudinal reinforcement uses Φ16mm HRB400 steel bars spaced at 200mm; circumferential reinforcement uses Φ22-25mm HRB400 steel bars spaced at 150-200mm. After the reinforcement is tied, steel formwork is installed to ensure its flatness and verticality. Then, C40 waterproof concrete is poured. During concrete pouring, a vibrator is used to compact the concrete and prevent defects such as honeycomb and pitting. The concrete pouring thickness is determined according to the tunnel design requirements, generally 300-500mm, and the curing time is no less than 14 days.

[0062] (v) Handling of special conditions

[0063] When encountering broken and collapsed areas during construction, pre-support by small-diameter pipe grouting or pipe roof grouting is adopted, combined with short-advance rapid support technology.

[0064] If the area of ​​the fractured and collapsed area is small and the degree of collapse is mild, pre-support by grouting with small guide pipes is adopted. The parameters of the small guide pipes are consistent with those of the pre-support small guide pipes in the segmented excavation. After the grouting is completed, short-cut excavation is adopted, with each excavation advance controlled at 0.5-1m. Initial support is carried out immediately after excavation to shorten the exposure time of the surrounding rock.

[0065] If the collapsed area is large and the collapse is severe, pre-support with pipe roof grouting is adopted. The pipe roof uses Φ108×6mm seamless steel pipes, with a length of 20m, a circumferential spacing of 40cm, and a longitudinal overlap length of ≥3m. The pipe roof is arranged within a 150° range of the arch. After the pipe roof construction is completed, grout is injected into the pipe roof. The grouting material is cement-water glass double-liquid grout, and the grouting pressure is 2.0-2.5MPa. After grouting, it is welded with the steel arch to form a pipe roof-steel arch combined support system. Then, short-depth excavation is adopted, with each excavation advance controlled at 0.3-0.5m. Support is provided in a timely manner after excavation.

[0066] (vi) Monitoring and Measurement

[0067] A monitoring and measurement system was set up in each construction section, with monitoring points arranged as follows: Rock convergence monitoring points and settlement monitoring points were set up at the tunnel arch crown, arch waist, and wall base, with a spacing of 10-20m between monitoring points. Rock convergence gauges were used to monitor the convergence deformation of the surrounding rock around the tunnel, and settlement observation instruments were used to monitor the settlement of the arch crown. Monitoring was conducted 1-2 times daily, and the rock convergence and settlement data were recorded in real time. When the deformation rate exceeded 5mm / d, the support parameters were immediately adjusted (e.g., reducing the spacing of the steel arch frames, increasing the thickness of the shotcrete, etc.) or construction was suspended. The cause of the deformation was analyzed, and targeted measures were taken (e.g., supplementary grouting to reinforce the surrounding rock). Construction resumed only after the deformation rate stabilized below 5mm / d.

[0068] Through the above-described embodiments, this invention adopts a construction strategy of curtain grouting combined with advanced support and staged excavation for different water-bearing geological conditions. This strategy can effectively solve the problems of water inrush and surrounding rock instability during the excavation of inclined ramps in water-bearing composite strata, achieve targeted treatment for the entire road section, improve construction safety and efficiency, and ensure the construction quality and service life of iron ore inclined ramps.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions, characterized in that, Includes the following steps: (1) Grouting construction: Based on the distribution range of the aquifer in the construction area, boreholes are drilled from the ground surface and curtain grouting is implemented. The grouting materials are single-liquid cement grout and two-liquid cement grout mixed with water glass. After the grouting is completed, core samples are taken to verify the grouting effect by testing the integrity and permeability of the core samples. (2) Advance water exploration: Before the tunnel excavation, advance water exploration is carried out. Water exploration boreholes are laid out to find out the water content and the effect of grouting to control water. If the effect of grouting to control water does not meet expectations, the working face pre-grouting construction process is adopted for secondary grouting. The secondary grouting material is a two-liquid grout mixed with cement grout and water glass. (3) Segmented excavation: First, advance small pipe support is carried out, and then the step-by-step method is adopted to divide the entire cross section into two steps, the lower step is further divided into left and right parts, and the left and right parts are constructed alternately on site. (4) Support: The initial support adopts I-beam steel arch frame to form a closed ring with steel bars for circumferential and longitudinal connection; 16 seamless steel pipe anchor rods are installed on the arch and both sides of each steel arch frame, and the anchor rods are welded and fixed to the steel arch frame; then steel mesh is laid and shotcrete is sprayed to form the initial support layer; the permanent support adopts a double-layer reinforced concrete structure. (5) Special conditions treatment: For the broken and collapsed area, the pre-support of small pipe grouting or pipe roof grouting is combined with the short advance rapid support technology.

2. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, The curtain grouting in step (1) adopts a plum blossom pattern of holes with a hole spacing of 3.5-4m; the grouting material is P.O42.5 grade cement and water glass, and the grouting liquid is divided into ordinary cement single liquid grout and cement-water glass double liquid grout. The final grouting pressure is 1.5-2.0MPa.

3. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, The principle for arranging water exploration boreholes in step (2) is as follows: at least four water exploration boreholes are arranged in a fan shape at the working face. The middle borehole is arranged along the roadway direction, the bottom borehole is opened at an angle downward with the roadway direction, and the side boreholes are inclined to the outside of the roadway. The final borehole of all water exploration boreholes is not less than 5m away from the roadway outline.

4. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, The pre-grouting of the working face in step (2) adopts the forward segmented grouting method. First, a grout stop wall is constructed on the working face. The core is drilled on the grout stop wall using an alloy steel drill. The drilling and grouting operations are completed simultaneously using a forward drilling and grouting integrated machine. The advance of each cycle is generally controlled at 1 to 2 meters. When the drill rod is drilled to a depth of 1 to 2 meters, the grout is injected until the grout is saturated. The drill rod is added and the drilling-grouting process is repeated. This cycle continues until the first 20-meter grouting section is completed. After water exploration and inspection to confirm that the water control effect meets the standards, the tunnel body is excavated.

5. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, The pre-grouting method for the working face described in step (2) is to use advanced small guide pipes. The advanced small guide pipes are made of hot-rolled seamless steel pipes with a length of 3-6m. The top of the pipe is conical, and grouting holes are opened in the pipe wall with a circumferential spacing of 350mm and an external insertion angle of 5-15°. After drilling, the small guide pipes are inserted into the holes, with an exposed end length of 20cm. The exposed end is supported on the steel arch frame behind the excavation face, and together with the steel arch frame, they form a pre-support system.

6. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, The construction sequence of step (3) is as follows: first, excavate the upper half of the tunnel body, and after completing the temporary support at the top, excavate the lower half; the staggered distance between the upper and lower steps is controlled within 20m, and the changes in the properties of the surrounding rock with the advance are observed in real time during the excavation process, and the staggered distance is adjusted in a timely manner.

7. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, The double-layer reinforced concrete structure described in step (4) uses Φ16mm HRB400 steel bars for longitudinal reinforcement and Φ22-25mm HRB400 steel bars for circumferential reinforcement. The concrete used is C40 waterproof concrete.

8. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, The pipe shed described in step (5) uses Φ108×6mm seamless steel pipe with a length of 20m, a circumferential spacing of 40cm, and a longitudinal overlap length of ≥3m. The pipe shed is arranged within a 150° range of the arch and is welded to the steel arch frame after grouting to form a pipe shed-steel arch frame joint support system.

9. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, When grouting the small guide tube in step (3), grouting holes are made. The holes are arranged in a five-point pattern with a circumferential spacing of 350mm and an external insertion angle of 5-15°. The initial grouting pressure is 0.5-1.0MPa and the final pressure is 2.0MPa.

10. The method for forward tunneling of an iron ore inclined ramp under water-bearing composite strata conditions according to claim 1, characterized in that, Each construction section is equipped with a monitoring and measurement system to monitor the surrounding rock convergence and settlement data in real time. When the deformation rate exceeds 5 mm / d, the support parameters are adjusted or construction is suspended.

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