LU502209B1 - Protective structure and grouting method for preventing tunnel grouting reinforcement from causing surface uplift - Google Patents

Abstract

The present invention provides a protective structure and grouting method for preventing tunnel grouting reinforcement from causing a surface uplift, and relates to the technical field of geotechnical engineering and civil engineering. The protective structure includes a tunnel body located below a ground surface. A downward arch formed by grouting from the surface is provided in a stratum directly above the tunnel body, and the downward arch protrudes downward. A support structure is provided on a roof-sidewall portion of an inner contour of the tunnel body. An upward arch is formed by grouting from a borehole, and provided outside the support structure to surround the roof-sidewall portion of the inner contour of the tunnel body. The upward arch protrudes upward. The present invention implements layered, multiple grouting, combined with a variety of passive support methods to form a stress bearing body, and form the downward and upward arches successively.

Description

DESCRIPTION LU502209

PROTECTIVE STRUCTURE AND GROUTING METHOD FOR PREVENTING TUNNEL GROUTING REINFORCEMENT FROM CAUSING SURFACE UPLIFT

TECHNICAL FIELD The present invention relates to the technical field of geotechnical engineering and civil engineering, and in particular to a protective structure and grouting method for preventing tunnel grouting reinforcement from causing a surface uplift. The present invention is applicable to permanent tunnel (lane) engineering in which pre-grouting reinforcement of a shallow tunnel (lane) passing loose rock and sand soil layers easily causes a series of problems such as surface uplift, road cracking and building tilt.

BACKGROUND With the development of economic globalization and the acceleration of the urbanization process, subway projects have increasingly become the main development direction of urban public transportation. The subway enhances the speed of travel, saves people's time, and promotes urban environmental protection. China is in a period of accelerated industrialization and urbanization, when millions of people are pouring into large cities, putting tremendous pressure on urban management and urban transportation. Compared with other project, the subway is a large-scale civil engineering project with large investment, long construction period and complicated technology. The subway project features concealment, uncertainty of the geological environment and complexity of construction technology, which will inevitably lead to a large number of risks and complicated types in the construction period, and even cause greater economic losses after accidents.

The subway is located in noisy, densely populated and densely built urban areas. The tunnels (lanes) of the subway are located in the shallow part of the crust and need to pass loose rock and sand soil layers, which undoubtedly increases the difficulty of excavation and support. In China, the subways are generally built about 20 m underground. According to statistics, the tunnels (lanes) built in Beijing, Tianjin, Guangzhou and Shanghai are about 20 m underground, and the depth of Beijing Subway Line 5 reaches 24 m. The construction depth of the subways also varies, depending on the soil, geology and line distribution. In Russia, England and some other countries, the subways are built about 50 m underground.

The tunnels (lanes) are located in loose rock layer and sand layer, and also pass through loose rock layer, existing road on the ground or other buildings and structures during construction. At present, usually only a very small end part of the tunnels (lanes) is constructed by the open-cut method, and 90% length of the route is constructed by the subsurface excavation method. The subsurface excavation method includes drilling and blasting (D & B) method,

shield method, tunnel boring machine (TBM) method and New Austrian tunneling method 502209 (NATM), etc. After the tunnels (lanes) are excavated, the stress state of the originally complete and stable rock-soil stratum is changed, causing stress redistribution. The weights of the overlying rock strata, buildings and structures will cause the tunnels (lanes) to deform. Therefore, the excavated tunnels (lanes) must be supported, and the loose rock and sand soil layers between the tunnels (lanes) and the ground surface must be reinforced. The depth of the loose rock and sand soil layers refers to a burial depth. As the burial depth is small, the tunnels (lanes) are close to the ground surface, and like a thin shell of the entire stratum. At present, this part of rock and soil mass is basically reinforced by grouting. In order to achieve grouting reinforcement, a large grouting pressure is generally required. However, excessive grouting pressure will cause the rock and soil mass to arch and the ground surface to uplift, leading to the destruction of the original state of the surface, cracks in the surface road and uneven settlement of buildings and structures. The uplift deformation of the surface can be controlled by reducing the grouting pressure, but a low pressure will directly cause the reduction in the slurry diffusion radius, thereby failing to achieve the reinforcement of the rock and soil mass. Experience indicates that the slurry diffusion radius is generally around 25 cm. In actual construction, in order to fully reinforce the rock and soil mass between the grouting holes, the spacing of the grouting holes is usually designed to be about 50 cm to enable the slurry diffusion radii of two grouting holes to overlap at the effective grouting pressure. Since the slurry diffusion radius is reduced due to the reduction of the grouting pressure, the conventional spacing of grouting holes cannot guarantee the full reinforcement of the surrounding rock and soil mass. As a result, the grouted mass is discontinuous, which affects the stress state of the slurry-rock-soil mixed mass. Therefore, the grouting method needs to be improved and innovated.

SUMMARY In order to solve the above problems in the prior art, an objective of the present invention is to provide a protective structure and grouting method for preventing tunnel grouting reinforcement from causing a surface uplift. The present invention effectively prevents the surface from uplifting due to grouting reinforcement.

To achieve the above purpose, the present invention provides the following technical solution.

The present invention provides a protective structure for preventing tunnel grouting reinforcement from causing a surface uplift, including a tunnel body, a downward arch and an upward arch located below a ground surface, where the downward arch is constructed in a stratum directly above the tunnel body; the downward arch is formed by grouting from the surface, and the downward arch protrudes downward; a support structure is provided on 14502209 roof-sidewall portion of an inner contour of the tunnel body; the upward arch is formed by grouting from a borehole, and provided outside the support structure to surround the roof-sidewall portion of the inner contour of the tunnel body; the upward arch protrudes upward, the upward arch, the downward arch and the support structure together form a combined support structure to prevent pre-grouting from causing the surface uplift.

Preferably, the support structure provided on an inner wall of the tunnel body, which is a mesh-shotcrete-bolt support, a steel arch support or a combined support thereof.

Preferably, the thickness of the downward arch is 3-4 m, and the thickness of the upward arch is greater than 2 m.

Preferably, a projected length of the downward arch on a horizontal ground in a width direction is L, which serves as a span of the downward arch; a depth from a lowest point of the downward arch to the horizontal ground is H, which serves as a rise; a rise-span ratio of the downward arch is AK, AK = H/L, which 1s equal to 1/5-1/6.

Preferably, a vertical centerline of the tunnel body, a vertical centerline of the upward arch and a vertical centerline of the downward arch are collinear.

Preferably, a pre-grouting pipe inclined toward the direction of the tunnel is provided in the roof-sidewall portion of the inner contour of the tunnel body; an outlet of the pre-grouting pipe is located between coverage areas of the upward arch and the downward arch.

The present invention further provides a pre-grouting method for a tunnel by using the above protective structure for preventing tunnel grouting reinforcement from causing a surface uplift, including the following steps: A. surface drilling and grouting: before the tunnel is constructed to an area to be protected, surface boreholes are drilled on a ground surface with a loose rock-soil stratum directly above the direction of a tunnel body; the surface boreholes are arranged in a plum shape; a top centerline of surface boreholes in the same row is perpendicular to the direction of the tunnel; in the same row of surface boreholes, the depth of a borehole in the center is the largest, and the depth of the boreholes decreases in sequence from the center to both sides; lower ends of the surface boreholes in the same row fall within the range of a design downward arch where a section 1s located; a reusable grouting pipe is installed in the surface borehole, and the reusable grouting pipe is used for grouting to combine slurry and the loose rock-soil stratum as an integral support structure to form the downward arch; LU502209 B. tunnel support: when the tunnel 1s constructed to the area to be protected, a gross section of the tunnel body is first excavated; then initial shotcrete is performed and a support structure is installed; finally, secondary shotcrete is performed, C. tunnel drilling and grouting: one day after the secondary shotcrete, a borehole is grouted to form an upward arch around a roof-sidewall portion of an inner contour of the tunnel body; D. pre-grouting: pre-grouting is performed between the downward arch and the upward arch; and E. floor pouring: concrete is poured on a floor of the tunnel to form a cross-sectional size of the tunnel that meets a design requirement.

Preferably, the design downward arch is located in the loose rock-soil stratum directly above the direction of the tunnel, and the design downward arch protrudes downward; a projected length of the downward arch on a horizontal ground in a width direction is L, which serves as a span of the downward arch; a depth from a lowest point of the downward arch to the horizontal ground is H, which serves as a rise; a rise-span ratio of the downward arch is AK, AK = H/L, which is equal to 1/5-1/6.

Preferably, the distance from lower ends of reusable grouting pipes to a lower end face of the design downward arch is equal.

Preferably, the grouting operation in step A is as follows: the lower ends of the reusable grouting pipe does not exceed 10 cm from the bottom of the borehole; the initial grouting is performed first, and solidifying slurry is injected into a grouting hole through the reusable grouting pipe; the initial grouting is fill grouting performed with slurry including Grade 325 cement, an additive and water with a ratio of 1:0.08:2 at a grouting pressure controlled to be less than 0.5 Mpa; after 2-3 h after the initial grouting, the slurry reaches an initial setting state to be initially bonded to loose rock and sand soil layers in the loose rock-soil stratum as a whole with a certain bearing strength; then secondary grouting is performed at a grouting pressure greater than the grouting pressure of the initial grouting and controlled to be less than 3 Mpa; the secondary grouting is retreating multistage grouting performed with slurry including Grade 325 cement, an additive and water with a ratio of 1:0.08:2; the thickness of the retreating multistage grouting is 3-4 m to form the entire downward arch to increase the strength of the loose rock-soil stratum; the initial grouting and secondary grouting form an internally-grouted reinforced mass, which combines the surrounding loose rock-soil stratum as an integrated support structure to form the 500009 downward arch for stress bearing.

Compared with the prior art, the present invention achieves the following beneficial effects: The protective structure and grouting method provided by the present invention organically combine the spatial stability theory of arches with conventional shotcrete-bolt support, steel arch + shotcrete-bolt support, combined support and other passive support forms. The present invention implements layered, multiple grouting, combined with a variety of passive support methods to form a stress bearing body, and form downward and upward arch structures successively. The present invention changes the stress distribution state of loose rock and sand soil layers around a tunnel (lane), and shifts a peak stress out of a three-zone stress region of the tunnel (lane). By fully utilizing the large bearing capacity of the arches, the present invention blocks the influence of dynamic and static loads of the ground surface on the tunnel (lane) and the influence of excessive pre-grouting pressure of the tunnel (lane) on surface roads, buildings and structures. The present invention ensures the mutual stability and realizes high-pressure grouting. In this way, the present invention controls the deformation of surface roads, buildings and structures, prevents surface uplift, and fully realizes the grouting reinforcement of the loose rock-soil stratum. The present invention carries out high-pressure grouting to restore the strength and rigidity of the loose rock and soil mass. The present invention improves the integrity and bearing capacity of the surrounding rock, and keeps the loose rock and soil mass in the upper part of the tunnel (lane) in a stable state for a long time. Therefore, the present invention achieves high-pressure grouting through the protective downward arch under the condition that the surrounding environment and rock and soil properties are not very accurate. The grouting method of the present invention is applicable to a wide range of fields, including newly excavated and repaired tunnels (lanes), particularly shallow tunnels (lanes) passing loose rock and sand soil layers. The present invention forms a complete set of construction techniques, and features simple method, easy implementation, convenient mechanized operation and good supporting effect. In addition, the present invention has engineering promotion and application value, and significant economic benefits in the continuous development of shallow underground engineering.

BRIEF DESCRIPTION OF THE FIGURES To describe the technical solutions in the examples of the present invention or in the prior art more clearly, the accompanying drawings required for describing the examples are briefly 502209 described below. Apparently, the accompanying drawings in the following description show merely some examples of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

FIG. 1 is a sectional view showing the overall arrangement of the present invention.

FIG. 2 is a sectional view of a downward arch according to the present invention.

FIG. 3 is a sectional view of a pre-grouting reinforcement area according to the present invention.

FIG. 4 is an overall plan of a method for preventing grouting reinforcement from causing a surface uplift by using a downward continuous arch according to the present invention.

Reference Numerals: 1. ground surface; 2. surface borehole; 3. reusable grouting pipe; 4. loose rock-soil stratum; 5. downward arch; 6. pre-grouting pipe; 7. shallow grouting hole; 8. tunnel body; 9. vertical centerline of tunnel body; 10. floor; 11. upward arch; 12. pre-grouting reinforcement area; 13. mesh-shotcrete-bolt support; 14. horizontal centerline of tunnel body; 15. gross section of tunnel body; and 16. steel arch support.

DESCRIPTION OF THE INVENTION The technical solutions in the examples of the present invention are clearly and completely described below with reference to the accompanying drawings in the examples of the present invention. Apparently, the described examples are merely a part rather than all of the examples of the present invention. All other examples obtained by a person of ordinary skill in the art based on the examples of the present invention without creative efforts should fall within the protection scope of the present invention.

In order to solve the problems in the prior art, an objective of the present invention is to provide a protective structure and grouting method for preventing tunnel grouting reinforcement from causing a surface uplift.

In order to make the above objectives, features and advantages of the present invention more understandable, the present invention is described in further detail below with reference to the accompanying drawings and specific implementations.

This example provides a protective structure for preventing tunnel grouting reinforcement from causing a surface uplift. As shown in FIGS. 1-4, the protective structure includes a tunnel body 8 located below a ground surface 1. A downward arch 5 formed by grouting from the surface is provided in a stratum directly above the tunnel body 8, and the downward arch 5 protrudes downward. A support structure is provided on a roof-sidewall portion of an inner contour of the tunnel body 8. An upward arch 11 is formed by grouting from a borehole, and 502209 provided outside the support structure to surround the roof-sidewall portion of the inner contour of the tunnel body. The upward arch 11 protrudes upward. The upward arch 11, the downward arch 5 and the support structure together form a combined support structure to prevent pre-grouting from causing the surface uplift.

In this example, in order to ensure the operation effect, the support structure is provided on an inner wall of the tunnel body 8, which is a mesh-shotcrete-bolt support 13, a steel arch support 16 or a combined support thereof.

In this example, the thickness of the downward arch 5 is 3-4 m, and the thickness of the upward arch 11 is greater than 2 m.

In this example, a projected length of the downward arch 5 on a horizontal ground in a width direction is L, which serves as a span of the downward arch; a depth from a lowest point of the downward arch 5 to the horizontal ground is H, which serves as a rise; a rise-span ratio of the downward arch is AK, AK = H/L, which is equal to 1/5-1/6.

If the ground surface is not horizontal, the datum of the horizontal ground is the lowest point.

A distance between the upward arch 11 and the downward arch 5 is greater than 2 m. As the tunnel in the underground space has a different burial depth, the distance between a vault of the downward arch (lowest point) and a vault of the upward arch (highest point) is determined according to the actual situation. Under the protection of the upward and downward arches, high-pressure grouting is carried out in an interlayer there-between to reinforce a surrounding rock mass, so that the surrounding rock mass and the grout work together.

In this example, a vertical centerline 9 of the tunnel body 8, a vertical centerline of the upward arch 11 and a vertical centerline of the downward arch 5 are collinear.

In this example, a pre-grouting pipe 6 inclined toward the direction of the tunnel is provided in the roof-sidewall portion of the inner contour of the tunnel body 8; an outlet of the pre-grouting pipe 6 is located between coverage areas of the upward arch 11 and the downward arch 5.

The pre-grouting pipe 6 is arranged according to the existing specifications. The pre-grouting pipe is generally inclined 30°-60° according to the corresponding direction of the tunnel, and the spacing is generally controlled at about 0.5 m. In case of special geological conditions, the drilling angle and spacing can be adjusted appropriately. The pre-grouting pipe i%)502209 a prior art. A grouting hole with a certain depth is drilled at the roof-sidewall portion of the tunnel (lane) to install the grouting pipe to perform medium-length hole grouting to form an internally-grouted reinforced mass. Under the protection of the downward continuous arch 5 and the upward arch 11, the pressure of the medium-length hole pre-grouting is appropriately increased, generally controlled below 8 Mpa. The slurry includes Grade 425 cement, an additive and water with a ratio of 1:0.08:2.

The roof-sidewall portion of the inner contour of the tunnel body 8 is composed of an upper arc-shaped portion and lower vertical side portions connected at both ends of the arc-shaped portion.

This example further provides a pre-grouting method for a tunnel for preventing a surface uplift by using the above protective structure for preventing tunnel grouting reinforcement from causing a surface uplift, including the following steps: A. Surface drilling and grouting Before the tunnel is constructed to an area to be protected, a temporary facility on a ground surface is relocated for convenience of construction. A grouting station is arranged at a suitable position to prepare for subsequent grouting for a downward arch. Surface boreholes 2 are drilled on the ground surface with a loose rock-soil stratum 4 directly above the direction of a tunnel body. The diameter of the surface boreholes is slightly larger than the diameter of a grouting pipe. The surface boreholes are arranged in a plum shape. A top centerline of boreholes in the same row is perpendicular to the direction of the tunnel. In the same row of boreholes, the depth of a borehole in the center is the largest, and the depth of the boreholes decreases in sequence from the center to both sides. The lower ends of the boreholes in the same row fall within the range of the design downward arch where a section is located.

The distance between the surface boreholes 2 is 0.4-0.6 m.

A reusable grouting pipe 3 is installed in the borehole. The reusable grouting pipe is a rigid, elastic polyvinyl chloride (PVC) pipe. The bottom end of the reusable grouting pipe is sealed, and a circle of small outlet holes are drilled on the wall of the pipe at intervals (such as 15-20 cm). A certain number of small holes (such as 3-4) are set at equal intervals in each circle. The relative height of the small outlet holes on the reusable grouting pipe is the same, so that the slurry spreads uniformly and equivalently around a grouting hole.

Through the grouting operation carried out by the reusable grouting pipe 3, the slury 500009 combines the loose rock-soil stratum 4 as an integral support structure to form the downward arch 5.

B. Tunnel support When the tunnel is constructed to an area to be protected, a gross section 15 of the tunnel body is first excavated, then initial shotcrete is performed and a support structure is installed; and finally secondary shotcrete is performed.

When the tunnel is constructed to the area to be protected, the gross section 15 of the tunnel body is first excavated. Then the initial shotcrete with a thickness of generally 20-30 mm is performed immediately. According to the characteristics and strength levels of the surrounding rock-soil stratum, a mesh-shotcrete-bolt support 13, a steel arch support 16 or a combined support thereof is provided in the excavated tunnel (lane) to form the support structure. The secondary shotcrete with a thickness of generally 80-100 mm is finally performed. After the secondary shotcrete is completed, an under-excavated part is manually excavated, an over-excavated part is filled, and exposed ends of anchor bolts and cables are properly handled. The entire tunnel (lane) is leveled to ensure that the shape and size of the section of the entire tunnel (lane) conform to the design.

C. Tunnel drilling and grouting One day after the secondary shotcrete, a borehole is grouted to form an upward arch 11 around a roof-sidewall portion of an inner contour of the tunnel body.

One day after the secondary shotcrete, a shallow grouting hole 7 with a depth of less than 2 m is drilled on the roof-sidewall portion of the tunnel (lane) to install a grouting pipe. The grouting pipe grouts with slurry including Grade 425 cement, an additive and water with a ratio of 1:0.08:2 at a grouting pressure generally controlled below 5 Mpa. In this way, the upward arch 11 is formed around the roof-sidewall portion of the tunnel (lane) to combine the support structure as a combined support structure.

D. Pre-grouting Pre-grouting reinforcement is performed in a pre-grouting reinforcement area 12 between the downward arch 5 and the upward arch 11.

Grouting holes with a certain depth are drilled at the roof-sidewall portion of the tunnel (lane) to install pre-grouting pipes 6 to perform medium-length hole grouting to form an internally-grouted reinforced mass. The outlet of the pre-grouting pipes 6 is located between the 500009 coverage areas of the upward arch 11 and the downward arch 5. Under the protection of the downward arch 5 and the upward arch 11, the medium-length hole grouting pressure of the pre-grouting pipes 6 is appropriately increased, generally controlled below 8 Mpa. The slurry includes 425# cement, an additive and water with a ratio of 1:0.08:2. The spacing of the pre-grouting pipes is generally controlled at about 0.5 m. In case of special geological conditions, the drilling angle and spacing of the grouting holes can be adjusted appropriately.

E. Floor pouring Concrete is poured on a floor 10 of the tunnel to form a cross-sectional size of the tunnel that meets the design requirement.

The design downward arch is located in the loose rock-soil stratum 4 directly above the direction of the tunnel, and protrudes downward. A projected length of the downward arch 5 on a horizontal ground in a width direction is L, which serves as a span of the downward arch; a depth from a lowest point of the downward arch 5 to the horizontal ground is H, which serves as a rise. A rise-span ratio of the downward arch is AK, AK = H/L, which is equal to 1/5-1/6.

The distance from the lower ends of the reusable grouting pipes 3 to the lower end face of the design downward arch is equal.

There are two methods to determine the depth of the surface boreholes.

A. The grouting from the ground surface to the downward continuous arch refers to surface grouting, and the depth of the boreholes is generally 6-7 m, depending on the thickness of the loose rock-soil stratum composed of loose rock and sand soil layers or the distance from the tunnel (lane) to the ground surface. L is calculated according to selected AK.

b. In fact, the width of the structure to be protected is easy to measure, so L is easy to determine. The depth H of the grouting hole is calculated after AK is appropriately selected. The distance between the upward arch 11 and the downward arch 5 should be greater than 2 m.

The grouting operation in step A is as follows: The lower end of the reusable grouting pipe does not exceed 10 cm from the bottom of the borehole. The initial grouting is performed first, and solidifying slurry is injected into the grouting hole through the reusable grouting pipe. The initial grouting is fill grouting, and the grouting pressure is controlled to be less than 0.5 Mpa to prevent excessive grouting pressure from destroying the shape of the downward arch 5 and affecting the bearing capacity of the overall loose rock-soil stratum. The slurry includes Grade 325 cement, an additive and water 502209 with a ratio of 1:0.08:2.

After 2-3 h after the initial grouting, the slurry reaches an initial setting state to be initially bonded to the loose rock and sand soil layers in the loose rock-soil stratum (4) as a whole with a certain bearing strength. Then secondary grouting is performed at a grouting pressure greater than the grouting pressure of the initial grouting and controlled to be less than 3 Mpa. The secondary grouting is retreating multistage grouting performed with slurry including 325# cement, an additive and water with a ratio of 1:0.08:2. The thickness of the retreating multistage grouting is 3-4 m to form the entire downward arch 5 to increase the strength of the loose rock-soil stratum. After the grouting is completed, the grouting pipe is rinsed with water to remove the residual slurry in the pipe. The initial grouting and secondary grouting form an internally-grouted reinforced mass, which combines the surrounding loose rock-soil stratum as an integrated support structure to form the downward arch 5 for stress bearing.

The retreating multistage grouting is a prior art. In brief, after the first grouting 1s completed, the grouting pipe is lifted by a certain distance, such as 20-30 cm for the second grouting; after the second grouting 1s completed, the grouting pipe is raised by 20-30 cm for the third grouting. The operations are repeated until the grouting thickness reaches 3-4 m.

The present invention organically combines the spatial stability theory of arches with conventional shotcrete-bolt support, steel arch + shotcrete-bolt support, combined support and other passive support forms. The present invention implements layered, multiple grouting, combined with a variety of passive support methods to form a stress bearing body, and form the downward and upward arch structures successively. The present invention changes the stress distribution state of loose rock and sand soil layers around a tunnel (lane), and shifts a peak stress out of a three-zone stress region of the tunnel (lane). By fully utilizing the large bearing capacity of the arches, the present invention blocks the influence of dynamic and static loads of the ground surface on the tunnel (lane) and the influence of excessive pre-grouting pressure of the tunnel (lane) on surface roads, buildings and structures. The present invention ensures the mutual stability and realizes high-pressure grouting. In this way, the present invention controls the deformation of surface roads, buildings and structures, prevents surface uplift, and fully realizes the grouting reinforcement of the loose rock-soil stratum. The present invention carries out high-pressure grouting to restore the strength and rigidity of the loose rock and soil mass.

The present invention improves the integrity and bearing capacity of the surrounding rock, and 502209 keeps the loose rock and soil mass in the upper part of the tunnel (lane) in a stable state for a long time. Therefore, the present invention achieves high-pressure grouting through the protective downward arch under the condition that the surrounding environment and rock and soil properties are not very accurate. The method of the present invention is applicable to a wide range of fields, including newly excavated and repaired tunnels (lanes), particularly shallow tunnels (lanes) passing loose rock and sand soil layers. The present invention forms a complete set of construction techniques, and features simple method, easy implementation, convenient mechanized operation and good supporting effect. In addition, the present invention has engineering promotion and application value, and significant economic benefits in the continuous development of shallow underground engineering.

Several examples are used for illustration of the principles and implementation methods of the present invention. The description of the examples is used to help illustrate the method and its core principles of the present invention. In addition, those skilled in the art can make various modifications in terms of specific examples and scope of application in accordance with the teachings of the present invention. In conclusion, the content of this specification shall not be construed as a limitation to the present invention.

Claims (10)

CLAIMS LU502209

1. A protective structure for preventing tunnel grouting reinforcement from causing a surface uplift, comprising a tunnel body (8), a downward arch (5) and an upward arch (11) located below a ground surface (1), wherein the downward arch (5) is constructed in a stratum directly above the tunnel body (8); the downward arch (5) is formed by grouting from the surface, and the downward arch (5) protrudes downward; a support structure is provided on a roof-sidewall portion of an inner contour of the tunnel body (8); the upward arch (11) is formed by grouting from a borehole, and provided outside the support structure to surround the roof-sidewall portion of the inner contour of the tunnel body (8); the upward arch (11) protrudes upward; the upward arch (11), the downward arch (5) and the support structure together form a combined support structure to prevent pre-grouting from causing the surface uplift.

2. The protective structure for preventing tunnel grouting reinforcement from causing a surface uplift according to claim 1, wherein the support structure provided on an inner wall of the tunnel body (8), which is a mesh-shotcrete-bolt support (13), a steel arch support (16) or a combined support thereof.

3. The protective structure for preventing tunnel grouting reinforcement from causing a surface uplift according to claim 1, wherein the thickness of the downward arch (5) is 3-4 m, and the thickness of the upward arch (11) is greater than 2 m.

4. The protective structure for preventing tunnel grouting reinforcement from causing a surface uplift according to claim 1, wherein a projected length of the downward arch (5) on a horizontal ground in a width direction is L, which serves as a span of the downward arch; a depth from a lowest point of the downward arch (5) to the horizontal ground is H, which serves as a rise; a rise-span ratio of the downward arch (5) is AK, AK = H/L, which is equal to 1/5-1/6.

5. The protective structure for preventing tunnel grouting reinforcement from causing a surface uplift according to claim 1, wherein a vertical centerline (9) of the tunnel body (8), a vertical centerline of the upward arch (11) and a vertical centerline of the downward arch (5) are collinear.

6. The protective structure for preventing tunnel grouting reinforcement from causing a surface uplift according to claim 1, wherein a pre-grouting pipe (6) inclined toward the direction of the tunnel is provided in the roof-sidewall portion of the inner contour of the tunnel body (8); an outlet of the pre-grouting pipe (6) is located between coverage areas of the upward arch (11)

and the downward arch (5). LU502209

7. A pre-grouting method for a tunnel by using the protective structure for preventing tunnel grouting reinforcement from causing a surface uplift according to claim 1, comprising the following steps: A. surface drilling and grouting: before the tunnel is constructed to an area to be protected, surface boreholes are drilled on a ground surface with a loose rock-soil stratum (4) directly above the direction of a tunnel body; the surface boreholes (2) are arranged in a plum shape; a top centerline of surface boreholes (2) in the same row is perpendicular to the direction of the tunnel; in the same row of surface boreholes (2), the depth of a borehole in the center is the largest, and the depth of the boreholes decreases in sequence from the center to both sides; lower ends of the surface boreholes (2) in the same row fall within the range of a design downward arch where a section is located; a reusable grouting pipe (3) is installed in the surface borehole (2), and the reusable grouting pipe (3) is used for grouting to combine slurry and the loose rock-soil stratum (4) as an integral support structure to form the downward arch (5); B. tunnel support: when the tunnel is constructed to the area to be protected, a gross section (15) of the tunnel body is first excavated; then initial shotcrete is performed and a support structure is installed; finally, secondary shotcrete is performed; C. tunnel drilling and grouting: one day after the secondary shotcrete, a borehole is grouted to form an upward arch (11) around a roof-sidewall portion of an inner contour of the tunnel body; D. pre-grouting: pre-grouting is performed between the downward arch (5) and the upward arch (11); and E. floor pouring: concrete is poured on a floor (10) of the tunnel to form a cross-sectional size of the tunnel that meets a design requirement.

8. The pre-grouting method for a tunnel according to claim 7, wherein the design downward arch is located in the loose rock-soil stratum (4) directly above the direction of the tunnel, and the design downward arch protrudes downward; a projected length of the downward arch (5) on a horizontal ground in a width direction is L, which serves as a span of the downward arch; a depth from a lowest point of the downward arch (5) to the horizontal ground is H, which serves as a rise; a rise-span ratio of the downward arch is AK, AK = H/L, which is equal to 1/5-1/6.

9. The pre-grouting method for a tunnel according to claim 8, wherein the distance from lower ends of reusable grouting pipes (3) to a lower end face of the design downward arch (5502209 equal.

10. The pre-grouting method for a tunnel according to claim 7, wherein the grouting operation in step À is as follows: the lower ends of the reusable grouting pipe (3) does not exceed cm from the bottom of the borehole; the initial grouting is performed first, and solidifying slurry is injected into a grouting hole through the reusable grouting pipe (3); the initial grouting is fill grouting performed with slurry comprising Grade 32.5 cement, an additive and water with a ratio of 1:0.08:2 at a grouting pressure controlled to be less than 0.5 Mpa, after 2-3 h after the initial grouting, the slurry reaches an initial setting state to be initially bonded to loose rock and sand soil layers in the loose rock-soil stratum (4) as a whole with a certain bearing strength; then secondary grouting is performed at a grouting pressure greater than the grouting pressure of the initial grouting and controlled to be less than 3 Mpa; the secondary grouting is retreating multistage grouting performed with slurry comprising Grade 32.5 cement, an additive and water with a ratio of 1:0.08:2; the thickness of the retreating multistage grouting is 3-4 m to form the entire downward arch (5) to increase the strength of the loose rock-soil stratum; the initial grouting and secondary grouting form an internally-grouted reinforced mass, which combines the surrounding loose rock-soil stratum as an integrated support structure to form the downward arch (5) for stress bearing.