CN115653612A - Construction method for converting three-step seven-step method of large-section tunnel into double-side-wall pit guiding method - Google Patents

Abstract

The invention discloses a construction method for converting a three-step seven-step method of a large-section tunnel into a double-side-wall pit guiding method.

Description

Construction method for converting three-step seven-step method of large-section tunnel into double-side-wall pit guiding method

Technical Field

The invention relates to the technical field of tunnel construction, in particular to a construction method for converting a three-step seven-step method of a large-section tunnel into a double-side-wall pit guiding method.

Background

In the national transportation meeting in 2020, related responsible persons show that the transportation in the next year can finish 8000 billion yuan of railway investment and 1.8 trillion yuan of highway waterway investment, the southwest region is the most main region of the country at present, the southwest region belongs to a mountainous region, and during the process of constructing the expressway and the railway, the construction of the tunnel is inevitable, along with the development of economic high speed, the construction of the expressway with large cross section is more and more, the geology of the southwest region is complex, the grade of the surrounding rock of the tunnel is greatly changed, and the clear width and the clear height of the tunnel are increased, which brings great difficulty for field constructors. At this time, it is important to select an excavation construction method suitable for the grade of the surrounding rock.

Firstly, performing annular excavation on an upper arc guide pit by a three-step and seven-step method, and constructing an arch part primary support; secondly, excavating the middle step and the lower step in a left-right staggered manner, and constructing primary wall support; and finally, reserving core soil in the center for excavation, excavating the tunnel bottom, and constructing primary support of the tunnel bottom. And each part is excavated and then should be supported in time, and the primary support at the bottom of the tunnel should be constructed as an inverted arch in time and closed to form a ring as soon as possible. The double-side-wall pilot tunnel excavation method is that two side pilot tunnels are excavated in advance, and then the upper part and the lower part of the middle part are constructed. During construction, each block is closed after excavation.

According to detailed survey data, the main unfavorable geology of a tunnel site area is karst, fault, soft surrounding rock and the like, and the karst develops along joint cracks and develops unevenly; the fault is a tensile reverse fault, the rock body is broken and is mostly in a block shape, and due to the existence of the fault, the hydraulic connection of the underground water in the vertical direction is enhanced, and a strong water bursting and mud bursting phenomenon can occur. The three grades of surrounding rock are mainly III, IV and V.

The three-step seven-step excavation method for the large-section tunnel is a tunnel construction method which takes arc pilot tunnel excavation and core soil retention as a basic mode, divides seven excavation surfaces of three steps, namely a middle step and a lower step, staggers excavation and supporting of each part along the longitudinal direction of the tunnel and advances in parallel. The construction of III, IV grade surrounding rock section tunnels with certain self-stabilizing conditions, the three-step and seven-step excavation method has the following characteristics: the construction space is large, the mechanized construction is convenient, the parallel operation of multiple operation surfaces is realized, the flexible and timely conversion of construction procedures is convenient when the geological conditions change, the construction method is adjusted, the disturbance on soft surrounding rocks is large, the control deformation capability is weak, and the like. The double-side-wall guide pit excavation method has the following characteristics: the construction process is complicated, the progress is slow, the cost is high, the large section is a small section, the support is closed into a ring in time, the deformation capability of the surrounding rock is well controlled, and the method is suitable for the V-grade weak surrounding rock.

However, in the existing large-section tunnel construction process, when various surrounding rock grades exist in a construction tunnel, the three-step and seven-step construction method cannot meet the deformation value of construction, and if the double-side-wall pit guiding method is adopted for construction, the construction period is greatly prolonged.

Disclosure of Invention

The invention aims to provide a construction method for converting a three-step seven-step method of a large-section tunnel into a double-side-wall pit guiding method, and overcomes the defects of the prior art.

In order to achieve the purpose, the invention provides the following technical scheme: a construction method for converting a three-step seven-step method of a large-section tunnel into a double-side-wall pit guiding method is characterized in that three steps in the middle of the three-step seven-step method are converted into a middle rock pillar of the double-side-wall pit guiding method, the middle rock pillar is finally dismantled, the middle rock pillar of a reserved tunnel can bear upper load, and the purpose of small settlement is achieved.

A construction sequence of a construction method for converting a three-step seven-step method of a large-section tunnel into a double-side-wall pit guiding method is as follows:

step one, when a tunnel environment needing to be converted is reached, namely the tunnel construction method is converted from a three-step seven-step method to a double-side-wall pit guiding method; constructing a section of a tunnel to be excavated, wherein a chaplet surface of the tunnel is used as a tunnel section II; taking a strut surface as a starting point, and performing section division in the direction of a tunnel to be excavated in an equidistant mode to respectively form a tunnel section III, a tunnel section IV and a tunnel section V; in the original three-step seven-step method, the intersection surface of the step 6-1 and the step 6-2 is used as a tunnel section I;

step two, excavating core soil of 6-1 part of the step in the original three-step seven-step method to reach a tunnel section II;

2.1, excavating the upper part of the right guide pit; excavating the core soil on the right side of the step 1 part in the original three-step seven-step method to reach the section V of the tunnel, and changing the backward pit guiding of the three-step seven-step method into the forward pit guiding of the double-side-wall pit guiding method to form the step (1) in the double-side-wall pit guiding method; primary support and temporary support are carried out on the periphery of a guide pit of the step (1), namely, concrete is sprayed initially, a reinforcing mesh is laid, a primary support steel arch frame and a temporary steel frame are erected, a foot locking anchor rod is arranged, and after a radial anchor rod is drilled, concrete is sprayed again to the designed height;

2.2, excavating the upper part of the left guide pit; excavating the core soil on the left side of the step 1 part in the original three-step seven-step method to reach the section III of the tunnel to form a step (2) in the double-side-wall pit guiding method, and performing primary support and temporary support on the periphery of the pit guiding of the step (2) part;

step three, excavating core soil of 6-2 parts of the steps in the original three-step seven-step method to reach a tunnel section II;

3.1, excavating the middle part of the right guide pit; excavating core soil at the step 3 part of the original three-step seven-step method to reach a tunnel section IV to form a step (3) in the double-side-wall pit guiding method, and performing primary support and temporary support on the periphery of the pit guiding at the step (3) part;

3.2, excavating the middle part of the left pilot tunnel; excavating core soil of 2 parts of steps in the original three-step seven-step method to reach a tunnel section IV to form steps (4) in the double-side-wall pit guiding method, and performing primary support and temporary support on the periphery of the pit guiding of the steps (4);

fourthly, excavating core soil of 6-3 parts of the steps in the original three-step seven-step method to reach the section I of the tunnel;

4.1, excavating the lower part of the right guide pit; excavating core soil of 5 parts of steps in the original three-step seven-step method to reach a tunnel section IV to form the steps (5) in the double-side-wall pit guiding method, and performing primary support and temporary support on the periphery of the pit guiding of the steps (5);

4.2, excavating the lower part of the right guide pit; the core soil of the 4 parts of the steps in the original three-step and seven-step method is not required to be excavated, and the steps (6) in the double-side-wall pit guiding method are directly formed.

Fifthly, performing tunnel construction according to a double-side-wall pit guiding method; after finishing the specific tunnel environment; the construction is converted into a normal three-step seven-step method for tunnel construction; this is repeated.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention relates to conversion of two construction methods, namely three-step and seven-step construction and double-side-wall pit guiding construction, wherein when various surrounding rock grades exist in a tunnel and the three-step construction method cannot meet the deformation value, safety and other factors of construction, the construction method can provide a conversion method for converting the three-step construction into the double-side-wall pit guiding method, and the tunnel construction can be completed under safer conditions.

2. In the excavation process of various large-section tunnels with surrounding rocks, construction method conversion is needed for the conditions that the sedimentation amount is strict or the deformation of the surrounding rocks is difficult to control such as karst strata, weak strata and the like, and a three-step and seven-step method is converted into a double-side-wall pit guiding method.

3. According to the conversion method, the core soil is excavated in a layering manner from top to bottom, and the rest lower-layer core soil can still support and block the working surface; the right side pilot pit is changed from a backward pilot pit to a forward pilot pit, and the working surface can be continuously pushed by utilizing the steps of the original construction method, so that the delay of the construction progress caused by the construction method conversion is reduced; the middle rock pillar and the temporary support are formed and installed at the original tunnel face, so that the core soil is not interfered to be dug and removed, and a larger operation space can be provided for the subsequent procedures; the method is characterized in that three steps in the middle of the original three-step seven-step method are excavated from top to bottom to the surface of a tunnel support, meanwhile, three steps of left and right side pilot pits on two sides of the original three-step seven-step method are excavated in advance, and the three steps of the left and right side pilot pits are staggered with each other, so that a tunnel model structure similar to a double-side-wall pilot pit method is finally formed, and construction of the double-side-wall pilot pit method is facilitated.

Drawings

The invention is described in further detail below with reference to the figures and specific embodiments.

FIG. 1 is a schematic cross-sectional view of a three-step seven-step method tunnel;

FIG. 2 is a schematic cross-sectional view of a double-side-wall tunnel construction method;

FIG. 3 is a process flow diagram of this embodiment

FIG. 4 is a plan view of the tunnel construction of the present invention;

FIG. 5 is a longitudinal sectional view of the tunnel construction according to the present embodiment;

FIG. 6a is a first schematic diagram illustrating a conversion of the tunnel construction method according to the present embodiment;

FIG. 6b is a second schematic diagram illustrating a conversion of the tunnel construction method according to the present embodiment;

fig. 6c is a schematic diagram illustrating a conversion of the tunnel construction method according to the third embodiment;

FIG. 6d is a fourth schematic diagram illustrating a conversion of the tunnel construction method according to the present embodiment;

fig. 6e is a schematic diagram illustrating a conversion of the tunnel construction method according to the present embodiment;

fig. 6f is a schematic diagram illustrating a conversion of the tunnel construction method according to the sixth embodiment;

FIG. 7 is a longitudinal section view of a quasi-double-side-wall pit-guiding method finally formed in the embodiment.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention.

Referring to fig. 1 to 7, the embodiment provides a construction method for converting a three-step seven-step method of a large-section tunnel into a double-side-wall pit guiding method, the method can be applied to conversion of two construction methods of the large-section tunnel, multiple surrounding rock grades exist in one tunnel, the construction progress and the construction cost are relatively short, the deformation value of the surrounding rock cannot meet the standard requirement when the three-step seven-step method is selected for construction in unfavorable geology, the construction progress and the cost cannot meet the owner requirement when the double-side-wall pit guiding method is selected, the three-step seven-step method is converted into the double-side-wall pit guiding method for tunneling in the unfavorable geological section, and the construction advantages of the two construction methods can be utilized.

The process principle of the method comprises the following steps:

1. the construction method is characterized in that a three-step and seven-step construction method and a double-side-wall pit guiding method are used as guidance centers, when unfavorable geology is encountered, the construction settlement amount of the three-step and seven-step method cannot meet requirements, the construction method is used for quickly converting the three-step and seven-step construction method into the double-side-wall pit guiding method, and a middle rock pillar is reserved in the double-side-wall pit guiding method, so that disturbance to surrounding rocks is reduced, and primary support and temporary support are carried out immediately.

2. When the two construction methods are used for construction conversion, construction monitoring measurement needs to be enhanced, the supporting effect is verified through monitoring measured data, the safety, the reliability and the applicability in the conversion process are determined, and experience is provided for the information construction of the tunnel.

3. The construction method for converting the three-step seven-step method of the large-section tunnel into the double-side-wall pit guiding method mainly has the outstanding process principle that three steps of the three-step seven-step method are converted into a middle rock pillar of the double-side-wall pit guiding method, the middle rock pillar is removed at last, the middle rock pillar of the reserved tunnel can bear upper load, the purpose of small settlement is achieved, the construction process is safer, and the process requirements of all conversion processes are controlled so as to meet the design requirements.

4. The method considers the influence of factors such as the area of the section of the tunnel, the geological condition, the safety, the economic cost and the like on the construction of the tunnel, thereby providing control factors and construction key points and obtaining detailed construction steps and processes; meanwhile, key factors such as settlement deformation, stress strain and the like in the conversion process are monitored and measured, the conversion reliability is fed back in real time, the construction quality of the tunnel is further ensured, and when the tunnel cannot meet the requirements of bearing and deformation amount in the three-step and seven-step construction, the tunnel is converted into the double-side-wall pit guiding construction through the construction method, so that the safety and the reliability of the tunnel in the construction process are ensured.

The process flow of the embodiment is shown in the attached figure 3;

the operation is as follows:

1. preparation for construction

In order to ensure the safe operation of the exchange between the two methods, the following construction preparations should be made to ensure the smooth operation of the whole construction process.

1. Document material, comprising: design drawing and related documents of key steps of conversion of two construction methods

2. Before construction, technical background and training are carried out on site constructors, so that the site constructors can understand key steps and safety precautions of conversion.

3. Vehicles, tools and the like required for construction include: the system comprises a transportation vehicle, a working platform, a measuring tool, a construction tool, a lighting tool, a communication tool, a safety device and protective equipment.

4. Wind, water pipes, electric wire laying, construction access, construction site arrangement, mechanical equipment, personnel configuration, material preparation and waterproof and drainage facility construction.

5. According to design data of a construction method conversion process, geological and hydrological data obtained by advanced prediction are analyzed, a reasonable conversion scheme is formulated, and meanwhile, a monitoring measurement scheme and a settlement analysis scheme are formulated.

2. Concrete construction sequence

According to the related design drawings converted by the two construction methods, the specific construction sequence is as follows:

as shown in FIG. 6b, 6-1 part of the core soil is dug to reach a section II;

as shown in fig. 6, a part (1) is excavated from the right pilot tunnel, the excavated length is about 15m from 3 times of the step width to a section v, the right pilot tunnel is changed from a backward pilot tunnel of a three-step seven-step method to a forward pilot tunnel of a double-side-wall pilot tunnel method, primary support and temporary support around the pilot tunnel of the part (1) are performed, namely, concrete is initially sprayed, a reinforcing mesh is laid, a primary support steel arch frame and a temporary steel frame are erected, foot locking anchor rods are arranged, and concrete is sprayed again to a designed height after radial anchor rods are drilled;

as shown in fig. 6d, excavating part (2) of the left pilot tunnel to the section III, and performing primary support and temporary support on the periphery of part (2) of the pilot tunnel;

as shown in fig. 6e, 6-2 parts of core soil are dug to reach a section II, a part (3) is dug to reach a section IV in the right pilot tunnel, and primary support and temporary support around the pilot tunnel of the part (3) are constructed;

as shown in fig. 6f, 6-3 parts of core soil are excavated to the section I, the right pilot tunnel is excavated to the section III, primary support and temporary support around the pilot tunnel of the section (5) are constructed, so that construction method conversion is completed, a middle rock pillar is formed from the section II, pilot tunnels on the left side and the right side are excavated in three steps, and temporary supports are installed on the section II and backwards;

as shown in fig. 7, the steps of each step of the rock pillar in the double hole are generally set to 5m. After the step is excavated, the preliminary support is constructed in time, and the distance between the primary support of the arch part and the tunnel face is generally not more than 0.5m. After core soil is excavated, the primary support needs to follow in time, the distance between an inverted arch and a middle rock pillar does not exceed 15m, secondary lining is applied after the primary support is stable, the distance is generally less than 40m, and the primary support needs to follow in time when the geology is poor.

3. Organization of labor force

According to the requirement of the construction method conversion and the actual engineering characteristics, 1 construction team is arranged on each excavation type working surface to ensure the smooth operation of the construction method conversion. Each construction team is provided with an excavation work class, a transportation work class, a comprehensive work class, a reinforcement work class, a concrete spraying work class, an arch frame supporting work class and a lining work class to be responsible for tunnel construction. The tunnel was operated continuously for 24 hours. The tunnel construction labor organization table is shown in table 1.

TABLE 1 Tunnel construction labor organization chart

4. Materials and apparatus

1. Material requirements

Before material purchasing, the supplier is evaluated, and qualified suppliers are selected to purchase the materials. The primary material entering the site is strictly regulated and designed. The purchased materials must be accompanied by quality certificates such as specifications, qualification certificates, technical check and verification and the like. And after the material enters the field, performing sampling inspection according to batches, and checking the quality to be qualified so as to be available. The materials stored in the construction site are separately placed according to the inspected materials and the materials to be detected, and are strictly forbidden to be mixed.

The material equipment management personnel compile a material usage plan by stages according to the construction progress, make a material supply plan according to the material variety, specification, quantity and quality requirements required in different stages, determine the supply time and ensure that the variety, quantity and quality of the main ground materials meet the requirements of the construction plan.

2. Tool and equipment

Whether the tunnel construction machinery is matched reasonably or not has great influence on construction. The matching machines are more, which causes the waste of the machines, otherwise, the efficiency is low. Therefore, the reasonable arrangement of the machinery not only can accelerate the construction progress, but also can save the construction cost. And carrying out reasonable configuration according to the tunnel excavation method and the construction period requirement. The matched production capacity is about 1.2 to 1.5 times of the balanced construction capacity.

The tunnel single-opening construction is carried out, a large excavator or a small excavator is configured according to the excavation method to operate in parallel, and a loader is additionally arranged to carry out mucking construction, a large dump truck, an air compressor and a rock drill.

Specific amounts are shown in table 2 below.

TABLE 2 Equipment and tools configuration parameter table

5. Quality control

1. Reference is made to national, local or industry standards.

2. Quality control measures

The construction process, the settlement range, the construction time of the forepoling, the length of the anchor rod, the thickness of the secondary lining and the like of the tunnel must be constructed strictly according to specifications, design documents and drawings, the construction quality should meet the regulations of specifications, regulations, design drawings and the like, and the settlement amounts of the main structure and the buildings around the main structure are respectively shown in the following table 3.

TABLE 3 settlement control of the main structure and the buildings surrounding the main structure

The construction method relates to the conversion of two construction methods, and the tunnel constructed by adopting a double-side-wall pit guiding method has the advantages that the grade difference of surrounding rock grades and large deformation are realized, the advance support must be constructed strictly according to the design, and the external insertion angle and the lap joint length must meet the requirements of the design and the specification.

The main materials entering the construction site are strictly regulated and the design requirements are kept, and all factory-made materials have the factory pass certificates and necessary inspection and test sheets. Strictly inspecting the fed materials and the equipment according to technical quality standards and samples, and determining key inspection materials in advance.

Strict construction technology is adopted, the quality of operators is trained and checked regularly, the operators are trained to construct according to design and standard requirements strictly, and the quality of construction engineering is ensured.

And sealing and looping in time in the construction process, simultaneously performing monitoring and measuring work practically, performing data analysis in time, and dynamically adjusting support parameters and reserved deformation.

And (4) making advanced forecasting measures, analyzing geological conditions according to the drilling conditions, and adjusting the construction scheme in time.

6. Benefit analysis

The construction method for converting the large-section three-step seven-step method into the double-side-wall pit guiding method provides a complete set of mature and reliable process method flows, detailed regulations are made in the aspects of construction preparation, time, personnel organization, tools and the like, so that the whole tunnel construction flow is simple, clear, efficient and reliable, reliable decision bases and technical indexes are provided for tunnel construction later, the novel and mature process method technology can promote the progress of the construction technology, and the social benefit and the environmental benefit are obvious.

(2) The construction method well solves the safety problem of excavation of the large-section tunnel, and has the advantages of simple structure, safety, reliability, flexibility and remarkable economic benefit.

(3) The construction method is a complete set of complete subway tunnel construction theory and operation method summarized in construction on the basis of some theories by using a three-step seven-step method and a double-side-wall pit guiding method. The method is a technical method for building the tunnel by small surface subsidence under the condition of karst medium surrounding rocks. Its outstanding advantages are no pollution and noise, and suitability for tunnel.

(4) The steps of the three-step seven-step method are converted into the double-side-wall pit guiding method, the reserved medium rock pillar is used as a natural support, and the stability of the tunnel is greatly improved. The construction method has the advantages of achieving 'short footage, early support, duty measurement and speed feedback' in the construction process, ensuring the structure safety, and successfully solving the problems of complex process, large mutual interference, surface subsidence control and the like of the tunnel. The feedback of the measurement information in the construction has strong guiding effect on the cycle footage, the supporting form and the secondary lining. The method has a good reference function for the surrounding rock construction of the large-section tunnel, particularly the tunnel from good to bad.

7. Examples of the applications

1. Brief introduction to the engineering

The Yanbanian highway is an important component part of a Guizhou '678' highway network 'second longitudinal' highway along a river to the Yangjiang highway, and the starting point of the project is connected with the Shanghan-Kun national highway, and the end point is connected with the Xianhong national highway. The seventh contract section of the ficus microcarpa freeway, which is built by a seventh engineering limited company of the central office, is located in the south sentry town of the city of the Jian river, and the road channel is too congested and reaches the Lang town of the county of the ficus river. The construction paragraphs are: k44+325-K51+828, and a tunnel shared by the whole line is 0.5+2+0.5 seat (6936 m long in a single hole), the branch correcting tunnel under the key project of the project is located at the east edge of the Yunobao plateau, and the slope platform land where south foot of east segment of mountain range of seedling mountain is transited to Xianggui hilly belongs to the district of south Yangxi of Jianhe county. The landform type belongs to erosion-denudation type middle-low ridge-shaped furrow landforms, the earth surface is strongly eroded and denudated, and the topography fluctuation is large. The full length of the left width of the tunnel is 1413m, and the maximum burial depth of the top plate at the base line is 220m.

Bad geological phenomena and road water and mud gushing

1.1, unfavorable geology

According to the detailed exploration data, the main unfavorable geology of the tunnel site area is karst and fault, and the erosion depression and the erosion groove valley with close relationship between landform and karst development history are the karst landscape with the most typical characteristics.

1) Karst

The condition of no water erosion trace in the fracture and the distribution rule of other karst troughs and valleys on the region can be known, and the karst phenomenon is characterized by a residual hill and an erosion fracture. Karst development in the region has remarkable bedding characteristics. Due to the structural extrusion effect, a plurality of tension joint cracks are formed on the dorsiflexed shaft part, the cracks are generally big at the top and small at the bottom, and atmospheric rainfall infiltrates and migrates along the cracks to gradually form a karst channel developing along the joint cracks. The trough is influenced by the control of the zone transverse strength crack and the transverse erosion trough, the trough has the characteristic of transverse expansion, the transverse expansion of the trough is obviously widened in the transverse direction, the width of the trough at the tunnel part is only 50m, and the width of the trough at the south end is nearly 550m.

2) Fault of a moving object

The ZK51+ 100-ZK 51+194 section is an F1 fault fracture zone, has the tendency of south-west, the inclination angle of 40-50 degrees, is a tensile reverse fault, is broken by rock mass, is mostly in a block shape, has a loose structure and has poor self-stability of surrounding rock. When the tunnel passes through the section, surrounding rock instability is easy to occur, and the tunnel top and the tunnel wall collapse. The fault trend is basically consistent with the structural line trend and is intersected with the tunnel axis at an angle of 110 degrees. The fault distance is about 20m, the width of a ground surface fault broken belt is about 25-30 m, and the width of an upper and lower disc fault affected belt is about 10-15 m.

1.2 Water and mud outburst of tunnel

The tunnel crossing section is positioned in the vertical circulating zone, the zone is not strong in water-rich property, but good in water permeability, and is a good water guide channel, so that abundant water sources can be provided for closed corrosion caves or karst pipelines in the zone to form underground water collecting bodies, and once the tunnel crosses the water collecting bodies, serious water burst and mud burst phenomena can occur. The ZK51+ 100-ZK 51+194 section is an F1 fault fracture zone, the fault is a tensile reverse fault, a rock mass is fractured and is mostly in a block shape, the hydraulic connection of underground water in the vertical direction is enhanced due to the existence of the fault, and a stronger water inrush and mud inrush phenomenon can occur in the section.

2. Working conditions

2.1 the main support parameters of the tunnel lining structure are as follows:

1) The initial spraying of the concrete: c20 shotcrete with a thickness of 24 cm.

2) System anchor rod: phi 25 hollow grouting anchor rod, L =3.5m;

3) Reinforcing mesh: adopting phi 6.5 steel bars and 20 multiplied by 20cm grids, and arranging the whole ring in a double-layer way; the reinforcing mesh should be welded firmly with the tail end of the anchor rod.

4) The steel frame is an I18I-shaped steel frame, and the distance between the I18I-shaped steel frame and the I-shaped steel frame is 60cm.

5) Secondary lining: the C30 waterproof reinforced concrete with the thickness of 50cm is subjected to the seepage resistance grade P12; c15 concrete is filled in the lower part.

2.2 the tunnel arch and wall excavation reserved deformation is temporarily set to be 10cm, the field monitoring and measuring condition can be adjusted according to the situation in the construction process, and the situation that the primary support deformation is too large and invades into a secondary lining limit is avoided; in the construction process, the field monitoring and measurement and advanced geological forecast work are enhanced, and information is fed back in time so as to adjust related design parameters.

3. Engineering evaluation

In the construction, through the practice of the right branch tunnel under the seventh contract section of the ficus microcarpa highway, the deformation rule of the tunnel in the conversion process from the three-step seven-step method construction to the double-side-wall pit guiding method is basically mastered, and the construction process conversion technology, the tunnel settlement control construction technology of the bad geological section and the like are summarized and accumulated. The construction technology of converting the large-section three-step seven-step method into the double-side-wall pit guiding method is applied, so that the construction safety of the ficus microcarpa high-speed tunnel under the complex geological condition is successfully solved, the construction quality is ensured, the construction efficiency is improved, the construction cost is controlled, and the tunnel deformation is controlled. A plurality of experiences are accumulated, a set of construction scheme and process which are economical, feasible and advanced in technology are summarized, and the experiences are accumulated for the construction of the same type of tunnels. The construction period and the quality are ensured, and better social and economic benefits are obtained.

4. Development prospect

At present, infrastructure is vigorously built in each province and city, and under the influence of hydrogeology, a plurality of engineering technical problems similar to those in the construction of a right branch tunnel are inevitably faced, and the construction method provides valuable reference for the construction of the engineering.

Finally, it should be noted that, when describing the positions of the components and the matching relationship therebetween, the present invention is usually illustrated by one/a pair of components, however, it should be understood by those skilled in the art that such positions, matching relationship, etc. are also applicable to other/other pairs of components.

The above description is intended to be illustrative of the present invention and is not intended to limit the scope of the invention, which is defined by the appended claims.

Claims (2)

1. A construction method for converting a three-step seven-step method into a double-side-wall pit guiding method for a large-section tunnel is characterized by comprising the following steps of: the method converts three steps positioned in the middle of a three-step seven-step method into a middle rock pillar of a double-side-wall pit guiding method, the middle rock pillar is finally dismantled, the middle rock pillar of a reserved tunnel can bear upper load, and the purpose of small settlement is achieved.

2. The construction method for converting the three-step seven-step method of the large-section tunnel into the double-side-wall pit guiding method according to claim 1 is characterized by comprising the following construction sequence:

step one, when a tunnel environment needing to be converted is reached, namely the tunnel construction method is converted from a three-step seven-step method to a double-side-wall pit guiding method; performing section construction on a tunnel to be excavated, wherein a strut surface of the tunnel is used as a tunnel section II; taking a strut surface as a starting point, and performing section division in an equidistant mode towards the direction of a tunnel to be excavated to respectively form a tunnel section III, a tunnel section IV and a tunnel section V; in the original three-step seven-step method, the intersection surface of the step (6-1) and the step (6-2) is used as a tunnel section I;

step two, excavating core soil of the step (6-1) in the original three-step seven-step method to reach a tunnel section II;

2.1, excavating the upper part of the right guide pit; excavating the core soil on the right side of the step (1) part in the original three-step seven-step method to reach the section V of the tunnel, wherein the right side pilot pit is changed from a backward pilot pit of the three-step seven-step method to a forward pilot pit of the double-side-wall pilot pit method, namely the step ((1)) in the double-side-wall pilot pit method is formed; primary support and temporary support around the pilot hole of the step ((1)), namely primary concrete spraying, steel bar mesh laying, primary support steel arch frame and temporary steel frame erecting, foot locking anchor rods are arranged, and concrete is sprayed to the designed height after radial anchor rods are drilled;

2.2, excavating the upper part of the left guide pit; excavating the core soil at the left side of the step (1) part in the original three-step seven-step method to reach the section III of the tunnel, forming a step ((2)) in the double-side-wall pit guiding method, and performing primary support and temporary support on the periphery of the pit guiding at the step ((2)) part;

step three, excavating core soil of the step (6-2) part in the original three-step seven-step method to reach a tunnel section II;

3.1, excavating the middle part of the right guide pit; excavating the core soil of the step (3) part in the original three-step seven-step method to the section IV of the tunnel to form a step ((3)) in the double-side-wall pit guiding method, and performing primary support and temporary support on the periphery of the step ((3)) part of pit guiding;

3.2, excavating the middle part of the left pilot tunnel; excavating core soil of a step (2) part in the original three-step seven-step method to a tunnel section IV to form a step ((4)) in the double-side-wall pit guiding method, and performing primary support and temporary support on the periphery of the step ((4)) part of pit guiding;

fourthly, excavating core soil of the step (6-3) part in the original three-step seven-step method to reach the section I of the tunnel;

4.1, excavating the lower part of the right guide pit; excavating core soil of a step (5) part in the original three-step seven-step method to a tunnel section IV to form a step ((5)) in the double-side-wall pit guiding method, and performing primary support and temporary support on the periphery of the step ((5)) part of pit guiding;

4.2, excavating the lower part of the right guide pit; the step (4) part core soil in the original three-step and seven-step method is not required to be excavated, and the step ((6)) in the double-side-wall pit guiding method is directly formed.

Fifthly, performing tunnel construction according to a double-side-wall pit guiding method; after finishing the specific tunnel environment; the construction is converted into a normal three-step seven-step method for tunnel construction; this is repeated.

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