CN106988754A - Narrow space shield tunneling machine starting method - Google Patents

Abstract

The invention discloses an initial method of a shield machine in a narrow space, which comprises the following steps: a. the original underground diaphragm wall is replaced by plain soil concrete in a layered replacement mode from bottom to top by the original tunnel portal replacement; the steel ring of the starting tunnel portal is prolonged, so that the starting end of the shield is reinforced to achieve a preset effect, and the smooth starting of the shield machine is ensured; b. inspecting, maintaining and debugging the shield machine; c. and carrying out shield launching by means of the reaction frame and the negative ring pipe piece. The ground layer outside the starting well and the end ground layer do not need to be reinforced additionally, the occupied area of the starting well can be reduced, the influence on peripheral traffic is reduced to the minimum, construction can be realized under the condition that peripheral pipelines do not need to be changed, investment is reduced, disturbance to residents is reduced, the situation is met, and the method is economical and reasonable. The method is suitable for construction under the condition that the shield machine initial end well cannot be reinforced.

Description

Starting method of shield machine in narrow space

technical field

The invention relates to a tunnel construction method, in particular, to a starting method for a shield machine in a narrow space under unconventional conditions.

Background technique

The starting of the shield machine is one of the most risky links in shield construction, and preventing accidents such as collapse and gushing is the focus of construction.

The conventional launch plan of the shield machine is: the formation outside the launch shaft is reinforced by the outer row of jet grouting piles, chemical slurry reinforcement method, freezing method, etc. However, the reinforcement effect of the end formation reinforcement method and the chemical slurry reinforcement method often cannot achieve the expected effect, and the construction cost of the freezing method is expensive. If the tunnel is deeply buried and the groundwater pressure is high, conventional reinforcement methods will not be able to meet the requirements of safe construction.

In the construction of a tunnel rail transit line in a certain area, the end structure of the construction site is a working well originating from a shield machine. Due to the complex geological conditions at the end, the upper part is a sandy pebble stratum, there are many ground pipelines and it is difficult to relocate, so ground reinforcement cannot be carried out. The horizontal reinforcement used in the working well in the early stage was also unable to meet the reinforcement requirements due to the abundant groundwater and excessive pressure, and the horizontal reinforcement method also failed.

Contents of the invention

The technical problem to be solved by the present invention is to provide a narrow shield that can solve the technical problem that the starting construction position of the existing shield machine is facing complex conditions and cannot be reinforced in the vertical and horizontal directions, thereby causing construction risks. The starting method of the space shield machine.

In order to solve the above-mentioned technical problems, the starting method of the narrow space shield machine provided by the present invention includes the following steps: a. The starting hole replacement adopts a bottom-up layered replacement method, and the original ground connecting wall is replaced with plain soil Replace the concrete; extend the steel ring of the launching portal so that the reinforcement of the starting end of the shield machine can achieve the predetermined effect and ensure the smooth starting of the shield machine; b. Check, maintain and debug the shield machine; c. Rely on The reaction frame and the negative ring segments are used for shield tunneling.

Specifically, for the layered replacement in step a, the height of each layer is 0.5m to 1.5m; emergency supplies are prepared during the replacement construction to prevent the underground water-rich area from collapsing.

Specifically, the extension of the steel ring of the starting portal in step a is as follows: installing a steel ring for extending the portal at the starting portal, setting at least two sealing steel brushes inside the steel ring, and pre-setting the steel ring on the side of the steel ring. Leave grouting holes to facilitate the injection of grease and water stop during the starting process.

Specifically, it also includes the demolition of the original portal during the replacement process of the original portal, specifically: using manual cooperation with machinery to destroy the concrete of the inner ground connecting wall of 0.5m to 1.5m in each layer, and then cut off the steel bars of the inner layer; Cut off the steel bars of the inner layer, then break the concrete of the outer ground connecting wall, and then cut off the outer steel bars; ensure that the steel bars are cut flush with the steel ring of the opening door; when breaking the concrete of the outer ground connecting wall, ensure that the original The structure of the concrete protective layer on the earth-facing surface of the ground connection wall is complete to reduce the probability of water leakage and sediment collapse.

Specifically, every time a floor is completed when the starting portal is demolished and steel bars are removed, a layer of C25 sprayed plain soil concrete is used to replace it; the thickness of the plain soil concrete replacement is 1m to 1.5m to ensure the stability of the portal.

Specifically, during the plain soil concrete spraying process, reserve 50PVC drainpipes, the drainpipes should be set at a distance of 0.8m to 1.2m, and arranged in a plum blossom shape; bamboo chips and bamboo chips for connecting the plain soil and concrete of the upper and lower layers are arranged at the overlapping positions of two adjacent replacement layers. The distribution spacing of the bamboo is 0.3m ~ 0.8m, and the bamboo slices are arranged in two layers inside and outside.

Specifically, before the replacement of the original portal, the sleeve valve pipe is used to grout the soil of the original portal with water glass grout to stop water and reduce the water content of the formation, so as to ensure the normal construction of the original portal replacement. Carry out; the starting door opening is reinforced with steel supports to reduce the impact of the pressure generated when the shield machine is starting on the starting door opening and surrounding soil.

Specifically, the specific implementation steps of step b include: maintenance of the tool and the supporting equipment of the shield machine; inspection or Replacement; check the tool holder and replace it if it is seriously worn; check and repair the supporting trolley, battery car and gantry crane to ensure that the equipment is in good condition.

Specifically, the specific implementation steps of step c are: start to install the negative ring segment, and while installing the negative ring segment, the shield machine advances toward the hole ring; The cutter head damages the hole seal, apply lubricating oil on the cutter head and the hole seal to reduce friction.

Specifically, the shield gradually moves closer to the soil of the starting tunnel, so that the head of the shield machine cuts into the soil, and then the cutter head rotates to cut the soil, filling the soil chamber of the shield machine, and begins to build up the frontal soil pressure to balance the shield. The positive earth pressure ensures that the displacement of the soil is minimized; the construction parameters of the initial stage of the shield tunneling are pre-determined based on multiple simulation tests. Evenly press-inject hydraulic grout to the outside of the negative ring segment to fill the gap to prevent grout leakage; when the shield machine starts to advance, observe whether the reaction force frame and the diagonal brace behind the reaction force frame are deformed, so as to prevent the displacement caused by excessive displacement. Destruction; Before advancing, apply lubricating oil on the base surface of the shield to reduce the resistance of the shield.

The present invention has the following beneficial effects:

The launching method of the narrow space shield machine provided by the present invention aims at the high risk that the end of the launching shaft cannot be reinforced to receive the soil, and directly replaces the structure of the launching hole, and replaces the original ground layer by layer with plain soil concrete. Connect the wall to achieve the purpose of reinforcement, thereby reducing and avoiding risks and ensuring the safety of the initial construction. By extending the steel ring of the starting portal, a confined space of "shield plus shield" is established, the starting end of the shield is reinforced while the starting distance is delayed, and the shield machine is inspected, maintained and debugged before starting. After the commissioning of the machine is completed, rely on the reaction frame and the negative ring segment to start the shield tunneling, so that the shield tunneling start is as close as possible to the normal excavation state, and the multi-factor superimposed accident risk such as collapse and gushing is staggered, so as to ensure the shield tunneling construction Safety. There is no need for additional reinforcement of the stratum outside the launch shaft and the strata at the end, which can reduce the area occupied by the launch shaft and minimize its impact on surrounding traffic, and can realize construction without the need for surrounding pipelines to be relocated, reducing Investment and reduction of disturbing residents are in line with the actual situation and economically reasonable. It is suitable for the construction where the starting end well of the shield machine cannot be reinforced.

In addition to the objects, features and advantages described above, the present invention has other objects, features and advantages. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings.

Description of drawings

The drawings constituting a part of this application are used to provide a specific understanding of the present invention, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

Fig. 1 is a flow chart of steps of a method for starting a shield machine in a narrow space according to a preferred embodiment of the present invention.

detailed description

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in various ways defined and covered below.

Fig. 1 is a flow chart of steps of a method for starting a shield machine in a narrow space according to a preferred embodiment of the present invention. As shown in Figure 1, the starting method of the shield machine in a narrow space in this embodiment includes the following steps: a. The starting hole replacement adopts a bottom-up layered replacement method, and the original ground connecting wall is replaced with plain soil Replace the concrete; extend the steel ring of the launching portal so that the reinforcement of the starting end of the shield machine can achieve the predetermined effect and ensure the smooth starting of the shield machine; b. Check, maintain and debug the shield machine; c. Rely on The reaction frame and the negative ring segments are used for shield tunneling. The launching method of the narrow space shield machine of the present invention aims at the high risk that the end of the launching shaft cannot be reinforced to receive the soil, and directly replaces the structure of the launching hole, and replaces the original ground connection wall layer by layer with plain soil concrete from bottom to top , in order to achieve the purpose of reinforcement, thereby reducing and avoiding risks and ensuring the safety of initial construction. By extending the steel ring of the starting portal, a confined space of "shield plus shield" is established, the starting end of the shield is reinforced while the starting distance is delayed, and the shield machine is inspected, maintained and debugged before starting. After the commissioning of the machine is completed, rely on the reaction frame and the negative ring segment to start the shield tunneling, so that the shield tunneling start is as close as possible to the normal excavation state, and the multi-factor superimposed accident risk such as collapse and gushing is staggered, so as to ensure the shield tunneling construction Safety. There is no need for additional reinforcement of the stratum outside the launch shaft and the strata at the end, which can reduce the area occupied by the launch shaft and minimize its impact on surrounding traffic, and can realize construction without the need for surrounding pipelines to be relocated, reducing Investment and reduction of disturbing residents are in line with the actual situation and economically reasonable. It is suitable for the construction where the starting end well of the shield machine cannot be reinforced.

In this embodiment, for the layered replacement in step a, the height of each layer is 0.5m-1.5m. Prepare emergency supplies during replacement construction to prevent collapse of underground water-rich areas.

In this embodiment, the steel ring for extending the originating portal in step a is specifically: install a steel ring for extending the portal at the originating portal, set at least two sealing steel brushes inside the steel ring, and at the same time install a steel ring on the steel ring side Grouting holes are reserved on the side to facilitate the injection of grease and water stop during the starting process.

In this embodiment, the demolition of the initial portal during the replacement process of the primary portal is specifically: using manual cooperation with machinery to demolish the concrete of the inner ground connecting wall of 0.5m to 1.5m per layer, and then cut off the steel bars of the inner layer. After cutting off the steel bars of the inner layer, the concrete of the ground connection wall of the outer layer is broken, and then the steel bars of the outer layer are cut off. Make sure that the steel bar is flush with the steel ring of the opening door after the steel bar is cut. When breaking the concrete of the outer ground connection wall, ensure the structural integrity of the original concrete protective layer on the soil surface of the ground connection wall to reduce the probability of water leakage and sediment collapse.

In this example, every time a layer is completed after the opening door is removed and the steel bars are removed, a layer of C25 sprayed plain soil concrete is used to replace the layer. The replacement thickness of plain soil concrete is 1m~1.5m to ensure the stability of the portal.

In this embodiment, during the plain soil concrete spraying process, reserve 50PVC drainpipes, the distance between the drainpipes is 0.8m ~ 1.2m, and they are arranged in a plum blossom shape. Bamboo slices are arranged at the overlapping position of the two adjacent replacement layers for connection between the plain soil concrete of the upper and lower layers. The distribution spacing of the bamboo slices is 0.3m~0.8m, and the bamboo slices are arranged in two layers inside and outside.

In this embodiment, before the starting portal is replaced, the sleeve valve pipe is used to grout the soil of the starting portal with water glass grout to stop water and reduce the water content of the formation, thereby ensuring the replacement of the starting portal. Construction is proceeding as normal. The starting door opening is reinforced with section steel support to reduce the impact of the pressure generated by the shield machine on the starting door opening and surrounding soil.

In this embodiment, the specific implementation steps of step b include: performing maintenance on the cutting tool and the supporting equipment of the shield machine. Inspect or replace front reels, edge reels, center double-edged reels, severely worn scrapers, and severely worn cutters. Check the tool seat and replace it if it is severely worn. Check and maintain the supporting trolley, battery car and gantry crane to ensure that the equipment is in good condition.

In this embodiment, the specific implementation steps of step c are: start to install the negative ring segment, and while installing the negative ring segment, the shield machine advances toward the hole ring. In order to reduce the propulsion resistance at the start of the shield and avoid the cutter head on the cutter head from damaging the hole sealing device, apply lubricating oil on the cutter head and the hole sealing device to reduce friction.

In this embodiment, the shield gradually moves closer to the soil at the originating portal, so that the head of the shield machine cuts into the soil, and then the cutter head rotates to cut the soil, filling the soil chamber of the shield machine, and begins to build up the frontal soil pressure to balance The earth pressure on the front of the shield ensures that the displacement of the soil is minimized. The construction parameters of the initial stage of the shield tunneling are pre-determined based on multiple simulation tests. After the shield machine enters the hole ring as a whole, the hydraulic grout is evenly injected to the outside of the negative ring segment through the grouting hole of the negative ring segment to fill the gap. to prevent leakage. When the shield starts to propel, observe whether the reaction frame and the diagonal brace behind the reaction frame are deformed, so as to prevent damage caused by excessive displacement. Before propulsion, apply lubricating oil on the base surface of the shield to reduce the propulsion resistance of the shield.

During implementation, a shield machine starting method in a narrow space is provided, and the specific implementation steps are as follows:

a. Replacement of the starting portal

Since the reinforcement at the starting end failed to achieve the expected effect, in order to ensure the smooth starting of the shield machine, the method of extending the steel ring of the starting portal was used to carry out the starting excavation of the shield machine, and plain concrete replacement was required for the ground connection wall . At the same time, in order to ensure the stability of the starting portal, the thickness of plain concrete was increased to 1.2m.

When replacing the starting portal, it should be replaced in layers, each layer is 1m high, and the replacement should be carried out from bottom to top. The groundwater at the end is rich, and the starting portal is located in a sandy pebble layer, which is prone to collapse accidents. Sufficient emergency materials such as sandbags, formwork, and square logs should be prepared during replacement construction.

When demolition of the starting portal, the 1m inner ground wall concrete of each layer is firstly removed manually and mechanically, and then the inner layer steel bars are cut off. It is flush with the steel ring of the opening door, and when breaking the concrete of the outer ground connecting wall, try not to damage the concrete protective layer of the ground connecting wall facing the soil, so as to reduce water leakage and sediment collapse.

After demolition and reinforcement removal, each layer is replaced with C25 shotcrete. The displacement thickness is 1.2m. During concrete spraying, reserve 50PVC drainpipes, with a spacing of 1m and a plum blossom arrangement; at the same time, bamboo chips are arranged at the overlapping position of the upper and lower layers for the connection of the upper and lower layers of concrete, with a spacing of 0.5m between the bamboo chips, and the inner and outer layers are arranged.

During the replacement process of the starting portal of the construction on the left line, due to the high water content of the strata, normal replacement cannot be realized. Therefore, before the replacement construction of the starting portal, the sleeve valve pipe is used to perform water glass grouting on the soil of the starting portal Used to stop water. After the grouting and water sealing are completed, the starting portal replacement construction will be carried out to ensure the safety of the construction.

At the same time, it is considered that when the right line starts, the starting pressure may be too large, which will have a certain impact on the stability and stability of the left line soil and the starting portal. Steel supports are used for reinforcement at the starting portal.

b. Shield starting

First of all, repair the cutting tool and the supporting equipment of the shield machine. The knives include front hobs, edge hobs, center double-edged hobs and severely worn scrapers and cutters for replacement. Check the tool seat and replace it if it is severely worn. And check and maintain the supporting trolleys, battery cars, gantry cranes and other equipment to ensure that the equipment is in good condition.

Install and extend the steel ring of the starting hole at the starting hole, set two sealing steel brushes inside the steel ring, and reserve grouting holes on the side of the steel ring to facilitate the injection of grease and water stop during the starting process.

After the shield machine is debugged, rely on the reaction force frame and the negative ring segment to start the shield. Start to install the negative ring segment, and while installing the negative ring segment, the shield machine advances towards the hole ring. In order to reduce the propulsion resistance at the start of the shield and avoid the cutter head on the cutter head from damaging the hole sealing device, apply lubricating oil on the cutter head and the hole sealing device to reduce friction.

The shield gradually moves closer to the soil of the starting tunnel, so that the head of the shield machine cuts into the soil, and then the cutter head rotates to cut the soil, filling the soil chamber of the shield machine, and begins to build up the frontal soil pressure to balance the frontal soil pressure of the shield , to ensure that the displacement of the soil is reduced to a minimum. The construction parameters of the shield tunneling stage are determined based on multiple tests. When the shield machine enters the hole ring as a whole, the hydraulic grout is evenly injected into the outside of the segment through the segment grouting hole to fill the gap to prevent grout leakage. When advancing, pay attention to observe whether the reaction frame and the rear diagonal brace are deformed to prevent damage caused by excessive displacement. In order to reduce the propulsion resistance of the shield machine, apply lubricating oil on the base surface of the shield machine before propulsion.

c. Reaction frame, support and embedded parts

Reaction frame and its support

The shield reaction frame is composed of steel ring, back shield frame and steel support. The width of the steel ring is 50cm. The precision requirement of the steel ring is: the flatness of the ring surface is 5mm, so that the concrete segment is evenly stressed; The back shield frame is made of steel, and the steel ring and the back shield frame are welded and fixed and supported by Φ529mm steel pipes. The reverse force of the back seat during shield excavation is transmitted to the bottom plate and side wall of the main structure through the steel support, and the steel support is welded on the prefabricated Buried steel plate or planted reinforcement steel plate.

Diagonal bracing at the top and bottom of the reaction frame: 4 HW200×200 steel supports are evenly arranged and reinforced on the top, and the diagonal braces transmit the force of the reaction frame to the middle plate; 4 HW250×250 steel supports are used at the bottom. The reinforcement is evenly arranged, and the diagonal brace transmits the force of the reaction frame to the bottom plate.

Welded steel plates are properly prepared at the contact surfaces where the steel supports are in contact with the concrete slabs or beams. First, chisel off the concrete protective layer at the corresponding position, so that the steel plate is welded on the structural steel bar. The thickness of the steel plate is 15mm, and the size must be larger than the support surface. The parts that need to be processed on the bottom plate include: the bottom of the reaction frame, the diagonal brace and other parts. The specific location will be determined on-site during implementation.

d. Surface subsidence monitoring

(1) Surface subsidence monitoring

① Implementation method of monitoring

Base point embedding: The base point should be buried in a stable area outside the scope of settlement influence, and should be buried in a place with a wide view and good visibility conditions; the number of base points should be set according to the need, and the base point should be firm and reliable.

Embedding of settlement measuring points: Drill holes on the surface with a percussion drill, then put in round-head steel bars with a length of 200mm to 300mm and a diameter of 20mm to 30mm, and fill the surroundings with cement mortar.

Measurement method: The observation method adopts the precise leveling measurement method. The initial elevation is obtained by joint measurement of the base point and nearby benchmarking points. During the observation, the tolerances should be strictly controlled, and the reading height difference of each measuring point should not exceed 0.3mm. For observation points that are not on the leveling route, one measuring station should not exceed 3. If it exceeds, the reading of the backsight point should be re-read for verification. For the first observation, two consecutive observations should be made at the measuring point, and the difference between the two elevations should be less than ±1.0mm, and the average value should be taken as the initial value.

Calculation of settlement value: When conditions permit, lay out the wire network as much as possible to facilitate adjustment processing and improve observation accuracy, and then perform adjustment according to the station to obtain the elevation of each point. Before construction, the initial elevation H0 of the observation point of the uplift is measured from the base point by leveling, and the elevation measured during the construction is Hn. Then the height difference △H=Hn-H0 is the settlement value.

②Data analysis and processing

The surface settlement measurement is carried out along with the construction progress, and is monitored in time according to the excavation site and steps, and the settlement values of each settlement measurement point are drawn into a settlement change curve, a settlement change speed diagram, and an acceleration curve diagram.

e. Surface crack observation

The monitoring of surface cracks is usually used as one of the important basis for the influence degree of subway open cut and shield construction. Using the method of direct observation, number the cracks and mark out the reading position. If necessary, you can use a steel ruler to measure and read. The number and location of monitoring shall be determined according to the site conditions.

f. Surface building settlement, inclination and crack monitoring

(1) Building settlement monitoring

① Implementation method of monitoring

Embedding of measuring points: Buildings within the vertical and lateral influence range of surface subsidence should be monitored for building subsidence and inclination, and the embedding of base points is the same as for surface subsidence observation. To bury the settlement measuring point, use a percussion drill to drill a hole on the foundation or wall of the building, then put in a curved steel bar with a semicircular head with a long diameter of 20mm to 30mm, and fill it with cement mortar around it. The buried height of the measuring points should be convenient for observation, and protective measures should be taken for the measuring points to avoid damage during construction. Generally, 4 observation points are arranged on each building, and 6 observation points are arranged on particularly important buildings.

Measurement method: the same as the surface subsidence observation.

Subsidence Calculation: Same as Surface Subsidence Observation.

②Data analysis and processing

Use comparative method, drawing method and mathematical and physical models to analyze the magnitude, change law and development trend of each monitored physical quantity, so as to evaluate and make decisions on the safety status of the project and the measures that should be taken.

Draw a scatterplot of time-displacement curves and a scatterplot of distance-displacement curves. If the change of displacement gradually becomes stable with time, it means that the surrounding rock is in a stable state and the support system is effective and reliable. In the abnormal curve, if there is an inflection point, it means that the displacement has an abnormal and sharp increase, indicating that the surrounding rock and support are already in an unstable state, and corresponding engineering measures should be taken immediately.

After obtaining sufficient data, an appropriate function should be selected according to the data distribution of the scatter diagram, and regression analysis should be performed on the monitoring results to predict the maximum displacement value that may occur at the measuring point and predict the safety status of the structure and building .

(2) Building crack observation

The settlement and inclination of the building will inevitably lead to the stress adjustment of the structural components to produce cracks, and the monitoring of crack development is usually one of the important basis for the degree of construction impact. Usually, the method of direct observation is used to number the cracks and mark out the reading position to observe the occurrence and development process of the cracks. When necessary, the crack width is measured and read by the crack observer. The number and location of monitoring shall be determined according to the site conditions.

g. Monitoring frequency and standards

Construction monitoring measurement value control standard table

According to the above-mentioned monitoring and management standards, the monitoring frequency can be selected: generally, the monitoring frequency is appropriately enlarged in the management stage of level III; Reach 1-2 times/day or more.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A shield machine starting method in a narrow space, characterized in that: comprising the following steps: a. The replacement of the starting portal adopts a bottom-up layered replacement method, replacing the original ground connection wall with plain soil concrete; extending the steel ring of the starting portal so that the reinforcement of the starting end of the shield reaches the predetermined level effect, to ensure the smooth starting of the shield machine; b. Check, maintain and debug the shield machine; c. Relying on the reaction frame and the negative ring segment to initiate the shield tunneling. 2. The starting method of the shield machine in a narrow space according to claim 1, characterized in that: the layered replacement in the step a, the height of each layer is 0.5m ~ 1.5m; emergency supplies are prepared during the replacement construction, with Prevents collapse in subsurface water-rich areas. 3. The starting method of a shield machine in a narrow space according to claim 1, characterized in that: the steel ring for extending the starting door in the step a is specifically: installed at the starting door for extending the door There are at least two sealing steel brushes on the inner side of the steel ring, and grouting holes are reserved on the side of the steel ring to facilitate the injection of grease and water stop during the starting process. 4. The starting method of shield machine in narrow space according to claim 3, characterized in that: it also includes breaking the starting hole in the process of replacing the starting hole, specifically: Manually combined with machinery to remove the concrete of the inner ground connection wall of each layer of 0.5m ~ 1.5m, and then cut off the steel bars of the inner layer; Cut off the steel bars of the inner layer, then break the concrete of the outer ground connection wall, and then cut off the steel bars of the outer layer; Ensure that the steel bars are flush with the steel ring of the opening door after cutting; When breaking the concrete of the outer ground connection wall, ensure the structural integrity of the original concrete protective layer on the soil surface of the ground connection wall to reduce the probability of water leakage and sediment collapse. 5. The starting method of the narrow space shield machine according to claim 4, characterized in that: the starting hole is broken and the steel bar is cut off and every layer is completed, the replacement layer is replaced by C25 sprayed plain soil concrete; the replacement of plain soil concrete The thickness is 1m ~ 1.5m to ensure the stability of the portal. 6. The starting method of shield machine in narrow space according to claim 5, characterized in that: during the plain soil concrete spraying process, the tunnel surface is reserved The drainage pipes shall be set at a distance of 0.8m to 1.2m and arranged in a plum blossom shape; bamboo chips for connection between the plain soil and concrete of the upper and lower layers shall be arranged at the overlapping positions of two adjacent replacement layers. The distribution spacing is 0.3m ~ 0.8m, and the bamboo slices are arranged in two layers inside and outside. 7. The starting method of shield machine in narrow space according to claim 6, characterized in that: before the starting hole is replaced, the sleeve valve pipe is used to carry out water glass slurry grouting to the starting hole soil to carry out Stop the water to reduce the water content of the ground, so as to ensure the normal construction of the starting door opening replacement; use steel support for reinforcement treatment at the starting door opening, so as to reduce the pressure generated by the shield machine when starting the starting door opening and its surroundings influence of the soil. 8. The starting method of a shield machine in a narrow space according to any one of claims 1 to 7, characterized in that: the specific implementation steps of step b include: Carry out maintenance on the tool and the supporting equipment of the shield machine; Check or replace frontal hobs, edge hobs, center double-edged hobs, severely worn scrapers, and severely worn cutters; Check the tool seat and replace it if it is seriously worn; Check and maintain the supporting trolley, battery car and gantry crane to ensure that the equipment is in good condition. 9. The starting method of a shield machine in a narrow space according to any one of claims 1 to 7, characterized in that: the specific implementation steps of the step c are: Start to install the negative ring segment, while installing the negative ring segment, the shield machine advances towards the hole ring; In order to reduce the propulsion resistance at the start of the shield and avoid the cutter head on the cutter head from damaging the hole sealing device, apply lubricating oil on the cutter head and the hole sealing device to reduce friction. 10. The starting method of the shield machine in a narrow space according to claim 9, characterized in that: the shield machine gradually moves closer to the soil body of the starting hole, so that the head of the shield machine cuts into the soil body, and then the cutter head rotates and cuts The soil is filled with the soil chamber of the shield machine, and the frontal earth pressure begins to be established to balance the frontal earth pressure of the shield to ensure that the displacement of the soil is minimized; The construction parameters of the initial stage of the shield tunneling are pre-determined according to multiple simulation tests. After the shield machine enters the hole ring as a whole, the hydraulic grout is evenly injected to the outside of the negative ring segment through the grouting hole of the negative ring segment to fill the gap. to prevent leakage; When the shield starts to propel, observe whether the reaction frame and the diagonal brace behind the reaction frame are deformed to prevent damage caused by excessive displacement; Before propulsion, apply lubricating oil on the base surface of the shield to reduce the propulsion resistance of the shield.