With the accelerating pace of urbanization, the utilization of the above ground space is limited, and the slotting excavation has been difficult to meet the needs of underground space construction
.
Therefore, in 1842, the shield machine was invented by French engineer M.L
.
brunet
.
The first is the air pressure shield
.
Excavation of tunnel under Thames River in London, UK
.
Since then, the shield mechanical equipment has been continuously innovated and improved, which has been widely used in the construction of underground tunnels, underground pipelines and other projects, and has achieved great economic and social benefits
.
1
.
The earth pressure balance tunneling is characterized by earth pressure balance shield, which fills the earth bin between the excavation face and the diaphragm with the excavated soil sand, injects the improved materials according to the needs, and ensures the stability of the excavation face with appropriate earth pressure
.
Through the screw conveyor set through the diaphragm, the waste can be discharged at the same time
.
2
.
In order to ensure the stability of excavation face, the pressure of soil bin should be maintained properly
.
Generally, if the pressure of soil bin is insufficient, the risk of water inrush or collapse will increase
.
If the pressure is too high, it will cause the increase of the torque or thrust of the cutterhead, resulting in the decrease of the propulsion speed or the uplift of the ground
.
As the upper limit, the static earth pressure is used to control the ground settlement as much as possible; As the lower limit, a small amount of ground settlement can be allowed, but active earth pressure can be used for the purpose of ensuring the stability of the excavation face
.
The main methods to maintain the earth pressure in the process of advancing are to control the rotation number of the screw dumper and the advancing speed of the shield Jack (the former two combined control)
.
The purpose of the three methods is to carry out the earth volume management
.
In order to maintain the stability of the excavation surface and advance smoothly at the same time, it is necessary to carry out the appropriate amount of dumping, so as to maintain the balance between the amount of dumping and the amount of advancing
.
The management methods of waste volume are volume management method and weight management method
.
4
.
The properties of muck modified and improved muck have good plastic flow state, good viscosity, low internal friction and low water permeability
.
The commonly used improvement material is foam or bentonite slurry
.
5
.
The key points of EPB shield tunneling are that the earth bin should be filled with the excavated dregs, the earth bin pressure of the dregs stroke should be balanced with the water and soil pressure outside the cutter head excavation face, and the amount of waste soil and the amount of excavated soil should be balanced
.
According to the tunnel engineering geological and hydrogeological conditions, buried depth, line plane and slope, surface environment, construction monitoring results, shield posture and experience in the initial stage, the driving parameters such as shield cutter head speed, driving speed and earth bin pressure should be set
.
In the process of tunneling, it is necessary to monitor and record the operation of shield machine, the change of tunneling parameters and the removal of dregs, and timely analyze the feedback, adjust the tunneling parameters and control the shield posture
.
According to the engineering geological and hydrogeological conditions, the modifier should be injected into the front of the cutter head and the soil bin, and the residue should be in the flow plastic state
.
6
.
The features of mud water pressure driving are: using mud to maintain the stability of the excavation face, and using mechanical excavation at the same time
.
The muck is transported to the ground by mud
.
The operation of the system should fully consider the setting and management of the conditions such as the amount of waste, the quality of mud, the state of the excavation face, the grouting behind the wall, the flow rate of sending and discharging mud, and the flow rate of discharging mud
.
7
.
Segment assembly generally starts from the lower standard (type A) segment, and the standard segments are installed alternately on the left and right sides, then the adjacent (type b) segment is assembled, and finally the wedge (type K) segment is installed
.
During the assembly, it is forbidden to retract the jack at the same time
.
First tighten the circumferential (between segments) connecting bolts, and then tighten the axial (between rings) connecting bolts
.
When assembling the radial inserted wedge-shaped segment, it should be overlapped and jacked up radially first, and then inserted longitudinally
.
After pushing the position that the jack thrust cannot affect, use the torque wrench to tighten the connecting bolt again
.
8
.
The types of post wall grouting include synchronous grouting, secondary grouting and water plugging grouting
.
The purpose of grouting behind the wall is to make the annular space between the segment and the surrounding rock establish the support system of grouting body as soon as possible, prevent the ground loss caused by the collapse of soil around the tunnel and the loss of groundwater, control the ground settlement value, and then ensure the stability of the segment early lining structure
.
As the reinforcement layer of tunnel lining structure, it has durability and certain strength
.
It can avoid or greatly reduce the chance of direct contact between groundwater and segment, thus becoming the protective layer of segment, avoiding or slowing down the erosion of groundwater to segment, and improving the durability of lining structure
.
9
.
The main task of linear control of shield attitude control is to make the geometric center line of the constructed lining structure linear and smooth and within the allowable error range of the design center line by controlling the shield attitude
.
10
.
The deformation control measures of shield construction are to understand the situation of the new shield tunnel crossing or adjacent to the existing underground pipelines, traffic facilities and buildings
.
Through detailed investigation, analysis and prediction, protective measures and special construction scheme are formulated; During the construction process, the safety of existing structures is ensured by monitoring and measuring feedback to guide the construction
.
11
.
Ground change control measures for shield tunneling to prevent deformation caused by unbalanced earth water pressure on the excavation face: the earth pressure balance shield can make the pressure in the pressure chamber correspond to the earth water pressure on the excavation face by adjusting the advancing speed and the rotation speed of the spiral plotter
.
Measures to reduce the deformation of surrounding rock in the process of Shield Crossing: control the shield posture well and avoid unnecessary deviation correction operation
.
Measures to reduce the ground deformation caused by shield tail detachment: synchronous grouting is used to fill the tail gap in time
.
Measures to prevent the deformation caused by lining: in order to prevent the deformation of segment ring, shape retention devices must be used to ensure the assembly accuracy of segment, and the joint bolts must be fully tightened
.
Measures to prevent underground water level from falling due to excavation or lining leakage: in order to prevent water leakage from segment joints, grouting holes behind the wall and other parts, segment assembly and waterproof operation must be carried out carefully
.
12
.
For the prediction and construction monitoring of stratum deformation, the necessary items include the surface heave and subsidence in the construction area, the deformation of buildings (structures) and underground pipelines along the line, and the deformation of tunnel structure; The selected measurement items include deep horizontal displacement and layered vertical displacement of rock and soil, internal force of lining ring, contact stress between stratum and segment
.
13
.
The applicable conditions of shield construction are applicable to the relatively homogeneous geological conditions except hard rock
.
The buried depth of the tunnel should be sufficient, and the soil depth should not be less than 1D (tunnel diameter)
.
14
.
Preliminary investigation of construction preparation: Geology and hydrology, buildings within the scope of Engineering influence, underground obstacles, underground structures, underground pipelines, environmental investigation, power introduction conditions of shield equipment
.
15
.
Technical preparation of engineering geological and hydrogeological investigation report, environment along the tunnel, buildings, underground pipelines and obstacles, design drawings and engineering technical requirements documents required for construction, contract documents related to engineering construction, construction organization design and relevant data of shield to be used
.
When the location and construction method of the working shaft are selected for shield construction, it is generally necessary to set the working shaft at the beginning and end of the shield tunneling, the starting working shaft and the receiving working shaft
.
The section size of working shaft is determined as follows: shaft wall shield launching portal; The underground shield foundation, reaction frame 16 and shield construction site shall be arranged within the construction scope
.
The road traffic, material warehouse, material storage yard, temporary house, large construction equipment, soil (mud) pit, mixing system, temporary water and electricity pipelines, vertical transportation equipment of fire fighting equipment, etc
.
shall be reasonably planned and arranged
.
17
.
The shield construction stage is divided into normal tunneling and receiving launching, which means that the shield starts tunneling from the base of the shield in the launching shaft to the completion of the initial tunneling (usually 50-100m)
.
After the completion of launching, the temporary segments, temporary supports and reaction frames shall be removed, and then the normal excavation shall be conducted
.
The receiving means that the self driving distance is 100 m from the receiving shaft to the shield reaching the receiving base in the receiving shaft
.
18
.
Chemical grouting, mortar backfill, deep mixing, high-pressure jet grouting and freezing are used to reinforce the soil at the entrance.
.
