Ground deformation control for shield tunneling

1. Proximity construction management

【Formula】Regulation and project supervision

First of all, the engineering conditions, geological conditions, and environmental conditions (i.e., the current conditions and safety requirements of the existing structures) should be investigated in detail, and the analysis and prediction should be carried out on the basis of the investigation, and protective measures should be formulated.

secondly, formulate a special construction plan;

Finally, during the construction process, the safety of the existing structure is ensured by monitoring and measuring feedback to guide the construction.

2. Causes of formation deformation

【Formula】Pressing and disturbing the groundwater

1) The soil and water pressure of the excavation face and the pressure of the shield pressure chamber are unbalanced, causing the surface settlement or uplift in front.

2) Due to the disturbance of the surrounding rock caused by the friction and curve advancement and deviation correction of the shield shell, the formation settlement or uplift is caused.

3) The synchronous grouting behind the wall is not timely or insufficient, which leads to the occurrence of the shield tail void and causes the formation settlement.

4) Due to the insufficient fastening of the joint bolts and other reasons, the deformation and displacement of the primary lining are caused, thereby increasing the subsidence of the formation.

5) Excavation or lining leakage leads to a drop in the groundwater level, causing formation consolidation and settlement.

In general, the stratum deformation induced by shield propulsion is the overlapping effect of stratum uplift or subsidence caused by the above reasons.

3. Formation deformation stage of shield construction

【Formula】It is longer before and after the past

Stage 1: Occurs before the shield reaches the section. For sandy soils, the early subsidence is caused by the drop in the water table; The early settlement of soft cohesive soil is caused by excessive soil extraction at the excavation face.

Stage 2: Before the shield passes through the fault, if the shield controls the earth pressure (slurry pressure) is insufficient or too large, the formation settlement or uplift is caused by the deformation of the soil on the excavation face.

Stage 3: Formation settlement or uplift occurs due to over-excavation, curve excavation or deviation correction, friction between the shield shell and the surrounding soil when the shield passes through the section.

Stage 4: The deformation of the shield after passing through the section is caused by the stress release caused by the appearance of the gap at the tail of the shield or the excessive grouting pressure behind the wall. Most of the stratum settlement deformation caused by shield construction is this type of deformation.

Stage 5: The settlement deformation that still continues to occur for a long time after the shield passes through the section is mainly caused by the stratum disturbance and relaxation caused by the shield tunneling, and the construction performance is most obvious in the weak cohesive soil, while the construction basically does not occur in the sandy soil or dense hard clay soil.

4. Influencing factors of stratum deformation

【Formula】The ratio of soil cover to the soil, the viscosity reduction of the sand is the opposite

The size of the formation deformation caused by shield construction is related to the formation conditions and the soil cover ratio (the ratio of the covering thickness to the shield diameter) and other factors. In the case of flood strata and alluvial sandy soils, the deformation of the strata decreases in the process of being transferred to the surface. On the contrary, the alluvial clay soil continues for a long time after the shield passes, and even if the soil cover ratio is large, the final surface subsidence is the same as the ground subsidence. In the construction of soft soil strata, the effect of shield construction is often controlled by the stratum loss rate.

5. Deformation control measures caused by unbalanced earth-water pressure on the shield excavation face

【Formula】Speed regulation adds adjustment characteristics, and cooperates with auxiliary construction

The EPB shield can adjust the propulsion speed and the rotation speed of the spiral unearther, so that the pressure chamber pressure corresponds to the earth-water pressure of the excavation face. In addition, appropriate additives are injected as needed to increase the plastic fluidity of the excavated soil. The slurry pressurized shield can adjust the mud characteristics according to the permeability of the soil layer of the excavation face, and carefully manage the mud, so that the pressure chamber pressure always corresponds to the earth-water pressure of the excavation face. While implementing the stability management of these open control faces, the corresponding auxiliary construction methods should also be studied as needed to ensure the stability of the surrounding rock.

6. Control measures for deformation of surrounding rock during shield crossing

【Formula】Attitude control is less suitable, drag reduction and less over-digging

Control the attitude of the shield to avoid unnecessary deviation correction operations. When there is a deviation, it should be operated in line with the principle of "diligent correction, less correction, and moderation". If over-excavation is required during deviation correction or curve excavation, the over-excavation radius and over-excavation range should be reasonably determined to reduce over-excavation as much as possible. When the EPB shield is excavated in weak or loose formations, when the viscous resistance or friction between the outer periphery of the shield and the surrounding soil is large, drag reduction measures should be taken.

7. Formation deformation control measures caused by shield tail prolapse

【Formula】 Timely filling of slurry

Use synchronous grouting to fill the tail gap in time; According to geological conditions, engineering conditions and other factors, the single-liquid grouting or double-liquid grouting should be reasonably selected, and the grouting materials and mix ratio should be correctly selected, so as to stabilize the assembled lining structure in time; Strengthen the control of grouting volume and grouting pressure; Carry out secondary grouting in time.

8. Deformation control measures for shield construction lining

【Formula】Tighten fully and maintain the shape

In order to prevent the segment ring from deforming, it is necessary to ensure the accuracy of segment assembly by using a shape holding device, etc., and at the same time to tighten the joint bolts adequately.

9. Control measures for the decline of groundwater level caused by shield construction excavation or lining leakage

【Formula】Segment group defense

In order to prevent water leakage from segment joints and grouting holes behind walls, it is necessary to carefully assemble and waterproof the segments.

10. Prediction and construction monitoring of formation deformation

【Formula】The value is set by the Yuan Change

In order to reduce the deformation of the formation, it is necessary to make a prediction based on past construction experience and the finite element method before advancement, and set a benchmark value for the management of soil silo pressure or slurry silo pressure based on the prediction results. At the same time, the management benchmark value is adjusted in a timely manner according to the deformation monitoring results during the advancement.

11. Layout of shield construction stratum deformation monitoring points

【Formula】The middle line and both sides, three at the same step

Deformation monitoring points are to be set on the tunnel centerline and within the range of both sides. Monitoring points on the ground and in the tunnel should be laid in the same section; After the shield passes, the monitoring data in the same section should be collected synchronously, and the shield tunneling parameters should be collected at the same time.

12. Shield construction stratum deformation monitoring project

【Formula】The surface tunnel is changed, and the internal deep sorting is connected

The construction monitoring project shall comply with the provisions of Table 1K413035. When crossing waters, buildings (structures) and other sections with special requirements, it should be determined according to the design requirements.

Construction Monitoring Items Table 1K413035
category	Monitoring projects
Required Items	The surface of the construction area is subsided, and the buildings (structures) along the line are deformed and the underground pipelines are deformed
Deformation of tunnel structure (vault subsidence, tunnel circumference convergence)
Selected test items	Horizontal displacement and layered vertical displacement of rock and soil mass
lining ring internal forces
The contact stress between the formation and the segment

13. Formation deformation monitoring method for shield construction

【Formula】Vertical level flat guard edge, net 3 sensor pier photo

The vertical displacement monitoring can be carried out by the leveling measurement method, and the leveling base points should be buried outside the deformation influence range, and there should be no less than 3; When the static leveling method is used for vertical displacement monitoring, the burial, connection, observation and data processing of the static level should meet the requirements of the current relevant national standards, and the measurement accuracy should be the same as that of the leveling requirements.

Horizontal displacement monitoring can be carried out by means of corner measurement or satellite positioning, and a horizontal displacement monitoring and control network should be established, and the observation pier and illumination device with a mandatory centering device should be used for the horizontal displacement monitoring control point; When physical sensor monitoring is used, the sensor burial shall comply with the provisions of the instrument burial and the monitoring scheme;

Yesterday 速记口诀5/15

1. Classification of post-wall grouting

The second step is to block the water

2. The role of synchronous grouting

Fill brace anti-collapse control

3. The role of secondary grouting

Stop water and reinforce the soil

4. The role of water plugging and grouting

Water-rich waterproof compactness

5. Basis for the selection of grouting method

Geological surface rings require equipment performance

6. The purpose of grouting behind the wall

Durable reinforcing layer, early support to prevent uncontrollable sinking, fast strength without support lining and early stability

7. Selection of grouting materials

Authentic rings

8. Performance parameters of grouting materials

Condensation environmental protection strong current charge

9. Grouting parameters

Pressure and fast charging coefficient

10. Basis for determining synchronous grouting pressure

Preparation of buried pipe grouting

11. Basis for determining the secondary grouting pressure

Annular bar sinking monitoring

12. Slurry regulations

Seven properties of mixing, pressing, and transportation, and miscellaneous are easy to dense and condense and condense

13. Key points of grouting construction behind the wall

Prepare for the inspection worker, transfer and clear the seal

14. Basis and method of shield attitude adjustment

Horizontal and vertical deviation and over-digging reversal

Three days ago, shorthand mantra 5/13

1. Pressure management of slurry water tank

Stabilize the upper and lower limits, and detect the magnetic sound

2. Discharge management

Flow density meter soil level

3. Key points of slurry balance shield tunneling

Dynamic parameters regulate and control the soil leveling, and relieve the pressure of granular slag

Seven days ago, shorthand mantra 5/9

1. The type of shield is classified according to the form of supporting strata

Natural mechanical earthy gas

2. The type of shield is classified according to whether the excavation face is closed

Water and soil hand half machine

3. The type of shield is classified according to the shape of the section

Round horseshoe, multi-class moment

4. The configuration of the cutterhead of the shield machine

Body knife measuring rod tube

5. Cutterhead design matters

The structure uses an open knife

7. The function of the cutterhead

Dig and stir

8. The applicability of the shield to geological conditions

The soil is clay, muddy and watery

9. Selection basis

Survey and set up a broken safety ring, and the field period is auxiliary to the class

10. The basic principles of selection

Fit for the first time

11. Requirements for shield selection and configuration

The shell disc drives the cylinder with snail mud, and changes the human reaming guide

Two weeks agoShorthand mantra 5/2

1. Groundwater control objects

Latent micro

2. Groundwater control methods

Interception and recharge group

3. Basic requirements for groundwater control

Cut-off and downgrading

4. The purpose of using the water separation (interception) curtain

Resistive subtraction gradient

5. The basis for the selection of foundation pit water isolation method

Engineering hydrogeology

6. Isolation (interception) water curtain

Stir and spray and bite down and close the suspension

7. Cement-soil mixing pile curtain

Diameter and width of the ash ratio mud, 1568 notes

8. High-pressure jet grouting curtain

Corner width, 123, ash than mud, 1 nearly half.

五周前速记口诀4/12

1. Prestressed concrete raw materials

Priority should not be obtained, gravel anti-chlorine rust

2. Prestressed concrete pouring

Strengthen vibration and avoid collisions

3. Basic provisions of prestress tension

The force core is poor, and the anchor is initially recorded

4. Pre-tensioning prestressed construction

The center of the seat beam force, tensioning and releasing the broken pipe reinforcement

5. Prestressed tendon pipeline installation

Casing positioning ribs, welded through the hole

6. Installation requirements for prestressed tendons

Detection of moisture (salt) shall not be installed

7. Tensile requirements for prestressed tendons

Forced demolition and testing of Zhang Chao

8. Anchoring

After stabilization, the anchor seals the cutting head

9. Hole grouting

Check the secret in time to assess the temperature, and the mud sealing anchor is lifted to move strong