Cause analysis (1) the earth entry opening rate of shield cutterhead is too small and the earth entry is not smooth; (2) The soil quality of the stratum at the front of the shield changes; (3) The front face of the shield encounters large obstacles; (4) Leakage in the propulsion Jack fails to reach its own maximum rated oil pressure; (5) The setting of front balance pressure is too large; (6) Preventive measures for serious wear of cutter head (1) reasonably design the size of soil hole to ensure smooth excavation; (2) Before the tunnel axis design, a detailed geological survey shall be conducted along the shield crossing line to find out the specific location and depth of obstacles affecting the shield propulsion along the line, so as to make the axis design take this situation into account; (3) Understand the soil condition in the shield propulsion section in detail, so as to timely adjust the earth pressure setting value, propulsion speed and other construction parameters; (4) Frequently overhaul the cutterhead and propelling Jack to ensure their good operation; (5) Reasonably set the balance pressure, strengthen the dynamic management of construction, and timely adjust and control the balance pressure value.
The screw of the screw machine forms an “earth stick”, the screw machine cannot be excavated, or the blocking load in the screw machine increases, and the motor cannot drive the screw machine to rotate and cannot be excavated.
Preventive measures (1) correctly set the balance pressure to make the excavated volume of the shield close to the theoretical value, reduce over excavation and under excavation, and control the posture of the shield; (2) In the process of shield construction, the measurement base station shall be frequently corrected, retested and rechecked; (3) In case of deviation of shield posture, it shall be corrected in time to make the shield move forward correctly along the tunnel design axis; (4) When the shield is in uneven soil layer, the propulsion speed shall be properly controlled and the soil shall be cut with cutter head to reduce the uneven resistance during propulsion.
If conditions permit, large excavation construction method can also be used to clean up front obstacles; (2) Add Jack to increase the total thrust of shield.
Cause analysis (1) the balance pressure on the shield excavation surface is too low to form sufficient pressure in the screw machine, and the screw machine cannot enter the soil normally or be excavated; (2) The screw of the screw machine is not concentric with the shell, and the shell is worn during operation, which increases the gap between the blade and the shell, and the excavation efficiency is low; (3) When the shield is pushed in sandy soil and cohesive soil with high strength, the friction between the soil and the spiral casing is large, the rotation resistance of the spiral machine increases, and the motor cannot rotate; (4) Large boulders enter the screw machine and jam the screw; (5) The screw drive motor stops working because of long-time high load work, overheating or high oil pressure.
(5) When the shield is constructed in extremely weak soil layer, the relationship between advancing speed and soil inflow shall be mastered to control the loss of front soil; (6) Before assembling the segments of the arch bottom block, the garbage at the bottom of the shield shell shall be cleaned to prevent impurities from being mixed between the segments and affecting the tunnel axis; (7) Grouting shall be carried out according to the quality and quantity during construction to ensure the mixing quality and injection volume of slurry.
Treatment method (1) open the cover plate of the screw machine and clean the blocked part of the screw machine; (2) Replace the worn screw.
It is also possible to use foam or bentonite to excavate the surface to improve the soil and make the propulsion more smoothly.
Treatment methods (1) adopt auxiliary technology to promote obstacle cleaning in the working face as far as possible.
Excessive fluctuation of front pressure of earth pressure balance shield during shield propulsion and segment assembly, abnormal fluctuation of balance pressure on the excavation surface occurs, which is greatly deviated from the theoretical force value or set stress value.
Preventive measures (1) correctly set the construction parameters of shield propulsion to make the propulsion speed match the excavation capacity of screw machine; (2) when the soil strength is high and the spiral machine is not well discharged, the amount of water or foam can be properly injected into the screw or earth bin to improve the efficiency of unearthed.
Preventive measures (1) when the auger slips, increase the set value of the balance pressure on the excavation surface of the shield and the propulsion speed of the shield to make the auger enter the soil normally; (2) Pay attention to the accuracy when installing the screw machine, and strengthen the lubrication of the bearing during operation; (3) Reduce the propulsion speed to reduce the soil input of the screw machine and the load of the motor of the screw machine per unit time; (4) add water, mud or foam in the screw machine to reduce the friction between the soil and the spiral case and reduce the load of the motor.
If the clearance between advance and stop is too long, the shield will sink when the front balance pressure is lost; (6) When assembling segments, the shield shell at the arch bottom block is not cleaned up, and impurities are mixed in the joints of two adjacent ring segments, which will lead the lower part of the segment and the axis upward, affecting the control of the shield propulsion axis; (7) Insufficient synchronous grouting quantity or poor slurry quality will cause tunnel settlement after bleeding, which will affect the control of propulsion axis; (8) The unconsolidated slurry causes the deformation of the tunnel under the action of large thrust.
Excessive rotation of shield during shield propulsion, resulting in poor connection between shield and frame, unstable equipment operation, increased difficulties in measurement, capping and rapid assembly..
Cause analysis (1) over excavation or under excavation of the shield causes poor posture of the shield in the soil, resulting in excessive deviation of the shield axis; (2) Deviation of axis caused by shield measurement error; (3) The deviation correction of shield is not timely or in place; (4) When the shield is in uneven soil layer, that is, in the zone where two different soil layers intersect, the compressibility, compressive strength and shear strength of the two soils are different; (5) The shield is in a very weak soil layer.
Cause analysis (1) the propulsion speed does not match the rotation speed of the screw machine; (2) When the shield is constructed in sandy soil, the screw machine is blocked due to large friction or soil plug, and the excavation is not smooth, resulting in a sharp rise in the equilibrium pressure on the excavation surface; (3) The shield retreats to reduce the equilibrium pressure on the excavation surface; (4) The earth pressure balance control system fails, resulting in the deviation between the actual pressure and the set earth pressure.
Source: the copyright of Baidu Library belongs to the original author.
The earth pressure balance shield screw machine is not excavated smoothly.
The phenomenon of excessive front resistance of EPB shield causes difficulties in shield propulsion and ground uplift and deformation due to excessive front resistance during shield propulsion.
When the soil is very soft and the dumping will soon affect the establishment of front pressure, properly close the gate of the screw machine to ensure the establishment of balanced earth pressure; (3) During segment assembly, the expansion jack shall be correctly, and the oil pressure and the number of extended jacks shall be strictly controlled to ensure that the shield does not retreat during assembly; (4) Correctly set the balance earth pressure value and the control parameters of the control system; (5) Strengthen the maintenance of equipment, ensure the intact rate of equipment and ensure that there is no internal leakage of Jack.
Water pressure + earth pressure = Earth bin pressure deviation of shield tunneling axis during shield tunneling, the shield propulsion axis deviates too much from the tunnel design axis, affecting the axis of the ring segment.
The treatment method (1) injecting foam, water, and clay into the cutting surface to improve the performance of cutting into the soil of the soil bin, improve the discharging ability of the screw machine and stabilize the frontal earth pressure; (2) Maintain the equipment and reduce the leakage of the hydraulic system; (3) Reset the parameters of the control system to meet the use requirements.
Treatment methods (1) adjust the jack grouping of the shield or adjust the oil pressure in each area, and correct the shield axis in time; (2) Overbreak the excavation surface to make the shield advance along the overbreak side; (3) When the axis of the shield cannot be corrected due to the obstruction of the segment position, the wedge ring segment is used to adjust the perpendicularity between the annular surface and the tunnel design axis to improve the back seat surface of the shield.
