6.2.1 Shield Tunnel Common Faults and Maintenance
6.2.1.1 Common Faults of Shield Tunneling and Treatment Methods
1）Shield manufacturing is unified，but in the face of various environmental challenges，unified configuration is always flawed and cannot cope with all environments.So the shield cannot move forward is generally caused by environmental conditions
If the water content in the construction site is large，it will lead to the increase of soil viscosity.There are several serious problems when the shield is moving forward：the shield may squeeze the cohesive soil into a wall that is difficult to excavate and has a large density，which hinders the shield from moving forward.The soil surface with high moisture content will also be relatively smooth，resulting in the failure of the shield cutterhead to find the digging point，which makes the cutterhead empty and white loss of energy power，and even causes the cutterhead to fall off due to empty rotation.When the moist soil enters the soil cabin，due to the large viscosity，it may even cause the soil cabin to be unable to discharge and clean up the internal soil in time，making the soil cabin blocked，and the shield cannot carry out the construction operation normally，so it is forced to stop moving forward.The earth pressure is too large，which makes the shield load exceed the standard，cannot be effectively recycled，and also makes the shield unable to move forward.
If the soil is hard and contains a large number of rock fragments，resulting in shield cutterhead working pressure，and may even damage the cutterhead，which is one of the important reasons for shield cannot continue to move forward.In dealing with such problems，it is generally considered that the characteristics of different geographical environments are taken into account in the construction of shields，and the corresponding maintenance and use equipment will be served for shield support to help shields face and deal with tunnel construction problems under various geographical conditions.For example，when wet soil is encountered，the artificial construction team strength can be added to help quickly clean up the wet soil with large viscosity，and help shield obstacles，so that normal work can be carried out.Some chemical agents can also be added to make the moist soil solidified，so that the shield can quickly and easily solve the problem of excavation obstacles.When facing the situation of hard soil，aiming at the improvement and innovation of cutterhead，the cutterhead is more solid，which can resist the problem of hard rock that is difficult to be broken.Stone crusher can also be used to assist the normal operation of shield.
2）Hydraulic system
Hydraulic technology is one of the most important operation links in shield.However，it is also the most prone to problems and faults.The most fatal problem is the contamination of oil in hydraulic components，which can lead to a series of component failures.Oil is tainted，and the temperature of the first tank filled with oil will rise sharply during operation，reaching the limit of overload，the tank may be scrapped.
Oil pollution may contain some particles，which will increase the friction between the components.When the friction is too fast，it may lead to burning and failure of the components.Oil pollution may lead to oil agglomeration，which will block the channel and filter of shield hydraulic system，so that the oil cannot flow smoothly，resulting in the hydraulic system can not work normally，and even cause damage and operation obstacles of other systems.In the face of this problem，the most fundamental operation is to timely clean up the oil，clean up the components，and replace the oil.Avoid oil pollution，from the most basic，the most fundamental place to solve the most serious problems.When cleaning components，the same oil is used to rinse them to ensure that lubrication between components prevent excessive friction damage.When replacing oil，you must use the same kind of oil to fill and supplement to prevent the possibility of chemical reactions between different oils.In the hydraulic system，if some parts are damaged，they must be repaired or replaced in time to prevent secondary pollution after oil supplement，resulting in paralysis of the hydraulic system and unable to be used again.
6.2.1.2 Maintenance of Shield Machine
The maintenance of shield machine follows the principle of paying equal attention to maintenance and putting prevention first，and adopts the combination of daily maintenance，regular maintenance and forced maintenance.Main contents of maintenance are：cleaning，fastening，adjusting，lubrication，anti-corrosion，etc.，also known as“10 word practice”.
（1）For the shield used for the first time，a comprehensive inspection and maintenance should be carried out after the completion of 100 m test driving.The hydraulic system filter should be replaced，and the gear oil driven by cutter head should be replaced.During the test period，the inspection of equipment should be strengthened，the frequency of inspection should be increased，and the precursor of possible failure in the first load test should be found in time to avoid unnecessary losses.
（2）The mechanical and electrical engineers of the project department should inspect the operation status of the shield and the supporting equipment every day，check and confirm the“Operation records of shield machine”filled out by the shield operators and the“Daily maintenance records of shield machine”filled out by the maintenance personnel item by item，find out the hidden trouble in time，and do a good job of preventive maintenance to keep the shield in good condition.
（3）It is forbidden to dismantle and change the components on the shield without authorization.It is forbidden to change the components for different purposes at will.It is forbidden to dismantle sleeves for hydraulic and electrical control components.It is forbidden to dismantle safety and indicative sensors，safety valves，instruments，relief valves，etc.If damaged or inaccurate，it should be found and replaced in time.
（4）The maintenance of shield must be carried out under the premise of ensuring safety.Only when the shield stops running，can the maintenance of shield be carried out.In electrical maintenance，the electrical switch should be disconnected，and the warning sign of“prohibiting closing”should be suspended.After the end of maintenance，the warning sign is confirmed by the electrician who suspends the warning sign and removes the warning sign to close the switch.High voltage electrical equipment maintenance should discharge first.Before the maintenance of the hydraulic system，the relevant valves must be closed and the pressure must be reduced to prevent the hydraulic cylinder from retracting and the accidental operation of the hydraulic motor.Hydraulic system maintenance must pay attention to cleaning，strictly prohibit the use of cotton yarn and other easy to wool articles cleaning pipe joint inner wall，grease bucket，pipe，etc.
（5）The maintenance of shield must first be familiar with its working principle and the relationship between electrical，hydraulic and mechanical，as well as the role of various parts in the equipment system，so as to solve the problem quickly and accurately.Equipment maintenance should follow the principle of“looking”first，“thinking”later，and“doing”again.When a machine fails，it is necessary to first see what fault is，and do not blindly do so，so as not to affect the maintenance speed or even expand the problem，and find the root of the problem before doing it.Equipment maintenance should be external and internal，such as in electrical maintenance，first check whether the wire is broken，broken，shedding and other obvious problems，often simple and obvious problems are most likely to be ignored.Do a good job of equipment fault handling records and summarize to improve the speed of similar fault handling.
（6）The daily maintenance and maintenance of equipment are also very important.Proper maintenance can reduce the failure rate of equipment，improve the service life of equipment，and increase production and efficiency.
（7）When the shield machine is suspended for a long time，necessary inspection and maintenance should be carried out，and the following work should be done：the storage site should be hardened，and there should be a roof for rain and sun protection.Apply grease on the joint surface exposed to air，attach it with felt and cover it with rainproof cloth.Regular lubrication maintenance.Winter to do a good job of cold and antifreeze.