4.4 Embankment Deformation Monitoring and Reinforc...
Although shield tunnel construction technology has little impact on the surrounding environment，it is affected by geological conditions and human factors.In the process of construction，it will inevitably disturb the soil，cause surface subsidence，and then leave some security risks to the construction.When shield passes through embankments，ground buildings，underground pipelines and other areas，the control requirements of surface subsidence and deformation caused by construction are very high.If the construction method is slightly wrong，it will cause immeasurable losses.Therefore，in order to control the ground settlement during the shield tunnel construction，the construction personnel often monitor the ground settlement during the construction period，and reinforce it if necessary.In order to ensure the safety of subway construction，it is necessary for relevant units to study the surface settlement monitoring during the construction of subway shield tunnels.When the embankment buildings are deformed，timely reinforcement is carried out，so as to better complete the tunnel construction.
Taking the construction of the flood control embankment of the north bank of the Yangtze River at RK3+73.7 in Nanjing Yangtze River Tunnel as an example to introduce the monitoring of embankment deformation with reinforcement technology.
The flood dike of the Yangtze River is an important flood control project，and the protection level is set to be level two.When the shield passes，it must be ensured that the flood dike is infallible.The position relationship between the Yangtze River flood dike and the shield tunnel is shown in Fig.4.24.When the shield passes through the Yangtze River embankment twice，the stratum at Pukou Pass is muddy silty clay stratum.The construction time was selected in March 2008，belonging to the dry season of the Yangtze River.When the shield crosses the Yangtze River embankment，the shield tunneling face is prone to instability，resulting in stratum collapse，which leads to the collapse of the embankment，and the river water gushing endangers the life and property safety of the nearby masses.Shield tunneling may also be due to excessive mud pressure breakdown of the overburden，resulting in river water from the tail of the shield seal or segment waterproof weak position into the tunnel，pose a threat to construction personnel and equipment.Due to the high flood control level of the embankment，the surface settlement control requirements must be controlled at+10 to-30 mm.Moreover，due to the obvious change in the thickness of the ground cover，it is difficult to control the technical parameters of shield tunneling construction.
Fig.4.24 Position relationship between shield tunnel and Yangtze flood control levee
（1）The initial crossing of the Yangtze River embankment section mainly consists of 4 layers of silty silty clay and 6 layers of silty clay with silt，7-2 layer of silt.
（2）The maximum risk of crossing the Yangtze River Dike is k3+738～k3+78.The cover soil in this area is increased rapidly and shallow，and the shield tail is still in shallow soil.The difference between the incision and the pressure of the shield tail water and soil is large，which can easily lead to the settlement of the embankment at the excavation surface or the roof of the shield tail，endangering the safety of the flood control embankment.