4.3.1 Control of Excavation Parameters
When crossing the embankment during the construction of the slurry shield，due to the complicated conditions of the stratum under the river，it is necessary to take corresponding measures strictly control the shield tunneling parameters to prevent deformation of the protection levees caused by shield tunneling and ensure construction safety.
1）Cutting water pressure control
The setting of the cut slurry pressure is the key to control the water-soil pressure balance of the excavation surface.Due to the shallow overburden at the top of the shield during the construction of the river bottom，it is more difficult to control the cut water pressure.If the incision water pressure fluctuates too much，it will increase the disturbance of the front soil，leading to the loss of the front soil，and the excavation face is difficult to maintain stability.Therefore，the fluctuation of incision water pressure should be reduced as much as possible.In technology，the operator is required to change from automatic control to manual control，adjust the construction parameters in real time，and control the fluctuation value of incision water pressure between±20 kPa to ensure the stability of soil.In the actual construction process，the mud pressure value of the incision should be adjusted in time according to the monitoring information.
2）Shield attitude control
Good shield attitude control ensures uniform force on the segments and avoids uneven or uneven pressure on the segments damaged.At the same time，it can reduce over-excavation and construction disturbance，reduce settlement loss and disturb soil consolidation settlement.Poor attitude control of the shield will not only increase the building void and stratum disturbance，but also increase the displacement of the stratum，and will cause the tube to break due to the extrusion of the segment，reduce the assembly quality of the segment and increase the difficulty of assembling the segment.Therefore，the control of the shield attitude should be strengthened during the advancement process.Once the shield posture is found to be poor，measures should be taken immediately.
In order to avoid excessive deflection of the shield during construction，the cutter head torque can be appropriately reduced under the premise of ensuring smooth excavation of the excavation surface，and the cutter disc rotation should be alternated clockwise and counter clockwise.Once the shield is found to be deflected too large in one direction，the cutter head in this direction to correct the shield deflection.Once the lateral offset of the shield is found to be too large or the“head”and“head lift”are too large during construction，the adjustment jack should be used to correct the deviation，and the simultaneous grouting management should be strengthened to ensure the grouting effect，so that the looped tunnel remains stable and the correction is improved.
When the shield enters the influence range of the flood dike，the shield operation management should be strengthened to maintain the smooth advancement in the excavation process，reduce the deviation correction，reduce the shield deflection and lateral deviation，prevent the occurrence of snake，reduce the disturbance to the front soil，and maintain the stability of the stratum.The plane position is controlled within±50 mm，and the elevation is controlled around-50 mm when crossing the breakwater，considering the shallow overburden and the drift of shield.Shield tunneling speed is controlled at about 15 mm/min to prevent large impact on the front soil due to too fast tunneling speed.
3）Other major driving parameters
Excavation speed，cutter torque，mud discharge and cutter thrust have certain influence on construction.In order to reduce pressure fluctuation，low speed uniform propulsion is used in construction.On the premise of ensuring the smooth excavation of the excavation face，properly reducing the torque of the cutter head can reduce the disturbance of the cutter head rotation on the surrounding strata and the wear of the cutter head，and reduce the deflection of the shield，thereby reducing the circumferential friction between the shield shell and the surrounding soil layer.Strengthening mud management and monitoring of excavated volume can prevent formation disturbance caused by overbreak and underbreak.The thrust of the cutter head，i.e.the force of the cutter head supporting the excavation face，is one of the important factors to maintain the stability of the excavation face，and its value is still a difficult problem internationally.Usually in the construction process of the incision pressure setting is not taken into account，only as a safety reserve.In fact，in the process of tunneling，the supporting effect of cutterhead on the excavation surface cannot be ignored.It is of great significance to play the supporting role of cutterhead in maintaining the stability of excavation face to reduce the disturbance of soil.The shield tunneling parameters interact with each other，and each tunneling parameter should be coordinated，which not only reduces the formation loss，but also reduces the construction disturbance and reduces the long-term consolidation of disturbed soil.