4.3.3 Mud Management
During shield tunneling，slurry must be injected into the stratum to form a dense mud film on the surface of the excavation face.The mud pressure acts on the mud film to balance the water and soil pressure in the stratum，so as to maintain the stability of the excavation face.Therefore，there are higher requirements for the quality of mud and mud film in the construction.The stratum of the middle section of the river crossing by slurry shield is generally complex.According to different geological conditions，the corresponding mud is used to ensure the safe and efficient tunneling of the shield.If there is a serious mud filtration in the construction，the excavation face is difficult to form a mud film and the instability of the accident，it will produce large ground disturbance，endanger the stability of surrounding embankments and other buildings，and increase the risk of river crossing.Therefore，the slurry management should be strengthened in the construction process，and the slurry properties should be adjusted according to the permeability of the surrounding strata in order to maintain the balance between the slurry tank pressure and the water and soil pressure of the excavation face.
1）Mud transport system work management
The mud conveying system consists of slurry pump，slurry pump，flow meter，control gate valve，slurry pipeline and ground mud separation system.The slurry transportation system mixes the excavated slag soil with slurry and then transports it to the ground through the slurry pump and slurry pipeline for slurry separation.The separated slurry is transported back to the slurry tank by the slurry inlet pump and slurry inlet pipeline for recycling.The configuration principle of slurry pump and pipeline is that the slurry flow rate in the pipeline is not less than 4 m/s，and the maximum flow rate is not greater than the flow rate when the pump efficiency is 70％.Reasonable distribution of mud tank slurry flow，close to 60％of the total flow of the mud circulation system is appropriate.
2）Work management of mud pressure regulation system
Mud pressure needs to balance groundwater pressure and soil pressure.The value of soil pressure has different calculation modes.When the thickness of the overburden above the tunnel（soft clay or sand and other soft strata）is less than the diameter of the tunnel excavation，the soil pressure is calculated by the formula of static earth pressure or active earth pressure.When the thickness of overburden layer（sand layer，gravel layer and hard clay layer）is larger than the diameter of tunnel excavation，the soil pressure can be calculated by the height of Tyzaghi loose soil due to the arching effect of strata.The automatic control system can automatically adjust the pumping pressure of mud pump according to the real-time monitoring data to balance the short-term fluctuation of mud pressure.However，the actual construction should be adjusted at any time according to the influence of surface buildings such as embankments above the tunnel.
3）Slurry treatment system work management
The index values of mud include density，sand content，viscosity，yield value，gel strength，filtration rate，pH value and so on.The index values of mud required for forming mud film on the palm surface of different formations are also different.The application range of each index calibration must be determined by targeted film forming test.In order to strengthen the supporting capacity of the front soil and prevent the ground slurry from falling，heavy slurry propulsion should be adopted.The specific gravity of slurry inlet was controlled at 1.15-1.20，and the viscosity was controlled at 2-25 s.The slurry was modulated by high-quality bentonite combined with different levels of macromolecular materials and new materials assembled by original plant fibers and inert minerals.As the excavated residual soil continuously enters the slurry tank，the slurry index value in the slurry tank will change greatly.In order to maintain the basic stability of the slurry properties，the residual soil entering the slurry system must be removed，and the removal of slag and mud is completed by the slurry treatment system.In order to ensure the quality of mud，the mud treatment personnel should increase the test frequency of mud and adjust the mud parameters in time to ensure the smooth progress of excavation.
4）Slurry quenching and tempering system work management
The remaining mud after treatment by the slurry separation device enters the mud treatment pool.The site laboratory samples and tests the slurry of the treatment pool，obtains the actual index value of the mud composition，and compares it with the calibration index value.If the test results show that the density is too high，a part of high density slurry must be discarded to the sedimentation tank for sludge removal.The high density mud can be diluted by adding fresh water or low density bentonite slurry to the mud of the treatment pond after some space is released.If other indicators of the slurry cannot meet the requirements，fine sand，carboxymethyl cellulose（CMC），polyacrylamide（PAA）and other additives can be selectively added to the slurry of the treatment tank to adjust and improve the slurry properties，and then the slurry is pumped back to the slurry tank and air cushion tank of the shield for recycling.