# Criteria for Cutting Head Clogging Occurrence during Slurry Shield Tunneling
## 1 Introduction
(2016) [12] investigated the effects of slurry on the stickiness of excavated clays of the slurry shield tunneling, and found the stickiness of the excavated soil correlated with the shear resistance of the slurry. As a result, increased slurry strength, while beneficial for excavations in coarse soils, may increase susceptibility to clogging under mixed face conditions. [PERSON] et al. (2017) [13] investigated the adhesion potential of kaolinite and montmorillonite using pull-out tests, and the results revealed differences between minerals concerning adhesion value and behavior because of their differences in the microstructural properties and dominant sticking mechanism of each clay mineral. [PERSON] and [PERSON] (2017) [3] conducted experiments to analyze the influence of two elements, i.e., the pore water tension (suction) of the soil and the permeability of the soil, on the adhesion of cohesive soils to solid surfaces, and presented the results of adhesion tests and pore water tension measurements during the adhesion tests. [PERSON] et al. (2018) [2] provided a state of the art report on the clogging potential of tunneling machines, and existing research work on mechanisms of clogging, factors affecting the soil adhesion to a steel surface, laboratory tests to assess clogging potential, clogging potential diagrams, and mitigation and countermeasures were well summarized. [PERSON] et al. (2018) [14] indicated that the initial water content, the roughness of shear plate, and the percentage of additives have a significant effect on clogging potential, and an empirical diagram to understand the clogging potential by relating the clogging potential to soil properties was also plotted. The occurrence of the cutting head clogging is closely related to the physical and mechanical properties of the soils in the cutting face. However, the soils encountered in each cycling of the soil cutting and segment assembly of the close face shield tunneling cannot often be determined beforehand due to the irregular changes of the natural ground. The methodology for evaluating clogging potential relying only on the soil types is sometimes unrealistic and impractical. The clogging effect continues to be a serious issue in tunnels construction in clayey soils because the current criteria for evaluating clogging occurrence have proven to be only partially effective due to the unknown soils and unknown properties of the soils. Notwithstanding, once cutting head clogging happens, the shield machine performance parameters such as cutter head torque, total thrust, advance rate, etc., will experience rapid changes. Usually, the cutting head torque and the total thrust of the machine increase, and the advance rate and the penetration depth per revolution decrease. Therefore, establishing criteria for cutting head clogging during soft ground shield tunneling based on the machine's main driving parameters is feasible and of great engineering significance. This approach for evaluating cutting head clogging based on the key shield machine performance parameters is validated in three shield tunneling projects. Figure 1 shows the geological map where the three shield tunnel cases are located.