Mechanics of tunnelling machine screw conveyors: a theoretical model

A new theoretical model describing the total pressure gradient and torque in a tunnelling machine screw conveyor is proposed. The theory develops new equations relating the pressure gradient and torque to the screw geometry, the shear stresses acting in the screw conveyor, and the material flow. The equations are expressed in dimensionless form, allowing application to screw conveyors of different scales. The theory is validated against measurements from laboratory model screw conveyor tests with clay soils with varying properties and operating conditions. The theory successfully describes key features of the observed mechanics of the model conveyor operation, and accurately predicts the test measurements. The proposed theory provides insight into the fundamental mechanics of screw conveyor operations, and can be used in the design of tunnelling machine screw conveyors. The theory can also be applied to other forms of screw conveyors and extruders operating with plastic materials.