Mechanics of tunnelling machine screw conveyors: model tests

Abstract

Control of the excavation process of an earth pressure balance (EPB) tunnelling machine depends on control of the soil flow through the screw conveyor. An instrumented 1:10 scale model screw conveyor was designed and commissioned, and tests were performed with consolidated kaolin and compacted London Clay and Lambeth Group samples pre-conditioned with soil conditioning agents commonly used in EPB tunnelling machines. During steady-state operation, the measured shear stress acting on the conveyor casing was found to be constant along the conveyor, leading to a linear total pressure gradient. The casing shear stress was approximately equal to the un-drained shear strength of the soil, and the screw torque increased linearly with the casing shear stress. Effects of varying sample strengths, screw speeds, screw geometry and the discharge outlet restriction on the total pressure gradient, casing shear stress, and screw torque are illustrated by the test results. The tests provide new insight into the behaviour of soil flow through screw conveyors.

Adaptability to stratum characteristics for layout of thrust system in tunneling machines based on variation coefficient

“…In the tunneling process, rotating cutters fixed on the cutterhead excavate the soil, which, in turn, passes into a pressurized head chamber; the whole machine is then pushed by hydraulic cylinders with a thrust system that applies pressure on the segments. 3,4 A screw conveyor removes the excavated soil from the head chamber. Among the three principal subsystems-cutting system, thrust system, and lining system-the thrust system plays the most important role in the shield machine.…”

An evaluation of fine grained sedimentary materials in terms of geotechnical parameters which define and control excavation performance of EPB TBM’s

“…Yoshikawa (1996) performed full scale tests on plastic soils with different screw speeds, Bezuijen et al (1999) performed full scale and small scale screw conveyor test in order to investigate the behavior of conditioned soils. The research conducted with collaboration of Oxford and Cambridge Universities focused on the effect of soil conditioning on the operational parameters of screw conveyor (Pena, 2003;Mair et al, 2003;Merritt and Mair, 2006). A 1/10 scale screw conveyor developed in Politecnico di Torino University to test extraction of conditioned soil from a pressurized tank and studies targeted on the torque and pressure distribution along the screw conveyor Peila et al (2007), Vinai et al (2008) and, Borio and Peila (2011).…”

Analysis of the carrying capacity of the propelling mechanism of tunneling machines

“…During the excavation process, the rotating cutter excavates the soil that passes into the pressurized head chamber. The machine is then advanced by jacks on the propelling mechanism that applies pressure on the segments [6][7][8]. The screw conveyor removes the excavated soil from the head chamber.…”