A computational scheme coupling PFC3D (Particle Flow Code in 3 Dimensions) and FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) was performed to investigate influences of sand conditioning on the tunneling behaviour of earth pressure balance (EPB) shield in sandy ground. A detailed EPB shield and its near ground were modelled in the PFC3D while the other ground was simulated in the FLAC3D. Decreasing friction coefficients were used to characterize the fluidity improvement of conditioned muck particles. The results indicate that the residence time of muck in the excavation chamber is associated with its position and rotation directions of the spoke. The muck pressure and its difference in front of and behind the cutterhead decrease with the improvement of conditioning degree in a certain conditioning range, and an appropriate soil conditioning scheme can facilitate the control of chamber pressure. In addition, the torque of cutterhead decreases more significantly than the thrust with an improvement of soil conditioning degree within a normal conditioning range.

Coupled Discrete Element–Finite Difference Method for Analysing Effects of Cohesionless Soil Conditioning on Tunneling Behaviour of EPB Shield

Apparent density evaluation methods to assess the effectiveness of soil conditioning

A Shear-Slip Mesh Update – Immersed Boundary Finite Element model for computational simulations of material transport in EPB tunnel boring machines

Influence of muck properties and chamber design on pressure distribution in EPB pressure chambers – Insights from computational flow simulations

Earth pressure balance tunnel boring machines (EPB TBMs) may sometimes face, during excavation of soft soils, with some challenges of which one of them occurs when mixture of the excavated soil and water generates a sticky muck that adheres to the metal sections of the TBM such as cutterhead, cutting tools and transportation system. This phenomenon commonly referred as clogging leading to blockages and stoppages that decrease the advance rate and increase the project costs, since the excavation process could only be continued after cleaning operation of the blocked parts. This study was conducted in Istanbul Akfirat Waste Water Tunnel to determine the effects of clogging and foam injection ratio (FIR) on the EPB TBM excavation performance (torque, EPB TBM thrust, specific energy, unit penetration rate and/or net cutting rate). The studied tunnel section was divided in three zones with respect to clogging behavior of soils such as high, medium and low clogging zones. Soil sample could only be collected from the tunnel face belonging to high clogging zone during excavation of the tail tunnel. Particle size distribution was analyzed and Atterberg limit tests were conducted on the soil sample. In order to investigate the consistency behavior of the soil sample, slump and flow table tests were performed with changing water contents. Flow table test was performed with two different anticlay foams to investigate the effect of soil conditioning on consistency behavior of the soil sample. Field observations indicated that increasing clogging potential decreased the overall performance (daily advance rates) due to muck transportation problems and frequent stoppages to clean up the clogged cutterhead. Increased FIR reduced the transportation problems and stoppages. However, data analysis indicated that increasing FIR did not improve the penetration rate for open mode (without face pressure) working conditions since the soil on the face was quite firm for the anticlay foam to penetrate into. The mean FIR values were measured three times higher for the high clogging zone than for the low clogging zone. The mean specific energy values for the low and medium clogging zones were almost the same and half of the value obtained during excavation of high clogging zone. The EPB TBM thrust and cutterhead torque values did not exhibit any correlation with adhesion potential.

Effect of Clogging on EPB TBM Performance: A Case Study in Akfirat Waste Water Tunnel, Turkey

This thesis examines excavation chamber pressure behavior within a 17.5 m diameter earth pressure balance tunnel boring machine (EPBM) used on the Alaskan Way viaduct replacement tunnel project in Seattle, Washington, USA. The study examines behavior during the first 150 rings of tunneling (10% of the project) through till and till-like deposits, granular soils, and cohesive silts and clays. A portable laboratory was established on the project site to characterize key properties of the muck as it came through the screw conveyor and onto the belt conveyor, namely, vane shear strength, density, slump, consistency and grain size distribution. Testing was performed on representative muck samples from a series of rings. Machine data, including excavation chamber pressures, screw conveyor pressures, soil conditioning inputs, and key operating parameters such as thrust, cutterhead and screw conveyor torque, cutterhead and screw conveyor rotation speeds, etc., were studied in great detail to determine what parameters influenced chamber pressures and how. The results of detailed EPBM data analysis supported with field lab test results from muck testing produced a number of key findings. Excavation chamber pressures measured by 12 pressure sensors varied up to 3 to 3.5 bar from crown to invert. Chamber pressures varied during ring mining and standstill, and the responses from different heights in the chamber were synchronous. Chamber pressure variations during excavation were influenced by changes in volumetric flow rates into the chamber via the cutterhead and out of the chamber via the screw conveyor. Increases/decreases in net volumetric inflow caused increases/decreases in chamber pressure. The magnitudes of pressure changes were linearly correlated to the net volumetric flow rate changes. A quantitative analysis of these data produced estimates of chamber material compressibility that could provide useful information in assessing the effectiveness of soil conditioning. An understanding of the role of cutterhead force on EPBM advance rate was developed. By estimating the change in cutterhead force (thrust force minus chamber pressure force), a relationship to advance rate was observed, i.e., increased cutterhead force increased the advance rate. The same was not true between thrust force and advance rate. The increases/decreases in chamber pressure mentioned above were also related to decreases/increases in cutterhead force through the mechanical concept of compressibility. Increases in chamber pressure resulting from material compression and stiffening means that the chamber soil takes on more of the force at the face (owing to relative stiffness increase). The cutterhead force therefore decreases. The behavior also works in reverse. The vertical gradients of chamber pressure provided significant insight into muck consistency and behavior. Magnitudes of gradients matched reasonably well with muck densities. Changes in gradient both locally and globally provide information about muck density under pressure and whether the…

Kamyar Mosavat

Papers

Examination of excavation chamber pressure behavior on a 17.5 m diameter earth pressure balance tunnel boring machine