Mechanistic Modeling of Cutterhead-Ground Engagement Influence on Microtunnel Boring Machine Penetration Rate

Abstract

Planning of a microtunneling project requires prediction of microtunnel boring machine (MTBM) performance. One of the main performance indicators of MTBMs is the penetration rate. The prediction of MTBM penetration rate is difficult due to the complex interaction between the cutterhead and soft ground. Although the engagement of the cutterhead with the ground highly influences the penetration rate, this phenomenon has not yet been thoroughly investigated from a mechanistic perspective. Hence, this research aims to analyze this phenomenon and develop a mechanistic model of MTBM penetration rate that considers the influence of cutterhead engagement with the ground. To study this interaction and evaluate its influence on MTBM penetration rate, this research proposes a novel approach based on the theory of contact mechanics and develops an analytical model that takes into consideration the area of engagement between the cutterhead and ground at the tunnel face. Through analytical analysis of MTBM engagement areas and in consideration of the largest and smallest engagement areas between the cutterhead and ground, upper and lower boundary models for MTBM penetration rate prediction are developed. Mechanistic modeling of engagement of the cutterhead with ground provides insight into its influence on the penetration rate of MTBMs and defines a relationship between the cutterhead engagement factor with other penetration rate influential factors (namely operational loads and soil properties), which enables engineers to improve the performance of MTBM excavation. Moreover, the development of penetration rate boundaries based on the amount of cutterhead engagement area can assist practitioners in reducing the uncertainty of penetration rate prediction. Analysis of a microtunneling project case study shows that the actual MTBM penetration rate lies between the upper and lower boundaries for the penetration rate as determined by the mechanistic model.