Comparison between CSM and NTH hard rock TBM performance pre

COMPARISON BETWEEN CSM AND NTH

HARD ROCK TBM PERFORMANCE PREDICTION MODELS

By:

1Jamal Rostami, Levent Ozdemir1, and Bjorn Nilson2

1.Excavation Engineering and Earth Mechanics Institute

Department of Mining Engineering

Colorado School of Mines

Golden, Colorado, USA.

2. Dept. of Geology and Mineral Resources Engineering,

University of Trondheim

The Norwegian Institute of Technology

ABSTRACT

The important issues related to the performance and cost estimation of hard rock Tunnel Boring Machines (TBM) are presented and discussed in this paper. General approaches for performance prediction of TBM, which is one of the most popular mechanical excavators are addressed. Two of the most successful performance prediction models, namely the Colorado School of Mines (CSM) and the Norwegian Institute of Technology (NTH) models and their most recent modifications, improvements, and some recent applications are presented. A comparison is made between the results of both models in two tunneling projects.

1. INTRODUCTION.

TBMs are currently utilized in massive scale in underground construction and tunneling both in civil construction and the mining industry. In the recent years, along with the advancement of the machine manufacturing in many aspects, and rapid advances in technology as a whole, specially information and computer technologies, powerful and somewhat smart machines have been introduced in the market. These machines have generally increased productivity and set new excavation footage records. In spite of all these advancements, there seems to be a lack of complete understanding of the rock cutting process due to the very complex nature of the problem. As a result, not all the

parameters affecting the rock cuttability and hence machine performance in the field are identified and their effects fully explored.

Over the years, several researches have been conducted and models developed for performance prediction of mechanical excavators. In a nut shell, they can be pided into two distinguished approaches. One is based on the cutting forces acting on the inpidual cutters and the other is based on the achieved performance of the machine in the field as a whole system. Each one of these approaches has its own set of advantages and disadvantages, and similarly slightly different area of application.

Table 1. contains some information about the field of application as well as the area of strength and weaknesses of these models. As can be seen, both systems have evolved to a certain level of maturity and reliability, and as will be shown later in this paper. They produce fairly close estimates on machine performance. It must be noted that this paper will be equally applicable to performance prediction of all full face machines.

2. EMPIRICAL PREDICTION METHODS, NTH METHOD

Empirical performance prediction methods are based on the historical field performance of machines in certain rock types. Typically, the models are a set of empirical graphs and equations obtained from the regression analysis between rock properties, ground conditions, machine parameters, and rates of penetration. The main significance of these methods is the fact that they naturally incorporate the effects of the ground and the excavation system as a whole in their entire complexity. This means that all the effects of ground conditions, rock properties, machine parameters, and operational and practical constraints have already been accounted for. The estimates made by these methods are more easily accepted by the operators and, within the realm of current technology, are very reliable. Meanwhile, since these methods rely heavily on the past data, their forecasting capabilities are somewhat limited by the similarity of the old and the new systems. In other words, with the speedy progression of machine technology and capabilities, the predicting ability of these models are limited.

Table 1. Summary of issues related to the two approaches to performance predictions systems. Methodologies Force Empirical

Equilibrium Methods **

Issues Approach* Notes Cutter Forces Yes No

Cutter Geometry (type, shape, etc.) Yes No

Cutting Geometry (spacing & penetration) Yes Partially

Machine Design Issues Yes Partially

Face Layout Yes No

Diagnostics and Design Modifications Yes No

Adaptability and the Ability to Develop Yes Very Limited

New Technologies

Ability to Exchange Information Yes No

Between Different Excavation Systems

Rock Strength and Physical Properties Yes Partially

Rock Property Indices Partially Yes

Ground Conditions Indirect Yes

Rock Mass Properties (joints, faults etc.) Indirect Yes

Performance Prediction Yes Yes

Cutter Cost Estimation Yes Yes

No Some Operator Sensitivity / Judgment

Based on inpidual cutter forces ** Based on Field Performance

Some of the most referenced methods in this group are the NTH or Norwegian method (Listrud 1988, NTH 1995, Bruland et. al. 1995.), Total Hardness method (Tarkoy 1975), and Nelson’s method (Nelson et. al. 1985). Among the above mentioned methods, the NTH method is more widely accepted and used in the industry, specially in the Europe. This method has good merits, proven to be very reliable, and being up dated frequently through the time. The model was originated with the start of the tunnel boring operations in Norway, and was continuously upgraded as more projects were completed.

The NTH model uses a group of rock parameters and indices, which were originally developed for drillability of the hard Nordic rocks. These parameters were later tied into

Table 2. Parameters used by NTH Model.

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