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A Numerical Analysis of Non-destructive Tests for the Maintenance and Assessment of Corrosion of Rockbolts and Rock Anchors

Ö. Aydan
Tokai University, Dept. of Marine Civil Engineering, Shizuoka, Japan
S. Tsuchiyama, T. Kinbara, F. Uehara
Chubu Electric Power Company, Nagoya, Japan
N. Tokashiki
Ryukyu University, Faculty of Engineering, Okinawa, Japan
T. Kawamoto
Nagoya University, Faculty of Engineering, Emeritus Professor, Nagoya, Japan

Keywords: underground, powerhouse, corrosion, assessment, rockbolt, rockanchor

ABSTRACT: The assessment of support systems such as rockbolts and rock anchors are very important for the maintenance of existing rock-engineering structures. The utilization of non-destructive tests is preferable to destructive tests such as pullout tests. The dynamic responses of rock anchors and rockbolts could be used for non-destructive tests. These tests should generally provide some information on the constructional conditions, corrosion and axial force conditions. In the first part of this study, some theoretical models are developed for the axial and trasverse dynamic tests and then results of numerical simulations are presented by considering possible conditions in-situ. These conditions are the bonding quality, the existence of corroded parts or couplers and pre-stress. The results of the numerical simulations could be very valuable for interpretation of the wave responses to be measured in non-destructive dynamic tests in-situ.

  • Introduction
Rockbolts and rock anchors are commonly used as support members in underground and surface excavations. They are generally made of steel, which is resistant against corrosion. Nevertheless, the geo-environmental conditions imposed on rockbolts and rock anchors may be very adverse and they may cause some corrosion in a short period of time. While rockbolts are generally made of steel bars, rock anchors may be either high-strength steel bar or cables consisting of several wires. Since the surface area of cable rock anchors are much larger they are much more prone to corrosion as compared with steel bars. The maintenance of existing rock engineering structures such as underground powerhouses, dams and slopesrequires the re-assessment of support members. Although in-situ pullout tests would be the best option to assess the state of the rockbolts and rock anchors, the cost is quite high and the labourship is tremendous to perform such tests. Furthermore, they may require re-installation of rockbolts and rock anchors if they are pulled-out or broken. Therefore, the use of non-destructive tests is desirable in view of the cost and labourship. Although there are several attempts to assess the state of support members, it is very difficult to say that such techniques are satisfactory for practical purposes. Furthermore, the structural part to be used during the non-destructive tests is quite limited as compared with the overall size of the support system. The authors have been now attempting to develop a non-destructive assessment system for rock anchors and rockbolts. Since the structural part to be used during the non-destructive tests is quite limited, it will be necessary to utilize the numerical techniques to study the fundamental features of the expected responses, which may be used for the interpretation of measured responses in-situ non-destructive tests. With this in mind, some theoretical models are developed for the axial and traverse dynamic tests and then numerical simulations are carried out based on these fundamental equations by considering possible conditions in-situ. Specifically, the bonding quality, the existence of corroded parts or couplers and pre-stress are simulated through numerical experiments. The results of the numerical simulations are then used if the interpretation of the dynamic responses to be measured in non-destructive dynamic tests in-situ is possible or not.


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