Abstract
Passive rock bolts are commonly used to anchor concrete dams, and they may have a significant impact on stability-evaluations. However, these bolts are often omitted from dam safety analysis due to uncertainties regarding their condition and the size of displacements required in the dam-rock interface to mobilize significant bearing forces in the passive rock bolts. This paper address the latter question by studying the failure process of a small concrete dam anchored with rock bolts. Failure simulations were performed with the increased density method in a finite element model consisting of a dam, the corresponding part of the rock and rock bolts. Two types of approaches are used to simulate the anchorage of the rock bolts; a method where the anchorage to the rock is simulated using a fixed boundary condition; and a method where the anchoring of the bolts are modelled using springs. Depending on the method of analysis, the rock bolts contribute with 40–75% of the load-carrying capacity of the dam. The rock bolts increase the load-bearing capacity of the dam, partly through anchorage forces, but also by keeping the contact surface between rock and concrete together and thereby increase the shear capacity of the interface.
Highlights
Passive rock bolts are commonly used to anchor concrete dams, and they may have a significant impact on stability-evaluations
This paper aims to highlight the influence of rock bolts on the global dam safety and to present a methodology for including rock-bolts in FE-simulations, that can be adapted by dam engineers to different types of concrete dams
To study how rock bolts affect the failure process of a small concrete dam, the research in this paper was performed as a case study, where one monolith from an 8 m high buttress dam in northern Sweden was used as the studied object
Summary
Passive rock bolts are commonly used to anchor concrete dams, and they may have a significant impact on stability-evaluations. From a dam safety perspective, there are two major concerns with such bolts. It is not possible to determine the structural status of rock bolts due to their inaccessible placement [1]. This leads to large uncertainties regarding the strength of the bolts. The second concern is the failure process of a dam anchored with passive rock bolts that remain unloaded until movement occurs in the joint. For rock bolts under concrete dams, this means that a displacement of the dam must take place before the bolts are activated
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