Technical Review of the Lined Rock Cavern Concept and Design ...

Technical Review of the Lined Rock Cavern (LRC) Concept and Design Methodology 35
The probabilistic approach in the LRC design methodology is imbedded in the FLRC1
and FLRC2 models, which make use of Monte Carlo simulations to generate, for example,
a probabilistic distribution of rock-mass strength properties from a distribution of
rock index properties. Subsequently, a probabilistic distribution of steel-liner strain is
generated from simple models that use the stochastic input of rock mass properties and
conditions. The Monte Carlo method requires the entire probability density function of
each independent variable to be known initially. This is seldom the case. If assumed
functions are used, as the review documents indicate, the outcome (e.g., rock mass properties
or steel-liner strain) will be affected by the assumption!
One positive aspect of a probabilistic approach is that it provides an organized and disciplined
way of considering uncertainty (e.g., in the basic rock-mass properties) and its
affect on the response (e.g., steel-liner strain). However, in cases of sparse geophysical
data, it does not necessarily lead to a technically better or more economical design than
that obtained from traditional methods.
A reasonable check of the probabilistic prediction would be to perform a detailed design
analysis using a deterministic numerical model for credible lower-bound rock-mass properties
and conditions. The minimum acceptable result of this check would be a barely
adequate design.
6.0 CONCLUSIONS
The rock mechanics review of the Lined Rock-Cavern Storage Concept and Design
Methodology has focused on the feasibility of this technology, and the robustness of its
design methodology. The standard of the review has been the demonstrated principles of
designing large stable underground openings in rock. The conclusions that follow are
based on the design methodology’s adherence to these principles.
6.1 Summary and Observations of the Rock Mechanics Review
With some noted exceptions, the review documents convey the implementation of the
LRC concept as a carefully planned incremental design procedure. The procedure is implemented
in the two models FLRC1 and FLRC2, which use empirical relations and isotropic
and homogeneous analytical models to express the basic rock-mass conditions,
properties, and average mechanical response. Integrated with a probabilistic design approach,
the results of these models is a probabilistic distribution of the worst-point steelliner
response in terms of maximum strain and cyclic strain range.
Independent analyses of the concept were conducted using continuum and discontinuum
numerical models. These models show that a soil-anchor analogy, which is embedded in
limit equilibrium models for evaluating ground uplift, greatly oversimplifies the conditions
of potential uplift. The analogy and the LE models may not be well-suited to describe
the relatively complex rock-mass response from a pressurized LRC. Continuum