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This paper presents the results of plate loading test and discontinuum analysis, carried out to study the deformation behaviour and determine the deformation modulus of metamorphosed andesitic tuff found at the site of a underground oil storage facility in Korea. In the plate loading test, the maximum pressure of 14 MPa was applied to the bedrock, using a flat jack (1m in diameter) and the rock anchor system for the reaction against the applied pressure. The values of deformation modulus obtained from this test were compared with those of laboratory test, biaxial test and pressuremeter test. Discontinuum analysis was performed to study the influence of discontinuities on in-situ modulus by simulating the presence of joints and the calcite seam at the test area.
A correct estimation of the deformability of rock mass is essential to the design of various underground excavations. The plate loading test, an effective method determining the deformability of rock mass, is generally performed in a test adit or small tunnel in order to utilize restraint steel columns to secure the reaction against the applied loading. However, the plate loading test described in this paper was carried out in a large tunnel, using the rock anchor system for the reaction against the applied pressure. The modulus obtained from this test was compared with those from laboratory test, biaxial test and pressuremeter test. Discontinuum analysis using Universal Distinct Element Code (UDEC) was performed to study the influence of discontinuities on in-situ modulus and estimate mass modulus by simulating the presence of joints and the calcite seam at the test area.
The underground facility for oil storage at the test site is mainly composed of six storage caverns, construction tunnels, two shafts and water curtain tunnels, as shown in Figure 1. (Lee et al, 1995). Six storage caverns, to be left unlined at EL.(-)30~ EL.(-)60 m, are aligned parallel to each other in the direction of N 80° W and each of these caverns has horseshoe shape and its dimension is 18 m wide, 30 m high and 400 ~ 600 m long. The construction tunnel has also horseshoe shape and the dimension of 8 m wide and 7.5 m high. The tunnel elevation changes from EL.(+)10.0 m at the entry to EL.(-)60.0 m at the bottom level of cavern with about 12% slope in between these two levels. The bedrock at the site area is metamorphosed andesitic tuff of the Late Cretaceous Period. The tuff is dark grey colored and very tight and has welding texture at the boundary of rock fragments as a thermo metamorphic evidence. There are three joint sets (N70-80E/70-80NW, N10E/70-80SE and N45W/20SW) and random joints in the bedrock. 3
Plate loading test was carried out at the bottom of one of construction tunnels, as shown in Figure 1. Most of these joints were mainly tightly-healed, but two joints were coated or filled with calcite.
