ABSTRACT:

A design of the roller compacted concrete dam, 85 m high with a crest length of 705 m, was carried out to provide flood storage on the lower reaches of the Imjin river. The alluvium layer between gneiss and basalt rock masses, varying from fine silty clay to cobbles mixed with sandy-clay particles, is compressed by the overburden rock mass. The magnitude of the in-situ horizontal stresses were measured, using hydraulic fracturing method, and found to be higher than the overburden stress. Two different grouting techniques were carried out in the field and the test results suggest that for the rock masses both methods improve the deformation modulus. MSG (micro-silica grout) performs better than OPC (ordinary Portland cement) grouting. Both methods with low injection pressure appear inappropriate for the foundation treatment in the alluvium layer due to the presence of a wide range of particle size. Groutability was identified with core recovery, a borehole camera, a borehole elastometer test, and monitoring of the grouting injection pressure, respectively. For porous and massive rock mass the effect of grouting on the foundation stability appears to improve, but it is relatively small for the alluvium layer identified with fine to coarse material mixtures.

INTRODUCTION

By the end of 2001 there were 232 completed Roller Compacted Concrete (RCC) dams throughout the world with additional 31 under construction [1]. There are many advantages to RCC mix materials. Among them are that RCC does not utilize artificial postcooling, reducing the total amount of cementitious material by substituting a greater percentage of fly ash for cement, and quick construction [2].

The RCC is placed in lifts up to one meter thick, usually spread in approximately six layers each of which is semi-compacted by bulldozers. The final lift is compacted using a vibrating roller. After completion of the lift, the RCC is left for three days or more, the surface is green cut and mortar is spread over the whole surface. The dam is split into a number of sections ranging from 30 m to 60 m in width. The sections are constructed of lifts between the formwork. Within a section contraction joints are cut at 15-m centers. A large number of publications can be found that deal with RCC materials and dam construction [2, 3].

In this paper, an 85 m high gravity dam with a crest length of 705 m was proposed for a Hantan-river (Hantan-gang) dam. It would provide flood storage on the lower reaches of the Imjin river, a major tributary of the Hantan-river. The dam site is located approximately 70 km north of Seoul, Korea. The main higher section of the dam on the left abutment fills the existing steep-side river valley, 250 m wide at dam crest level. The remaining 450 m consists of a section 25 m high above existing ground level across a high-level terrace on the dam right abutment.

The dam body was proposed to contain flood control gates, sedimentation outlets, grouting and drainage galleries, a gated spillway over the dam crest, and environment-friendly fishway channel in the dam body. The dam consists of two main overflow and non-overflow sections for the right and the left abutments (Fig. 1).

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