Three factors should be considered for foundation rocks of gravity dams,

  1. strength

  2. deformability,

  3. permiability.

Necessary degrees of these factors will be different with the magnitude of loads or hydraulic Pressures. Necessary strength of rocks is different with the height of the dam. In other words, foundation rocks for lover dams, those for lover blocks, need only lover strength. However, necessary impermeability of foundation rocks does not always have renear relationship with the height of blocks. It will come from phenomena like as piping. Moreover, foundation rocks should have toleable uniformity because the design method of gravity dams is based on the uniform foundation in principle.

The foundation rocks of higher abutment a Hitokura Dam are weathered thickly. Although they satisfy necessary strength in related with height of blocks, impermeability and deformability of these rocks are questionable with sound rocks. Grouting tests for consolidation grouting at proper sites were performed in order to confirm the degree of improvement by grouting.

The effectiveness of improvement by consolidation grouting were estimated by following tests,

  1. water tests,

  2. bore hole lateral load tests,

  3. densimetry with RI tests,

  4. observation of the ground water lebel, for estimating degree of improvement, and

  5. measurements of upward movement of foundation rocks, for estimating movement of foundation rocks during grouting tests. Descriptions of the fifth item are leaved out in this paper.


Major rock types of the damsite are sandstone, slate and their alternate of Paleozoic and other rocks interpenetrate in some places. There are some small faults, and weathered rocks become thicker in proportion to the elevation of the valley.

Location of the test area

Location of the test area vas selected at an abutment of higher elevation at damsite because degree and thickness of weathered rocks fit purposes of the tests, and overburden had already excavated.

Kinds of tests

Measurements of bore hole lateral load tests' densimetry with RI tests and observation of the ground water lebel were performed supprementaly adding to basic grouting tests in order to obtain good estimation of improvement for foundation rocks. The location map of test holes is shown in fig. 1.

Grouting tests
Pattern and stage

Evely holes were drilled in vertical direction, and the description of the pattern are as follows, length of respective stage:4m numbers of stages per a hole:3 stages numbers of holes:10 holes.


Grouting tests were performed by the stage method of 4m in principle according to the following flow, Drilling→ Water test→ Grouting test.


Every holes were drilled with rotary type drills using 46mm size for holes of grouting tests, 66mm size for holes of measurements of bore hole lateral load tests and densimetry with RI tests.

Water test

Water tests were performed in order to check effects of grouting according to the following standards.

1. Checking effects of grouting: Effects of grouting were checked by water tests of the holes of next order.

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