To solve the problem concerning the safety of the rock foundation of the arch dam being designed in one of the countries of South-East Asia, field tests have been carried out dealing with rocks weakened by weathering and forming the main area of construction. Aleurolites and quartz sandstones of medium stratification were subjected to the tests.
Rocks in the gallery, where aleurolites were tested, are presented by a thick layer of diluvial formations which at a distance of about 30m from the portal are replaced by aleurolites through a vague contact. Aleurolites in their weathered part have a distinct horizontal stratification with the alternation of finely-and medium-stratified grey sandstones. Besides the stratification cracks crosscutting cracks in vertical and oblique directions were observed in the aleurolites. The cracks are filled with a sandy-clayish material sitilar to aleurolites in composition. The crack width varies between 0.002 and 0.05m.
Rocks in the gallery, where sandstones were tested, are characterized by the presence of deep cracks. The degree of rock crushing is so significant that they have lost their solidity and have an aspect of disconnected stratifications of blocks with a high content of voids. The cracks are, on the average, within 0.02–0.05 m wide. At some places, the cracks remain free of the filler and form voids. The general direction of the rock stratification is a horizontal one; it coin coincides with the aleurolites stratification and does not change all the way along.
To test each of the above mentioned types of rocks, in the galleries testing chambers were established, where were placed the reinforced concrete stamps of 1.0×1.0m, in plan view and of 0.6m in height. To eliminate the stamps interaction they were placed at a distance of at least 1.2m. This fact and the number of the stamps defined the testing chambers' length. To avoid the disturbance of the tested ground by explosions the cutting of the chambers was carried out by firing of small holes with successive treatment of the ground by pick-hammers.
As a stop for the transmission to the stamps of compressive load served the roof of the testing chamber. On the roof over each stamp the reinforced concrete thrust blocks were installed. They were secured on the roof of the gallery by anchors. The testing assembly was composed of three metallic slabs, a support and four hydraulic jacks. The settling of the stamps at the test was registered by measurers attached by the holders to the frame isolated from the load effect. Measurers were set against the metallic inserts built in the stamps. To reveal the skewing of the stamps in the test procedure, readings of six measurers were taken simultaneously. These measurers were fixed on the face of the lateral sides of the stamp (2 measurers on each side) and on the face of its front side.
The tests were carried out in cycles of incresing loads, each cycle being 0.25 and 0.50 MPa up to considerable displacements of the stamp.
