In Japan a bedrock classification method is used to reflect the bedrock mechanical property data obtained from the in situ tests at the design stage. In the present state of the art, however, the results of bedrock tests conducted for the same bedrock classification often vary. This paper analyzes in situ bedrock shearing test data obtained from a number of dam sites in Japan to determine the causes of the variations in the test data and to study the relationships between the bedrock classification of the dam foundation and those strength characteristics. This paper also discusses the procedures for conducting the in situ tests.
Au Japon, une methode de classification des roches utilise les caracteristiques mecaniques des roches. Les donnees sont obtenues in situ au stade de la conception des travaux. Cependant, jusqu'à present, les resultats de ces essais. effectues pour une même classification de roche, varient souvent entre eux. Cette communication analyse les donnees d'essais de cisaillement obtenues in situ à plusieurs emplacements de barrages au Japon afin de preciser les causes des variations des donnees d'essais et d'etudier les rapports entre la classification de la roche d'une fondation de barrage donnee et les caracteristiques de resistance au cisaillement. On examine egalement les procedes de realisation des essais in situ.
In Japan wird eine bestimmte Klassifikationsmethode des Gebirges von Staumauergruendungen benuetzt, in die die mechanischen Eigenschaften des Gruendungsfelsens entsprechend den in der Entwurfsphase durchgefuehrten in-situ Versuchen eingeht. Der gegenwartige Kenntnisstand ist jedoch noch unbefriedigend, da haufig verschiedenartige in-situ Versuchsergebnisse mit einer gleichen Gebirgsklassiftzierungsguete verbunden sind. In vorliegender Arbeit werden Gebirgsscherversuche an verschiedenen japanischen Dammbaustellen analysiert, um Hintergruende fuer die Variationen der Versuchsergebnisse zu gewinnen, und um Beziehungen zwischen Gebirgsguete yon Staumauergruendungen und Festigkeitscharakteristiken aufzuzeigen. Desweiteren werden Verfahren zur Durchfuehrung der in-situ Versuche diskutiert.
In Japan, bedrock is classified according to information obtained by boring, adit observation, so forth, to evaluate the mechanical properties of dam foundation bedrock. The physical properties used to evaluate, the mechanical stability of dam foundation bedrock include shear strength and modulus of elasticity. In Japan, dam foundations are usually classified into several groups according to the bedrock classification method. To improve design ac- curacy, it is of great importance to improve the correlation between the bedrock classifications and physical properties. At each dam site, in situ tests are made and a review of the bedrock classification and test data is carried out before and after the in situ tests. Accordingly, the correlation between the bedrock classification and test data is usually good for each dam site. The correlation is not always good between different dams or under different geological conditions, however. Although the bedrock classification is intended as an absolute classification of bedrock independent of geology and petrology, rocks of the same class often show different physical properties where the geography or geology differs.
Dam foundation bedrock is classified into several classes according to combinations of the classfying elements obtained mainly from observations of adits and boring cores at dam sites, and mechanical properties for each classified bed- rock are evaluated. The classifying elements and their combinations are specified in the Geological survey Methods of Dams published by the Rock Mechanics Committee of the Japan Society of Civil Engineers. There are three classifying elements: rock hardness, spacing of fissures, and state of fissures. Each element has three levels: A, B, and C for hardness; I, II, and III for spacing of fissures; and a,b, and c for the state of fissures depending on the adhesion, presence of each, and so forth. These are combined to obtain four classes (A,B,C and D) in the overall rating. The relationship between the combination of classifying elements and the four classes is clearly defined. Class C bedrock is subclassified into CH. CM and CL. In Japan, Class Band C bedrocks are usually used for dam foundations, and bedrock is selected according to the height of a dam to be constructed.
The in situ bedrocks shearing tests are divided into a block shearing test and rock shearing test (both being practiced in Japan) according to the Guidelines and Exposition for in Situ Bedrock Shearing Tests published by the Japan society of Civil Engineers in 1979. The test data discussed in this paper was obtained according to the test methods specified in the Guidelines.
A considerable number of shear strength test data on CH, CM, and CL bedrocks of recently built concrete dams were processed. From the in situ test data, a stress VS displacement curve was obtained, and the physical properties of classified bedrocks were determined.
