Consolidation grout improves rock property and restricts seepage flow of dam foundation. To perform consolidation grouting effectively and ration-ally, it is necessary to grasp detail geological conditions of foundation. This paper suggests geotechnical evaluation method and has applied the method for three actual large dam sites. As the result, applicability of this method is clarified.


Main purpose of consolidation grouting at concrete dam foundation is to secure the homogenity and intensity of the foundation which will support dam body as well as to Control leaking flux through the foundation. It is applied to entire dam foundation or part of it according to physical foundation properties, such that the load is too large because of the dam scale and its structure characteristics, or that of jointed rock mass. Consolidation grouting for fill type dam (blanket grouting) is applied to obtain a better affection of curtain grouting, and this makes dam foundation surface to be less porosity to prolong the permeable path to prevent from piping and to control the leaking flux. The purpose of geotechnical eveluation at Consolidation grouting is to carry out detail geological surveys on the dam foundation excavation surface to evaluate the engineering property for foundation and to execute an effective foundation treatment. This paper reports on approach way of the geotechnical evaluation for design, construction and the treatment affection of con solidation grouting for dam foundation when examining, and these actual application cases. We introduce 3 types of examination results at Oguchigawa Dam (concrete gravity type), Nagawado Dam (concrete arch type), and Niikappu Dam (rock fill type), which we carried out detail geological surveys at each construction stage.


Main purpose of geotechnical evaluation of dam foundation when constructing a dam is to examine foundation treatment method, selection of its application range, and the treatment affection. It can be consider the control factors of rock properties such as mechanical property and permeability are (1) consolidation of the rock itself (2) weathering degree (3) distribution conditions and properties of fractures. Based on such considerations, we carried out geological surveys on the dam foundation excavation surface to grasp detail weathering conditions, hardness, fracture distribution and properties, and examined on stability of foundation according to the fracture density and the rock quality distribution. Further, we developed these results intensively and evaluated them to obtain "Rock Mass Calculation (A)". When constructing consolidation grouting, the evaluation result of the "Rock Mass Calculation (A)" was adopted to select the treatment range. Moreover, "Rock Mass Calculation (B)", which includes permeable characteristics in addition to the "Rock Mass Calculation (A)", was obtained to evaluate and to examine. Following description is a rock mass evaluation method based on the abovementioned approach. Evaluation through fracture density When geological surveys are carried out on dam foundation excavation surface,' basically, aperture and trace length of fractures (fracture zone, seams and joints) of more than 3 m shall be grasped accurately, and they shall be gathered by each unit square of standard grid pattern for consolidation grouting.

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