This paper presents overall studies on grouting and groundwater drainage of the Xiaolangdi Multipurpose Dam Project, and identities problems in Standards and Specifications both in China and abroad. The achievements of the study include relative permeability and relative groutability, selection of parameters of grouting and groundwater drainage, orientation of grouting and groundwater drainage holes, stable grouting liquid dozing. Furthermore, new technology of grouting and groundwater drainage is provided. The advantage of the new technology is demonstrated by the practices in the Xiaolangdi Project. Since 1985, we have carried out survey and design of grouting and groundwater drainage of the Xiaolangdi Multipurpose Dam project, including systematic investigations and researches in line with related specifications(Chinese standard 1999.etc.). The project has a total of 762,300 km long grouting and drainage works. The complexity is so prominent that existing Chinese codes and specifications could not meet the requirements, and so international specifications were referred to. During construction period, it was found that both Chinese and International specifications have room for improvement. To solve some important problems of the project, a large number of laboratory and field tests and studies were performed, and significant results were achieved.
Clause 3.4.7 of Chinese Technical Specifications for Cement Grouting Construction of Hydraulic Works states, "All grout sections with curtain grouting holes of any permeability shall be grouted in accordance with technical requirements". And clause 4.4.2 of Geological Investigation Specifications for water Conservancy and Hydropower Projects requires, "Water pressure tests shall be conducted for boreholes in bedrock." Accordingly, during the investigation of over ten thousand meters of bedrock, the water pressure test shall be done for several thousands of sections, which constitutes a large portion of the preliminary costs. To assess whether such a high cost is necessary, alternative methods to reduce the amount of work were studied. The following classifications are divided according to the width of structural planes permeable to water and grout.
Different permeable rock structures develop different geological structural planes (mainly fissure planes). Sedimentary rocks, metamorphic rocks or igneous rocks are classified as the three permeable structures: deep- seated laminar or block structure, being distant from large faults, faults and fault-affected rock masses, weathered stress-release rock masses.
Faults and fault-affected rock masses consist of faults and intensely affected zones, faults and ordinarily affected zones. weathered stress-release rock masses include highly weathered stress-release rocks and ordinarily weathered stress-release rocks.
The lithologic character is the basis for the division of subsections. Different lithologic character indicates different cementing material, affecting the strength of rocks. For example, in the Xiaolangdi Project area, the strength of rocks reduces in the order of siliceous, calcareous and argillaceous cements.
The structural plane elements include dip, dip angle, spacing, Density. A great deal of survey data show that the width of the structural plane permeable to water and grout varies with different permeable structures.