In accordance with the plan for formulation and revision of water technical standards and the requirements of SL 1-2014 Specification for the Drafiting o f Technical Standards of Water Resources， SL 251-2000 Code for Investigation of Natural Construction Materiats for Water and Hydropower Projects has been revised and adjusted.
　　This code includes 8 chapters and 4 annexes with the main contents as follows：
　　-Extent and basic principles for investigation of natural construction materials.
　　-Requirements of investigation， sampling and testing，and quality indices for various natural construction materials，including sand and gravel materials， soil materials， rock materials， usable materials from excavations， land fillmaterials， hydraulic fill materials and impervious rolled-mudstone materials.
　　-Processing， analysis and reporting of investigation results of natural construction materials.
　　-Identification of alkali reactivity potential of concrete aggregate， particle-size classification of soils， discriminating criteria of dispersive soil， and common form of tables for natural construction materials investigation.