Study On Rock Mass Quality Of Dam Foundation For Ultra High Concrete Gravity Dam And Utilization Standard

Dam height of Lancang Huangdeng hydropower Station is202m and it is thefirst ultra high concrete gravity dam in our country (current design code on gravitydam stipulates that: the design for the concrete gravity dam of which the heightexceeds200m shall be researched technically. In consideration that there is noconcrete gravity dam with more than200m dam height in China presently, the papercalls the concrete gravity dam that the dam height is beyond200m as ultra highconcrete gravity dam). Due to large load for ultra high dam, high pressure of thereservoir water, and lack of relevant theory, technology and experience, the basic rockmass quality of dam foundation required by285m of ultra high concrete gravity damis revealed via inverting actual mechanical parameters with finite element dependingon the known dam foundation rock mass, design section, testing mechanicalparameters and deformation observed data during recent20years of the highestconcrete gravity dam Grande Dixence in the world on the basis of collecting theories,technologies and monitoring achievements from abroad ultra high gravity dams anddomestic high concrete gravity dams and oversea at100-186m level which wereestablished successfully so as to predict the requirements on foundation rock mass forultra concrete gravity dam. Rock mass of dam foundation for Huangdeng hydropowerstation is gravel lava containing a small quantity of lamellar tuff and mainly is hardrock mass. Apparent structure of rock mass on the left portion is good but the wavespeed is low and the mechanical parameter of rock mass is also low. So, whether suchrock mass can meet the requirements on rock mass strength of dam abutment anddeformation for the gravity dam and how to evaluate and select the rock mass forconstructing foundation of the ultra high concrete gravity dam at the river bed portionare the research topics with important significance in the field of current hydraulicconstruction. The paper focuses on studying the rock mass quality of dam foundationfor ultra high concrete gravity dam and selecting the fundamental plane forconstructing by taking the ultra high concrete gravity dam of Huangdeng hydropowerstation as the example and mainly obtains the following achievements:(1) On the view of factors affecting the rock mass quality of dam foundation, therepresentative indexes of various influence factors are evaluated preferably: uniaxial compressive strength of rock saturation, gap of structural surface, lugeon value,longitudinal wave speed of sound wave, deformation modulus, and shearing resistantstrength. The deformation modulus is taken as the controllable index for evaluating therock mass quality of dam foundation and the congruity of each index is researched too.(2) By combining lots of the field materials gained by the author and analyzingthe stresses, displacements, destroy modes and safety coefficients for ultra high damfoundations with different types of rock masses and the same dam foundation butdifferent dam heights on the basis of widely collecting domestic and overseasmaterials, conclude that the used rock mass of dam foundation for ultra high concretegravity dam must be Ⅲ1class at least via multiple researches. Propose the rock massutilization standard of dam foundation of ultra high concrete gravity dam and basicquantitative criteria by the rock mass situations of dam foundations of establishedgravity dams at200m level or hundred meter level based on the mentionedconclusion.(3) When the dam height is higher than340m and the seismic fortificationintensity is seven, the rock mass of dam foundation cannot meet the requirement ofanti-slide stability even if it is the rock mass at I level, which means that340m of damheight may be the ultimate height for the concrete gravity dam.(4) The rock masses at both sides of Huangdeng Dam have obvious “looseblocky structure”. Lumpiness of rock mass is large and should be classified assecondary blocky-integral blocky structure based on the gap of structural gap and thecorresponding rock level is Ⅲ1-Ⅰlevel. Thus, it is the excellent dam foundationwhich can be directly used for high dam based on the code.(5) Weathering and unloading and relaxation features of the rock mass in thisdam area are the major problems in the evaluation of available rock mass forHuangdeng hydropower station. In particular, rock mass weathering and unloadingproblems for the left side are conspicuous. By adopting multiple quantitative criteriato implement weathering and unloading evaluation for the rock mass in the dam area,the conclusions that the weathering and unloading depths for rock mass are deeperbecause of higher elevation and the weathering and unloading depths at the left side islarger than the right side.(6) According to the rock mass utilization standard of dam foundation forestablished ultra high concrete gravity dam, the rock mass quality in Huangdeng damarea is estimated and the available upper limit of rock mass in Huangdeng dam area isobtained by combining with the data on the filed deformation test and wave speed testand so on. Moreover, the selected rock mass for constructing foundation is checked toprove it reaches the requirements on stress, deformation and stability for Huangdengultra high concrete gravity dam.