大亚湾中微子地下实验室场地的工程地质条件评价

中微子实验目的是测定中微子混合角θ13,这是当前国际粒子物理、核物理、天体物理和宇宙学中一个急待解决的关键问题。目前研究中微子振荡一个国际前沿是利用反应堆中微子实验测量中微子混合角θ13。其地下实验室对场地工程地质条件和环境要求极高。大亚湾核电站的功率高,反应堆紧邻位于排牙山南麓实验预选场址;浑厚的花岗岩山体地下空间可屏蔽宇宙线本底,能提高混合角θ13量测精度。本文通过地形测绘、工程地质调查、综合地球物理勘探、钻探、孔内测试(地应力、钻孔电视和声波)和室内实验,系统分析研究了场址区工程地质条件,得出场区地层岩性和构造断裂不发育,燕山期花岗岩体完整,强度高,地应力不高,地下水主要赋存于裂隙中,岩体渗透系数很小的结论。拟选4个实验厅位置的岩体均属Ⅰ～Ⅱ类围岩,连接隧道的围岩81%属Ⅰ～Ⅲ类。工程地质条件评价结果说明,大亚湾中微子地下实验室可望成为世界上投资少精度最高的测量θ13理想场址。

EVALUATION OF ENGINEERING GEOLOGICAL CONDITION OF DAYA BAY FOR SITTING THE LABORATORY OF NEUTRINO UNDERGROUND EXPERIMENT

Neutrino Underground Laboratory is a special underground rock engineering project.Its site selection and operation put very rigorous on engineering geological conditions and engineering environment.A key question of the experiment is to find out the neutrino mixing angle(θ13) for particle physics,nuclear physics,celestial bodies physics and cosmography in the world.Nowadays,Reactor Neutrino Measurement of θ13 is a question under discussion worldwide.The site is adjacent to Daya bay reactor with high powers of Daya Bay Nuclear Power plant.The laboratories are planed at the south foot of the Paiya Mountain with highly altitude and the enough overburden for decreasing the background.This environment is benefit to the precision of Neutrino Measurement of θ13.This paper presents the analysis and assessment of engineering geological conditions.The works are based on data got from topographic survey,geologic investigation,geophysical exploration,drilling,borehole tests including geostress measurement,and lab tests etc.As a result,it is known that the rocks and tectonic conditions are simple,massive granite is with high strength,relative low geostress,groundwater is mainly limited in fissures with a low permeability coefficient.The four experiment caverns are located in rocks of Ⅰ~Ⅱ class,and the connection tunnel is sit in rocks with 81% of Ⅲ or above Ⅲ classes.After evaluation of engineering geological conditions,it is indicated that the Daya Bay neutrino underground lab will become a optimum location for measure θ13 in the world because of the low investment and the high measurement precision.