稻城海子山松散堆积物粒度成分空间变化特征

SPATIAL VARIATIONS OF GRAIN SIZE OF LOOSE SEDIMENTS IN DAO-CHENG HAIZI MOUNTAIN

稻城古冰帽中心海子山广布粒度成分不同的由冰碛物和冲洪积物等组成的松散堆积物,给高海拔宇宙线观测站(LHAASO)规划建设带来挑战。对高坡垄岗部位5处冰碛花岗岩砾石、堰塞盆地中2处阶地冲洪积物进行现场观测和取样分析。对106块砾石采用线面集中统计,得到冰碛物砾石数量占百分比较高的砾径为0.5~2.5 m,面积2.5~7.5m^(2),体积5m^(3)。块石形状多为长方体-厚板状,部分面接触为主。采用音频大地电磁法(AMT)等进行探测,解释得到场地冰碛体厚约30m。对冲洪积物的含砾土和细碎屑土的2个砂砾样品用筛分法和激光粒度法进行粒度成分测定,得中值粒径d_(50)=2mm、0.7mm,不均匀系数C_(u)=5.40、2.42,曲率系数C_(c)=0.60、0.95。这两种冲洪积物均为不良级配的土,即均粒土。这些成因和结构不同的冰碛物和冲洪积物对工程布设有不同影响,在工程实践中给予了区分利用。

Haizi Mountain in the center of Daocheng’s Quaternary ice cap is widely distributed with glacial moraine of different grain magnitudes.The site,covered with various loosed sediments underlying by granite as medium coarse grained biotite granodiorite,is to be used according to the planning and construction of China s Large High Altitude Air Shower Observatory(LHAASO).This paper describes and analyses five locations with granite gravels of moraine ridge and two locations with alluvial proluvial materials of terrace at the site.The statistical results of 106 huge gravels show that the moraine gravels of major percentages are 0.5~2.5m in diameter,and have 2.5~7.5m^(2)in area and 5m^(3)in volume to a certain extent.Two gravel samples of gravelly soil and fine debris soil of alluvial proluvium have the median particle size D_(50)=2mm and 0.7mm,the non-uniform coefficient C_(u)=5.40 and 2.42,the curvature coefficient C_(c)=0.60 and 0.95,respectively.Both are poorly graded soil,i.e.homogeneous soil.These moraines and alluvial proluvial deposits with different genetic structures and magnitudes have different important values for site planning and utilization,and have certain influence on the stability of excavation pit wall.Afterwards,the results in this paper were adopted for planning and designing of LHAASO.