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SPATIAL VARIATIONS OF GRAIN SIZE OF LOOSE SEDIMENTS IN DAOCHENG HAIZI MOUNTAIN
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摘要: 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2.5~7.5 m2，体积5 m3。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30 m。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d50=2 mm、0.7mm，不均匀系数Cu=5.40、2.42，曲率系数Cc=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。Abstract: 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 0.5~2.5 m in diameter,and have 2.5~7.5 m2 in area and 5 m3 in volume to a certain extent. Two gravel samples of gravelly soil and fine debris soil of alluvial proluvium have the median particle size D50=2 mm and 0.7mm,the non-uniform coefficient Cu=5.40 and 2.42,the curvature coefficient Cc=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.
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Key words:
- Daocheng /
- Moraine /
- Grain size /
- Moraine dam moraine /
- Sediments thickness
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图 1 研究区地理位置及区域构造概略图
资料来源：交通线路和水系：中国地图出版社(2010)；山峰和高程：国家测绘局(1975)；主要活动断裂及盆地：黄金忠等(1989)；①. 邓柯-乡城断裂，②. 甘孜-理塘断裂，③. 理塘-德巫断裂，双齿线为上盘逆冲；Ⅶ. 理塘盆地
Figure 1. Site location and framework of regional faults
图 2 围绕LHAASO场地中心地质调查采样及粒度测量点分布图(下方白色线为S217道路，其余亮白色线为河流；底图据Google Earth(2014))
Figure 2. Distribution of sampling locations and particle size measurement locations at LHAASO field
图 3 现场采集的5块花岗闪长岩标本(左列)及光学显微镜下单偏光(中间)和正交偏光图像(右列)
显微图像中矿物名称：Ap-磷灰石，Bt-黑云母，Hbl-普通角闪石，Kfs-钾长石，Pl-斜长石，Qtz-石英，Zrn-锆石. 样品采集位置见图 2
Figure 3. Five samples of granodiorite(left column) and single polarized(middle) and orthogonal polarized images(right column) of optical microscope
图 4 场地冰碛地貌形态(河道中箭头指向水流方向)
a. 场地中心处在河流Ⅰ级阶地呈现的低平岗地上(2014-9-17)；b. 河流切穿冰碛垄快速流过(2014-9-17)；c. 东西小河汇合后流过冰碛侧垄豁口后的塌岸(2014-9-28)
Figure 4. Photos of moraine landform of the site at different locations
图 5 LHAASO场区“盆垄沟岗”微地貌形态图
图中，中心点表示大圆所示直径1270 m的WCDA场地中间，ZPDT表示装配大厅位置
Figure 5. Micromorphological map of "basin,ridge,ditch and hillock"
图 6 现场6种不同微地貌单元所占面积百分比
Figure 6. Area percentage of 6 different micro geomorphic units on site
图 8 场区5处测窗(线)内冰碛砾石几何分布结果图(这里砾径指长轴长度)
a. 砾径频数百分比曲线；b. 砾石面积百分比曲线；c. 砾石体积百分比曲线；d. 砾径分布直方图; e. 砾石面积分布直方图; f. 砾石体积分布直方图
Figure 8. Statistical results of geometric distribution of different moraine gravels in five survey windows(lines) on the site
图 9 现场No.36漂砾表面倾向极点投影等密图
Figure 9. Site No.36 isometric map of boulder surface dips in pole projection
图 10 现场50块冰碛块石尺度测量结果投点图
a. 长轴(X)和短轴(Y)长度关系；b. 正交的3个方向轴长
Figure 10. Projection map of measurement results of 50 moraine blocks on site
图 11 现场松散砂砾石样品颗分曲线
Figure 11. Cumulative and distribution curve of on-site loose sand gravel samples
图 12 松散砂砾堆积台地现场出露位置及其稳定状况
a. 河流阶地相含砾土(2014-9-17近点DC9)；b. 湖滨相细碎屑土(2014-9-17点DC14)
Figure 12. hotos of exposed loose gravel-accumulation platform
图 13 AMT方法南北向N1勘探线电阻率剖面图
图中蓝色线为冰川漂砾层底界线；紫色线为基岩顶面；实红色线为断层；虚红色线为断层影响带
Figure 13. Resistivity profile N1 exploration line from north to south via AMT method
表 1 现场5处冰碛砾石几何特征表
Table 1. Geometric characteristics of gravels in five moraine ridges on the site
点号 砾石数/块 统计面积/m2 测区边走向/(°)/测线长/m/倾角/(°) 砾石优势体积/m3 地貌单元 野外岩性/砾石一般尺寸/m 砾石面积占测窗面积(线密度)/% 推测冰川运动方向/(°) 16 35 30×30 30//
112//2.5 终碛垄 浅白色粗粒花岗岩，石英含量高。含细晶花岗岩突起团块 15.1 112 36 11 200 140//30~45 25 半弧形终碛垄巨型块石分布 长：5.5~7.0
宽：3.5~5.0
高2.0~3.5140 51 40 95/5/
183/5/砂砾堆积缓坡区，冰盆边缘 (71)(57.4) 87 10 130/21/
220/25/25 终碛垄巨型砾石分布区 (77.1)(41.2) 91 10 15 侧碛垄大块石分布区 长3.5~5.5
宽2.0~3.0
高1.5~2.5
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表 2 砂砾土样3种粒组百分含量(%)及定名
Table 2. Percentage and designation of three grain components in gravel and soil samples
编号 卵砾组(>2 mm) 砂粒组(2~0.05 mm) 粉黏粒组(<0.05 mm) 定名 DC9-1 49.91 48.61 1.48 含砾土 DC9-2 45.22 53.37 1.41 含砾土 DC14-1 3.68 94.11 2.21 细碎屑土 DC14-2 3.65 93.65 2.70 细碎屑土
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