龙门山山前砂土液化初步研究

Research on the soil liquefaction in the piedmont region of the Longmen Mountain

对龙门山山前的成都平原(金马河以北)和川北丘陵区进行了地震液化现场调查。结果表明:液化点主要沿河谷底部和低阶地分布,液化集中区平行于NE向龙门山地震断层,与断层的转折、终止、出现部位相对应,与地震动最大峰值加速度(PGA)等值线主轴一致。液化喷出砾石最大粒径30 cm,最大喷砂量约15m3,堆积厚达4m,冒水高达775 cm,地表破裂长达1 000m。喷砂冒水与强震动相一致,强震过后,大部分液化点上的喷砂冒水现象消失。分析表明:冒水高度总体随震中距增加而降低,亦存在随震中距增加而增高和波动的趋势。液化砂土来自第四系不同地层,并出现了下更新统下段的红色强风化泥砾。

Field investigation for the Chengdu Plain （to the north of the Jinma River） and hilly area of the northern part of Sichuan province was made. The investigation shows that the distribution of the liquefaction points belong mainly to river valley, lie in flood plain and lower terraces, distribute near and parallelly with the earthquake faults of the Longmen Mountain striking in a north-east direction, aim at the turning point in the direction of the strike of the fault or places where the fault emerges or disappears, and are consistent with the main axis of the contour of PGA. The biggest grain diameter of gravel reaches 30cm, the biggest sandblasting volume at liquefaction point reaches about 15m^3, the biggest thickness is about 4m, the biggest height of water emitting reaches 775cm, and the longest surface rupture correlated with liquefaction is approximately 1 000m. The emitting progress of water and soil are in accordance with the main shock, and in the majority of sites the phenomenon emitting disappears after the main shock. Analyses of the liquefaction soil show that water emitting height decreases with the increasing epicenter distance in general, and has the tendency of increase and fluctuation with the increasing epicenter distance. The soil is red and heavy weathering boulder clay coming from the lower member of lower Pleistocene as well as coming from the different parts of Quaternary formation.