奉化江、姚江流域工程地质分区和工程地质问题

根据钻孔原位测试和岩土样品试验室分析结果，对奉化江、姚江面积约600km。流域的工程地质结构进行了研究，并对流域地表以下60m范围内进行了工程地质分区和工程地质问题探讨。结果表明：（1）全新统镇海组有3个工程地质层和5个亚层，上更新统宁波组有3个工程地质层和20个亚层，下伏基岩归入1个基岩工程地质层；（2）可选用的持力层为④1、④3-2、④3-3、⑤1、⑤3-1、⑤3-2、⑥1、⑥3-1、⑥3-2、⑥4工程地质亚层和基岩工程地质层，持力层地基承载力特征值fak≥160kPa；（3）流域内有两个硬土层，即岩性为粉质粘土的第一硬土层④1和第二硬土层⑤1；（4）根据各持力层的厚度和组合分布特征，研究区被划为6个工程地质分区，并提供了每一个工程地质分区的持力层、基础类型；（5）主要工程地质问题是地面沉降和软土震陷。

Engineering Geologic Zoning and Engineering Geologic Problem in the Fenghua River and Yao River Basin

Based on the data of in-situ tests and experimental analysis on rock and soil samples from different drills, engineering geologic structure of Fenghua River and Yao River basin whose acreage is about 600 square ki- lometers has been researched. From then, engineering geologic zoning and engineering geologic problem discus- sion have been carried on within sixty meters from the surface. The results are as follows：There are three engi- neering geologic layers and five engineering geologic subhorizons in Zhenhai Formation of Holocene. There are three engineering geologic layers and twenty engineering geologic subhorizons in Ningpo Formation of upper Pleistocene. The underlying bedrock is summed up one bedrock engineering geologic layer. The bearing strata of foundation are engineering geologic subhorizons of ④1、④3-2、④3-3、⑤1、⑤3-1、⑤3-2、⑥1、⑥3-1、⑥3-2、⑥4 and bedrock engineering geologic layer whose faks are also more than 160kPa. There are two hard pans of ④1 and ⑤1 whose lithological characters are also silty clay in the basin. According to features of depth, combination and dis- tribution between every bearing stratum, the basin can be divided into six engineering geologic zonings. More- over, bearing strata and foundation type of every engineering geologic zoning have been suggested. Geological di- sasters are ground setting and soft soil subsidence during the earthquake.