宁波洋沙山近岸海域浅部地层特征与不良工程地质现象

The geological characteristics in the off-shore area near Yangshashan of Ningbo

对宁波洋沙山近岸海域进行了浅部地层探测和浅部地层特征描述、分析,并结合前人的研究成果对该区地层中不良工程地质现象进行了分析和解释,结果表明:(1)在海底面以下约20m的剖面记录中,有3个反射界面比较清晰,地层自上而下可分为4个层组,前三层为全新世的海相沉积地层,第四层为晚更新世时期的沉积地层。(2)海底面以下地层中存在着埋藏基岩和浅层气等不良工程地质现象。埋藏基岩分布区共有4处,其中3处集中分布在洋沙山沿岸,基岩顶面埋藏深度一般为8～12m,最小埋深为3～4m;另一处埋藏基岩位于平石礁以南约1900m处,其顶面埋藏深度大多超过14m,最小埋深为9m。相当一部分海域地层中含有浅层气,分布面积约占调查海区面积的25%,其东部浅层气顶面埋深一般为6～8m,而西部埋深一般达11～15m,显示出该区浅层气分布较分散,强度不大,气顶面埋得较深等特点。

The results of the shallow layer detection in the off-shore area near Yangshashan indicate that there are 3 clear reflection interfaces and 4 stratum groups from the top down in the stratigraphical section records about 20 meters thick below the seabed. According to the analysis, the fourth stratum group belong to the deposit of the late Pleistocene, the first, second and third stratum groups are marine deposit stratum of Holocene. The unstable engineer geological phenomena, such as imbedded rocks and shallow layer gases and so on are found. There are 4 imbedded rock region in the research area,three of them are distributed in the coast of Yangshashan and the imbedded depth of the rock top is normally about 8~12 m and the smallest one is 3~4 m. The other imbedded rock is located about 1 900 m to the south of Pingshijiao, most of the top imbedded depths are over 14 m and the smallest one is 9 m. There is shallow layer gas under the seabed in the research area near the Yangshashan. The area is about 25 percent of the survey sea. The top imbedded depth of the shallow layer gas is about 6~8 m in the eastern part and 11~15 m in the western part. The result indicates that the top imbedded depth of the shallow layer gas is deeper but the intensity is small.