广西北海近海工程地质特征及特殊问题分析

Analysis of engineering geological characteristics and specific problems of the offshore area in Beihai,Guangxi

利用研究区物探处理解释资料及海底表层、钻探地质取样等综合地质调查资料,分析广西北海近海区域工程地质主要特征,并针对土层稳定性、砂土液化及地层承载力问题进行探讨。结果揭示:该区海洋工程地质环境复杂、多样;近岸海底地形起伏较大,坡降可达28‰;地貌类型主要包括潮间浅滩、水下三角洲、水下岸坡、古滨海平原、海底平原;地质灾害因素包括断层、地震、沙波、浅层气、浅埋基岩、埋藏古河道、槽沟、水下浅滩及凸地等;海底有9种土质类型,其中淤泥、粉砂混淤泥、中砂、粗砂分布较为广泛,区域垂向土层可整体划分为4个工程地质层。通过评价后得出研究区黏性土整体稳定性较好,而砂性土在极限波浪作用或强震作用下可能发生大面积液化现象。结合近海一般用桩情况,计算出第二、四工程地质层的承载力值相对较大,可作为区域类似插桩较好的持力层,40 m以内半径0.7 m单桩的极限承载力达26 822 kN。

This study used comprehensive geological investigation data including geophysical interpretation data, seabed surface and drilling sampling data in the offshore area of Beihai in Guangxi to analyze its main engineering geological features, and discussed the soil strata stability, bearing capacity, and sandy soil liquefaction. The result shows that （ 1 ） the geological environment of marine engi- neering in the area are complex and diverse; （2） the coastal submarine terrain has a large relief, with its slope gradient reaching up to 28%e; （3） landforms＇types include intertidal shoal, underwater delta, underwater slope, paleo-coastal plain and submarine plain ; （4） geological hazardous factors are mainly faults, earthquakes, sand wave, shallow gas, shallowly buried bedrock, buried paleo-channel, trench, underwater shoal and convex; and （5） there are 9 types of submarine soil, including the widely distributed silt, silty sand mixed with mud, medium sand and coarse sand, and the regional vertical soil layers can be divided into 4 engineering geological layers. It is evaluated that the overall stability of cohesive soil in the study area is good, and the sandy soil tends to undergo widespread lique- faction under the impact of extreme waves or strong earthquakes. Combined with the offshore pile foundations, the second and fourth en- gineering geological layers are calculated to have a large bearing capacity, which can be acted as a regional pile-bearing layer, and the bearing capacity of a single pile with a radius of 0.7 m within 40 m can be up to 26 822 kN.