雷州半岛玄武岩残积土的物质成分与结构特征

STRUCTURE AND COMPOSITION OF RESIDUAL SOIL FROM DECOMPOSED BASALT AT LEIZHOU PENINSULA

雷州半岛玄武岩残积土属于区域性特殊土,具有高液限、大孔隙比的较差的物理特性和高强度的较优的力学特性的异常组合,同时具有强收缩性、遇水湿化、易崩解的特殊性质。为探寻玄武岩残积土特殊的工程地质特性的机理,对其矿物成分、化学成分、结构形态、孔隙分布进行研究。结果表明,雷州半岛玄武岩残积土发育过程经历明显的富铝化、铁富集和盐淋失过程,黏土矿物以高岭石、三水铝石和伊利石为主,富含游离氧化铁、铝成分;微观结构类型为凝块结构和絮凝结构,游离氧化铁作为胶结物质以"包膜"形式包裹颗粒形成团聚体,增强了土的结构强度;孔隙以溶蚀孔隙以及团粒和絮凝体内微孔为主,微孔具有较大的比表面积和吸附能,吸水会产生较大的表面张力,引发软化、崩解现象。由于雷州半岛玄武岩残积土具有对水敏感,抗水性差特点,施工中应重点关注降雨引发的工程灾害。

Residual soil from decomposed basalt at Leizhou Peninsula is special regional soil.It has poor physical properties of high liquid limit and large void ratio,good mechanical properties of high strength,and extraordinary properties of strong contractility,humidification and disintegration.This paper attempts to examine the mechanism of the special engineering geological characteristics of the basalt residual soil.It studies the mineral composition, chemical composition,structure,and pore distribution from laboratory tests.Results show that distinct aluminum, iron accumulation,and salt leaching processes occur during the development process of the basalt residual soil.Clay minerals are mainly composed of kaolinite,gibbsite and illite.Furthermore,they are rich in free iron oxide and free aluminum oxide.Microstructure is mainly clot and flocculation structure.The free iron oxide acts as coating that clads particles to form aggregate,which enhances structural strength of soil.Pores mainly consist of denudation pores and micropores in the aggregate and flocculation,and with larger specific surface area and adsorption energy. Large surface tension occurs after immersion which leads to softening and disintegration.Therefore,close attention should be paid to engineering disasters caused by rainfall due to the water sensitive and poor water resistance of the basalt residual soil.