桂林红土的工程地质性质及其主要工程地质问题

Engineering Geological Properties and Problems of Guilin Laterite

在收集已有资料的基础上,通过野外调查和土工样品采集测试分析,结果表明:桂林红土主要由石英砂粒及高岭石、伊利石、绿泥石等次生粘土矿物组成,其体积分数为40%～75%;铁铝氧化物高度富集,一般w(Al2 O3)为15.3%～25.9%,w(Fe2 O3)为6.4%～11.2%.土中粘粒体积分数大都在50%以上;土的天然含水量、液限含水量、孔隙比及饱和度通常比较高,分别达26%～40%、42%～70%、0.8～1.1和90%～100%;抗剪强度较大,内聚力为40～85 kPa,内摩擦角为15°～30°;压缩系数和渗透系数一般较小,多小于0.3 MPa-1和1.5×10-6～5.0×10-8cm/s.桂林红土的主要工程地质问题是在基岩面附近,尤其是溶沟溶槽中多有软土分布,并常常导致土洞和地面塌陷的发生.桂林红土的这些工程地质特征主要由其特殊的成土环境条件所决定.

Depending on the field investigation, the tested results of soil samples and the previous data, the engineering geological characteristics of Guilin laterite were studied systematically. The minerals of the laterite mainly include Quartz sand and clay minerals （with a content of 40%-75%） such as kaolinite, illite and chlorite, and a few montmorillonite and vermiculite, etc. In the laterite, iron and aluminum oxides are rich with the content of Al2O3 =15.3%-25.9% and Fe2O3 = 6.4%-11.2%, and the content of clay grain is usually more than 50% ; the water content, the liquid limit, the void ratio and the saturabilityare high, i.e., ω,=26%-40%,ωL=42%-70%,e=0.8-1. 1,Sr=90%-100%~ the shearing strength is large（c= 40 - 85 kPa, Ф= 15°-30°） ; the compressibility and the permeability coeffi- cients are small with the value of 0.3 MPa^-1 and 1.5 × 10^-6 -5.0 × 10^-8 cm/s respectively. There are many engineering geological problems of Guilin laterite, such as a great quantity of earth caves in the laterite, a lot of soft soil developed in lapie of carbonate rock surface and that the thickness of soil layer varied within a little range. The collapse of land surface were often taken place by the earth caves and the soft soil. All engineering characteristics of Guilin laterite were completely depended on the forming environment of the laterite.