北京平原区新近沉积土基本工程地质特性分析

PHYSICOCHEMICAL AND GEOTECHNICAL CHARACTERISTICS OF THE RECENTLY DEPOSITED SOIL IN BEIJING PLAIN REGION

文章通过各种实验,分析了北京市新近沉积土的物质组成、化学成分、矿物成分及其基本的岩土工程特 性。结果表明,新近沉积土在总体上是工程地质性质较差的地层,一般来讲呈欠压密状态,具有较高的压缩性,强 度相对较低。但是对于新近沉积的砂质粉土而言,即当塑性指数Ip<7时,通过比较发现新近沉积土的实验数据则 接近于一般第四纪沉积土,并出现了交错,反映出新近沉积的砂质粉土与一般第四纪沉积的砂质粉土的力学性质 指标接近而不容易被区分。

We analyzed the particle distribution, physicochemical characteristics, mineral components, and the geotechnical characteristics of recently deposited soil in Beijing area. The results indicated that, (1) The granulometric composition of recently deposited soil in this area was even, with poor gradation. The percentage composition of SiO 2 is very high, approximately 56%～73%. The organic content with 1.25% is higher than that of general Quaternary deposited soil. The mineral composition mainly included smectite, illite, and kaolinite. Illite content occupies the dominant position. (2) The void ratio (e) is high, about 0.783 equally. The value of saturation degree (S r) approaches 1. The value of plasticity I P and liquidity I L is about 4.4～24.3 and 0.26～0.96. I L increases along with I P. Silt (I P<10) with the value of I L between 0.26～0.60 is plastic, cohesive soil (I P>10) with the value of I L between 0.60～0.96 is plastic or molliplastic. (3) The value of modulus of compression E S mostly is between 4～15MPa, obviously lower than that of the corresponding general Quaternary deposited soil. But, when the plasticity index I P of recently deposited soil is higher 7, the characteristics of recently deposited silt soil approximate that of general Quaternary deposited silt soil, and indicate that it is very difficult to distinguish these two kinds of silt soils. (4) The double logarithm relations curve of P-S is the simple fold line, and could be only determined by 4 eigen parameters. According to the statistical relations of 4 eigen parameters and all kinds of geotechnical indexes, the P-S curve of loading test could be obtained as long as we knows its geotechnical indexes, then the allowable bearing capacity of the recently deposited soil also could be determined.