西南煤系地层软岩地区坡麓相斜坡软土特性研究

在我国西南内昆、株六、水柏及六盘水枢纽等铁路勘察与施工中,在煤系地层软岩地区的山麓斜坡上常遇到一种特殊罕见的"坡麓相斜坡软土"(笔者简称),它是"陆相的饱水堆积物"而非"水相的水下沉积物"。这种土的物理力学特征与一般软土相似,同样具有天然含水量高(但一般不大于液限)、孔隙比大、高压缩性、低强度性、流变性、触变性等特点,并具有弱—中等膨胀性;常隐蔽于山麓斜坡地表较厚的硬壳层之下,非钻探或开挖揭露难以发现,且具有不连续、透镜状或鸡窝状分布、厚度变化较大、底部横坡较陡等特点;最突出的工程地质问题是天然地基的不均匀性及非稳定性,对工程的危害较大。工程施工中常发生路堤基底滑移沉陷、路堑边坡滑坡与坍塌、桥涵地基承载力不足、基坑边坡溜坍等地质灾害或工程病害,整治难度较大。笔者结合工程实例,系统论述西南煤系地层软岩地区坡麓相斜坡软土的分布、成因、定义、分类、物理力学特征及其工程特性,并对其命名问题进行探讨,对指导工程实践,防止工程病害具有重要意义。

On features of piedmont soft soil on slope in soft areas of coal strata in Southwest China

Recent years, in the practice of design and construction of railroads in the southwest regions like Neijiang-Kunming railway, Zhuzhou-Liupanshui railway, Liupanshui-Baiguo railway and Liupanshui railway Hub, etc. engineers have encountered a special and rare piedmont soft soil on slope in soft rock area of coal strata, which is a kind of continental facies water-saturated deposits but not marine faces deposits. Physical and mechanical features of this soft soil are similar to that of normal soft soil, such as high water content (generally not more than liquid limit), large porosity ratio, high compaction, low strength, rheological properties and thixotropic properties as well as weak-and-medium expansion. Such soil is normally covered by hard and thick crest on piedmont slope and cannot be found without exploring boring and/or excavation. Such soft soil locates discontinuously as lens-shape and henroost featured with large variation of thickness and steep bottom cross slope. The most obvious problem resulted from such soft soil to engineering projects is that the unevenness and instability of the natural foundation may cause large hazardous impact on projects, and because of this, geotechnical hazards and engineering hazards like road base sliding and/or settlement, slope sliding and/or collapse of road cut, inadequate bearing of bridge/culvert foundation, and collapse of foundation trench during construction are frequently encountered and difficult to deal with. Closely incorporating into engineering practice, the author has systematically presented and demonstrated the distribution, inducing factors, definition, classification, physical and mechanical features and engineering properties of piedmont facies soft soil. As well as, naming of such soft soil has been discussed. This article has significant importance in instructing engineering practice and prevention of geological hazards.