埃塞俄比亚铁路黑棉土勘察方法及工程特性研究

Research on Survey Methods and Engineering Properties of Black Cotton Soil of Ethiopian Railway

研究目的：黑棉土是埃塞俄比亚及非洲部分国家大面积分布的一种特殊的土层，呈灰黑色、灰褐色，当地俗称黑棉土，一般具有膨胀性。目前中资公司大量进入埃塞俄比亚勘察设计及施工市场，对黑棉土的研究较少，因此，有必要在无既有经验可循的条件下，研究一套适合该国国情的勘察方法，查清黑棉土的工程特性，为铁路工程选择合适的工程措施提供基础资料。研究结论：（1）黑棉土具有中～强膨胀性、中等一高压缩性等工程特性；（2）提出加强路基排水系统设置；堑坡高度≤3m，边坡采用灌草防护；堑坡高度〉3m，边坡采用骨架护坡等防护；边坡较高时，设挡土墙；弱中膨胀土路堑基床底层换填不小于0．5m，中-强膨胀土路堑基床底层换填不小于1m等处理措施；（3）本文研究成果可为埃塞俄比亚的铁路、公路、轻轨交通建设等的勘察设计工作提供指导及借鉴。

Research purposes： Black cotton soil is a special soil existed on a large area of Ethiopia and some other African countries, with dark gray or taupe color. Locally known as black cotton soil generally, the soil has expansibility Currently, a large number of Chinese companies enter into survey, design and construction market in Ethiopia, but few of them do research on black cotton soil. Therefore, it is necessary to study a set of survey methods suitable for the countryg national conditions since there is no existing experience which can be provided to follow, to identify engineering properties of black cotton soil, which can be provided as basic information when we choose appropriate engineering measures for railway projects. Research conclusions：（ 1 ） Black cotton soil has engineering properties like medium - strong expansion, medium - high compression, etc. （2） It proposes the following subgrade treatment measures： strengthening the subgrade drainage system; when cut slope height ~〈 3 m, using shrub and grass for slope protection; when cut slope height 〉 3 m, using skeletons protective slope to protect side slope; if the slope is high , set retaining walls; cutting subgrade bottom layer with weak - medium expansive soil shall have replacement no less than O. 5 m, cutting subgrade bottom layer with medium -strong expansive soil shall have replacement no less than 1 m. （3） It provides guidance and reference forsurvey and design work of railways, highways, light rail transit construction in Ethiopia.