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| Research on the Black Cotton Soil Swell-shrink Characteristics and the Depth of Black Cotton Soil Influenced by the Atmosphere in Ethiopia |
| ZHAO Ping，XU Zheng-xuan，TANG Lin, ZENG De-Ii |
| China Railway Eryuan Engineering Group Co. Ltd，Chengdu，Sichuan 610031，China |
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Abstract Research purposes; In Ethiopia , the constructed Sebeka-Dire Data section of Addis Ababa-Djibouti Railway, is located in the East African Rift Valley covered by volcanic material, and its surface is widely distributed with black cotton soil which has strong expansibility, as a result, the railway engineering has been greatly influenced. The swell-shrink characteristics of black cotton soil and the depth of it influenced by the atmosphere will directly affect sugared design measures and the replacement depth of cutting, which will further affect the quality and investment of engineering design. Therefore，the proposed research on the swell-shrink characteristics of black cotton soil and the depth of it influenced the atmosphere is necessary，which provides design basis for sub grade of black cotton soil section.
Research conclusions:(1)The black cotton soil of Ethiopia has following characteristics: small natural density & dry density，big natural void ratio，high free swell ratio，high montmorillonite content & canon exchange capacity，organic matter(loss on ignition) and strong expansibility, etc.(2)In rainy season, the soil is mainly shown as compression when there is load; in dry season, it has relatively strong expansibility under the condition of immersion.(3)The depth of black cotton swell soil area influenced by the atmosphere is 3. 5m and the depth of it distinctly influenced the atmosphere is 1 .6 m.(4)This article will be a reference to geological survey and subgrade design of other similar projects.
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Received: 23 November 2013
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2014, Vol. 31 
