THE ENGINEERING PROPERTIES OF CORAL LIMESTONE USED AS SUB BASE IN DAR-BAGAMOYO ROAD PROJECT

This paper presents and discusses the unusual poor engineering properties of coral limestone from Mpiji Borrow area in Bagamoyo District - Tanzania used as subbase materials during the construction of Wazo Hill – Bagamoyo Road. The discussion is based on the study and assessment of road subbase made of coral limestone at the project site in the coast of Dar Es Salaam and Coastal region, which involved about 148,000 square metres of pavement from chainage 28+900 to 42+800. The road length is 42.8 Kilometres starting at Wazo Hill Junction (Chainage 0+000) ending at Bagamoyo town (Chainage 42+800). The deterioration and damage of pavement started while the road construction was ongoing. The pavement failure warranted an immediate forensic investigation to establish the probable cause of the pavement failure. The geo-forensic investigation established that the primary cause of pavement failure was due to softening and swelling of coralline subbase caused by the imbibition of water supplied to the subbase layer during crushed base placing and compaction using ‘slushing’ compaction procedures.

本文介绍并探讨了坦桑尼亚巴加莫约地区姆皮吉取土场的珊瑚石灰岩，作为瓦佐山-巴加莫约公路施工底基层材料时所表现出的异常不佳工程特性。本次讨论基于对达累斯萨拉姆沿海及滨海地区项目现场采用珊瑚石灰岩作为道路底基层的研究与评估，该路段涉及桩号28+900至42+800范围内约14.8万平方米的路面工程。该公路全长42.8公里，起点为瓦佐山交叉口（桩号0+000），终点为巴加莫约镇（桩号42+800）。路面劣化与破损在公路施工期间便已出现，该路面失效问题亟需开展即时取证调查，以明确其潜在成因。本次地质取证调查查明，路面失效的主要原因为：在碎石基层铺筑及采用“冲碾”压实工艺开展压实施工时，供给至底基层的水分被珊瑚质底基层吸附，进而引发该底基层的软化与膨胀。