An Engineering Design of the Drainage Crossing at St. Lawrence Road in Rubaga Division

Abstract

This report presents results on the engineering design of the existing drainage crossing along St. Lawrence road in Ndeeba, Rubaga division Kampala district, based on Road Design Manual Volume II: Drainage Design 2010, Kampala Drainage Master Plan 2016 T2 – Design Standards for Stormwater Facilities and The Manual for Hydraulic Design of Highway Culverts Third Edition. The existing crossing was a 600mm concrete pipe culvert which is not of sufficient hydraulic capacity to carry storm water across the road from Nabunya channel into Kabaka’s lake. The effect was flooding which led to washing out of St. Lawrence road, interruption of traffic flow, pollution of the lake, and slipperiness. In order to mitigate the flooding, a box culvert was designed after assessment of the hydrology of the area. The designed culvert is a box culvert of two barrels each with a width of 3.5m and height of 1.7m spanning 10.5m, with reinforcement ofT12 and T16 high tensile bars. Culvert failure can occur for a wide variety of reasons including maintenance, environmental, and installation-related failures, functional or process failures related to capacity and volume causing the erosion of the soil around or under them, and structural or material failures that cause culverts to fail due to collapse or corrosion of the materials from which they are made. Therefore, before the culverts are constructed, the design and the review data must be checked always during the design stage. Ongoing culvert function without failure depends on proper design and engineering considerations being given to load, hydraulic flow, surrounding soil analysis, backfill and bedding compaction, and erosion protection. Improperly designed backfill support around culverts can result in material collapse or failure from inadequate load support.