THE PROPOSED PARTIAL DEMOLITION OF THE MURRAYSBURG BRIDGE (B3274) AT KM 1.22 ON MR607 OVER BUFFELS RIVER, MURRAYSBURG, WESTERN CAPE.

Guillaume Nel Environmental Consultants (GNEC) has been appointed by Malani Padayachee & Associates (Pty) Ltd (MPA) on behalf of the Western Cape Department of Infrastructure to facilitate the Environmental Impact Assessment (EIA) (Basic Assessment) process for the partial replacement of the Murraysburg Bridge (B3274) at km 1.22 on MR607 over Buffels River, Murraysburg, Western Cape (hereafter referred to as the proposed site).
During inspection of Bridge B3274, it was found that the bridge has a poor structural integrity, and urgent interventions is required. This bridge was constructed in 1936 and is located on the MR607 gravel road between Murraysburg and Richmond. This bridge is a critical link to the farming community north of Murraysburg and may result in a detour of 100 km or more in the result of closing this bridge.
The exiting bridge consists of 5 spans each 6.3 m long, with 3.75 m high piers. The bridge/ road is approximately 4.4m in width. The bridge deck is 630 mm thick and consists of 3 layers. The top layer has a significantly lower compressive strength than the bottom two layers due to it being the most exposed surface to concrete weathering. There is little to no reinforcement in the top layer whereas at the soffit there is exposed steel due to friable concrete wearing off.
Due to the bridge being constructed in 1936, an application in terms of Section 34 of the NHRA will be undertaken for the partial demolition of the bridge.
The bridge design was compiled based the following findings:
•The hydrology analysis summary:
o Catchment area = 1,241 km2
o Longest watercourse = 82 km
o Average slope = 0.006 m/m
• Bridge B3274, even though it has tall piers, is designed to be overtopped. The as-built drawings also shows that the original riverbed was about 2m higher than it currently is. Erosion over the years has exposed two-thirds of the pier.
• The existing topography, i.e., wide flood plain and flat area, does not allow the bridge to be raised to accommodate the high peak flow coming through. The proposals discussed below will therefore focus on retaining the existing structure.
The partial demolition of this bridge is summarized below:
• Demolish deck and replace with new precast deck slabs.
• Retrofit the columns by placing a concrete skin around it.
• A temporary bypass will have to be constructed on the downstream side of the bridge to accommodate travellers. The road reserve is 20m wide, 10m per side form the centreline of the bridge. A screenshot below indicates a cross- sectional layout of the bridge and proposed bypass (on the upstream side).
It is important to note that the majority of the construction works that will be undertaken will be to the deck of the bridge. The entire bridge deck will be demolished and replaced with new precast slabs. Due to the height of the exiting piers (3.75m), these works will not be undertaken within the watercourse and will be contained to the exiting bridge structure.
The main construction activities and proposed works that will be transpire within the watercourse will be a temporary bypass, reinforcement of the piers and protection works on the piers.
Bridge location: 31º57’09.56”S 23º45’42.90” E