Cwmbelam Culvert Invert Repairs and Construction of Otter Run

Cwmbelam Culvert Invert Repairs and Construction of Otter Run

Prior to entering the culvert, a calibrated gas monitor was used to test the atmosphere at the top, middle and bottom of the culvert, to ensure safe confined space entry. Once deemed safe, entry was issued by the confined space supervisor. The gas monitor remained in place and monitoring continued with readings recorded every 15 minutes.

Following the atmosphere test, each end of the culvert had to be cleared of any vegetation and debris, bed material removed for a depth of 500mm and discharge pipes installed within the culvert to over pump, creating a dry working area. The pipes were installed through the culvert and secured to the existing Armco structure with temporary fixings. Using Slip form shuttering, stanks were constructed around the upstream and downstream ends of the structure to form temporary dams to contain and prevent any pollutants from contaminating the watercourse. Operatives could then start the pumps and begin over pumping the water through culvert.

Kaymac operatives cleaned the existing invert with HP Water Jetting equipment to remove any further debris and loose material. With the invert cleared of all debris and loose materials, the installation of the reinforcement could commence. Sheets of A252 mesh were cut and bent into the required shape off site to follow the existing invert profile (as shown below). The sheets were laid in position on the culvert invert and spacer blocks secured underneath and on top of the reinforcement giving nominal concrete coverage of 50mm throughout.

Local excavation took place at either end of the culvert, formwork placed at the downstream end and at the end of section 1 and concrete poured to begin to form the new RC Invert.

Due to limited access, the concrete was dispensed from the wagon into wheel barrows and transported to the culvert. The concrete was placed onto the invert, compacted with a vibrating poker and tamped to the required thickness. The sides of the invert were formed manually using hand tools and finished in accordance with the client’s instructions.  

Once the first section was complete, the concrete was allowed to cure for a minimum of 24 hours before striking the temporary formwork, re-erecting at the end of the next section and pouring concrete. This process continued until the concrete invert and training walls had been completed.

Once sufficient curing time has elapsed on the final section, the surface of the concrete was cleaned of all cement fines using a LP water jetting pump to prevent pollution when reopening the watercourse.

The temporary dams were then removed and all associated materials recovered from site. All plant used had Bio-Oil and generators, compressors etc were situated at least 15m away from the watercourse on a plant nappy with liner to prevent any diesel/petrol or fuel oil contaminating the watercourse or bank. All refuelling took place at least 15m away from the watercourse, with a plant nappy placed underneath the filling point and a spill kit immediately available.

During the works, a Gabion Basket failure was identified downstream, and while mobilised on site we were instructed by the client to repair the gabions. We used Sprayed Concrete (Shotcrete) to repair the damaged area and placed rock armour to prevent any further damage.

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