The Civil Engineering Contractor July 2019 | Page 8

PROJECT OWNERS Bridging Limpopo together Project: Provincial roads Client: Roads Agency Limpopo Location: Limpopo The Roads Agency Limpopo (RAL) is forging ahead with the construction of a new road that will connect three villages in the mainly rural Sekhukhune District Municipality to two provincial roads, including the D1547 that is administered by the South African National Roads Agency Limited. When completed in September 2019, the new 13km single carriageway will provide citizens of Mmotwaneng, Legonaneng and Luckau with quick access to major urban centres in Limpopo and Mpumalanga. On site are Thabiso Phetla, site manager of Lonerock Construction, and Joseph Myoya, Ubona Engineers’ resident engineer-on-site. “As a typical Expanded Public Works Programme project, it has been designed to be extremely labour intensive. By November 2018, there were as many as 60 locals working alongside members of our team. This number will increase when we commence on the ancillary works, such as the installation of the guardrails and construction of the storm-water drains, in mid-2019,” Phetla says. Myoya adds that one of the challenges was quickly adapting the original engineering design that was completed more than eight years ago to current conditions without delaying the works programme. “While the engineering design was completed by another engineering consultancy in 2010, the construction of the road was delayed by RAL due to limited financing and other pressing responsibilities. The villages have since rapidly expanded with many properties located within the planned route. The road, therefore, had to be extensively realigned to avoid having to relocate more than 200 affected properties. Our approach, which also included reducing the width of the two-metre shoulder in areas, resulted in significant cost savings for the client, while also mitigating further delays to delivering this critical infrastructure to the communities,” he says. Moreover, the original design of the bridge over the Mankgatle River had to be adapted to align with the higher level of the new realigned road. It is one of two major and technically-complex structures that were built by Lonerock Construction as part of this project. At six metres in height, it is significantly taller than the original design and is, thus, well above the 20-year floodplain. Substantially more reinforcement steel was required for the taller concrete abutments and additional precast-concrete elements were needed to build the larger 20m long and 11.5m wide superstructure. The I8 precast-concrete beams and 126 precast concrete deck planks were manufactured and installed by CoreCivils, the precast-concrete bridge beam and parapet arm of 6 | CEC July 2019 The new bridge over the Mankgatle River is one of two large structures along the route. CoreSlab. The benchmark for quality was confirmed after the first element had reached a compressive strength of 45MPa and CoreSlab was instructed by the team to proceed with the manufacture of the remaining seven beams and deck planks. The design of the foundations of the bridge also had to be modified by Ubona Engineers considering that the terrain is overlain by rocks and large boulders. A decision was taken to anchor the foundations of the bases of the abutments into the large boulders as opposed to removing them by drilling and blasting. “Mass concrete was cast over the boulders and we then drilled through them to insert the dowels. This approach provided some cost savings for our client considering that up to 45 000m³ of rock had to be removed by drilling and blasting during the earthworks stages of the construction of the road. It also mitigated any delays as we decided to first prioritise the completion of the two large structures before working on the road,” Myoya says. Some of this material was crushed and used in the layer works of sections of the roads and in the foundations of the large cast in-situ three-barrel culvert. These challenging ground conditions were compounded by the perched water table in many areas along the route. Affected areas were excavated and then filled with crushed rock that was covered with a Bidim geotextile, before work commenced on the layer works. The road comprises a bedding layer compacted to 93% AASHTO density; selected layers compacted to 95% AASHTO density; and a C3 base course compacted to 98% AASHTO density. This road will then be primed and sealed with 13.2mm and 6.7mm thick bitumen layers. Quality G6 material for the sub-base layers was sourced on site from the various cuttings and the remaining material from two borrow pits that were opened specifically for this project. In terms of the stabilisation of the sub-base layers, the pockets of cement supplied to site by PPC were unpacked and spread by hand to ensure accuracy and to provide further www.civilsonline.co.za