Construction World January 2019

Temporary soil retaining wall.

widenings (up to 40 metres in height) involved the installation of a rock trap and barrier, the width and height of each being determined by the nature of the cut material and design slope configuration. Due to the varying nature of the geology, it was necessary to provide additional protection measures. Solutions included the provision of gabion tied back walls, the installation of high tensile wire mesh to the exposed face, as well as gunited sections in order to protect the drillers during the installation of the rock dowels. In order to minimise the disturbance of the excavated face during blasting, pre-splitting was necessary. Geometric re-alignment and widening of the fills by means of installing retaining walls was required in order to provide sufficient areas where arrestor beds could be installed. Design risk management HHO liaised closely with the Client in order to co-determine the most appropriate and cost effective design solutions. During the designs and even during the construction, it became evident that additional safety improvements were required. The installation of a second arrestor bed and concrete barriers were thus added to the scope of the work. Regular progress and planning meetings, as well as technical meetings were held. Site visits by the design specialists and site supervisory personnel were done in order to ensure that the design intent was being followed. The complex geological setting and geomorphological environment of the pass demanded geotechnical designs that would be adaptable to the conditions. Good communication and interaction between the profession team, main contractor, geotechnical sub-contractor and geotechnical suppliers was vital in dealing with the various challenges encountered, and in successfully implementing the geotechnical designs. Environmental Impact Consideration The construction methods adopted for the project were chosen in order to have the least impact on the environment and aesthetics. An environmental impact was carried out at the commencement of the project and all specialist studies and requirements built into the project. These included the removal of certain protected three species which were to be replaced at the end of the project. Monitoring of dust contamination at the quarry site and the monitoring of water quality was undertaken during the construction. Environmental Health and Safety audits were conducted monthly. Various training programmes formed part of the project, in order to provide social and technical training to the permanent employees of the contractor as well as the temporary staff employed form the local communities.

The completed Olifants Bridge.

showed that the quality of the material within the narrow roadway needed to be strengthened in order to provide a lasting design which took into account the type of traffic using the road. The structures required to either be re-built or widened. Structures needed to be strengthened due to the increased loading of a widened roadway. The geotechnical investigations confirmed a composite geology through the Kranspoort pass; with a combination of jointed and variably weathered quartzitic sandstone rock, talus material, residual clays as well as dolerite intrusions making up the complex geotechnical environment. Appropriate design solutions were needed that would provide a safe passage for all persons using the road. Construction innovation technology In order to achieve the objectives of providing a widened roadway over the various structures it was necessary to widen these. In particular, the Olifants River Bridge required that the 1,5 m cantilevers be demolished by means of hydraulic impact hammers, while retaining the reinforcement to be lapped onto the new longer cantilever reinforcement. As the substructure was going to be subjected to additional loads (dead weight and live loading) it was necessary to strengthen the longitudinal beams by means of installing fibre reinforced plates to the bottom of the beams. The piers were strengthened by means of providing external prestressing to the pierheads using 3 x 40 mm diameter DYWIDAG threaded bars on either side of the pierhead to counter the additional moments. These bars were encased in concrete. The cylindrical piers were strengthened by means of providing a 150 mm reinforced concrete jacket for the full height of the pier. The safety improvements in the Kranspoort Pass included widening to accommodate two lanes in each direction, geometric improvements, the installation of concrete barriers and the provision of two arrestor beds. Geotechnical design of the cut

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CONSTRUCTION WORLD JANUARY 2019