Considerations in the Design and Construction of Ventilation and Surge Shafts for the uMWP Phase 1 Water Transfer Tunnel
Authors: B.C. Rodrigues1, T. Mac Kellar1, G.J. Keyter2
Conference: SANCOT Symposium 2026
Date: April 13-14, 2026
1 Knight Piésold, South Africa
2 SRK Consulting, South Africa
ABSTRACT
This paper presents an overview of the key considerations governing construction method selection for ventilation and surge shafts for the Phase 1 water transfer tunnel of the uMkhomazi Water Project (uMWP-1). The uMWP-1 project site is located between Impendle and Hopewell, south of Pietermaritzburg in KwaZulu-Natal, and includes two ventilation shafts (1.5 m finished diameter, with depths of 125 m and 190 m, respectively) and one surge shaft (5.0 m finished diameter and 110 m deep), to be constructed in Karoo mudrocks and dolerites.
Geotechnical characterisation of the shaft sites was undertaken using borehole logging, downhole wireline geophysical surveys, and laboratory testing. These investigations identified sequences of weathered and fresh shale, dolerite intrusions, structurally disturbed intervals, and variable groundwater conditions. Anticipated rock mass behaviour, together with structural data evaluated using Rocscience Dips and Unwedge, informed the evaluation of design risks and preliminary ground support requirements for shaft stability.
The paper compares shaft sinking methods, including reverse circulation (RC) drilling as the preferred method for the ventilation shafts, and alternative methods for the larger surge shaft. The discussion focuses on the suitability of these methods relative to anticipated ground conditions, groundwater, working footprint, cost and programme implications, and site-specific environmental constraints, particularly at the outlet end of the uMWP-1 transfer tunnel. Relevant precedent experience and comparable case studies are referenced where applicable.
The paper also considers the influence of logistical constraints, anticipated water inflows, and variable surface conditions on construction planning and risk management. Practical aspects of ground support, groundwater management, and spoil handling are discussed. The paper concludes with recommendations on method selection and risk mitigation, informed by the current investigations, precedent experience from similar shaft projects, and ongoing design of the uMWP-1 works.
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