Quick, Efficient & Safe Preloading of High Capacity Hydraulic Modular Props-Paper

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The paper describes a hydraulic nut system developed to make preloading and removal of high-capacity hybrid props safer, faster, and more reliable.<br /><br />Preloading helps anticipate excavation loads and reduce retaining-wall deflection. Groundforce’s MP500 hybrid prop combines a 250-tonne hydraulic cylinder, used for rapid installation and initial preload, with two 160 mm mechanical locking screws that carry loads beyond the cylinder’s capacity. On some projects, props remained heavily loaded after construction, making the screws difficult to loosen. Earlier remote-jacking methods were complex, time-consuming, required specialist equipment and access platforms, and could apply damaging eccentric loads. In some cases, props had to be cut out.<br /><br />The new hydraulic nuts act directly beneath the locking-nut heads. During installation, the central cylinder extends the prop to the required length and applies an initial load; the locking screws are tightened, and the cylinder is depressurised. The hydraulic nuts are then pressurised in controlled increments, after which the final locking nuts are secured and the hoses removed. A load-monitoring pin is recommended to measure preload accurately and track load redistribution across the support system. Removal reverses the procedure.<br /><br />The system applies load directly and hydraulically, avoiding brute force and eccentric loading. It allows phased adjustments without handling heavy external jacks, reduces manual work and access requirements, and provides continuous load monitoring. The authors conclude that hydraulic nuts improve safety and reliability while reducing the time, cost, and difficulty of removing heavily loaded props.

Keywords

hydraulic nut system

preloading

hybrid props

retaining wall

load monitoring

mechanical locking screws

remote jacking

excavation support

load redistribution

prop removal