Good Reasons to Swap from Trench Cutter to Hydraulic Grab; Liebherr and Saos, Actual Cases from Florence, Rome and Milan-Paper

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The paper argues that hydraulic grabs can be a practical alternative to trench cutters for deep diaphragm-wall construction, particularly in dense urban areas with limited space, sensitive surroundings, and challenging ground conditions. Advances in heavy-duty crawler cranes and grab technology have made it possible to achieve high excavation depths, accuracy, and productivity while reducing noise, fuel use, and site disruption.<br /><br />Compared with mechanical grabs, hydraulic models offer controlled jaw operation, rotation, and deviation correction. Inclinometers provide real-time verticality monitoring, while integrated crane-and-grab controls support precise operation and data recording. The paper also highlights the advantages of dual winches, including lifting redundancy and reduced rope wear. These systems require suitable equipment and experienced operators.<br /><br />Three Italian projects illustrate the approach. In Florence, Liebherr crawler cranes and hydraulic grabs were used to excavate diaphragm walls up to 40 metres deep for the new high-speed railway station. In Rome, SAOS selected hydraulic grabs for the 56-metre-deep San Giovanni Metro C station after trench-cutter work at a nearby site encountered bentonite losses in gravelly ground. The grab’s excavation method reduced slurry recirculation and the associated risk of leakage. In Milan, SAOS used a hydraulic grab for M4 works, including deep panels, with monitoring to help meet verticality requirements. A sheet-pile stop-end method was also adopted to create clean, watertight panel joints.<br /><br />The authors conclude that hydraulic grabs can deliver reliable precision, productivity, and cost performance at depths exceeding 50 metres, as demonstrated by the Rome, Florence, and Milan projects. Success depends on modern, appropriately configured machinery and skilled technical teams.

Keywords

hydraulic grabs

diaphragm wall construction

deep excavation

trench cutters

crawler cranes

urban construction

verticality monitoring

dual winches

slurry leakage

Italian projects