The hydraulic jack is what makes it all happen. When we roll out the hollow-stem auger rig in Slough, it is the stressing equipment that really gives us the performance data. You see the ram extend, the pressure gauge climb, and you know exactly what that anchor tendon is holding in the London Clay. In Slough, the anchors have to lock into the stiff blue-grey clay at depth, well past the weathered brown crust. We typically proof-load to 1.5 times the working load, holding it for fifteen minutes while monitoring creep. A lot of contractors around the Bath Road corridor call us in specifically for this test, because the ground here transitions so fast from gravels into clay. Getting the fixed anchor length right means drilling into that competent stratum, and the jack tells the story. Complementing this, our team often runs a full site investigation with SPT to confirm the exact depth to refusal before we finalise the tendon bond length for any restrained excavation.
In the transition zone between River Terrace Gravels and London Clay, the free tendon length often dictates whether the anchor behaves actively or passively under load.
