The sand cone apparatus looks simple: a plastic jar, a brass cone and a base plate. But when you're standing on a windy site off the A4 in Slough, that device has to perform flawlessly. We pour dry, graded sand into a carefully excavated hole and measure the volume displaced. It's a direct method. No electronics. No guesswork. The jar weighs roughly 4 kg when full, and every gram matters when you're calculating in-place density. In our lab, we calibrate the sand before it ever leaves the bench because the rounded grains we use in Slough's conditions must flow consistently. The town sits on a mix of Taplow Gravels over London Clay, with pockets of made ground near the industrial estates. That built-up terrain means we often carry out a sand cone density test right after a plate load test to cross-check the bearing response.
You can't feel 95% compaction. You have to measure it — and in Slough's mixed ground, a single failed test can unravel a whole layer's acceptance.
