In situ tests simulating traffic-load-induced settlement of alluvial silt subsoil

In China, The Yellow River delta is the youngest large river delta, and the low liquid limit alluvial silt is widely distributed there. The silt is easy to liquefy so that the silt subsoil shows large settlement under traffic load. At present, few in situ model tests were conducted to study the traffic-load-induced settlement of silt subsoil. Therefore, a falling-weight simulation equipment of traffic load was developed. By adjusting the technical parameters such as the falling height of the weight, different types of traffic loads can be well simulated. With the equipment, in situ tests were carried out to study cumulative settlement of silt subsoil in the Yellow River delta. Tests indicate that the settlement and excess pore water pressures rapidly grow initially and then tend to be stable with increasing the number of load cycles, and they also increase with the magnitude of the traffic load. When the load attains a threshold value, liquefaction takes place in the silt subsoil. After terminating loading, the pore water pressure rapidly decreases and the settlement increases simultaneously, while after one hour they tend to stabilize. Based on Chai-Miura cumulative deformation model of soil, the traffic-load-induced cumulative settlement of silt subsoil was calculated and compared with the test results. The calculated cumulative settlement with increasing number of load cycles agrees well with the test results, except the initial phase of cyclic loading where the settlement observed in the situ tests is overestimated. This is mainly because Chai-Miura model assumes undrained conditions while the subsoil under traffic loads is partly drained.