Analysis on the Accident of Unhealthy Tank Foundations

Four tanks in a tank farm in Dagang area had an inclination problem. The soil in this area is soft Quaternary sediment mainly consisting of clay, which is featured by low intensity, unstable structure, logh softness and pertubility, and poor permeability. The following reasions for foundation inclination are analyzed: ①The soft foundation was not properly prepared, and measures for drainage improvement were not taken; ②The active load exceeded the foundation bearing capacity due to the fact that the control of loading rate and water filling rate had been ignored; ③The surface structure was destructed during construction. The best remedy to tank foundation is rotary cement injection with high pressure which can effectively prevent further foundation settlement.enlargement of the "kettle bottom" and inclination development. For the purpose of safe operation, the soft foundation shall be improved using the follow methods: specify loading and water filling rate according to engineering characteristics of bearing compression layer of the foundation; use natural, raft or sand pile foundation depending upon the tank features and load distribution; and design a safe distance between foundations for settlement.