Prediction model for settlement caused by damage of underground pipelines and its experimental verification

A set of test system of ground settlement caused by damage of pipelines in water-rich sand layers is designed. For 11 kinds of soil samples with frame diameter d₉₀ of 1.45~8.45 mm under 6 kinds of permeability ratio drops and full flow velocity of pipelines, the laws of ground settlement induced by seepage erosion of soil mass are studied. On this basis, a prediction model for ground settlement induced by damage of underground pipelines is proposed. The results show: (1) Whether the pipeline damage will induce settlement in the water-rich sand layers is mainly determined by the soil skeleton particle size d₉₀, the diameter D of the damaged mouth and the thickness span ratio h_S/D. The maximum value of the soil skeleton particle size d₉₀ that causes the settlement should meet both the conditions of the diameter D of the damaged mouth and the thickness span ratio h_s/D, and take the smaller value of the two. (2) In the water-rich sand layers, the area of pipeline damage-induced settlement is circular in plane and inverted triangle in section, and the slope angle is close to the saturated internal friction angle of soils. The top radius and settlement depth of settlement area increase with the increase of full flow velocity u and permeability ratio drop h_w/h_s, and decrease with the increase of thickness span ratio h_s/D. (3) Based on the Manning's formula, the prediction formulas for settlement radius and settlement depth are deduced, and are consistent with the test results in law and close to the test results in numerical value. They can be used to predict the settlement caused by damage of pipelines in water-rich sand layers.