The Ground Settlement and the Existing Pipeline Response Induced by the Nonsynchronous Construction of a Twin-Tunnel

Table 1

Basic mechanical parameters related to the soil layer and the shielding.

Material type	Thickness (m)	Density (kN·m^−3)	Elastic modulus (MPa)	Cohesion (kPa)	Friction angle (°)	Poisson ratio
Fill	4	17.5	9	10	8	0.39
Clay	25	19.8	16.1	55	15	0.29
Silty clay	11	19.6	23	36	18	0.28
Shield shell	0.05	78	2.5 × 105	—	—	0.2
Segment	0.3	25	3.8 × 103	—	—	0.2
Grouting layer	0.05	20	5.0 × 102	—	—	0.3
Concrete pipeline	0.1	25	2.5 × 104	—	—	0.2