A similar phenomenon can also be observed under the DWPC, as shown in Figure 10.
The calculated radial displacement of the PTCL under the CCTC and DWPC in six cases is shown in Figure 11, where 9 is the angle measured clockwise from the vertical plane.
The results in Figures 12(e) and 12(f) also show that partial parts of the PTCL's internal surface are subjected to tensile stresses under the DWPC. The tensile parts are mainly located at the upper semicircle of the PTCL.
In contrast, when T is less than 0.325 m, partial parts of the PTCL's external surface will be subjected to tensile stresses under the DWPC. As shown in Figure 13(d), the tensile parts are mainly located at the tunnel crown, and the maximum tensile stress of the PTCL's external surface is 0.37 MPa.
The above findings imply that the PTCL will be subjected to tensile stresses under the DWPC if the deficiencies in the tunnel crown thickness exceed a certain threshold.
(4) Cracks at the external surface of the crown and internal surface of the crown's adjacent parts may be expected under the DWPC. Because the cracks form during the filling of the tunnel with water, they may not be readily detected until serious damage to the lining has been produced, generally in the form of severe cracking, leaking, or even failure.
Caption: Figure 10: Deformations of the PTCL under the DWPC: (a) T = 0.45 m, (b) T = 0.40 m, (c) T = 0.325 m, (d) T = 0.28 m, (e) T = 0.22 m, and (f) T = 0.16 m.
Caption: Figure 11: Radial displacement of the PTCL: (a) CCTC and (b) DWPC.