JOURNAL OF ROCK MECHANICS

JOURNAL OF ROCK MECHANICS

Numerical Analysis of Tunnel Deformation Behavior and Surface Settlement in Layered Clayey Soils with Emphasis on the Cover-to-Diameter Ratio

Document Type : Original Article

Authors
Mohammad Pouria Aghaei 1
Sadegh Tarigh Azali 2
Armin Moghbeli 2
1 RahsazTarh consulting engineering
2 Rahsaz Tarh Consulting Engineers
10.22034/irsrm.2025.550181.1070
Abstract
This study investigates the effect of the cover-to-diameter ratio (H/D) on ground deformation and the response of the initial tunnel lining in layered clay soils using numerical modeling. The tunnel diameter was kept constant, and the H/D ratio was varied from 0.5 to 3.5 to simulate shallow to deep tunneling conditions. The analyses were performed using the finite element method with the Hardening Soil constitutive model. The excavation process and installation of the shotcrete primary lining were simulated in stages to realistically represent the construction sequence. The system response was evaluated using several indicators, including maximum surface settlement, settlement trough width, vertical and horizontal tunnel convergence, tunnel ovalization, and two-dimensional volume loss. In addition, settlement profiles were fitted using Peck’s Gaussian function to quantitatively evaluate settlement parameters. The results indicate that settlement behavior is strongly influenced by soil layering and stiffness variations. With increasing H/D within the stiffer upper layers, the settlement trough width decreased by about 30%, indicating a more concentrated settlement zone. As the tunnel entered a softer intermediate layer, the trough width increased by approximately 30%, reflecting greater lateral spreading of ground deformation. In contrast, the maximum surface settlement increased by about 30%, while the volume loss increased by more than 100%, indicating a greater development of the plastic zone with increasing cover. Tunnel structural response also intensified with increasing H/D: tunnel ovalization increased by about 75% and vertical convergence increased by about 85%, whereas horizontal convergence remained negligible. Radial displacement at the tunnel crown and invert increased by approximately 71% and 275%, respectively, indicating intensified deformation with increasing cover. Overall, the results demonstrate that increasing the H/D ratio amplifies both ground and tunnel deformations. Moreover, the presence of softer soil layers can significantly alter the settlement pattern by promoting wider settlement troughs. These findings highlight the importance of considering soil stratification and staged numerical analysis in the deformation-based design of urban tunnels.
Keywords
Tunnel Surface Settlement
Settlement Trough
Numerical Modeling. NATM Method
PLAXIS 2D
Subjects
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JOURNAL OF ROCK MECHANICS
Volume 9, Issue 3
Autumn 2025
Pages 97-116