Numerical Analysis of the Effect of the Soil-Cover-to-Excavation-Diameter Ratio on Surface Settlement and Ground-Strain Stability Screening of Shallow Tunnels in Clayey Soil Using PLAXIS 3D

Moradi, Gholam; Jader Abdulhasan, Noora

doi:10.22034/ijumes.2026.2108972.1425

Numerical Analysis of the Effect of the Soil-Cover-to-Excavation-Diameter Ratio on Surface Settlement and Ground-Strain Stability Screening of Shallow Tunnels in Clayey Soil Using PLAXIS 3D

Document Type : Original Article

Authors

Gholam Moradi ¹

Noora Jader Abdulhasan ²

¹ Department of Civil Engineering, University of Tabriz, Tabriz, Iran

² Department of Geotechnical Engineering, University of Tabriz, Tabriz, Iran

10.22034/ijumes.2026.2108972.1425

Abstract

Shallow tunnels in urban clayey ground must limit surface settlement, yet the combined influence of soil cover and excavation diameter is rarely quantified with transparent three-dimensional models. This study aims to quantify how the soil-cover-to-excavation-diameter ratio, where H is the soil cover above the tunnel crown and D is the excavation diameter, governs surface settlement and ground-strain stability of shallow tunnels in clay. Six staged-excavation models were analysed in PLAXIS 3D for D = 4.3 and 6.8 m and H/D = 0.58, 2.5 and 4.0, using a drained Mohr–Coulomb clay, a 0.30 m linear-elastic lining, 1.4 m excavation steps and case-specific face pressures of 80–100 kPa. Maximum ground strains were screened against Sakurai’s critical-strain criterion, and one case was cross-checked against Peck’s Gaussian trough. Crown-line surface settlement decreased monotonically with H/D, from 4.48 to 2.49 mm (44.4%) for D = 4.3 m and from 6.05 to 1.54 mm (74.5%) for D = 6.8 m. The larger diameter settled more at H/D = 0.58 and 2.5 but less at H/D = 4.0, indicating that diameter effects cannot be separated from absolute cover and face pressure. Maximum absolute ground strains (1.03–4.88 × 10⁻⁴) did not exceed 11% of the 4.5 × 10⁻³ critical strain. The Peck comparison gave a 7.42% centerline error and a mean absolute percentage error of 23.53%. H/D is therefore the dominant geometric control on settlement within the studied range, whereas ground-strain screening does not replace structural verification of segmental linings.

Graphical Abstract

Numerical Analysis of the Effect of the Soil-Cover-to-Excavation-Diameter Ratio on Surface Settlement and Ground-Strain Stability Screening of Shallow Tunnels in Clayey Soil Using PLAXIS 3D

Highlights

· Six staged PLAXIS 3D models of shallow clay tunnels with D = 4.3 and 6.8 m

· Surface settlement fell by 44.4% and 74.5% as H/D increased from 0.58 to 4.0

· Diameter effect cannot be isolated from absolute soil cover and face pressure

· Peak ground strain stayed at ≤ 11% of Sakurai’s critical strain in all cases

· Peck cross-check: 7.42% centerline error and 23.53% MAPE over three points

Keywords

Clayey soil

cover-to-diameter ratio

PLAXIS 3D

shallow tunnel

surface settleme

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