大断面隧道原位扩挖易诱发地表沉降，威胁周边建构筑物服役安全，然而，隧道原位扩挖上覆地层沉降规律尚不清晰。采用理论分析、物理模型试验和工程实践相结合的方法，研究隧道原位单侧扩挖上覆地层沉降规律，建立隧道扩挖沉降量理论模型。结果表明：隧道上覆地层沉降具有突增特征，扩挖沉降带呈抛物线分布特征，主要与岩体的黏聚力与脆性破断特征有关，地层沉降量与距隧道的距离呈非线性递增变化关系，主要受开挖卸荷扰动的非均匀衰减影响；理论模型曲线可以反映出与模型试验一致的沉降规律，试验值与理论值的平均误差为4.8%；考虑隧道支护的修正系数α对工程实测值的影响，α ＝ 0.7的模型值与α ＝ 0.4的模型值可以较好地预测隧道扩挖支护后隧道地表沉降的变化范围。研究成果可为隧道原位扩挖地层沉降计算提供理论方法。

Large section tunnel in-situ expansion excavation is prone to induce ground settlement, posing a threat to the service safety of surrounding structures. However, the settlement evolution of the overlying strata during tunnel expansion excavation are not yet clear. A method combining theoretical analysis, physical model testing, and engineering practice was adopted to investigate the settlement evolution of the overlying strata during expansion excavation of tunnels. A theoretical model for tunnel expansion excavation settlement was established. The research findings indicate that the settlement of the overlying strata above the tunnel exhibits a sudden increase characteristic, with the expansion excavation settlement zone showing a parabolic distribution, which is primarily related to the cohesive force of the rock mass and its brittle fracture characteristics. The strata settlement shows a nonlinear increasing relationship with the distance from the tunnel, mainly influenced by the non-uniform attenuation of excavation unloading disturbance. The theoretical model curves can reflect the settlement evolution consistent with the physical model tests, with an average deviation of 4.8% between the experimental and theoretical values. Considering the influence of the correction coefficient α for tunnel support on the measured engineering values, the model with α = 0.7 and α = 0.4 can better predict the range of surface settlement after tunnel expansion excavation and support. The research results provide a theoretical method for calculating strata settlement during tunnel in-situ expansion excavation.