Study on the distribution law of vertical earth pressure in the construction of a metro station using PBA method in a loess stratum

Abstract

The PBA method is essential to master vertical earth pressure distribution law in the subway station construction in the loess layer. Based on the engineering background of the Hejiaying Station of Xi'an Metro, this paper investigates the vertical earth pressure distribution of headings and buckle arches under different construction sequences based on numerical simulation and compares them with measured on-site data. The research results indicate the following. (1) The vertical earth pressure at the arch springing of headings A and D in the upper layer is approximately 1.06 times the vertical earth pressure at the arch crown. Moreover, the vertical earth pressure at the arch springing of headings B and C in the upper middle is approximately 1.015 times the vertical earth pressure at the arch crown, signifying that the vertical earth pressure at the middle heading B and C is more evenly distributed. (2) Comparing the different excavation sequences of the same layer of caves, the two sequences "excavating the upper layer first and then the lower layer" and "excavating the lower layer first and then excavating the upper layer" have a more significant impact on the vertical earth pressure of the headings. The heading initially excavated bears the slightest vertical earth pressure. (3) If Scheme 2 is applied to construct the buckle arch, the vertical earth pressure at the junction of the buckle arch and the heading is relatively large, approximately 1.69 times the vertical earth pressure of the buckle arch. Meanwhile, if Scheme 1 is applied for buckle arch construction, the force on the upper part of the buckle arch is relatively uniform. However, the earth pressure on the top of the arch is more significant than that of Scheme 2. It signifies that the earth pressure at the middle part of the arch is mainly transferred to the two ends of the arch when construction is performed using Scheme 2.