## 1 Introduction  
With the rapid development of China's economy, the demand for travel is increasing. Zero distance transfer and seamless connections have become important factors in people's choice of travel mode. The rapid transportation network that is composed of railway, rail transit and aircraft has entered the rapid construction period. The complex three-dimensional transportation network has gradually formed, and some more complex transportation construction projects have emerged, such as the construction of underpass tunnels or other underground buildings in the airport flight area (runway, airport taxiway, etc.). At present, the existing domestic and foreign tunnels under the airport airfield include: Taiwan Songshan municipal road underground runway crossing project, Taipei shield tunnel crossing runway engineering, Beijing Capital Airport underground service lane undercrossing I-shaped slideway project and the runway crossing project of Shanghai Hongqiao airport metro Lines 2 and 10, plus, the circular monozail tunnel under the Stuttgart Airport runway in Germany and the rail tunnel under the taxiway and apron of Heathrow Airport in the UK. In contrast to other shield undercrossing engineering projects, the normal operation of the airport runway cannot be interrupted during the construction of the shield tunnel. Additionally, airport runway construction has more stringent requirements on ground settlement. Excessive ground displacement induced by underground crossings can cause runway cracking; this phenomenon may cause airport outages or major accidents [1; 2]. So, excavating shield tunnels in non-stop airport flight areas is extremely challenging. It is necessary to carry out safety analysis and formulate a strict control scheme before construction. At present, much research has been performed on the settlement of the existing buildings and structures caused by shield tunnel construction. However, there is no clear and unified regulation on the allowable settlement of airport runways. The settlement control requirements of airport runways are mainly based on the experience of highway construction on soft soil foundations. There are few studies on the laws of airport runway settlement caused by an undercrossing shield tunnel. Aiming at the issue of ground surface settlement caused by shield tunnel construction, the research methods can be summarized as follows: empirical formula method, numerical analysis method, theoretical analysis method and model test method. In terms of the empirical formula method, [PERSON] [3] proposed a formula fitted by a Gaussian function regarding ground settlement induced by a tunnel. The Peck formula is widely accepted in tunnel engineering. On the basis of [PERSON]'s empirical formula, researchers have conducted more in-depth research on empirical parameters [4; 5; 6; 7; 8]. Compared with the empirical formula method, the theoretical analysis method is a conclusion analysis method based on some theoretical assumptions. Taking into account that the soil is elastic plane and incompressible, [PERSON] [9] proposed the strain solution of an elastic isotropic homogeneous body in the case of near-surface ground loss. Subsequent scholars solved the formation deformation under different boundary conditions through a complex potential function method [10; 11; 12; 13], stochastic medium theory [14; 15; 16; 17] and cavity expansion theory [18; 19; 20; 21], etc. With the rapid development of computer techniques, finite element numerical simulation is becoming the most efficient way to simulate the construction procedure of underground engineering under various complex environmental conditions [22; 23; 24]. For instance, [PERSON] et al. [25] investigated the effects of shield tunnel construction on the differential settlement and the soil dynamic stress of an adjacent culvert-embankment transition zone via finite element analysis. [PERSON] et al.