<p>There are few cases of double-arch tunnel excavation through fly ash deposits by underground excavation method in China, and the development of related technical fields is not mature. Using the Yanpingba large-section double-arch tunnel as a case study, this paper examines the structural load characteristics of a double-arch tunnel that crosses fly ash deposits to different invasion degrees by means of an indoor centrifuge model test and numerical simulation. The results show that surface and ground settlement troughs form above the tunnel, indicating that the large-section tunnel excavation in soft soil stratum resembling fly ash is prone to instability and deformation. The actual surrounding rock pressure is less than the theoretical calculation values due to the frictional restraint from the soil on both sides. The negative axial force of the lining is larger on the left than on the right, and larger on the upper than on the lower sides. The positive and negative bending moments are symmetrically distributed on the upper and lower sides, respectively, and the maximum bending moment is located at the inner arch foot. Due to stress accumulation and stratum change, the maximum load position of the lining is transferred from the arch foot to the spandrel, leading to the collapse of the middle stratum as the bearing capacity of the partition wall is insufficient. It is recommended to apply advanced support and stratum reinforcement in the fly ash area and strengthen the displacement monitoring. The conclusions of this paper can provide reference for the design and construction of similar projects.</p>