## 2 Overview of the Survey Area  
The Cedaya-S340 Holgutu Highway Construction Project is located in the Mongolian Autonomous Prefecture of Bayingolin, Xinjiang Uygur Autonomous Region (Figure 1). It is an important traffic channel that connects Luntai County and Hejing County at the southern foot of Tianshan Mountains in Bayingolin. It is also an important tourism highway in the Xinjiang Uygur Autonomous Region. The Cedaya-S340 Holgutu Highway directly or indirectly connects the G3012 Expressway, S340, G314, G218, and other trunk highways. The construction of this highway will further improve the regional road network, particularly its traffic conditions and transport efficiency. Simultaneously, the Cedaya-S340 Holgutu Highway opens the southward corridor of the famous scenic spot BayanbulakGrassland, considerably shortening driving distance from Bayanbulak to Korla and Luntai and playing an important role in promoting the development of the tourism industry in Bayingolin [26,27]. The Huola Mountain Tunnel, as the major control of the highway project (black box area in Figure 1), is located near Cedaya Township, Luntai County, Bayingolin. The tunnel passes through Huola Mountain as a whole. Huola Mountain is located in the middle of the Xinjiang Uygur Autonomous Region, at the junction of south Tianshan Mountains and the northeast edge of Tarim Basin, close to Rosten Lake, the largest inland freshwater lake in China. Huola Mountain is connected to the Great Youerudus Basin in the north, Kuqa Fold Belt in the west, and Yanqi Basin in the northeast. Korla, the second largest city in Xinjiang, is located in front of the southeast mountain. The mountain is NW-SE trending, with a total length of about 245 km and a north-south width of about 30-60 km. It gradually narrows from west to east, similar to a wedge-shaped distribution. The terrain is high in the west and low in the east. Elevation gradually decreases from nearly 4200 m in the northwest to about 1100 m in the southeast [28]. The regional strata mainly consist of Paleoproterozoic(Pt1 Ar), Devonian (D), Carboniferous (C), Neogene (N), and Quaternary (Q) materialsin the Huola Mountain Tunnel area. According to previous regional geological data, Huola Mountain Tunnel is crosscut by five faults (numbered F1 to F5, respectively) [26]. The four E-W-trending faults are nearly parallel. The F4 and F5 faults are crosscut by the F3 NW-SE trending strike-slip fault with about 300 m strike-slip distance. The F1 fault mainly occurs in the contact zone between the Carboniferous and the Quaternary strata. The F2 fault is present within the Carboniferous strata. The F3-F5 faults are present in the contact zone between the Carboniferous, Devonian, and Precambrian strata. The core Early Carboniferous strata is a uniform shallow marine carbonate sedimentary formation [27]. Figure 1: Location map and geological background of Huola Mountain. The tunnel site is predominantly in a medium-high mountain area. The tunnel entrance is located at K44+970 along the line. On the southern slope of the mountain, the terrain gradient is 40\({}^{\circ}\)-55\({}^{\circ}\) and the terrain is steep. The tunnel entrance trend intersects with the slope nearly vertically. The tunnel exit is located at the line K53+490. On the north slope of the mountain, the terrain gradient is about 35\({}^{\circ}\), terrain is steep, and slope vegetation is not developed. The tunnel exit trend intersects with the slope nearly vertically. The thickness of the overburden in the tunnel site is unevenly distributed. The overburden at the tunnel entrance and exit is thin. The bedrock in the tunnel is exposed. The lithology of the bedrock in the tunnel site is mostly calcareous sandstone and a small amount of limestone [26,27]. The entrance of the tunnel site is located in Keyilike Ditch, Cedaya Township, Luntai: its exit is located in the Malgaiti Ditch, Bayanbulak, Hejing County. The mountains on both sides of the entrance and exit are steep, and, thus, the area has no conditions of traffic.