Anisotropy of Q2 loess in the Baijiapo Tunnel on the Lanyu Railway, China

The predominately, wind-derived deposits forming the Loess Plateau in China are known as Wucheng loess (Q(1)), Lishi loess (Q(2)), and Manlan loess (Q(3)). Only Q(3) loess has been intensely studied in densely populated areas, revealing that the structural strength of these aeolian sediments is directly related to their variations (anisotropy) in compressibility, water content, and, particularly, vertical jointing. Knowing the stability level of Q(3) aeolian sediment is important in tunnel constructions through other types of loess. The research reported here has been mainly centered on obtaining the values of consolidation, unconfined compressive strength (UCS), direct and triaxial shear tests, Poisson's ratio, and modulus of deformation of the Q(2) loess in the Baijiapo Tunnel on the Lanyu Railway, Lanzhou, China. Included among the numerous results of these comprehensive laboratory tests are: the mean index of liquidity is 0.19; and the maximum modulus of compression in the vertical direction is 1.17. Furthermore, vertical and horizontal samples showed brittle fracture; the ratios of UCS and modulus of deformation in the vertical to the horizontal directions are 1.34 and 2.45, respectively. The wide range of various values of Lishi loess properties are closely related to variation in the density of the vertical jointing system. A new method for calculating comprehensive shear parameters is proposed and the related parameters for the Baijiapo Tunnel are recommended.