Mechanisms and controlling factors of heave in summer for high-speed railway cutting: A case study of Northwest China.

• The expansibility of mudstone in the foundation for cutting heaved area was investigated. • An in-situ experiment was carried out of the micro-expansion red-bed mudstone in foundation. • The heave mechanisms of cutting for the ballastless track in summer were studied. • The heave mitigation techniques using the water-blocking ditch was proposed. The cutting of the ballastless track for the Lanzhou-Xinjiang high-speed railway (LXHR) shows a transfinite heave deformation in the summer. This paper investigates the mechanisms of cutting heave by analyzing the water content, mineral composition, microstructure, and expansibility of mudstone in the foundation using drilling core sampling in the cutting heaved area for the (LXHR). Besides, an in-situ test is performed on a typical cutting heaving position to investigate the overall expansibility of the micro-expansion red-bed mudstone after absorbing water under different overlying loads. The results showed that the clay mineral content of the mudstone in the foundation was very low, and it does not belong to the category of expansive rock but only has micro-expansion. The in-situ experiment revealed that the swelling value of micro-expansion red-bed mudstone with a thickness of 80 cm was 12.61, 8.78, 7.31, and 5.77 mm under an overlying load of 0, 15, 30, and 45 kPa, respectively, which exceeded the tolerance limit (4 mm). In addition, the study proposed the possible mechanisms that lead to the heave deformation for the LXHR cutting in summer, including the micro-expansion red-bed mudstone in the foundation, the lateral water supply mechanism, and the excavation and unloading. As a result, it preliminarily suggests the heave mitigation techniques for the LXHR by using the water-blocking ditch. [ABSTRACT FROM AUTHOR]