Influence of debris flow gradation on movement characteristics and accumulation distribution: a case study of Huashan Mountain in Jinan, China - Wangyang Liu; Yan Ai; Fanmeng Kong; Yiguo Xue; Fei Guo; Tao Kong; Zhaocheng Liu; Jingkai Qu; Huaibing Wang; Zhenlong Xue (Bulletin of Engineering Geology and the Environment, 2026)