Research on the influence of width-height ratio and internal friction angle of the TT mode on the trapezoidal sliding surface of backfill behind the retaining wall

The morphology of sliding surface is an important factor in the earth pressure analysis. To study the characteristics of the sliding surface of backfill behind a rigid wall, taking the translational mode of wall (TT model) as an example, a model test was conducted through a self-made test device, and numerical modelling and theoretical analysis were carried out. The research shows: (1) The finite sliding surface morphology starts from the heel of the wall and consists of multiple “straight lines”. The smaller the width-height ratio and the internal friction angle, the more the number of straight line segments of the finite sliding surface. (2) The “length factor” of the sliding surface is introduced and defined. Through normalisation processing, the width-height ratio, internal friction angle, and length factor are linearly fitted, showing a high degree of linear correlation. (3) The study of the width-height ratio, internal friction angle, and length factor yields a binary quadratic surface function, which shows a high degree of linear correlation. The study fills the research gap of the joint influence of the width-height ratio and internal friction angle on the folded-line type sliding surface. It proposes a quantitative calculation formula for the determination of the finite soil.