## 1 Introduction  
Cemented filler is a synthetic, multi-phase composite material composed of the cementing agent, filling aggregate, and mixing water. The cemented filling technology of tailing sand as filling aggregate realizes zero discharge of tailing sand. It is the mainstream way of underground mine filling. The study of the mechanical properties of tailing sand cemented fill is the basis for designing the filling strength and constructing the fill [1; 2; 3; 4; 5]. However, in the actual downhole filling process, it is challenging to fully fill the extraction area at one time. The discontinuity of the filling operation causes delamination of the filling body at the interface between two fills, and the structural properties of the delamination will cause the mechanical properties of the filling body to change. [PERSON] [6] studied the strength reduction of layered cemented fillings with different concentrations and filling times and analyzed that the low-strength interlayer was the cause of the strength reduction of layered cemented fillings. [PERSON] [7] studied the compressive strength, elastic modulus, and crack evolution law of the layered cemented filler by changing the intermediate layer's height ratio with the help of PFC software. [PERSON] [8] investigates the mechanical properties of the assemblies of cemented filling materials with different ash-sand ratios for the delamination phenomenon and analyzes the coordinated deformation mechanisms using acoustic emission characteristics. [PERSON] et al. [9] combined acoustic emission and digital image correlation techniques to investigate interfacial roughness and angle effects on gangue colloidal fillings' damage evolution.  
In the existing studies of layered cemented fillings [10; 11; 12; 13; 14; 15], there are fewer studies on the interlayer dip angle of layering, which is an essential mechanical parameter affecting the strength of layered rocks; the dip angle of layering in this type of rock structure of fillings also affects its strength and damage form. Influenced by the inclination angle, the longitudinal and transverse deformation and strength of the layered layers have different expressions [16; 17; 18], with apparent inclination angle effects; their damage mechanism and mode are different from other rock bodies.  
In order to improve the adverse effects of layering and optimize the mechanical properties of the filler, this study introduces the sandblasting method used in concrete science to treat the interface between old and new concretes and applies it to the roughening of the layered surface of the filler [19; 20; 21]. At the same time, sand, which is common and inexpensive in mine production, was chosen instead for the treatment so that it could serve to link the upper and lower layered surfaces. In this study, the mechanical properties of the tailing sand cemented fill specimens with two types of layering, natural layering and sandblasting layering, were investigated at different dip angles and different maintenance ages by simulating the actual filling conditions in the field. In addition, a damage model of the layered cemented filler was constructed to determine the mechanical properties of the filler under different layered dip angles and to provide a theoretical basis and technical guidance for the actual filling construction.