## 1 Introduction  
In the underground mining process, filling the goafs with cemented paste backfill (CPB) mixed with tailings, cement, and water is an effective way to control ground pressure and treat mining waste [1, 2, 3]. However, limited by the properties of tailings and the cost of cement, the strength of CPB is usually quite low, especially the tensile strength. It is only about one-tenth of the compressive strength, and low tensile strength becomes an important hidden danger that causes damage to CPB [4]. Generally, the properties of specific tailings produced by mines are difficult to change. Increasing the usage of cement has become the main method to enhance the strength of CPB, which greatly increases the backfill cost of the mining enterprise [5]. How to improve the tensile strength of CPB economically and effectively is a topic of concern to related researchers. Driven by the demand, some scholars have studied the impact of using fibers, rubber crumbs, and nanomaterials as additives on backfill materials or cementitious materials [6, 7, 8]. [PERSON] et al. [9] incorporated glass fibers into shotcrete, and the results showed that the maximum tensile strength of the shotcrete added with glass fibers reached more than 300%, and the maximum increase in shear strength reached more than 500%. [PERSON] et al. [10, 11] studied the compressive properties, tensile properties, and microstructure of polypropylene fiber-reinforced CPB, and found that polypropylene fibers can enhance the stiffness and ductility of CPB, improve the residual strength of CPB after destruction, and reduce the porosity of CPB. [PERSON] et al. [12] found that the strength and strain of cement-stabilized sandy-clayincreased with the increase in polypropylene fiber content under indirect tensile stress. [PERSON] et al. [13] found that Spanish broom fibers can significantly improve the ductility of cementitious materials. [PERSON] et al. [14] found that concrete with basalt fibers significantly increased the tensile strength, flexural strength and toughness index. [PERSON] et al. [15] added Masson pine needle fibers to the concrete and found that the modulus of rupture, toughness index, and deflection of concrete could be improved by a maximum of 46.1%, 40%, and 129% respectively. [PERSON] et al. [16] improved the compressive strength and abrasive resistance of concrete by mixing steel fibers into concrete. These fiber materials have the advantages of high strength and good ductility, and adding fiber material is an effective method to improve the properties of cementitious materials [17; 18]. In general, natural fibers are more readily available than man-made organic and metallic fibers, especially plant fibers. However, the application of rice straw (RS) fiber, as an environmentally friendly and easily available material, in the field of mine backfill has rarely been reported. In agricultural production, a large amount of wheat straw and rice straw is abandoned or burned every year [19]. Although incineration in situ is economical and labor saving, it causes air pollution. In addition, they can also be used to generate electricity [20], make paper, fodder, or fertilizer [21; 22]. In some areas, straw and soil were used as construction materials. The addition of rice husks to lightweight concrete provided excellent mechanical and thermal properties, making it suitable for use as a building material [23]. Rice stalk bales could be used to build high-performance, environmentally friendly building walls [24]. Studies show that RS cement specimens meet the strength requirements of ASTM standard [25], and RS could significantly reduce the cost of cement bricks and the greenhouse gas emissions from cement production while achieving the same strength [26]. The elasticity modulus and compressive strength of the cementitious materials' specimens made with RS were also enhanced [26; 27]. These studies show that adding RS fibers into CPB is not only feasible but also environmentally friendly and cost effective.