# Axial Load Transfer Mechanism in Fully Grounded Rock Bolting System: A Systematic Review
## 1 Introduction  
The stability of underground spaces and surface slopes is paramount in civil, mining, and tunnelling engineering, ensuring safe working conditions for all activities. Excavating underground spaces disrupts the in-situ stress, causing a redistribution of forces within the surrounding rock and triggering potential rock block movement. Civil and mining engineers must thoroughly understand the ground stability/controlling conditions around the excavation to prevent these displacements and implement appropriate stabilisation measures. Rock improvement encompasses all techniques used to enhance the mechanical properties of a rock mass, thereby increasing its stability. Rock reinforcement, a subset of rock improvement, utilises various techniques and devices to strengthen the rock mass. These reinforcement methods can be broadly categorised into three main types based on length: (1) rock bolts (typically less than 3 m), (2) cable bolts (typically 3-10 m), and (3) ground anchors (typically exceeding 10 m) [1]. Rock bolting systems boast a rich history, with their origins dating back to at least 1872, when they were first employed in a slate quarry in North Wales [2]. Not long after, Germany and the United States adopted rock bolting systems in their coal and metal mines, in 1918 and 1927, respectively [3]. Australia's journey with rock bolting began in 1949, when it was used as a reinforcement element in a Snowy Mountains project [4]. Since its introduction, rock bolting has seen a continuous rise in popularity within mining and civil projects worldwide. By 2011, estimates suggested that Australia utilised over 5.25 million rock bolts, representing a significant 1% of the global consumption of 500 million rock bolts that year [5]. A rock bolting system typically consists of four crucial elements: surrounding rock, the bolt itself, internal, and external fixtures [6]. Internal fixtures refer to the material that fills the space between the bolt and the rock, such as cementitious grout, resin, or the friction created by the mechanical interaction between the bolt and the surrounding rock [7]. External fixtures, on the other hand, are the components visible on the outside of the rock, like the face plate and the nut. Rock bolting systems can be further categorised into three main types based on how the internal fixtures interact with the rock and the bolt [8]: continuously mechanically coupled (CMC), continuously frictionally coupled (CFC), and discretely mechanically or frictionally coupled (DMFC). Based on the interlocking mechanism between the bolt and the surrounding rock, three conventional types of rock bolts are commonly used [9], namely (a) mechanically anchored bolts: these bolts rely on a mechanical anchoring mechanism to achieve a strong connection with the rock; (b) frictional bolts: these bolts utilise friction between the rock and the bolt surface to create a stable bond; (c) fully grouted rock bolting systems (FGRBSs): in this type, a cementitious grout or resin fills the space between the rock and the reinforced element (bolt), creating a continuous medium and strong bond [10; 11] (Figure 1). This article exclusively investigates FGRBSs, categorised as CMC system according to the classification system. Split Set and Swellex bolts, belonging to the CFC category, will not be discussed here. FGRBSs are widely considered as the most versatile and efficient reinforcement solution for challenging ground conditions, offering superior adaptability compared to other systems [12; 13; 14; 15]. Indeed, they are the industry standard for both temporary and permanent support. Their versatility allows them to be used in weak or fractured rock formations, and even in corrosive environments [16]. This system comprises four key components: a ribbed steel or fibreglass rock bolt, a face plate for anchorage, the surrounding rock mass, and the grouting material, which can be either cementitious grout or resin [17]. Compared to other rock bolt types, fully grouted bolts offer significant advantages.