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Within this study, new bolt heads were designed to be able to expand in drill holes as the load applied on the bolt shank increases. The heads of newly designed rock bolts include a conic part and split rings encircling them. To determine load bearing capacities of new rock bolts with varying angles of the conic parts and expansion properties, a series of deformation controlled pull-out tests were carried out by using bolt samples grouted in rock blocks. In addition to the experimental studies, numerical modelling analyses were performed to better understand the support properties of newly designed rock bolts. Because of a negative Poisson’s ratio effect supplied by the head part expansion with the tension of the shank, new bolt heads are suggested to be defined as auxetic. According to the results of this study, the new head designs significantly improve the load bearing and energy absorption capacities of grouted rock bolts.

IntroductionAlthough shear strength of rock materials is an important parameter for many different rock engineering applications, there is still a necessity for development of a standard method and details for determination of shear strength of rock materials. The conventional direct shear strength (DSS) test method suggested by International Society for Rock Mechanics and Rock Engineering (ISRM) and standards like ASTM D5607 are not a proper way to test high strength rock materials because of possible failure of cement mortar instead of rock core specimens [1][2][3]. The cement moulding method to hold specimens is more suitable for testing rock joints rather than intact rock materials. As another topic, the conventional DSS test has additional problems of impracticality in specimen preparation process including two steps cement mortar casting as seen in Fig 1. In this study, a practical test method for determination of cohesion values of rock materials is investigated to assess whether accurate strength values can be measured using double shear jaw (DSJ) which is a basic apparatus to test numerous specimens instead of only one specimen as in cement moulding method of holding. Within this purpose, new steel jaws for testing cohesion of rock materials were designed and manufactured in this study.Need for waiting the curing time of several days for holding specimens in the casted mortar method should be stated as another disadvantage of the conventional DSS test. As an important issue which prevents to measure the strength value under pure shearing, significant bending/tension effect is induced as the rock specimen loaded in the soft cement mortar. Having the bending effect in the specimen causes to measure smaller strength values than that determined under pure shearing condition [4][5][6][7]. In this study, a new method of using DSJ was investigated for the aim of having ideal loading condition. For the conventional DSS equipment in rock mechanics laboratories, manual load application by using the hydraulic jack is an additional lacking to cause a personal effect on the strength results. On the other hand, double shear jaws (DSJs) let specimens to be loaded vertically with a constant rate which can be supplied by the load controlled compressive equipment.

Reinforced concrete grouped silos-commonly employed in the industry to store granular materials- also needs to be designed in earthquake-prone areas. Silos experience a higher rate of structural failures than the majority of other types of construction. And one of the main causes of silo failure is the dynamic overpressures caused by stored materials under seismic loads. However, the principles determining loads on such structures and requirements for their structural analysis aren’t precisely specified in relevant codes of design. Instead of emphasizing grouped silos that interact strongly, the present dynamic design only concentrates on a single silo which can lead to unrealistic solutions for grouped silos. Therefore, it is necessary to determine the seismic behavior of grouped silos more accurately. This paper aims to investigate the seismic behavior of RC on-ground grouped silos compared to single ones by using a numerical model because of its adaptability, which allows for the analysis of a wide range of silo problems. In this context, a three-dimensional finite element model, that considered the interaction between stored material and silo wall as well as the continuity of the silo walls, was performed using ANSYS software. Two different aspect ratios and three different internal loading cases were taken into account for the parametric study to demonstrate their influences on dynamic overpressures and equivalent base shear forces in RC-grouped silos. It is concluded that designing the on-ground slender grouped silos with a high aspect ratio as individual single silos is unreasonable and may produce very low values for the base shear force.