Tunnels in hard and jointed rock are normally excavated in an arch shape to enable the rock mass to support its weight. Since the beginning of the 1980's, fibre reinforced shotcrete (FRS) in combination with rock bolts have been the dominating support method for hard rock tunnels. This type of rock support is a complex composite structure in which the structural behaviour depends on interaction between shotcrete, rock and bolts. The design is commonly based on a rock mass classification system in combination with analytical solutions or finite element (FE) modelling. However, the in-situ variations of important properties of the shotcrete are normally neglected.

The aim of this thesis is to describe and explain how the variations in shotcrete thickness and bond strength affect the structural behaviour and capacity for a shotcrete lining. Especially, the influence of local variations in shotcrete thickness and bond strength has been studied in detail. For this purpose, a numerical framework capable of simulating bond failure, cracking of FRS and pull-out failure of grouted rock bolts have been developed. Moreover, in-situ data for shotcrete thickness and bond strength have been collected and analysed to characterize  the variations in important shotcrete parameters.

The results in this thesis show that when shotcrete is subjected to shrinkage, local variations in shotcrete thickness affects the crack pattern. However, the number and width of the cracks are similar to the case with uniform thickness. Most importantly, a pattern of fine and narrow cracks develops in unreinforced shotcrete subjected to shrinkage when a continuous bond to the rock exists. When shotcrete is subjected to the load from a loose block, the force is transferred to the surrounding rock through bond stresses distributed over a narrow band. Simulations have shown that the structural capacity, with respect to bond failure, depends on the shotcrete thickness. Moreover, a strong linear correlation was found between the mean value of the bond strength and shotcrete thickness around the perimeter of the block and the structural capacity. Local weak areas, i.e. with low bond strength or thickness, may exist around the perimeter without having a significant effect on the structural capacity. Design of bolt-anchored shotcrete linings is based on failure modes previously derived from experimental testing. This thesis has contributed to an increased understanding of the failure mechanisms of the lining and has confirmed that the design can be based on individual failure mechanisms.

Sedan borjan av 1980-talet har stalfiberarmerad sprutbetong i kombination med bergbultar varit den dominerande bergforstarkningen for tunnlar i hart berg. Den har typen av forstarkning ar en komplex samverkanskonstruktion vars strukturella beteende styrs av interaktionen mellan sprutbetong, berg och bult. Dimensioner­ingen baseras vanligtvis pa ett klassificeringssystem for bergmassan i kombination med analytiska losningar eller modeller baserade pa finita elementmetoden. I dessa fall bortser man oftast fran de i fa.It forekommande variationerna hos sprut­betongens viktiga egenskaper. Syftet med denna avhandling ar forklara och beskriva hur variationerna i sprut­betongens tjocklek och vidhaftning paverkar <let strukturella beteendet och bar­formagan hos bergforstarkningen. Framforallt har lokala variationer i sprutbeton­gens tjocklek och vidhaftning studerats. For att genomfora detta har ett numeriskt ramverk utvecklats som kan simulera uppsprickning av fiberarmerad sprutbetong, vidhaftningsbrott och utdrag av injekterade bergbultar. Dessutom har faltdata samlats in och analyserats for att karaktarisera fordelningen av viktiga sprutbe­tongegenskaper. Resultaten i den har avhandlingen visar att lokala variationer i sprutbetongens tjocklek paverkar sprickmonstret nar sprutbetongen krymper. Antalet sprickor och <less vidd ar liknande dem som uppstar nar tjockleken ar jamn. En viktig slutsats ar att ett manga sprickor med liten sprickvidd uppstar nar oarmerad sprutbetong med kontinuerlig vidhaftning till berget krymper. Nar sprutbetongen utsatts for lasten fran ett lost bergblock overfors lasten till den omkringliggande bergmas­san langs ett tunt band. Numeriska simuleringar har visat att barformagan med avseende pa vidhaftningsbrott beror pa sprutbetongens tjocklek. Dessutom visade simuleringarna att <let finns ett starkt linjart samband mellan medelvardet for sprutbetongens tjocklek och vidhaftningshallfasthet langs block­ets periferi och <less barformaga. Lokala ytor med liten tjocklek eller vidhaft­ningshallfasthet kan finnas runt periferin utan att paverka barformagan. Dimen­sioneringen av bultforankrad sprutbetong ar baserad pa brottmoder framtagna utifran experiment. Den har avhandlingen har bidragit med en okad forstaelse kring dessa brottmoder och visat att dimensioneringen bar baseras pa individuella brottmoder.