Temporary support of tunnel excavations with spiling is common in projects featuring difficult ground conditions. However, there is a lack of systematized guidelines for its design, which frequently requires an individualized approach. For example, the loads acting on spiles are usually estimated based on the weight of the rock mass from a core of loose rock or overlying rock mass for shallow tunnels. This load is uncertain and might be influenced by features in the rock mass such as block size and joint orientation. In this paper, we investigate how the block size of the rock mass and joint orientation affect the loads on the spiles and the deformations of the tunnel section. Two-dimensional numerical analysis of a shallow excavation is conducted in UDEC. In the model, the support of the spiles is modeled as springs. A 10 m wide tunnel in a fractured rock mass with 140 mm pipe spiles is considered. Both block size and joint orientation are modified in the study. The results show that the orientation of rock joints has a clear influence on deformation at center spiles. As the dip of joints increases from 45/45° to 90/0°, deformations increase. There is a tendency that smaller block size decreases the scatter of results with respect to joint orientation. In summary, the results show that the common assumption in design that the load acting on the spiles taken as the weight from the rock mass is associated with significant uncertainties. The load may be up to 30% higher for the 90/0° joint configuration and 30% lower for the 45/45° orientation.