A New Pre-Supporting system (the Geo-Flex Beams system) was developed for the prevention of caving-in of the working face during non-open-cut excavation beneath a railway or road, for example, Yamamoto et al. [1]. The system consists of grout-infused packers developed underground using a flexible drilling machine. The diameter of each beam is about 150 to 200 mm, and the drilling machine is capable of developing the beams 50 m underground. As reported in this paper, field tests were carried out to investigate the workability, construction accuracy, and asbuilt design of the Geo-Flex Beam, and its effects on the ground. The major results were almost as expected, although the ground was slightly displaced. Field loading tests were also used to simulate the tunnel and, it was confirmed that the beam provided sufficient strength.