PURPOSES : In this study, the amount of core stone breaking in the size of boulders by excavator braker work was analyzed quantitatively through on-site test construction. In addition, the factors affecting workload were studied. METHODS : In the field test, 30 core stones of boulder sizes (1–4 m3) that appeared during earthworks, such as road construction and site construction, were collected from three locations, and the rock breaking work was carried out simultaneously using three excavator breakers(1.0-m3 volume). During the core stone breaking, progress was analyzed through video recordings. RESULTS : After the completion of rock breaking, the amount of breaking work was analyzed by direct loading and weighing using a 15- ton dump truck. As a result of the test construction, there was a significant difference in the amount of work completed per hour. CONCLUSIONS : It was found that the results were greatly affected by not only the performance of the excavator braker equipment, but also the skill of the driver and the size of the core stones.

PURPOSES: It is difficult to estimate tunnel stability because of lack of timely information during tunnel excavation. Tunnel deformability refers to the capacity of rock to strain under applied loads or unloads during tunnel excavation. This study was conducted to analyze a methods of pre-evaluation of stability during tunnel construction using the critical strain concept, which is applied to the results of tunnel settlement data and unconfined compression strength of intact rock or rock mass at the tunnel construction site. METHODS: Based on the critical strain concept, the pre-evaluation of stability of a tunnel was performed in the Daegu region, at a tunnel through andesite and granite rock. The critical strain concept is a method of predicting tunnel behavior from tunnel crown settlement data using the critical strain chart that is obtained from the relationship between strain and the unconfined compression strength of intact rock in a laboratory. RESULTS: In a pre-evaluation of stability of a tunnel, only actually measured crown settlement data is plotted on the lower position of the critical strain chart, to be compared with the total displacement of crown settlement, including precedent settlement and displacement data from before the settlement measurement. However, both cases show almost the same tunnel behavior. In an evaluation using rock mass instead of intact rock, the data for the rock mass strength is plotted on the lower portion of the critical strain chart, as a way to compare to the data for intact rock strength. CONCLUSIONS : From the results of the pre-evaluation of stability of the tunnel using the critical strain chart, we reaffirmed that it is possible to promptly evaluate the stability of a tunnel under construction. Moreover, this research shows that a safety evaluation using the actual instrumented crown settlement data with the unconfined compression strength of intact rock, rather than with the unconfined compression strength of a rock mass in the tunnel working face, is more conservative.

For PHC pile, mechanical connection joints can be essential to connect PHC piles over 15m in length for deep foundation. This study was examined flexural capacity of PHC pile connected with high-performance connection device. To examine flexural capacity of PHC pile, two PHC piles with 5m length were connected using ring-type connecting plate developed recently. Its connection capacity and failure mode were evaluated through four-point flexure test.