A Study on Estimation of End Bearing Capacity of a PHC-W Pile in Building Underground Additional Wall Using the PHC-W Earth Retaining Wall

PHC-W 흙막이 벽체를 이용한 건축물 지하증설벽체에서 PHC-W말뚝의 선단지지력 산정에 관한 연구

Abstract

With the recent concentration of urban populations, the constructions of large structures are increasing, along with the development of foundations for large structures. PHC Piles have been used in many structures ever since Japanese introduced the technology at the end of the 20th century. Recently, many studies on the use of the PHC Pile have been carried out as earth retaining using the merits of PHC piles. In this study, static axial compression tests were conducted on the PHC-W piles constructed as column-type in building underground additional wall using the PHC-W earth retaining wall. The end bearing capacity of pile was calculated using the axial load transfer measurement that was obtained from the static axial compression test result. Since end bearing capacity of the PHC-W pile embedded in weathered rock showed a different behaviour from the conventional PHC pile, the calculation method of end bearing capacity for column-type PHC-W piles would be proposed. The unit ultimate end bearing equation proposed for single and group PHC-W pile embedded in weathered rock is $q_b=13.3N_b$ and $q_b=6.8N_b$.

최근 도시 인구의 밀집으로 대형구조물의 건설이 증가하고 있으며 이와 더불어 대형구조물의 기초도 발전하고 있다. 2000년대 말에 일본의 기술을 도입하여 PHC말뚝은 많은 구조물에 사용되고 있다. 최근 PHC말뚝의 장점을 이용하여 흙막이 벽체로의 사용에 대한 연구가 많이 진행되고 있으며, 이 연구에서는 PHC-W 흙막이 벽체를 이용한 건축물 지하증설벽체에서 PHC-W말뚝을 주열식으로 시공하여 연직 압축정재하시험을 실시하였으며, 하중전이 측정을 통하여 PHC-W말뚝의 선단지지력을 산정하였다. 풍화암에 근입된 PHC-W말뚝의 지지력은 기존 PHC말뚝의 지지력과는 차이를 보였으므로, 주열식으로 시공된 PHC-W말뚝의 선단지지력 산정식을 제안하였다. 풍화암에 근입된 PHC-W말뚝의 단위극한선단지지력 산정식으로 주열식 군PHC-W말뚝과 단일PHC-W말뚝에서 각각 $q_b=6.8N_b$와 $q_b=13.3N_b$로 제안할 수 있었다.

Fig. 1. Improved section of PHC pile (Choi, 2014)

Fig. 2. Construction method of SDA (Cho, 2007)

Fig. 3. Construction step (Choi, 2014)

Fig. 4. Outer wall of underground parking lot (Ryu, 2015)

Fig. 5. The conceptual diagram of the additional wall

Fig. 6. Borehole positions and soil profile

Fig. 9. Load-displacement curve of group pile (TP-G)

Fig. 10. Axial load distribution of group pile (TP-G)

Fig. 11. Skin friction and end bearing of group pile (TP-G)

Fig. 12. Load-displacement curve of single pile (TP-S)

Fig. 13. Axial load distribution of single pile (TP-S)

Fig. 14. Skin friction and end bearing of single pile (TP-S)

Fig. 8. Details of sensor installation

Fig. 7. Layout of test pile

Table 1. B.S.T results

Table 2. P.M.T result

Table 3. Results of static axial compressive load test

Table 4. Results of axial load transfer test

Table 5. Comparisons of unit end bearing values

Table 6. Suggested formular by test values