Specifications, strength and bearing capacity of jointed-timber piles in soft ground

Single-Timber Piles (STP) were used as the pile foundation of the small-scale buildings in the soft ground of Saga Lowland, where differential settlement occurred. The timber piles’ tip was required to reach the supporting stratum at greater depth to overcome the problems. To reach the stratum, these timber piles are connected with several joints. However, there is no detailed study to describe the strength of these Jointed- Timber Piles (JTP) and their material specifications. This study describes the specification of the materials used and then explains the laboratory tests that evaluate the strength of the JTP. Further, it discusses the method to determine the bearing capacity of the JTP in terms of bearing capacity coefficients α and β. Later, the back-calculated values of α and β from the axial load’s relationship with depth obtained from the strain gauge field measurements verified the bearing capacity evaluation method. The test results from the laboratory demonstrate that the concrete-timber stake joints reduced the compressive strength by around 2%, and the upper timber stake-lower timber stake joints reduced the strength by 11%. However, the reduction factors of 10% to the concrete-timber joints, and 15% to the timber-timber joints are adopted for the safe construction.