Speaker
Description
The use of porous rock is generally not adopted in rubble mound foundations due to its higher porosity, which results in lower apparent specific gravity and unconfined compressive strength (UCS). However, in response to rising rock material costs, a rubble mound foundation at Shimizu Port, Japan, is planned to utilize materials sourced from Mount Fuji, including both dense and porous rocks. To evaluate the feasibility of porous rock, the bearing capacity behavior of the two materials was examined through two approaches: (1) large-scale triaxial tests with a specimen diameter of 0.3 m conducted under confining pressures of 50, 200, and 400 kPa to determine shear strength parameters for the Bishop method, and (2) centrifuge model tests of a caisson on rubble mounds performed at a centrifugal acceleration of 50g to reproduce the behavior of large-scale structures. The results indicate that the apparent cohesion and mobilized internal friction angle are within a similar range for both materials ($c_d$ = 29.49 kPa and $ϕ_d$ = 36.97° for dense rock; $c_p$ = 32.95 kPa and $ϕ_p$ = 35.62° for porous rock), despite an approximately threefold difference in UCS. Consequently, the allowable operational load for porous rock is reduced by only about 8% compared with dense rock, which has an estimated bearing capacity of approximately 1430 kPa at a safety factor of 1 based on the Bishop method. The response of rubble mounds under caisson overburden stress obtained from centrifuge model tests also demonstrates nearly identical displacements for both materials up to 300 kPa, corresponding to the expected operational stress level of a 15-m-high caisson, as well as ultimate bearing capacities consistent with theoretical predictions. These results suggest that porous rock can also provide adequate performance for rubble mound foundations. By bridging the gap between theoretical analysis and practical engineering applications through laboratory testing, this study highlights the potential of porous rock as an alternative material for port foundation construction.