The Research On Bearing Characters And Settlement Calculation Method Of Soft Rock-socketed Pile Groups Subjected To Vertical Load In Harbor Engineering

The soft rock is widely distributed in coastal area in which harbors and bridges aremainly located in the Three Gorge Reservoir Area in southwest china. The large diametercast-in-situ soft rock-socketed piles have been used extensively to meet the demand forbuildings that is high, heavy and huge scale, however the dolphin type berth whosefoundation generally apply large diameter cast-in-situ rock-socketed pile group is widelyapplied in harbor engineering in the reservoir area. The harbor engineering codeconsiders that the rock-socketed pile group whose pile spacing exceed2D has no grouppile effect and the design should depend on bearing capacity calculation, but the code hasno deformation control, and other code analysis the bearing performance for therock-socketed pile group according to common pile group bearing character. Because thesoft rock has the character of low bearing capacity, large deformation, poor waterstability and the negative effects resulted from the periodic changes of the reservoir waterlevel on strength of soft rock, which has greater negative influence on plateau reservoir.Above all, the bearing performance for the large diameter cast-in-situ rock-socketed pilegroup should be further studied.An improved load-transfer function for rock-socketed pile in soft rock has beenproposed and The "Load Transfer-FEM" named united model has been put forwardaccording to the improved load-transfer function to analysis the bearing performance forrock-socketed pile in soft rock. Then, research the bearing behavior of the large diametercast-in-situ rock-socketed pile group and its change law with strength deterioration ofsoft rock, analysis the interaction mechanism for "cap-pile-soft rock" as well, which arebased on the water-rock-cycle interaction experiment with saturation-air drying to softrock specimens and the physical model test about soft rock-socketed pile. advance thehybrid calculation method for pile group settlement based on the analytical method ofbearing capacity of single pile at last.The efficiency coefficient of pile groups in soft rock increases with increasing pilediameter or increasing pile spacing and decreases with increasing rock-socketed length atthe condition of the same cap vertical displacement, Especially, it increases withincreasing cap load or cap displacement. The water-rock interaction has the negativeimpact on bearing capacity for bedrock, but it expand the scope of elastic bearing for pile groups relatively, which make the load distribution more nonuniform with increasingfrequency of water-rock interaction. the "load-settlement" curve of soft rock-socketedpile is generally smooth and belongs to slowly-develop type and it is more smooth forpile groups in soft rock, which recommends that the ultimate bearing capacity should bedefined according to functional requirement. The pile group effect should not be ignored,due to the efficiency coefficient of pile groups in soft rock decreases with increasing thefrequency of water-rock interaction, which recommend that the pile group effect shouldbe considered with the different functional requirement and the changes of the reservoirwater level when designing the rock-socketed pile group foundation in soft rock.