چكيده به لاتين
Commonly, preparing the required bearing capacity and reducing the settlement to an appropriate level are two main reasons of using piles in raft.
When piles are connected to the raft, large axial stresses is created in the piles due to static and dynamic load. The location of pile connection to raft should be enlarged because of increasing the piles bearing capacity and preventing from structure damaging, however it causes non-economic design of foundation system. Hence, for reducing the large stress between pile and raft, piles should be disconnected from rafts and should be used as a reinforcement in soil like a structural element. So, evaluation of connected and non-connected pile raft system on dynamic and static load effect is so important. Comparing the behavior of connected and non-connected pile raft system shows stress concentration and bearing capacity of raft reduction in non-connected system but lateral displacement is more than connected system. When a static load is applied to non-connected pile raft system, the bearing capacity and settlement of raft are shown different behavior depending on the arrangement of the different piles. In real condition, due to Asymmetric of loading and plan, eccentrically Load is applied to raft system. However, a few studies are conducted about evaluating non-connected pile raft system under of static eccentrically Load. Comparing the behavior of connected and non-connected pile raft system under of static eccentrically load is the main purpose of this study. So, performance of each system is evaluated by parameters such as bearing capacity, settlement, raft rotation, Bearing pile index (BPI). Effect of length and distance of pile, raft shape and deviation from the axis in both connected and non-connected pile raft system are presented.
In this study, 32 tests are conducted by using sandy soil (D161- Firoozkoh) with relative density 55%. Tests are conducted in three series including connected pile raft system, non-connected pile raft system and unpiled raft system. In non-connected a 10 centimeter gravel cushion is used.
The summary of the results shows that square, circular and strip raft in the case of S / D = 3 and L / D = 8, the bearing capacity of the non-connected piles is more than that of the connected piles.The results of the experiments showed pile length is more effective than the pile spacing in connected pile raft system. However by decreasing pile spacing, bearing capacity is increased in non-connected pile raft and pile spacing is is more effective than the pile spacing in non-connected pile raft system.
Comparison of bearing capacity and settlement indicates in the non-connected piles ,the longer piles not only has not much effect in increasing bearing capacity significantly, but also has lower effect on the reduction of the settlement. Also in non-connected pile raft system by increasing the pile spacing reduced BPI( bearing pile index) wile in connected pile raft system increased.
Raft shape is presented a effective parameter in increasing bearing capacity and reducing settlement. The result shows squre raft has more bearing capsity than the circle rafts. Thus geometric factor in calculating of bearing capacity of shallow foundations is used in the non-connected pile raft systems.
