21-10-2016, 04:51 PM
1460400628-piledraftfoundationseminar.ppt (Size: 1.94 MB / Downloads: 10)
Design Philosophies of Piled Rafts
Conventional Pile Design Method
Disregard of the capacity of raft
Increase the number of piles or length of piles
Very small allowable settlement
Piled Raft Design Method
Design for fully utilization of pile capacity
Settlement Reducing Pile
Design for the calculation of settlement
Consideration of Complex Soil-Structure Interaction(Pile-Raft-Soil)
Consideration of the optimal location of piles to decrease the differential settlement and bending moment of raft
Design Philosophies of Piled Rafts
Curve 0 : raft only(settlement excessive)
Curve 1 : raft with piles designed for conventional safety factor
Curve 2 : raft with piles designed for lower safety factor
Curve 3 : raft with piles designed for fully utilization of capacity
Application of Piled Raft Foundations to Civil Structure
Modeling Summary
Pile-Soil Interaction
Kondner(1963)
Pile-Soil-Pile Interaction
Apparent stiffness reduction due to ground settlement generated by pile settlement(Randolph & Worth, 1979)
Pile-Soil-Pile Interaction
Superposition of settlement with the effects of the adjacent pile’s settlement makes apparent stiffness reduction in the group pile.
The slip of pile does not affect to adjacent pile’s settlement.
Raft-Soil-Pile Interaction
Apparent stiffness reduction of soil spring in raft by piles
Raft-Soil-Pile Interaction
Stiffness hardening of piles by raft would be considered by increasing the effective stress and unit skin friction
Raft-Soil-Pile Interaction – reduced scale test
Set-up of Test Piles
Comparison with 3D FEM Analysis(PLAXIS 3D Foundation)
Example models for the evaluation of developed analysis program
Comparison with 3D FEM Analysis
3D FEM mesh model for piled raft analysis
Comparison with 3D FEM Analysis
Analysis results of raft foundation without piles
Comparison with 3D FEM Analysis
Analysis results of single pile
Comparison with 3D FEM Analysis
Pile behaviors from the piled raft foundation analysis
Comparison with 3D FEM Analysis
Raft behaviors from the piled raft foundation analysis
Comparison with 3D FEM Analysis
Total behavior of piled raft
Comparison with other approximate programs
Comparison with linear elastic analysis programs
Conclusions
An approximate method has been developed for the practical design of piled raft foundations, which analyze non-linear behaviors and soil-structure interaction effects efficiently in multi-layered soils.
This method considers the apparent stiffness reduction in piles by the adjacent piles and raft and apparent stiffness reduction in raft by the piles and generates very similar results to 3D FEM analysis.
The effect of stiffness hardening of pile is under estimated. So, it makes conservative results in comparison with 3D FEM analysis.
The results of comparisons with 3D FEM analysis also show the sufficient applicability to practical analysis and design of piled raft foundations.
Further Study
Intelligent soil spring
Linear spring for raft-soil interaction was applied in this study.
Intelligent soil spring is needed to model true raft-soil interaction and depend on the followings;
the relative stiffness of the raft and soil
the plan size and shape of the foundation
the distribution of applied loading on the raft
Intelligent soil spring will be determined by the iterative process of soil spring reaction and ground settlement analysis.
Variable shape of raft foundation
Field test Proto type field test Centrifuge test