Equivalentpilespringstiffness.docVIP

Equivalent pile spring stiffness Guang Song May 2012 1, Pile lateral capacity by geo-technical engineer using L-Pile 2, Pile lateral capacity modeling using Risa3D 2.1 Calculation of soil spring constants along the pile length Assumption: The pile top is 300mm above the ground, and 1m of the soil underground doesnt make contribution. The soil will exhibit linear elastic material property during compression. The maximum lateral deflection of piles at ground is 6mm or less in order to maintain the soil adjacent to the pile in the elastic zone. Table 3 on page 10 of the soils report gives two values of Kh. Kh=5/D for well compacted clay fill Kh=10/D for native clay till. To simplify the calculation, using equation: Spring constants=Kh*D*L Where D is the pile diameter, and L is the segment length (0.5m) The majority of the depth of the pile would be in undisturbed native clay till, therefore using Kh=10/D. The spring constant = Kh*D*L= (10/D)*D*0.5 =5.0kN/mm The soil spring constants used is 5kN/mm for each segment of 0.5m. Each node in the model has the same spring constants. If the piles are more likely to be placed in compacted fill, rather than in native till, use Kh=5/D, Spring constants=Kh*D*L=(5/D)*D*0.5=2.5kN/mm 2.2 model a pile which is about 8-12m long using Risa3D. Minimum pile length=8m Fix the Y rotation. Try different lateral loads 5kN, 10kN, 15kN…….30kN For each loads, get a deflection for the pile top. Plot the deflection and load curve Most likely, the curve is a linear. 2.3 Equivalent pile spring stiffness For a structure supported by a pile, the pile can be modeled as a spring. The pile equivalent spring stiffness can be calculated as follow: For example When load applied on top of the pile is 30kN and get 10mm pile lateral deflection, the spring stiffness K=30kN/10mm=3000kN/m