Hi all,
I designed a axially loaded pile system (total length = 10m) with properties shown and applied line load 100 kN/m.
The results are shown below.
i need some clarifications
01) Normally base resistance comes into action once skin friction dissipates but the results shows the base resistance, what is the reason?
02) Applied loading is 200 kN and slef-weight like 47.112 kN, which is get from the skin friction {(0.5x2.7x12.12x2) + (10-2.7)x12.12x2)} and base friction (24.71 x 2). but axial force showing different value, please explain how axial force output is calculated and shown?
Thanks,
For the first part of the question; I can assure you that the simplified pile behavior (i.e. skin friction mobilizes first, after it is fully mobilized, tip resistance comes into action.) is not true. Skin friction and tip resistance mobilizes at the same instance, however, skin friction mobilizes much faster (around 0.01D) while tip resistance continues to increase for a longer deformation range. For a simple example, you can see the figure below.
I am sure people from Plaxis will join the discussion, but for the second part of the question, I can explain the first figure. You have applied 100 kN/m. In the left figure, you can see that around 75% of your load is resisted by side resistance while the remaining 25% reaches the tip. You have something around 100 kN/m load at pile which is equal to what is loaded on the pile: 100 kN/m.
For the right side (skin friction figure), you have a little lower than 12.12 kN/m for the top 7.3 m, so if we calculate per meter, it is around 86.5. I think a more dedicated area calculation using an excel spreadsheet should yield the mobilized frictional force which is around 75 kN/m. Skin_Resistance = 0.5 * 2.7 * 10 + (10-2.7) * 10 = 86.5
Hi Mr. Berk Demir,
You spend your value time to reply, thank you so much for that.
So let says the axial force diagram represents how much force is resisted by skin friction (can be calculated from the skin friction output) and base resistance , my question is I applied 100kN/m with 2m spacing so loading in the pile is 200 kN and selfweight is 47 kN, so total is 247kN.When we do manual calculation for single pile system we neglect the self-weight of the pile as due to the removal of soil over-burden pressure, it equals the self-weight. Does plaxis 2D consider that effect in analysis? and does it reduce the force due to uplift of the water pressure (as soil model with full water table)? If these 2 effects not there then starting of the axial force diagram need to be 123.5 kN/m (247/2) {correct me if i'm wrong).
Thanks.
Can you please check your weight calculation again?
What problem in the weight calculation?
The weight imposed on pile is calculated by Plaxis as the difference between soil weight and pile weight. Therefore, we should consider that too. Support will join the discussion, I am sure, and they can inform you better on this and detailed hand-calculation to match the pile forces.