Good day Plaxis support engineers.
I'm new on Plaxis, so apologize me if the issues I'm bringing here may seems irelevant.
I will detail how did my model (I will skip the soil creation):
After creating the one layered soil profile I drew a polycurve and then created a surface based on it. Then I extruded the surface to -12mbgl and I deleted the polycurve and the surface remaining only with the created volume.
After that I decomposed the volume into surfaces and I deleted the upper surface (deleting or not the upper surface has an influence on the final model or results, or something else?), remaining with the lateral and bottom surfaces which I used to create Positive Interfaces.
After that I created a vertical point load of 1000 kN (less than the pile bearing capacity), generated the mesh (medium elements distribution for soil and fine distribution for the volume pile).
After running the calculations, I visualized the structural forces using the Structural Forces in Volume Piles. The values of N are presented on the image below:
I didn't face any issue with the calculation. Based on my step-by-step explanation,
I tried to model a dummy beam to compare the results with the previous model. The beam properties are:
I choose the (EA)real/(EA)dummy to be 10^6. So maintaining the beam diameter the same as the volume pile diameter (0.8 m), the E,dummy is 26 kN/m^2.
Is my point of view correct?
The results of the structural forces in the dummy beam are:
Based on this formula:
The values of N are 5.67 kN (minimum) and 60.34 kN (Maximum). These values are smaller compared with that obtained using volume piles.
Thanks for you attention.
Best Regards
Hi Christina,The modelling technique is correct. I couldn't have done it better myself! Unless the top surface serves some purpose in your model, you can delete it. It will not have any influence on the results. However, I have a couple of comments regarding the results.As you may already know, piles develop resistance to axial loads through two different mechanisms, side friction and end bearing. Given that you are modelling the interfaces around the pile, I will assume there is also soil. Therefore, you should expect frictional forces to develop between the surface of the pile and the soil surrounding the pile.As far as the dummy beam is concerned, it should be weightless. Otherwise, you risk having a pile with twice the regular weight (soil volume weight + dummy beam weight). Now, depending on the mesh density, the axial force calculated with the "structural forces in volume piles" should be close to the one from the dummy beam). However, given the limited information, there is no easy way to tell why there is a discrepancy.
You can always contact our Support team for further investigation.
Good day Vasileios Basas
Thank you for your quick response. In fact, I did well the modelling thanks to the tips that all Plaxis team gives to the members of this community.
Returning to my model, I would like to know what I shall expect by adding a cap on top of the pile (piled-raft foundation):
Thanks in advance
Dear Cristina,
What results to expect is something you should determine yourself, and then check the PLAXIS calculation to see if your expectation is matched. And if it isn't of course raise the question why not. It makes not so much sense for us to expect results for your project.
With respect to the load transfer, yes, the load will be partially transferred by the raft and partially by the piles. To determine how much is transferred by the piles, simply add the axial forces in the piles just underneath the raft. The external load minus the pile loads is the load transferred by the raft.
With kind regards,
Dennis Waterman