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14. Pile driving_Tutorial Manual_2020_Page 190-200

Nitharshan

Hi all and    

Sorry if my questions are seemed to be very small things but i need to know the answers that's why i'm asking. My questions are

01. In the multiplier definition, what is the meaning of the amplitude here (as we defined unit load as dynamic load) ? does here amplitude value represents the load which is dropped on the pile to push in ?

02. When interface is provided, what is the purpose of providing interface below (in the sand area), even though there is no pile element?

03. Can't be used embedded beam element or plate for this pile driving work? if so then we can continue the analysis: for example if we are using solider pile deep excavation analysis, we will stimulate the solider pile driving effect and continue the analysis for each excavation phases?

04. In the pile driving phase, the pile is drived all in one go but actual situation is it has been driving step by step, in that case how we can stimulate the analysis as next half of the wave is negative ?

05. The displacement result from the pile driving seemed to the effect is only to base of the pile, but there is disturbances on the adjacent ground also due to driving and vibrations. Why analysis results not given that effect and if we need to see that result how to change the analysis?

Thanks.

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  • 0 Offline in reply to Nitharshan

    Hi,

    Please note that is a forum where users can ask each other and learn from each other and this may take a while. If you need an answer urgently you should put a support request.

    01) Please check Reference Manual 5.6.2, the first equation explains.

    02) Please check Reference Manual 5.7.6 - Interfaces around corner points.

    03) The pile driving tutorial is an axisymmetric problem in order to represent a single pile. If it would be a plane strain problem it would represent an infinite wall or infinite of piles. In case of a soldier pile wall that would mean you're driving an infinitely long row of soldier exactly simultaneously, which is not so realistic. Note that a plate element is not suitable to model a pile it has no foot resistance, only skin resistance.

    04) The pile is not driven all in in one go. We only model the situation that the pile has already been driven in beforehand and we only model 1 blow of the hammer at a certain moment. How the pile was exactly driven in up to the level that we're assessing is just not part of the model.

    05) The purpose of this tutorial is to see the dynamics effects when a pile at a certain point during installation is hit by a hammer, and not to show disturbance of the soil along the shaft. It is possible to model that disturbance but it would require a different kind of model set up and that is not part of this tutorial.

    With kind regards,

    Dennis Waterman

  • 0 in reply to Dennis Waterman

    Dear Mr. Dennis, 

    Thanks for the great reply for the questions and sorry for my rush as i didn't know the rule of the forum, Extremely sorry for that again.

    For reply 5) could you please tell me in order to check the disturbances of the soil during pile driving what type of model do we need?

    (i refer this tutorial exercise to get the understanding of this => I have to model the deep excavation and near that area some utilities there. So i want to check the induced deflection and stresses on them due to sheet pile or soldier pile installation and excavations. So the purpose of my study here is to understand the installation of the sheetpile (not all in one go) using forces and study the ground and utilities effect due to that. That's why i asked those questions above to get some ideas.

    Thanks.

  • 0 Offline in reply to Nitharshan

    Hi,

    There are 2 ways to do this...

    1. Model that the soil is pushed aside by the installation of the pile
      1. Apply a radial prescribed displacement over the full length of the pile with a value equal to the radius of the pile
      2. Step by step from top to bottom activate the prescribed displacement to simulate pile installation
      3. Note that by doing this the pie itself is not modelled, only the soil being pushed aside.
    2. Model that the pile adds volume to the soil
      1. Create an influence slightly larger than the pile. So let's say the pile has a diameter of 60cm, then create a zone with a diameter of let's say 100 cm.
      2. Apply in the zone of 100 cm a volume strain equal to the volume of the pile. Again, do this stepwise from top to bottom.

    Note that method 1) is more accurate and realistic, but due to the high deformations close to the pile numerically very difficult to  calculate. You may need to do a lot of trial-and-error with the mesh to calculate it. Generally, the mesh elements should not be too small as small elements suffer more from extreme deformation and thus cause more numerical issues.

    Method 2) calculates easier, but the accuracy depends highly on how large you chose the influence zone. 

    Both methods are not accurate enough for a class A prediction of the soil behaviour and should mainly be used for a back analysis of for instance the skin friction of the pile due to increased stress levels.

    With kind regards,

    Dennis Waterman

  • 0 in reply to Dennis Waterman

    Dear Mr. Dennis Waterman

    After study the "interface around corner points" (as you mentioned previously), i have one question. 1) To what extend we need to extend the interface element when modelling rigid and soil interactions (as i found this statement in reference manual)?

    For the plate soil interactions (i  modelled using only 1 soil), what is the reason for sudden high change in the interface effective stress near the base of the plate? if it is not a real case how to eliminate this one?

    Thanks.

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