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### This Post Has 14 Comments

1. Shekh Muhsen Uddin Ahmed

//units: u[m], depth[m], D[m], sigma v[kPa], sigma v eff[kPa],
//c[kPa], phi [degree), phi interface[degree], max skin friction [kPa]
//return value: friction [kPa]
function tz (u, depth, D, sigma_v, sigma_v_eff, c, phi,phi_interface, K, max_skin_friction, para0, paral, para2)
{
return 1000*u
}

what is u in this function

1. u is displacement.

2. David

I have a question related to the input parameters associated with Reese O’Neil model for sand for drilled shaft . It asked for “phi”and “K” parameters but we are not sure how it is working actually, the reference document asked for N60 results, but in this case the software q-z pile didn’t use this information for the computation. Same as for Reese O’Neil model for clay it ask for Nq and the recomendaded value is 9 that value is Nc value?

1. Hi David, regarding cohesionless soil, the phi is the pile-soil interface friction angle and K is the coefficient of lateral earth pressure. The calculation of the skin friction is generally follow beta method. The N60 is actually used to estimate K and the end bearing.
You are right, for the clay the requested Nq should be Nc. The Nq is used to make the parameters compatible with the API soils.
The actual curves used for drilled shaft is the trend curves. If you would like to use different curves, feel free the define your own curves with JavaScript functions.
I will look into the drill shaft and see if I can make it more consistent with FHWA Drilled Shaft 2018 version.
Thanks for pointing it out.

3. Enrique Barragan

Hi Yong, I am trying to program my own soil models. But I am having some problems, could you please provide me an example of the API curve javascript to modify it?

Also, how do I get the user-defined model to display the Ultimate Pile Skin Friction in the GUI?

1. Hi Enrique, do you mind letting me take a look at your JavaScript code? Please use the correct units though.
You are right, the Ultimate Skin Friction with user-defined model cannot be displayed in the GUI. I couldn’t find a practical way to have the ultimate skin friction for an arbitrary function. Please let me know if you have any suggestions.

4. Ziyang Xi

Hello, Yong. Could you introduce which code or paper did you take referrence?

1. Hi Ziyang, you should be able to find tons of papers about t-z and Q-z curves for pile axial load analysis. QzPile uses FEM with springs and column element to simulate the pile load axial response. The specific soil spring model types are presented in the program, such as API Sand, API Clay. You can find the soil models in different code accordingly. You can specify your own model too.

Please let me know if you have any other questions.

5. Andreas

Hi Yong, I’ve tried to use elastic perfectly plastic soil model in “QzPile” to simulate a concrete pile 48 m long, diameter 0.80 m embedded in sand (shear angle 27°, K=0.55) till the depth of 41 m then “rock” elastic perfectly plastic. For the rock I used the following parameters; skin stiff. 340000 kN/m3, end bear.stiff. 830000 kN/m3, ultimate skin fric. 400 kPa, ultimate end bear. 1800 kPa. The program give me strange results in the “Ult-fric depth” graph: Ultimate skin friction and Total , Shaft and Toe values seems moltiplied for 1000. Thanks in advance, Andreas.

2. Hi Andreas, the unit display error for elastic perfectly plastic soil has been fixed in v0.1.1. Thanks for reporting this error.

1. Andreas

Hi Yong, I tried the last upgrade, now the results are ok. Thanks Andreas

6. Khaldoun

Can you share with me an example of Qz pile.