First of all I want to thank you, Dr. Roozneh, for giving us the possibility to use a great freeware FEM software like Adonis. I have a couple of questions, about the way you calculated the initial stress in the "Anchored Sheet Pile wall Tutorial".
- How did you get the initial value syy=11995.2 Pa for the top clay layer?
- All the stress values are positive, but I thought that the sign convention for compression, adopted in Adonis, has negative sign. Should I use the negative sign for stress, in that case? 
Probably these questions are trivial for Flac-like software users, but I am more familiar with Phase2 (Rocscience software).
Thanks in advance for your reply
Luca

Hi Luca,

thanks for the comments. regarding your questions:

1- in order to come up syy0 and the gradient values (i.e. Vy_yy) you need t solve the equation shown below:

syy = syy0 + vx_yy ? x + vy_yy ? y

syy is known at each depth for instance at -4, syy should be equivalent to stress at the bottom of the sand layer 1735?9.8?4.0. you can estimate the syy at depth y=-18. Now if you put the known values in the equation above the syy0 and vy_yy will be estimated.

2- you are correct, compression in FEM has negative sign but as you notice the depth has (-) sign so if you use the indicated values for syy0 and vy_yy you will see that syy is going to be negative at specified depth which is consistent with sign convention.

please note that ADONIS uses this equation (syy = syy0 + vx_yy ? x + vy_yy ? y) to come up with stress at each depth. You simply need to back calculate the Syy0 and vy_yy in a way that corresponds with stress distribution of your model.

hope these answer your questions. please let me know if you need additional information.
   
-Roozbeh

Can you do a hand calculation I just dont understand this at all

Let's say you want to assign variable stress in vertical direction only for simplicity. The equation you need to solve is:

syy = syy0 + vx_yy * x + vy_yy * y

syy0, vx_yy and vy_yy are unknown. x and y are the coordination at which syy is desired. since we only want variable stress in y direction therefore vx_yy=0 so equation simplified to:

syy = syy0 + vy_yy * y

now if you want syy=-10 at y=0 and syy=-100 at y=-10 you need to simply put them in the equation above and solve the system of equation. it should not be very difficult.

-10 = syy0 + vy_yy * 0
-100 = syy0+vy_yy * -10

syy0 = -10 and vy_yy = 9

syy0 and vy_yy will be your input for ADONIS. Same concept for variable stress in x direction. I hope it's clear enough

-Roozbeh

Dr Roozbeh
Thank you makes it so much clearer, Im new to FEM and trying to set up a model to review Stone Columns and Rigid inclusions so I might need a bit of help later

Most helpful though

Dr Roozbeh
Im sorry but I must be really stupid, I have now tried so many times to follow the tutorial ang get this but failing every time.
Can you give me the guidance on how you have worked out the stresses on tutorial 7 - sequential tunnel.

Syy has tabulated following

Initial Value Pa               Y Variation Pa          x limit                y limit
0                                   19130                    -60,60                -2,0
4905                              21582                    -60,60                -25,-2
53955                            23544                    -60,60                 -40,-25

Im sure it is something very simple but im missing it and its getting a bug for me to solve, so thought easrier to ask the the professional tutor

are you getting error massage from the program?

please send me the script file you created so far.

Im not running any program Im trying to follow the tutorial by reading and filling in the math behind the scenes and i just dont get how the values are generated in the table of the tutorial as i quoted before

let me ask you this, from what you learned from your soil mechanic courses, how do you calculate vertical stress for the soil with density=1950 kg/m3 at depth 2 m below the ground surface? use g=9.81 m/s2 in your calculation.

Well from what i recall 1950 x 9.81 x 2.0 = 38259Pa or 38.259Kpa

Can I ask you to perform the hand calculation to show how the values in Tutorial 7 are obtained please

now, using system of equation shown above calculate syy0 and vy_yy for the case that stress at y=0 is syy=0 and stress at y=-2 is syy=-38259. you will end up with the parameters in the table.

0 = 0 + 19130 * 0
-38260 = 0 + 19130 * -2

hence

Initial Value Pa               Y Variation Pa          x limit                y limit
0                                   19130                    -60,60                -2,0

Totally get this but it is the next line IM having a mental block on

stress at -25 = -534645

so is it
-534645 = 38260 + Vy x -25

stress at y=-25 is syy = -(1950*2+2200*23)*9.81= -534645
stress at y=-2 is syy = -38260

-38260 = syy0 + vy * -2
-534645 = syy0 + vy * -25

syy0 = 4905 and vy = 21582

hence

Initial Value Pa               Y Variation Pa          x limit                y limit
4905                              21582                    -60,60                -25,-2

Light bulb moment - Thank you very much lets see how i get on now sorry for being so slow on this