// STATE BOUNDARY SURFACE (SBS) OF THE MODIFIED CAM CLAY MODEL 
// p'-q-e space
// Project: Animating Soil Models https://soilmodels.com/soilanim
// by: Gertraud Medicus, University of Innbruck, 09/2021
//
// Software: asymptote.sourceforge.io
// Asymptote Web Application: http://asymptote.ualberta.ca/

import graph3;
size3(200,400,200,IgnoreAspect); // size
currentprojection=orthographic(-500,1,400); // view
scale(Linear(-1),Linear,Linear); // axes; -1: set p' axis reverse

// fill in parameters
real phi=25*pi/180;
real M=6*sin(phi)/(3-sin(phi));
real N= 2;
real lambda=0.06;
real kappa=0.008;


// define stress range p_0 to p_end to plot
real p_0=25;
real p_end=500;
real e_min=N-lambda*log(p_end) -1;
real e_max=N-lambda*log(p_0) -1;


// The sbs is formulated as parametric surface by x(p0,p/p0), y(p0,p/p0), z(p0,p/p0)
//
triple f(pair l) {
real p0=l.x;  
real p_p0=l.y; // p/p0
real v_plot=(N-lambda*log(p0)+kappa*log(1/p_p0));
return (  
(p0*p_p0),
(v_plot-1),
(sqrt(M^2*p0*p_p0*(p0-p0*p_p0)))
);
}

surface sbs=surface(f,(p_0,.01),(p_end,1),20,200,Spline);
draw(sbs,green+opacity(0.9),meshpen=green,render(merge=true));

// axes
draw(Label("$p'$",1),(0,e_min,0)--(-p_end*1.1,e_min,0),black,Arrow3);
draw(Label("$e$",1),(0,e_min,0)--(0,e_max*1.15,0),black,Arrow3);
draw(Label("$q$",1),(0,e_min,0)--(0,e_min,p_end/2*1.1),black,Arrow3);