Solution approaching wrong value

Hello, I have written the following code as an analytical solution to excess pore pressure in 1D soil consolidation:

z=(1:-delZ:0)';
tt=[0.01,0.1,0.2,0.5,1,2];
a=4/pi; pa=pi/2; pp=pa*pa;
Wan=zeros(21,1);
    for k=1:5
        jj(k)=(2*k-1);
        for ii=2:N+1
        Wan(ii)=Wan(ii)+(((-1)^(k-1))/jj(k))*cos(jj(k)*pa*z(ii))*exp(-jj(k)*jj(k)*pp*tt(1));
        end
    end      

My problem is it results in this graph for t=0.01, with the values approaching 0.8 when they should be approaching 1.0. Can anybody spot where I've gone wrong with this? Thank you!

[James Tursa]

What are the underlying equations you are solving?

[Abigail Grein]

Where at T=0, W=1, 0

With boundary conditions: W=0 at Z=1 for T greater than zero and

at Z=0 for T greater than zero

[Torsten]

James means the infinite sum you are trying to implement.