UMAT Implementation in Abaqus (Hypoplastic clay Subroutines)

Hi,
I am working in Abaqus, aiming to model double porosity clay consolidation data by using hypoplastic clay model with meta stable structure. First, i just wanted to verify basic model using simple axisymmetric geometry (Triaxial Test) in Abaqus. So i used material Parameters as : 22.611e-5,.11,.016,.4 and rest all zero. As a standard procedure i included umat_hcea.for file in the job module and ran my job. I got the error that UMAT was missing, so i opened the umat_hcea.for and replaced first word after usersubroutine by UMAT and finally job completed successfully. I am simply loading under isotropic conditions and then unloading but my when i checked the void ratio upon unloading, it didn’t follow k line it retracted along lambda curve only. Also the void ratio is decreasing not along butterfield’s criteria but along e-lnp’ space (i checked by hand calculations). Can any one suggest me where i could be wrong and also, is there any change that i have to make in the fortran file like the one mentioned above?. Any help would be great .