hi
you can leave gravity activated all times...you'd need to deactivate the whole embankment during the first step(check model change command in abaqus) and start activating its sets step by step (assume for example that the embankment hieght is 6 m..and you are building it 2 m by 2 m..so you should divide the embankment to 3 sets 2 m each..and activate them one by one in each step)
lets assume the whole embankment set is called emb..and then you divided it into 3 sets (2m each)emb1,emb2,emb3
so during the first step in you analysis
step1
*model change, type=element, remove
emb
step2
*model change, type=element, add
emb1
step3
*model change, type=element, add
emb2
step4
*model change, type=element, add
emb3
Just make sure there is perfect contact between different sets