assuming the victim does not possess the earthglide ability, and that you can't take someone with you: they would be potentially grappled/pinned but not pulled into your square and you would have cover to some degree. in effect you would both be pulled to the edge of your respective squares and occupy a virtual square in between or something.
if you can take someone with you, or they don't exceed your allowed encumbrance: then they would get pulled into the ground. and you could likely then leave them there. i suppose a dm ruling might allow part of them to be pulled into the ground proportional to the encumbrance allowed that equates the percentage pulled into the ground. so if you have 50 pounds left, and the victim weighed 100 lbs, then you could pull them about half-way into the ground, maybe three quarters depending on weight distribution.
i think the grapple check would suffice for purposes of a saving throw to resist this effect.