You should consult a local real estate attorney as soon as possible. Your neighbor owes you some duties, such as not causing water to run onto your property that formerly would have stayed on his property or drained off another direction. There is also a common law duty of support, meaning that your neighbor cannot cause your land to shift by changing the amount of lateral support provided by his land. You may not have a cause of action until his construction is complete under the Oja case (your attorney will know about it or find it), but it is best to consult with someone soon. With protecting your rights, you are better off early than late.
The foregoing is not intended as legal advice, but solely as general information. No attorney/client relationship exists between the poster and the answering attorney.
I agree with Mr. Stromberg. If the construction on the neighbor's property is causing drainage issues - or soil shifting that may impact the structural integrity of your home - you should retain competent counsel as soon as possible.
If this answer was helpful, please mark it as helpful or as a best answer. This answer is for general education purposes only. It neither creates an attorney-client relationship nor provides legal guidance or advice. The answer is based on the limited information provided and the answer might be different had additional information been provided. You should consult an attorney.
In addition to seeking legal counsel, you should also bring this to the attention of the jurisdiction that gave your neighbor the permit to do their work (either the City of Kent or the County). It seems likely that the construction is not being done according to the permit that they have been given, and the permitting jurisdiction may help get this cleared up. If you have not already,consider bringing this to the attention of your neighbor, and their construction company so they can try to address the issue from their side and repair things on yours - they have an incentive to avoid a lawsuit. Finally, you do have rights in this situation, and you may wish to consult a land-use or real-estate attorney to assist you.