There have a 48" cooling water pipe from underground to piperack.For the poor backfilled soil condition of this jobsite,a big settlement will occur.In my concern,an expansion joint should be selected to absorb the sttlement.But the client think it's not necessary,their supported reason is the pipe will move down when buried into the soil,the later movement will be very small,can be ignored.
I am not convinced.The big settlement can destroy the beam of the piperack,because more weight of the pipe have to be withstanded by the first support in piperack.
Any concerns about this topic will be appreciated!

In my opinion, piperack cannot be collapsed as long as a differential settlement is less than few inchs and a civil/structure engineer designs it with common sense.

First of all, tell me which part will have more settlement and what's pipe size, how big differential settlement do you expect ? Is it going to be 10 inch settlement with 100 in cooling water line ????...no, probably less than one inch with 24" pipe size because it runs on piperack.
I will assume 24" cooling water line which runs horizontally as buried pipe and has one inch differential settlement, and there is no frost heave effect at winter season.
If piperack has more settlement, the pipe weight load at first support of rack will be transferred to next support of piperack. If buried cooling water pipe settle more, the first support of piperack will have a little bit higher weight load rather than undertake the entire length of buried pipe weight. That is, the buried cooling water pipe will not be settled around off-piperack area and the pipe weight of this area will be distributed to soil and the first support of piperack..it would be less than two tons.

It's 48" cooling water pipe.Now the civil engineer can not provide detail settlement for this project.But acoording to same area plant,the settlement can reach 200-500mm for no piled and no foundation part.
The piperack is piled,but no measures taken for the big underground pipe.The settlement difference will be very big.
Expect more concerns!

Rockey Cheng,
There seems to be need for more flexibility between the pipe rack and the buried piping, but the use of an expansion joint must be carefully considered. A simple expansion joint without any tie rods may have enough axial movement for the settlement, however the cross section area for 48" diameter may result in very high pressure thrust load. The thrust load for 50 lb/in cooling water could result in almost 86,750 lbs uplift to the pipe on rack. The tie rods are usually installed on an expansion joint to control the pressure thrust, but then there is not the axial movement needed.
The buried pipe might need to have a thrust anchor at the elbow directly below the pipe rack. The civil engineer probably would want to include the underground thrust anchor as part of the foundation footing of the pipe rack. If the thrust anchor and the foundation footing are thus connected, then differential settlement would not occur.

Mr. Cheng,

It is unusal to run 48" cooling pipe on main piperack. I would not layout 48" cooling water line on main piperack because piping design must be done by common practice.

Anyhow, if a huge settlement of buried pipe is true and there is no choice for alternative layout, I would consider two options and choose cost saving design;
First, when piping layout on rack portion can minimize the support load by using spring hanger/can, put a spring support and let this spring absobe settlement.
Second, use flexible joint as Mr. Yee suggested. The metal bellows with tie-rod is not a good idea because cooling water may include excessive chloride and commercial austenitic stainless steel may not be applicable. Rubber bellows is alternative but it may not be applicable too because max. applicable pressure is very low for 48" rubber bellows and 10" deflection is too much for rubber bellows. You may consider slip joint on vertical portion of off-piperack but you will need the anchor on piperack to control pressure thrust.
Therefore; I would like to recommend to use a pair of Victaulic Coupling or Dresser Coupling at the horizontal portion of off-piperack. For dresser coupling, you may need tie-rod device but not for Victaulic Coupling.