How to support PE pipe on mud soil

[bnard]

Hi guys hope you can help me with this. We are to relocate the existing 375 AC pipe at the toe of the road batter by laying a new 400 PE mainline about 25m from its original location. The road will be upgraded into 4 lanes and the existing ground is mud soil about 2-4m depth. Here are my queries.
1. What is the best effective protection strategy in laying the new PE mainline
2. The AC pipe has been there for more than 30 yrs and it is expected that settlement has already been taken place but there are section in the road upgrade where immediate road approaches will cross over the AC pipe and that portion of pipe will not be relocated. How shall we protect them from the additional loading that it will carry. Will concrete slab be adequate enough to distribute the loads on the sides?

Help guys pls thanks

 

[bimr]

The soil classification encountered in the trench would change the trench bedding design. It is necessary to provide a stable formation before pipe laying. Such conditions commonly occur in peat, silty ground soft clays, running sand, or in fill material.

Although sometimes trench formations are filled with concrete, this is unlikely to assure long term stability in all cases, and a form of flexible bedding construction is the preferred method of dealing with the situation.

The trench formation should be over excavated by 24" to 30", depending on the bearing strength of the soil. Gravel reject material is then compacted in layers to form a firm trench bottom. A 2" thickness of lean-mix concrete is then placed as blinding. The pipe is then laid on granular bedding material.

Slurry is usually used as a blinding layer. Clays and silts are highly susceptible to softening when in contract with water. Clay formations are protected with blinding concrete or with foundation concrete as soon as possible after completion of the excavation. If not protected, the clay will swell and then must be removed.