settled pipeline
settled pipeline
(OP)
Hello everybody.
I have another site problem. An underground drain (beneath a little road) has deflected. This was revealed during a CCTV inspection. The pipe is 250mm dia 15m long and 3m below ground level. The centre of the pipe appears to have settled by 150mm between manholes.
There are many ideas floating around our team from testing it/ partially filling it to reduce the dip/ post tensioning it to straighten it/ digging it out/ boring another pipe......
Is there any tried and tested way of repair which could be done without disturbing the road?
nb
I have another site problem. An underground drain (beneath a little road) has deflected. This was revealed during a CCTV inspection. The pipe is 250mm dia 15m long and 3m below ground level. The centre of the pipe appears to have settled by 150mm between manholes.
There are many ideas floating around our team from testing it/ partially filling it to reduce the dip/ post tensioning it to straighten it/ digging it out/ boring another pipe......
Is there any tried and tested way of repair which could be done without disturbing the road?
nb





RE: settled pipeline
The first thing you should investigate is why the pipe deflected. Is it a result of soil during road construction which has setteled, etc... or has a joint opened which is washing away the soil thru the pipe structure
RE: settled pipeline
I believe Compaction Grouting may be a possible solution for your situation. The grout injection below the pipe bedding could possibly partially realign and and provide support for the pipe.
I tend to prefer Compaction Grouting for underpinning because the lifting can occur quite a few feet below the structure, distributing the uplift forces and using the existing soils as a 'cushion' The grouting can also be accomplished without a lot of disturbance around the structure, oftentimes allowing continued use during the repair.
RE: settled pipeline
The excavation beneath this pipe may not have been compacted properly after excavation. The ground being sand with a high water table.
Would pressure grouting be able to raise the pipe and the 3m of soil above it or would we need to flush some sand away from the top of the pipe?
nb
RE: settled pipeline
Some minor raising or heave of the road will probably occur. The amount depends on the condition and density of the native and the backfill soils. This procedure is normally used to stabilize a settling pipe and partially raising the pipe is a secondary result. The task is not impossible but, you would be stretching the 'comfort zone' of most engineers and many of the Specialty Contractors.
You must also be advised that some grouting jobs, after a lot of effort and expense, do not accomplish the goal. I have generally had good to excellant success with compaction grouting, but only when the Specialty Contractor has been experienced and willing. This is one of those techniques in which the contractor is as much an 'artist' as a technical type. Those that have the 'touch' do the best work.
A final note, the best contractors want a detailed Geotechnical, Subsurface Report. Beware the ones who are ready to go at a minutes notice.
RE: settled pipeline
I shall investigate if any specialists subbies are available.
nb
RE: settled pipeline
RE: settled pipeline
A 6" sag in a 12" pipe? How does that affect your capacity? Any? Considering that intentionally sagged lines have been known to work quite happily in sanitary systems for many years, it does seem that answering this question should be your first step.
Bill Holt
RE: settled pipeline
I fear our Client will not accept any defective work regardless of what i can prove by calculation or otherwise.
In such circumstances an extended guarentee may assist - but this becomes a contractual issue.
An interesting problem better to get it right first.
nb
RE: settled pipeline
I imagine, however, that in this situation any repair acceptable to the owners that leaves out the lawyers will be less costly than any solution that includes them.
Bill Holt