grout pressure

[cvg]

Looking for a reference for pressure drop for tremied concrete. Product is a minimally flowable sanded cement grout through a tremie pipe. Grout will flow from the pump through say 50 feet plus/minus of hose and then another 100 feet plus/minus of horizontal pipe and then into a cavity which needs to be completely filled. I am trying to estimate the pumping pressure required, maintaining minimal pressure in the cavity at the end of the tremie.

 

[miningman]

Cant help with the theoretical calculations but I do have significant experience with this type of job. Without wanting to state the obvious, there is of course almost zero pressure at the end of the tremie pipe untill the cavity is 98% full. It is in those last few moments of pumping that pressures get interesting. In my case, I was always dealing with underground rock and the critical pressure is that which will lead to hydrofracturing if exceeded. In some cases I was comfortable going to 600psi, in other cases only 10% of this value. And even then , theres a lot of judgement involved because the water part of the grout will always tend to bleed away into the local rock ( often carrying fine cement with it ) Suggest you determine the depth below surface you are working with and also ensure that the "bulkhead" at the mouth of the cavity can withstand significant pumping pressure. The type of pump and exact flow characteristics of the grout are also critical.

 

[cvg]

agree
depth is not an issue, bulkhead design is questionable
depends on a lot of things including pumping rate, hose and pipe size, grout viscosity and density etc.
based on a lot of assumptions and little data, I am getting about 1 psi pressure drop per foot of 2 inch hose/pipe which is giving me a pumping pressure of about 150 psi. I know that I will need upwards of 20 psi to completely fill the cavity, so a total gage pressure at the pump of about 170 might do it. An air vent will help to limit pressure surges at 99% full. But so far, I have found little to no published data to base these calculations on. Placing the pressure gage at the bulkhead would be more useful than at the pump.

 

[miningman]

150-180 psi doesn't contradict my experience with these things, and if anything might be a bit high but as you state, density, viscosity etc would have to be known before calculations could be refined. There is a nice little grout pump manufactured by Chemgrout that reaches 180psi but obviously its suitability or otherwise is partially determined by the likely quantity of material to be pumped.


The South African mining industry developed a number of designs for hydraulic plugs in the 1960/70s . This work was refined in the 1990s in Canada by Brennan Lang............his paper published in 1999, presented at the CIM conference in Calgary Alberta titled "Design and Construction of Tunnel Plugs and Bulkheads " may have some of the references you are seeking.

 

[rconner]

Is this e.g. a pipe abandonment completely filling a pipe, are you instead grouting between a casing and carrier pipe at a crossing or what?

 

[cvg]

abandonment, not a casing

 

[rconner]

Aye - can see why you need a sturdy bulkhead if any pressure built up, as you said. I gather also you probably don't have topside access for vertical grout tubes that I understood may be easier to control head/pressure? On a side note, I once saw a bricklayer lay a bulkhead in a 60" pipe end with remarkable speed, and with the mortar and bricks laid axially (so one could see the ends). He claimed it would hold a good bit of pressure, but don't know if it was tested!

 

[cvg]

the brick and mortar method is being used. however, since the pipe joints are not restrained, high pressure could pop the entire pipe off at the first joint. So for 24 inch pipe and 10 psi, we could see 4.5 tons of force on the bulkhead, potentially enough to move it and the pipe if the friction or other restraint is not sufficient

 

[miningman]

What is the length of this pipe?? How do you intend ensuring that the grout will move laterally from the point of discharge??? In my experience, the angle of repose of grout slurry is surprisingly large.

 

[cvg]

the pipes are not very long and several grout pipes at different lengths will be used to distribute the grout along the full length with vents at both ends.

 

[rconner]

A short (gooseneck upward?) "vent" at the top of the bulkheads sounds like a good idea, as long as they are of sufficient size to prevent a pressure build-up at the bulkhead when the grout once full hits the inner bulkhead/vent openings.