4-axle front discharge ready-mix truck

[RHTPE]

I am preparing a report that discusses the failure of a foundation wall due to the close proximity of the ready-mix truck when delivering the basement floor slab concrete. The truck took one heck of a ride into the basement.

This was a bare foundation, approximately 24' X 50' X 8' high, fully backfilled, with no floor framing in place at the top of the foundation wall. I will be interviewing the driver tomorrow morning to better understand the position of the truck relative to the foundation wall.

Does anyone on this forum have any insight regarding the load distribution to the front axle and how it changes as the discharge of concrete begins? Remember that a substantial portion of the 10 CY in the drum moves up the inner ribs and closer to the open end of the drum as discharge begins.

I'm well aware of the issues associated with back-filling a bare foundation wall, as well as the danger of high levels of ground surcharge immediately adjacent to the walls. At this point I'm really more interested in the load distribution to the truck's axles.


Ralph
Structures Consulting
Northeast USA

 

[Ron]

Tryan....a good lawyer (solicitor, etc.) would likely get by that "legal contract" issue. I believe your legal system, like the US, is based on English Common Law. If so, you can't disclaim negligence, even by contract.

 

[Tryan]

Ron
Point taken of course,but over here we have a strict system regarding building sites involving safety and risk assessment training. To get on to a site you must have the appropriate licence or documentation, ie worker, machine operator, delivery, inspector or visitor. You then have to go through an induction, which can take 1 hr, pointing out the specific risks, vehicle movements and general dos and don'ts of the site. You then sign it saying you understand and accept it. The responsibility then reverts to the signee,but, as you rightly pointed out Ron, you can't "disclaim negligence". For instance, if the safety officer identifies a danger, then you can't just warn people about it, you have to make it safe.
There is a "Chain of Responsibility" which creates a very visible paper trail. To find the broken link, just follow the trail!
I think there was a lot of things wrong here before the concrete truck even got to the site. 50'long wall,8'high,backfilled and unreinforced? Over here that may have been classed as an excavation deeper than 5' with a high risk of sudden failure, therefore no workers are allowed in it without the appropriate shoring!
There is a system of risk assessment which works from 1 to 5 ie. highly likely to unlikely and 1 to 5 ie.a risk of death to a papercut. That situation,if there were workers down the hole, should have been rated a 1.
Can't get that unreinforced wall out of my mind,is that normal practice? Even if it is eventually fixed top and bottom[?], what about the middle?

 

[RHTPE]

Tryan, Here in the Northeastern US this practice is far too common. There doesn't seem to be anything explicit in the relevant codes to prevent it from occurring.

It is not unusual to see footings formed and placed on Monday, footing form stripped and wall forms installed on Tuesday (or even late Monday), walls placed late Tuesday or Wednesday morning, wall forms stripped late Wednesday or Thursday morning, damp-proofing applied on Friday, and the walls back-filled on Saturday if the excavator needs to move to the next one. Perhaps an extreme example, but not too far from reality.

Keep in mind that this is in the category of residential construction (single family home), so there's little oversight by any officials or design professional. The risks taken by the builder in the process are amazing, with little thought given towards the long-term quality of the work. Those that do the wood framing that should be in place before the walls are back-filled would scream very loud at having to deal with a foundation that has not been back-filled, as it makes their work more difficult.

Having close ties to a ready-mix producer, I hear the horror stories about how they get blamed for bad concrete because the foundation wall cracked. Never mind the fact that the foundation guy added lots of water to increase the slump so the concrete flows farther and the site guy backfilled with ordinary fill as soon as the damp-proofing is dry.

Not right, but far too common.

Ralph
Structures Consulting
Northeast USA

 

[csd72]

Conservatively I would take the whole bucket and concrete load on the front 2 axles. You should be able to find this in the specs though as I am sure you are not the first person to need this information.

I would recommend that any heavy loads like this stay outside the 45 degree zone of influence (i.e. at least 8 foot in your case).

 

[darthsoilsguy2]

The Contractor owns the site and is responsible for the coordination. It is likely the concrete producer has access provisions in there terms.

Trucks are typically stocked with 4 or 5 chutes. If I were in your shoes, i would also investigate whether access was provided to place concrete for the slab.

Getting complex on the analysis of the truck surcharge doesn't seem appropriate since there are also complexities that get simplified out in the geotechnical retaining wall calcs too. Why not just run it as a flat simple truck? It's the simplest and most favorable to your client, unless you can show a slope away from the wall. I assume you are doing all of this to establish a load on the wall to compare pound-for-pound against the loads the contractor put on the wall by backfilling early for some sort of percent damages at fault scenario.