huangyhg

sand filled tube used as a temp. sup. column
i am looking for any information about the said subject. specifically, i have a 14" square tube, with 3/8" walls, with a welded plate acting as a bottom cap. this tube is standing vertically, resting on a bed of h piles (as sleepers) and partially filled with silica sand, out of the bag (no moisture). resting on top of the sand, inside the tube, is an h pile, with a shoe well fitted to the inside dimensions of the tube. a 500 psi load will be transferred to the sand.
i know this method was used quite often in the early 1900's to provide temporary support. i have searched my library, knowing it was diagramed in the book "modern construction techniques" published around 1915. any information would be appreciated.
can i ask why you are using this method for temporary support?
it is cheep, easy, quick, and you can use up alot of cut off's with it. if you build your base correctly, you eliminate any rotation problems, and by differing the level of the sand, you obvisously can differ the height of the column. any info ?
why not load test it at, say, twice your expected service load?
we are in the process of trying to educate a governmental agency the we did not "just invent this". that is why i have been trying to locate any supporting references to this type of system.
a very old reference is...purported construction of the pyramids. it is said stones were supported by sand. when the sand was allowed to flow at the bottom the stones went unto position to lock passages...would have to look for what book exactly.
on the other hand at least your problem is quite clean from an engineering viewpoint, i think all significant parameters are quite immediately derivable.
main concern here is the same than in any short stub shoring, namely bracing at the level of the tip of the stub. you would have to use fitting to fixity fall-in shoring struts to avoid this problem, and this may be contrary to your convenience and the simplicity of the idea.
these kind of failure i know to have existed in works in my area about 20 years ago (there were still wood stubs).
this is a type of device i have used on a number of occasions. it is called a sand jack. it is cheap and reliable, and easy to "deflate" providing the sand remains dry.
for my application, i used a cylinder within a cylinder. the wall and end plate sizes were calculated using pressure vessel standards. a design working pressure of 15mpa (2160psi) was used for a 100t unit. the outer tube was 323x12.7, and the plates 25 thick. the inner tube was machined to a 2mm clearance fit, as we didn't have time to check whether a larger gap was possible.
one was tested to 125t. it deflected 2.3mm under load, and sprung back all but 0.2mm of that. this was repeated twice with just a small increase in deflection.
in that particular application, the sand jacks were to supplement permanent elastomeric bearings for a temporary situation during construction. it was pleasing to note that the deflection of the sand jacks was of the same order as that of the elastomeric bearings - so they did in fact share the load.
in your particular case, you have used 14" rhs with 3/8" wall to 500psi. treating the wall as a fixed end beam, the bending moments at the corners will be far in excess of yield, and the rhs will try to turn itself back into a cylinder. this will relieve the pressure, and the sand might leak out the sides. meanwhile, as the centre of the column of sand there will remain some confinement, and it could well continue to perform. i would test one before i put it into service!
hope this helps.
russell keays
i agree entirely with rhk.
i have only ever known sand jacks to be made from cylinders, and i have always thought that they were in common usage. at least i have known of their use in the uk and australia.
definitely test before use, particualrly if you have had no direct experience with them.
p.s.
in response to bridgeman - 'why are you using...'. as asdf and rhk have said - it is cheap. but more than that.
sand jacks provide reliable support, free from any risks of hydraulics failures, but also give you a simple method of lowering very heavy loads.
asdf, as for proving that you 'didn't just invent that', i suggest that you try to dig up a copy of the proceedings of the institution of civil engineers, september 1964. go to paper no. 6812 "medway bridge - construction, by kier, hansen and dunster", (disussed in june 1965).
(in its day, medway bridge claimed the world record for prestressed concrete girder bridge spans, and raised the uk record from 275 ft to 500 ft, built before there was such a thing as a bs code of practice for prestressed concrete).
about 60% down page 68 you will find reference to a 'three-legged sand jack', which is shown in very cryptic form on page 70, 'fig 36: west bank launching procedure'.
apart from the added complexity of linking three sand jacks in parallel to support a three legged trussed framework, and designed to provide controlled lowering through a distance of 10 feet, their principle was the same as yours.
on the basis of a hazy memory, i think that i am correct in saying that the 'cylinders' were made out of rendhex hexagonal pile sections (again, rather like your scheme, cutoffs from temporary piling required to found some of the major falsework towers).
no, clearly you have not just invented it, and there is at least some documentary evidence to support that position. if it was good enough for christiani and nielsen and also for kiers (both very reputable bridge builders in their days) then it ought to be good enough for your government authority?
gents, thank you for your responses. just to bring you up to date, we used the sand jack about a year ago, very successfully i might add. my previsous experiences with sand jack included square sections, with loads up to 10t+-. our testing did prove out that we needed 12" dia. pipe, with 1" wall thickness. a framework, similar to that of a shoring tower was installed to brace the jacks, including an adequate foundation. we were able to temporarily support and eventually cast a series of 70t girders, without incident.
the only dificulty throughout the entire operation was educating the self proclaimed experts that we could do it. remarkably, even after completing the work, the chief state bridge engineer stated that he would refuse to allow the systems use again.

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