From your query, I am assuming that it is a water supply borehole that you wish to construct. From the location you indicate (next to a lake), I assume that the hole is collapsing because of the inflow of water. I am also assuming you have a basic knowledge of borehole construction.
As long as the sediment is sand (and not clay) you need to use a vibro-bailing or washbore approach – there are a number of variants, most of which require you to have some lengths of solid casing (rigid tubing – usually metal - of a significantly larger diameter than your intended completed borehole diameter and of short lengths [<1.5m] that you can securely attach to the next length as required) through which you operate the auger and/or bailer or jetting tool while pushing the casing into the ground behind the disturbed sediment. I am not familiar with the specific kit which you have to hand but the Oxfam hand-augering kit includes lengths of casing (and the attachments to help you drive it into the ground – chain pipe wrenches may suffice if you have nothing better to hand) that allow you to do just this. It’s not too difficult to improvise but if you are unfamiliar with this technique, I’m not sure my explanation will help. However, I would be surprised if you couldn’t find several drillers in Mozambique who are familiar with this technique – it’s a standard approach in wadi/fadama well construction. The basic principle is that you want the casing to descend into the sediments while you evacuate the sediments from inside the casing. You then end up with the casing at your desired depth (don’t expect to get deeper than 6 or 7 metres max – it’s too hard to get lower than this by hand) through which you can insert your slotted borehole pipe. Withdrawing the casing is almost as much of a palaver as inserting it so make sure you hold your borehole pipe (which will tend to be slightly buoyant in water) in place while the sections of casing are removed (and if the connection between casing lengths is screw-thread, be sure any rotation is not unscrewing the casing or you will leave it in the ground forever!). Once the sediments at depth have collapsed around your borehole tubing, it should be held in place by the sediment while you remove the casing.
1) Using a bailer: For this method you need a bailer attachment (also standard part of the Oxfam hand-augering kit) to the auger rod – this is a kind of narrow bucket of the same diameter as the auger, with a one way clapper closure that allows sediment to push up into the bucket but not come back out again. Auger/hand dig some way into the sediment then sink a length of casing into the space. Hold the first length of casing in place – if you have no more sophisticated tools to ... (more)
I agree with Lucy's comprehensive response. Also to say, as a direct answer to the original question, that making any sort of hole in sand, especially water bearing, probably fairly uniform sand, will require casing. Jetting could be effective and quick - you'd need an air compressor, ideally - but I guess that, as you have the rig, you want to use it.
Having looked up the Vonder rig, I see that it is a hand-operated tripod device. I assume that you are using some sort of baler tool with a flap valve or some way of retaining loose sand (as described by Lucy). You should be able to work the tools inside a casing, which, if conditions are right, might penetrate under its own weight as the drilling proceeds and the sand is excavated from beneath the casing. more likely, you'd have to add force to drive the casing down, as described by Lucy. Therefore, steel casing would probably be better as you could hammer it if necessary - but if you do have to hit the casing, use a collar to avoid damage to it - you may have to add casing sections.
Don't know how much this helps.
I am struggling with memory but wasn't there a very simple hand over the top of the tube technique used in very soft soils in Bangladesh?I guess rwsn can fill in the detail but I didn't get past this web site. https://www.rwsn.ch/prarticle.2010-03-01.8939202478/prarticle_view Regards Alan
For some instructive videos on hand drilling techniques go to www.vimeo.com and search for EMAS and water They show use of temporary casing and hand auger or sand bailer to advance the casing. There are several hours of video on various hand drilling and sell supply hand pump techniques using very limited resources. Even sessions on solar water heaters, ferrocement tanks and constructing ram pumps. https://vimeo.com/8356556, https://vimeo.com/8357733
A lot of times it is easier to understand from video than a text description.
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