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Hi Joanne/Toby

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 hand, a couple of chain pipe wrenches should be attached in a sense that allows you to rotate the casing without either of them coming undone and so that the handles protrude from the casing roughly opposite each other. Attach the bailer attachment to the auger stem and while one team is operating the casing the other team should be operating the bailer inside the casing. You can use a variety of techniques to get the casing (and bailer) to descend – vibrating, rotating, percussion (but take care not to damage the ‘cutting’ edge of the bailer) – but you must remove the sediments at the same time as you are getting the casing to descend (to avoid more sediments flowing into the space you have just created). Once the casing length has descended into the ground (you’ll have to keep moving the wrenches up as the casing descends) so there is only a short length protruding, attach the next casing length and keep going. Make sure that you do not remove the last cable wrench from the casing length until the next casing length is securely attached! You should look at the sediments as they come out in the bailer and lay them in logical order, piling them in say 1m intervals. Evaluation of the sediment properties (size, sorting) will help you determine where to put the slotted section of your tube well. 2) Jetting: You need a source of water and a means of creating some pressure. Depending on the sediments you can jet the casing in but you will not be able to select the best sediments against which to set the tubewell slots. As before, you are trying to get the casing to descend into the space just created by evacuating sediments. You jet the water down the centre of the hollow casing while pushing/rotating the casing into the ground. The water/sediment mix exits however it can, through the middle, up the sides. It depends on a number of factors that I haven’t the time to cover right now. This technique is wonderfully messy – expect to get covered in slurry!

The following links give synopses of various borehole construction techniques, including hand augering, vibro-bailing and jetting.
https://www.lboro.ac.uk/well/resources/technical-briefs/43-simple-drilling-methods.pdf https://www.fao.org/docrep/w7314e/w7314e0v.htm#shallow%20tube%20well%20construction%20techniques

If you google ‘washbore’, you will probably get a number of other references that may be helpful.

It’s quite possible I’ve missed some important steps so please pitch in anyone else on the TSS if you observe any glaring omissions!

Hi Joanne/Toby Joanne

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 hand, a couple of chain pipe wrenches should be attached in a sense that allows you to rotate the casing without either of them coming undone and so that the handles protrude from the casing roughly opposite each other. Attach the bailer attachment to the auger stem and while one team is operating the casing the other team should be operating the bailer inside the casing. You can use a variety of techniques to get the casing (and bailer) to descend – vibrating, rotating, percussion (but take care not to damage the ‘cutting’ edge of the bailer) – but you must remove the sediments at the same time as you are getting the casing to descend (to avoid more sediments flowing into the space you have just created). Once the casing length has descended into the ground (you’ll have to keep moving the wrenches up as the casing descends) so there is only a short length protruding, attach the next casing length and keep going. Make sure that you do not remove the last cable wrench from the casing length until the next casing length is securely attached! You should look at the sediments as they come out in the bailer and lay them in logical order, piling them in say 1m intervals. Evaluation of the sediment properties (size, sorting) will help you determine where to put the slotted section of your tube well. 2) Jetting: You need a source of water and a means of creating some pressure. Depending on the sediments you can jet the casing in but you will not be able to select the best sediments against which to set the tubewell slots. As before, you are trying to get the casing to descend into the space just created by evacuating sediments. You jet the water down the centre of the hollow casing while pushing/rotating the casing into the ground. The water/sediment mix exits however it can, through the middle, up the sides. It depends on a number of factors that I haven’t the time to cover right now. This technique is wonderfully messy – expect to get covered in slurry!

The following links give synopses of various borehole construction techniques, including hand augering, vibro-bailing and jetting.
https://www.lboro.ac.uk/well/resources/technical-briefs/43-simple-drilling-methods.pdf https://www.fao.org/docrep/w7314e/w7314e0v.htm#shallow%20tube%20well%20construction%20techniques

If you google ‘washbore’, you will probably get a number of other references that may be helpful.

It’s quite possible I’ve missed some important steps so please pitch in anyone else on the TSS if you observe any glaring omissions!

Hi Joanne

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 hand, a couple of chain pipe wrenches should be attached in a sense that allows you to rotate the casing without either of them coming undone and so that the handles protrude from the casing roughly opposite each other. Attach the bailer attachment to the auger stem and while one team is operating the casing the other team should be operating the bailer inside the casing. You can use a variety of techniques to get the casing (and bailer) to descend – vibrating, rotating, percussion (but take care not to damage the ‘cutting’ edge of the bailer) – but you must remove the sediments at the same time as you are getting the casing to descend (to avoid more sediments flowing into the space you have just created). Once the casing length has descended into the ground (you’ll have to keep moving the wrenches up as the casing descends) so there is only a short length protruding, attach the next casing length and keep going. Make sure that you do not remove the last cable wrench from the casing length until the next casing length is securely attached! You should look at the sediments as they come out in the bailer and lay them in logical order, piling them in say 1m intervals. Evaluation of the sediment properties (size, sorting) will help you determine where to put the slotted section of your tube well. 2) Jetting: You need a source of water and a means of creating some pressure. Depending on the sediments you can jet the casing in but you will not be able to select the best sediments against which to set the tubewell slots. As before, you are trying to get the casing to descend into the space just created by evacuating sediments. You jet the water down the centre of the hollow casing while pushing/rotating the casing into the ground. The water/sediment mix exits however it can, through the middle, up the sides. It depends on a number of factors that I haven’t the time to cover right now. This technique is wonderfully messy – expect to get covered in slurry!

The following links give synopses of various borehole construction techniques, including hand augering, vibro-bailing and jetting.
https://www.lboro.ac.uk/well/resources/technical-briefs/43-simple-drilling-methods.pdf https://www.fao.org/docrep/w7314e/w7314e0v.htm#shallow%20tube%20well%20construction%20techniques

If you google ‘washbore’, you will probably get a number of other references that may be helpful.

It’s quite possible I’ve missed some important steps so please pitch in anyone else on the TSS if you observe any glaring omissions! omissions! Lucy