Construction Advice

[Diablo Bob]

I don't know what the rest of the world thinks about this but I need at least overnight to begin to understand it. Er, um, so you had a lazy day then!

No, not a lazy day, but a very long one....... working on a tender which is due in the morning, took a break to get it off my mind so read about retaining walls! God, I need to get a life..........

Edited January 8, 2007 by Diablo Bob

[chownah]

Those Carolina Brick Association drawings remind me of my work back in the states. This type of drawing is typical of the specifications used in the US in cities, counties, and states by their infrastructure buildings. This drawing is almost assuredly not what the OP is looking for....way too expensive and way overbuilt. When I worked for a small city back in the US even we wouldn't use such an overbuilt type of wall for low retaining wall construction in non-critical areas. Notice that the width of the foundation is about equal to half of the wall height. For the 120 cm tall wall the OP wants to build the equivalent would be the 4 foot wall form the drawings...and the foundation width would be 2 foot 3 inch which is about 65 cm and it would be and would be 10 inches thick which is about 25 cm and this would run the entire length of the wall!!! Way way overbuilt. This type of wall is called a cantilever wall. The way it works is that the weight of the foundation and the dirt that sits on it hold it in place and the verticle rebars which are securely anchored in this mass along with the grout and bricks create a verticle beam which resists the overturning force of the fill.

This design will certainly work but is way way overbuilt and way way too costly.

Chownah

[Diablo Bob]

Those Carolina Brick Association drawings remind me of my work back in the states. This type of drawing is typical of the specifications used in the US in cities, counties, and states by their infrastructure buildings. This drawing is almost assuredly not what the OP is looking for....way too expensive and way overbuilt. When I worked for a small city back in the US even we wouldn't use such an overbuilt type of wall for low retaining wall construction in non-critical areas. Notice that the width of the foundation is about equal to half of the wall height. For the 120 cm tall wall the OP wants to build the equivalent would be the 4 foot wall form the drawings...and the foundation width would be 2 foot 3 inch which is about 65 cm and it would be and would be 10 inches thick which is about 25 cm and this would run the entire length of the wall!!! Way way overbuilt. This type of wall is called a cantilever wall. The way it works is that the weight of the foundation and the dirt that sits on it hold it in place and the verticle rebars which are securely anchored in this mass along with the grout and bricks create a verticle beam which resists the overturning force of the fill.

This design will certainly work but is way way overbuilt and way way too costly.

Chownah

Chownah

I agree on the overbuilt.... and the foundation will be costly, the skin (If he can use the red clay brick) probably a push on the cost of block, The reinforcement, well at 450mm OC with the 10mm horizontals, probably a liveable cost. The question becomes the foundation, do you have any ideas to simplify. I am thinking maybe he should go to CMU and see if they have any soils data to fine tune the design.

Also, remember the OP wants to build the wall in excess of 2m, I think 2.5m and retain the soil, that is a lot of force to restrain. Any way we look at it the foundation will be deeper and wider than for a common barrier wall.

For what it is worth, I looked at gravity walls also, substancial in size but it would be an attractive wall.

[lingling]

2) I don't know if the brick in Thailand is clay fired, and more importantly does it make a difference. I will continue my search.

I have seen a thai brick wall literally rain away. The local red bricks need to be protected from rain.

[chownah]

The retaining part of the wall is only 1.2 metres tall....this is not alot of dirt to hold up.....especially the cohesive soil prevelant in Northern Thailand which will almost stand up vertically by itself.

I'd like to hear from chiang mai about whether the grade beam can be built on undisturbed earth or not. It would also be good if he could go dig at a couple of the post locatations to see if the foundations will be in undisturbed earth or not.....also see what the dirt looks like down there....and if there is any water there.....was this a rice paddy before filling?...or what?

I think another good thing to do would be to go find some retaining walls that have fallen down and examine them to try to find out why they fell...did the posts fall over or did the grade beam get pushed out or did the top beam break or.....whatever. I'll bet that you will not find any posts with braces that have fallen over....a post with a proper foundation (like what I described) with a properly constructed brace will almost assuredly not overturn....in my opinion.

Chownah

[Diablo Bob]

The retaining part of the wall is only 1.2 metres tall....this is not alot of dirt to hold up.....especially the cohesive soil prevelant in Northern Thailand which will almost stand up vertically by itself.

I'd like to hear from chiang mai about whether the grade beam can be built on undisturbed earth or not. It would also be good if he could go dig at a couple of the post locatations to see if the foundations will be in undisturbed earth or not.....also see what the dirt looks like down there....and if there is any water there.....was this a rice paddy before filling?...or what?

I think another good thing to do would be to go find some retaining walls that have fallen down and examine them to try to find out why they fell...did the posts fall over or did the grade beam get pushed out or did the top beam break or.....whatever. I'll bet that you will not find any posts with braces that have fallen over....a post with a proper foundation (like what I described) with a properly constructed brace will almost assuredly not overturn....in my opinion.

Chownah

Chownah.................. YOU ARE ABSOLUTELY CORRECT! Somehow, when reading the OP I got the impression that initially he was building 1.2 meters of retaining wall then at a later date bringing it up to 2.5 meters AND bringing in more fill!

You see, 2 heads are better than one, and in this case 1.1 heads yours being the whole number!

[Loom]

I recently read that if a slope is below a certain grade, the land will generally hold up OK. We had a small plot infilled a few years ago, probably 2m high, with slopes on the sides at about 45 degrees and from what I've heard, it's holding up fine. Maybe not so well a few years from now, but we'll see.

We also had a chunk of a small retaining wall slump over last year during the rains. I've ingored it so far but now have some basis of evaluating the problem. Thanks...

[chiang mai]

The retaining part of the wall is only 1.2 metres tall....this is not alot of dirt to hold up.....especially the cohesive soil prevelant in Northern Thailand which will almost stand up vertically by itself.

I'd like to hear from chiang mai about whether the grade beam can be built on undisturbed earth or not. It would also be good if he could go dig at a couple of the post locatations to see if the foundations will be in undisturbed earth or not.....also see what the dirt looks like down there....and if there is any water there.....was this a rice paddy before filling?...or what?

I think another good thing to do would be to go find some retaining walls that have fallen down and examine them to try to find out why they fell...did the posts fall over or did the grade beam get pushed out or did the top beam break or.....whatever. I'll bet that you will not find any posts with braces that have fallen over....a post with a proper foundation (like what I described) with a properly constructed brace will almost assuredly not overturn....in my opinion.

Chownah

Chownah.................. YOU ARE ABSOLUTELY CORRECT! Somehow, when reading the OP I got the impression that initially he was building 1.2 meters of retaining wall then at a later date bringing it up to 2.5 meters AND bringing in more fill!

You see, 2 heads are better than one, and in this case 1.1 heads yours being the whole number!

Sorry for any delay but I took yesterday to drive down to the village to check out a few things - the location is just outside Sukhothai in central Thailand, four hours from where I live!!!

First of all, answers to some specific questions raised: Yes it is possible to build the grade beam on undisturbed earth and no the land was never used for rice paddy. The water table is usually very high and the land is prone to flooding each year, hence the need to raise the land in the first place. But regardless of these factors we may have come up with a pragmatic hybrid solution.

It is clear that the proper solution to this problem is not as straight forward and inexpensive as I had first imagined. The imperative currently is to get some form of habitable structure onto the land before the rains in May. In thinking about the most cost efficient, expediant and appropriate way to do this I had initially thought of two approaches. The first was to build a small house out of block on a flat concrete foundation - that approach would certainly require a retaining wall to be built given the narrow size of the building plot. The second approach was to buy an existing wood house and to transfer it to the family plot and rebuild it on posts - this approach would require less of a need for a retaining wall since the raised posts on which the house sits will be sunk below the level of the raised ground. It therefore seems probable that what we shall do is to reduce the level of the raised ground to between 0.50 and 0.75 metres (which will still be high enough to ensure the house site remains dry during flooding). A relative in the village has found a large teak house that measures some 30 feet by 40 feet and the wood is in excellent condition. We believe that house can be reduced in width easily and reconstructed on the family plot. As far as the raised land is concerned: the raised land comprises sub soil that was dumped there last year and compressed by a bull dozer. In fairness the land has not moved at all since it was put there and the surface of the ground appears as if the soil is mixe4d with cement dust - it is very hard!

The raised wood house is a good solution since it is in keeping with the other houses nearby and all the other factors are right. Unbelievably the cost to purchase the house is very inexpensive when compared to the cost of buying new wood and this of course is attractive. Neither my wife nor I or indeed the family are interested in spending lots of money to build a modern or expensive structure hence the native wood style house fits well for everyone. So there you have it, as I said earlier a pragmatic solution.

I am extremely grateful to DB and Chownah for their efforts in trying to crack this problem and to others who have contributed ideas and comments. My area of specialism is IT systems and telecommunications program management so if I can ever be of help with queries you may have in the future on those topics I owe you at least quid pro quo.

Many thanks again.

[Loom]

House sounds nice...We are going through something similar to this. To avoid any possible surprise later on, try to get an accurate estimate of the costs in addition to just buying the house. For us, the cost of the house included notifications and approvals from the local authorities before moving, the cost of tearing down and moving the house. Additional costs involved a house design for submission to the local authorities (even though it will be essentially reconstructed as it was before), labor, equipment and management costs for reconstruction, and the cost of materials like cement, rebar, roofing, plumbing, electrical, water supply (well), etc. The additional costs more than doubled the purchase price of the house alone. It may be less costly and troublesome in your situation since you're buying and building in the family's village, however. Rgds,

[Ground Engineer]

For a 1.2m high cutting, try using a reinforced earth retaining wall. THis can be achieved very cheaply by placing geofabric material in 600mm layers and overwrapping each layer to contain the earth. A search on the internet will describe how to construct. The face of the wall can be battered back at an angle of say 75 degrees and seeded to create an aesthetic finish instead of concrete. Alternatively you can build a free standing wall infront of the reinforced earth wall if you wish.

Regards,

Ground Engineer

B.Eng (Hons Civ Eng)

[chownah]

For a 1.2m high cutting, try using a reinforced earth retaining wall. THis can be achieved very cheaply by placing geofabric material in 600mm layers and overwrapping each layer to contain the earth. A search on the internet will describe how to construct. The face of the wall can be battered back at an angle of say 75 degrees and seeded to create an aesthetic finish instead of concrete. Alternatively you can build a free standing wall infront of the reinforced earth wall if you wish.

Regards,

Ground Engineer

B.Eng (Hons Civ Eng)

Is geofabric of the type req'd available in Thailand? and if so where?

How many lifts of geofabric would you use for a 1.2m mse wall and at what levels would you place the geofabric?

How far into the fill would the geofabric have to extend?

Would special fill have to be used over the geofabric or will any soil do?

How long would exposed geofabric last when exposed to the sun?

Chownah

[grumpy_old_retired]

chownah......diablo bob......chiang mai

I am at the stage of wanting to build a 'retaining wall' as well. My experience at looking at some of the walls that have been built the 'Thai way' is that they fall down after a few years!

I am not an engineer. I have absolutely no or limited knowledge regarding construction methods and techniques. I did find the following image of a retaining wall that looks promising but do not know if it will be any better than the 'Thai built walls' I see every day.

Any ideas regarding the attached would be helpful.

Al

Edited January 15, 2007 by grumpy_old_retired

[chownah]

Sure...it will be better than what is usually built in Thailand and should be totally adequate....and very expensive.

Chownah

[chownah]

The wall in the picture has a detail that should be clarified. The drawing makes it look like the verticle steel bars are placed in the blocks close to the exposed face of the wall when in fact they should be placed close to the fill side of the wall.

Since this wall is way overbuilt for the approximately one metre of fill it is retaining perhaps the detail I just mentioned does not matter but I mention it anyway just to indicate what should be done for good design practice. Another similar detail which might not matter but which could be designed better is the horizontal bottom part of the verticle steel. It is shown running close to the top of the footer. If the verticle part is placed close to the fill side of the wall and the horizontal part is placed close to the top of the footer then there is a possibility of pull out of the bar at the bend. Since the horizontal part should be close to the top of the footer for strenght and since the verticle part should be close to the fill side of the wall, I would not do this with one piece of steel. I would run the verticles all the way down to the bottom (about 5 cm from the bottom) of the footer and end it in a hook....I would then use a seperate piece to run the entire width of the footer....and I'd probably put a hook on both ends. Remeber that when using smooth rebar you always should put a hook at every end....and on deformed rebar it is a good practice but in some situations it is not necessary but doesn't cost much so might as well give it a hook....or at least a 90 degree bend and a few inches.

Designs like this usually also have at least one and usually two bars running along the length of the footer.....I'm surprised they didn't use one but it is probably ok without it since its only retaining about 1 metre of fill and this entire design is way way overbuilt for holding up 1 metre.

Chownah

[grumpy_old_retired]

The wall in the picture has a detail that should be clarified. The drawing makes it look like the verticle steel bars are placed in the blocks close to the exposed face of the wall when in fact they should be placed close to the fill side of the wall.

Since this wall is way overbuilt for the approximately one metre of fill it is retaining perhaps the detail I just mentioned does not matter but I mention it anyway just to indicate what should be done for good design practice. Another similar detail which might not matter but which could be designed better is the horizontal bottom part of the verticle steel. It is shown running close to the top of the footer. If the verticle part is placed close to the fill side of the wall and the horizontal part is placed close to the top of the footer then there is a possibility of pull out of the bar at the bend. Since the horizontal part should be close to the top of the footer for strenght and since the verticle part should be close to the fill side of the wall, I would not do this with one piece of steel. I would run the verticles all the way down to the bottom (about 5 cm from the bottom) of the footer and end it in a hook....I would then use a seperate piece to run the entire width of the footer....and I'd probably put a hook on both ends. Remeber that when using smooth rebar you always should put a hook at every end....and on deformed rebar it is a good practice but in some situations it is not necessary but doesn't cost much so might as well give it a hook....or at least a 90 degree bend and a few inches.

Designs like this usually also have at least one and usually two bars running along the length of the footer.....I'm surprised they didn't use one but it is probably ok without it since its only retaining about 1 metre of fill and this entire design is way way overbuilt for holding up 1 metre.

Chownah

Thanks for the clarification. I have 1 rai of land that has a drop off on one side and was considering using the design shown rather than use fill dirt that would not be very stable. The drop off is approximately 1 meter lower than the rest of the land. Rather than place posts in the fill dirt I was considering using, again, the design shown as I think it might be much more stable. I will take the suggestions that you provided and try and have the contractor use them. After the retaining wall is built I can then use fill dirt to level that portion of the land.

Al

[grumpy_old_retired]

Another design that I have been considering is shown below. This design is much more in line with what is normally built here in Thailand. The 60 cm shown is above ground level. As I will have to place approximately 45 cm of fill dirt after the fence and house is constructed to allow for run-off from rain and also to raise the land above the street level. At present, the land is (rice field) and is relatively solid fill (8 years) and I did not want to build in or above new fill dirt. The foundation of the house will be raised 60 cm above present ground level with 45 cm of fill dirt added after the house is built.

Any obvious problems that I may have overlooked?

Thanks, Al

Edited January 16, 2007 by grumpy_old_retired

[chiang mai]

chownah......diablo bob......chiang mai

I am at the stage of wanting to build a 'retaining wall' as well. My experience at looking at some of the walls that have been built the 'Thai way' is that they fall down after a few years!

I am not an engineer. I have absolutely no or limited knowledge regarding construction methods and techniques. I did find the following image of a retaining wall that looks promising but do not know if it will be any better than the 'Thai built walls' I see every day.

Any ideas regarding the attached would be helpful.

Al

Grumpy: I had some serious landscaping work done at my home in the UK a few years ago and professional engineers designed the retaining walls which then had to be approved by the planning authorities. The wall they designed and which was subsequently built was almost identical to your drawing. The only difference was that the block wall was positioned at the low land edge of the base rather than the inside or high edge - I was told this provided greater strength to avoid tipping the wall over. The wall was constructed on a very steep slope to a height of 2.5 metres and held back some serious amount of land - it worked well. As far as cost is concerned; I am simply not an expert in these matters but my thoughts are that it should be an inexpensive way to go. Nine inch concrete block sells for 3.5 baht each in my neck of the woods and ready mixed concrete goes for 1.200 bat for four cubic metres. The appeal of this design for me personally is that it requires less skill to construct than many of the alternatives and could be classified as a DIY project. The cost of a JCB (macro) rental to dig the trench for the footings worked out at 600 baht an hour so I figured I could get away pretty cheaply on the entire project.

[chownah]

The wall in the picture has a detail that should be clarified. The drawing makes it look like the verticle steel bars are placed in the blocks close to the exposed face of the wall when in fact they should be placed close to the fill side of the wall.

Since this wall is way overbuilt for the approximately one metre of fill it is retaining perhaps the detail I just mentioned does not matter but I mention it anyway just to indicate what should be done for good design practice. Another similar detail which might not matter but which could be designed better is the horizontal bottom part of the verticle steel. It is shown running close to the top of the footer. If the verticle part is placed close to the fill side of the wall and the horizontal part is placed close to the top of the footer then there is a possibility of pull out of the bar at the bend. Since the horizontal part should be close to the top of the footer for strenght and since the verticle part should be close to the fill side of the wall, I would not do this with one piece of steel. I would run the verticles all the way down to the bottom (about 5 cm from the bottom) of the footer and end it in a hook....I would then use a seperate piece to run the entire width of the footer....and I'd probably put a hook on both ends. Remeber that when using smooth rebar you always should put a hook at every end....and on deformed rebar it is a good practice but in some situations it is not necessary but doesn't cost much so might as well give it a hook....or at least a 90 degree bend and a few inches.

Designs like this usually also have at least one and usually two bars running along the length of the footer.....I'm surprised they didn't use one but it is probably ok without it since its only retaining about 1 metre of fill and this entire design is way way overbuilt for holding up 1 metre.

Chownah

Thanks for the clarification. I have 1 rai of land that has a drop off on one side and was considering using the design shown rather than use fill dirt that would not be very stable. The drop off is approximately 1 meter lower than the rest of the land. Rather than place posts in the fill dirt I was considering using, again, the design shown as I think it might be much more stable. I will take the suggestions that you provided and try and have the contractor use them. After the retaining wall is built I can then use fill dirt to level that portion of the land.

Al

I want to be clear that I am not qualified to give professional advise in structural engineering or wall design in any capacity. You posted a design drawing and I have given my comments about it and these should not be taken as engineering advise but merely as opinions of an interested person. Any of my suggestions which you decide to use are at your discression and the design changes you make on your project are to be considered as your own.

If I were to build this wall on my property I would probably put the verticles at the centerline of the block because of the 16 inches between them.

Chownah

[chownah]

The pilaster design shows steel only in the pilasters....seems like there should be some elsewhere. Also there are some discrepencies in the drawing....the pilasters are shown 2.61 m from top to bottom but the drawing shows 15cm top beam 180cm block web, 60cm grade beam, and 66cm under the grade beam.....this adds up to more than 2.61 metres.....and I'm not sure if a 40x20x7 pilaster block would measure the 27 cm overall required....and the drawing is not to scale for the dimensions shown in red...it makes me think that someone took an old drawing and changed the dimensions for some reason which is a risky thing to do without the proper training.

Chownah

[astral]

These two shots give an idea of the butressed wall we had built.

You can see the main piers with the butresses held in place by the weight of the soil.

The main piers have vertical slots so that the horizontal beams slide down between them.

On top is a normal breeze block wall for privacy.

[chownah]

chownah......diablo bob......chiang mai

I am at the stage of wanting to build a 'retaining wall' as well. My experience at looking at some of the walls that have been built the 'Thai way' is that they fall down after a few years!

I am not an engineer. I have absolutely no or limited knowledge regarding construction methods and techniques. I did find the following image of a retaining wall that looks promising but do not know if it will be any better than the 'Thai built walls' I see every day.

Any ideas regarding the attached would be helpful.

Al

Grumpy: I had some serious landscaping work done at my home in the UK a few years ago and professional engineers designed the retaining walls which then had to be approved by the planning authorities. The wall they designed and which was subsequently built was almost identical to your drawing. The only difference was that the block wall was positioned at the low land edge of the base rather than the inside or high edge - I was told this provided greater strength to avoid tipping the wall over. The wall was constructed on a very steep slope to a height of 2.5 metres and held back some serious amount of land - it worked well. As far as cost is concerned; I am simply not an expert in these matters but my thoughts are that it should be an inexpensive way to go. Nine inch concrete block sells for 3.5 baht each in my neck of the woods and ready mixed concrete goes for 1.200 bat for four cubic metres. The appeal of this design for me personally is that it requires less skill to construct than many of the alternatives and could be classified as a DIY project. The cost of a JCB (macro) rental to dig the trench for the footings worked out at 600 baht an hour so I figured I could get away pretty cheaply on the entire project.

Are you sure about the prices....you are getting 9inch blocks at about the same price I pay for 3inch blocks and you are buying concrete cheaper than I can buy crushed rock!!!!

Chownah

[oxymoron]

The wall in the picture has a detail that should be clarified. The drawing makes it look like the verticle steel bars are placed in the blocks close to the exposed face of the wall when in fact they should be placed close to the fill side of the wall.

Since this wall is way overbuilt for the approximately one metre of fill it is retaining perhaps the detail I just mentioned does not matter but I mention it anyway just to indicate what should be done for good design practice. Another similar detail which might not matter but which could be designed better is the horizontal bottom part of the verticle steel. It is shown running close to the top of the footer. If the verticle part is placed close to the fill side of the wall and the horizontal part is placed close to the top of the footer then there is a possibility of pull out of the bar at the bend. Since the horizontal part should be close to the top of the footer for strenght and since the verticle part should be close to the fill side of the wall, I would not do this with one piece of steel. I would run the verticles all the way down to the bottom (about 5 cm from the bottom) of the footer and end it in a hook....I would then use a seperate piece to run the entire width of the footer....and I'd probably put a hook on both ends. Remeber that when using smooth rebar you always should put a hook at every end....and on deformed rebar it is a good practice but in some situations it is not necessary but doesn't cost much so might as well give it a hook....or at least a 90 degree bend and a few inches.

Designs like this usually also have at least one and usually two bars running along the length of the footer.....I'm surprised they didn't use one but it is probably ok without it since its only retaining about 1 metre of fill and this entire design is way way overbuilt for holding up 1 metre.

Chownah

Thanks for the clarification. I have 1 rai of land that has a drop off on one side and was considering using the design shown rather than use fill dirt that would not be very stable. The drop off is approximately 1 meter lower than the rest of the land. Rather than place posts in the fill dirt I was considering using, again, the design shown as I think it might be much more stable. I will take the suggestions that you provided and try and have the contractor use them. After the retaining wall is built I can then use fill dirt to level that portion of the land.

Al

As said the thing is way over designed, BUT my question is where in LOS are you going to get the 12 inch blocks with a compressive strength of 25 Mpascals??

Assuming you can get the blocks who is going to <deleted> them over 1.2m of reo?

I have followed this thread with interest for some time now and have not seen anyone present the simple design which Thai Village constructors can build. All you need to do is build two form shutters using 12mm ply on 75x50mm channel iron or wood and pour the wall in 2.4m sections. If you intend building a "din block" fence later do not forget the standard THAI 8mm in 100mm box format "sow" starters at 2m intervals inserted in the top 300mm of the retaining concrete wall. For retaining 1.2m a 500mm footing (as you show) the retaining wall tapering from 250mm at bottom to 150mm at top (vertical face on low side) Y12 reo at 600mm centres (as you show connecting footing to wall) 2xY12 reo horizontal first at 300mm next at 750 mm (as you show on50mm in from the vertical face, Chowna I am sorry is wrong the "bending moment is on the vertical low side as the pressure is on the tapered side. Think of a 2 story house slab the steel is 40mm up from the bottom as the weight pressure is on the top. I also put F53 mesh in the taper side 30mm from the surface. I admit this is marginally over-designed but since we did not have CPAC all concrete was mixed on site and as there was no internet or phone in those days I could not do a slump test to confirm the concrete strength. Every 2m put a piece of 50mm plastic pipe through the wall for drainage to the low side. By the way it is not the water pressure that pushes down Thai walls, it is the nature of Thai clay soil being expansive when wet. 18 years ago I developed this design for our property in Maeon and we have well over 90m retained and it has not move more than the designed deflection of 8mm. In our village just like underground power and concealed electrical cable which I also introduced it has become pretty much a standard.

Oxymoron MIE Aust CPENG

[chiang mai]

chownah......diablo bob......chiang mai

I am at the stage of wanting to build a 'retaining wall' as well. My experience at looking at some of the walls that have been built the 'Thai way' is that they fall down after a few years!

I am not an engineer. I have absolutely no or limited knowledge regarding construction methods and techniques. I did find the following image of a retaining wall that looks promising but do not know if it will be any better than the 'Thai built walls' I see every day.

Any ideas regarding the attached would be helpful.

Al

Grumpy: I had some serious landscaping work done at my home in the UK a few years ago and professional engineers designed the retaining walls which then had to be approved by the planning authorities. The wall they designed and which was subsequently built was almost identical to your drawing. The only difference was that the block wall was positioned at the low land edge of the base rather than the inside or high edge - I was told this provided greater strength to avoid tipping the wall over. The wall was constructed on a very steep slope to a height of 2.5 metres and held back some serious amount of land - it worked well. As far as cost is concerned; I am simply not an expert in these matters but my thoughts are that it should be an inexpensive way to go. Nine inch concrete block sells for 3.5 baht each in my neck of the woods and ready mixed concrete goes for 1.200 bat for four cubic metres. The appeal of this design for me personally is that it requires less skill to construct than many of the alternatives and could be classified as a DIY project. The cost of a JCB (macro) rental to dig the trench for the footings worked out at 600 baht an hour so I figured I could get away pretty cheaply on the entire project.

Are you sure about the prices....you are getting 9inch blocks at about the same price I pay for 3inch blocks and you are buying concrete cheaper than I can buy crushed rock!!!!

Chownah

Honest injun! The price I originally got in Sukohothai was 9 baht per block. But when I checked out the prices here in CM I found one place that sells them for 3.5 baht. The only difference with the CM block is that they are 4 core not 2 and they are made on site by a small family business.

[chownah]

I hope this drawing will shed some light on wall design...

http://www.oregon.gov/ODOT/HWY/ENGSERVICES...t/y02_br705.pdf

Notice that the sloped face is on the low side (aka exposed face or front face) and the verticle face is on the high side (aka fill side or back side). The verticle face can be place on the low side but that will reduce the gravity effect of the weight of the verticle portion of the wall.

Also notice that the large reinforcement is placed 50mm from the high side face of the wall. This steel provides tension where it is needed....the smaller steel on the exposed face is compressive steel and the same size bar is used regardless of height because as the wall gets taller the base gets thicker and there is more concrete there to provide compressive strength as well.

When considering a bending moment and how to resist it you need to consider how to create an opposing force couple and in concrete reinforced construction this force couple will be composed of (usually) a tensile force and a compressive force. The tensile force is assumed to be provide by the steel and the compressive force is provided by concrete and steel if compression steel is provided (almost always in Thailand because you can't rely fully on the strength of Thai concrete). I can provide a fairly intuitive example of how to know where you need tension and where you need compression if anyone would like to hear it.

Also notice that the main verticle steel goes to the bottom of the footer before it bends....just as I recommended and that the top steel in the footer is a seperate piece from the verticle.

Chownah

[chownah]

Honest injun! The price I originally got in Sukohothai was 9 baht per block. But when I checked out the prices here in CM I found one place that sells them for 3.5 baht. The only difference with the CM block is that they are 4 core not 2 and they are made on site by a small family business.

Does this meant that the labor cost is 3.5 baht per block and you have to supply the materials?...also, some small time block makers use just sand with minimal cement so they end up with really weak blocks....the vent blocks made locally here are that way...they are strong enough to make a part of a wall but I wouldn't want to use them for anything structural.

Chownah

[chiang mai]

Honest injun! The price I originally got in Sukohothai was 9 baht per block. But when I checked out the prices here in CM I found one place that sells them for 3.5 baht. The only difference with the CM block is that they are 4 core not 2 and they are made on site by a small family business.

Does this meant that the labor cost is 3.5 baht per block and you have to supply the materials?...also, some small time block makers use just sand with minimal cement so they end up with really weak blocks....the vent blocks made locally here are that way...they are strong enough to make a part of a wall but I wouldn't want to use them for anything structural.

Chownah

No, the sale price of the block is 3.5 baht each - but I can agree they may be as you have described and not the best thing with which to build a very tall and strong wall.

[chownah]

Honest injun! The price I originally got in Sukohothai was 9 baht per block. But when I checked out the prices here in CM I found one place that sells them for 3.5 baht. The only difference with the CM block is that they are 4 core not 2 and they are made on site by a small family business.

Does this meant that the labor cost is 3.5 baht per block and you have to supply the materials?...also, some small time block makers use just sand with minimal cement so they end up with really weak blocks....the vent blocks made locally here are that way...they are strong enough to make a part of a wall but I wouldn't want to use them for anything structural.

Chownah

No, the sale price of the block is 3.5 baht each - but I can agree they may be as you have described and not the best thing with which to build a very tall and strong wall.

It might be that the reason they make them on site is that they are too fragile to deliver.

Chownah

[grumpy_old_retired]

chownah......diablo bob......chiang mai

I am at the stage of wanting to build a 'retaining wall' as well. My experience at looking at some of the walls that have been built the 'Thai way' is that they fall down after a few years!

I am not an engineer. I have absolutely no or limited knowledge regarding construction methods and techniques. I did find the following image of a retaining wall that looks promising but do not know if it will be any better than the 'Thai built walls' I see every day.

Any ideas regarding the attached would be helpful.

Al

Grumpy: I had some serious landscaping work done at my home in the UK a few years ago and professional engineers designed the retaining walls which then had to be approved by the planning authorities. The wall they designed and which was subsequently built was almost identical to your drawing. The only difference was that the block wall was positioned at the low land edge of the base rather than the inside or high edge - I was told this provided greater strength to avoid tipping the wall over. The wall was constructed on a very steep slope to a height of 2.5 metres and held back some serious amount of land - it worked well. As far as cost is concerned; I am simply not an expert in these matters but my thoughts are that it should be an inexpensive way to go. Nine inch concrete block sells for 3.5 baht each in my neck of the woods and ready mixed concrete goes for 1.200 bat for four cubic metres. The appeal of this design for me personally is that it requires less skill to construct than many of the alternatives and could be classified as a DIY project. The cost of a JCB (macro) rental to dig the trench for the footings worked out at 600 baht an hour so I figured I could get away pretty cheaply on the entire project.

Are you sure about the prices....you are getting 9inch blocks at about the same price I pay for 3inch blocks and you are buying concrete cheaper than I can buy crushed rock!!!!

Chownah

Honest injun! The price I originally got in Sukohothai was 9 baht per block. But when I checked out the prices here in CM I found one place that sells them for 3.5 baht. The only difference with the CM block is that they are 4 core not 2 and they are made on site by a small family business.

Chownah - Thanks for the advise. Would not hold you or anyone else responsible if MY wall fell down. My initial plan was to build 'something' that would stay up! Some of the walls (fences) I have seen in Thailand are in pretty bad shape - leaning, about to fall over, braced in many different ways, etc. Having read through all of the replies I have come to the conclusion that I will just hire a crew and let them build it the 'Thai way'. If it stay's up great. If it falls down, I'll just rebuild - that seems to be the going standard here in Thailand. As the saying goes - 'We get what we pay for", hopefully.

Thanks to everyone else that has submitted their ideas and advice. As a "Dummy' when it comes to construction of anything, I value the input that people like yourselves are willing to provide. This is the big reason I have researched throughout the internet for 'ideas'.

Al

Edited January 17, 2007 by grumpy_old_retired