Beach Foundations

Hello nilechamp

You are looking for trouble, it seems, all statistics for weather and storm damage are working against you.

Can you send me a PM with the location, or re-post here with it, so the local site can be checked via Google Earth.

Kind Regards....

Build it like a boat because no matter what you do, it will, one day, get washed away.

With global warming causing rising sea levels, don't worry about the foundatations, rather get your plans from some boat builders for your new dwelling.

Hello nilechamp,

just a thought............have you thought of searching in Countries that are mostly if not all sand?......Or have you searched at all on beach building methods?.......

I am interested in large building, and watched the building of one of the largest Hotels in the World in Dubai and, from memmory I think it was just a few hundred metres from the ocean. It was built entirely on sand. I know your place is not on the same scale but you probably will have to use similar technique's, all be it on a smaller scale. I will try and find the program details and let you know either the program or the build details.

jfmfit

I live in the Caribbean and hae en involved in a significant amount of building activities. My advice is to be very careful of the data available in modern day reading matter you should only use general engineering data from these references.

Each island has its own set of difficulties ranging from hurricane force winds, earth movements resulting live/dormant volcanic and earthquake activities as well as tidal pressures since you are talking about beachfront construction.

Without know which specific island is involved its difficult to offer any advice except to say that each island has a lot of indigenous data relative to the our structural/foundation requirements. Another point to bear in mind is that the engineers/builders of the 17th and 18th centuries had it right. A lot of their structures survives the rigours of nature over the years gone by and in my opinion sufficient recognition has not been given to the skill of these professionals of yesteryear.

I feel that you can not go wrong if you take a page out of their books rather than the modern day literature which still has to address conditions in places like the Caribbean.

In the even you may wish to discuss this further outside the forum, please feel free to contact me at buckman@cwdom.dm

Hello again nilechamp,

I realise now, after looking that the details about the Dubai Hotel is not relevant.

I searched using homes on sand-beach and found this info, which even on an 'ordinary' home is relevant. I have copied part of a big forum from

the James Randi Education site. http://forums.randi.org/showthread.php?p=3102686

I will paste the bit I think was interesting and something you will need to bear in mind...........apart from the regular super storms. This shows you will have to build on stilts to protect the local flora, and will probably have to build on stilts as, after a storm, assuming your home is still there, the sand will grow up through any deposited sand around your home and could end up starting to bury it. read the piece below please.

jfmfit

Hi,

this is really a great information: undisturbed dunes give protection and disturbed dunes will not.

Building on stilts will be a very good solution: near the stilts there will be a higher wind velocity so it seems necessary to add some extra structure that calms down the velocity so far that sand is deposited there. (Like mangrove having many roots that facilitate mud accumulation.

Same may be necessary below the main body of the construction as there is a higher wind velocity too. So I would expect either very many stilts that can do this slowing down of very strong winds or only a few stilts (3, 4, 5?...12) and around these and between the sand and the lower part of the house a curtain of small (Bamboo?) ones that are not used to support any load.

If you want to be protected against any possible wind velocity this will be very difficult.

In Europe any house has to be protected against winds that can exert 500N/m² , this is often exceeded by storms of magnitude 8 (68km/h) because in vortices the maximum velocity is much higher than the maximum longterm velocity.

Storms exceeding magnitude 12 (125km/h) are very very rare in Europe but in the Caribbeans there have been measured wind velocities up 450Km/h!

This ultrahigh velocity is occurring if the hurricane grows so fast and big that the shear velocity around the central vortice is generating additional surrounding vortices.

This is a function of Reynolds number as any vortice generation in shear flow.

So if you want to protect your building against this highly improbable but really possible super hurricane only a fully metallic UFO-like object with low drag will be realistic: built like an airplane and subject to similar wind velocities.

So I think it may be a good idea to have a small compartment (survival shell) with these characteristics and a more conventional house both on a set of high stilts. The conventional house will be blown to ? if any high intensity storm is coming up - think about an insurance or don't put any valuables in.

Think about hollow stilts to get the water up and a small desalination plant and an elevator (20m above ground?) and some rope ladder if the storm has blown away or damaged all these.

Very interesting project. I would allow 1 to 2 cubic meter of volume per person for the emergency part.

What about using coconut palms as stilts? What else is good? Metals: no, glass-fiber: maybe, plastics: not stable in sunlight, how to repair and replace if no longer good?

Please report your decisions and let us know the results, the building process and the first big storm survival.

RHABE

A potential model for your structure may be found on Turks and Caicos - Provideciales - BWI. New large structures are being contiuously erected at Grace Bay. Talk to some of the engineering firms involved with those projects. I know for a fact, that even if you can create a stable foundation, the beach continues to shift, and large equipment must be employed on a continuing basis to maintain the shoreline. Also, be aware that there are no ERs on the West Indies. If you, or anyone in your family requires emegency medical attention, your only option is an air ambulance from the USA. Current cost, about $18,000.

Certain geological features will affect the design. For example, Procidenciales is largely surrounded by a barrier reef which helps to dissipate storm surge wave energy. The result is that Grace Bay water remains relatively calm, even during major storms. The West Indies are an idlylic location. If your property has other buildings adjacent to it, I'd take that as a good sign. If there are no other buildings near your property, there is probably a reason.

I am not a Civil Engineer, but a Mechanical, but we completed a 150 sq meter boat store about ten years ago. This is a large concrete and block construction with beam and block roof designed for parking vehicles and boats on the roof and more boats inside..

The building is built entirely on sand.

The construction stands on a solid reinforced concrete slab which is 800 mm thick at the edges and under the centre walls, and 400 mm over the remainder.

The outer ring foundations have two lower layers of 12mm steel reinforcing grid and the whole has two layers of the same 12 mm at 20 X 20 cm steel grid. Thus the outer ring and centre walls positions have steel at 50 and 100 mm from the top and 80 and 180 mm from the bottom.

With regard to levels, and global warming, the latest figures released here in the UK are for a 1,5 metre maximum rise within the next 200 years. Thus I would build my slab so its top surface was at least 2 metres above the highest tide recorded in the LAST 100 years. Then my house would stay dry.

I leave it to others to suggest how to keep the house fixed to the slab, and surviving the hurricanes

Good luck

There isa fundamental that must be respected. In order fro a man-made structure to survive storm wave action and 'storm-surge' inundation and battering, the structure must either: allow the waves and surge to pass through (build on pilings) : or be massive , reinforced concrete --an artificial rock cliff so-to-speak.

Piling structures will be destroyed if there is significant large debris in the wave front and surge--the battering-ram effect is tremendously powerful. If the storm waves do not have a debris field to pick up and use against your house--that's good.(and bad) Good in that no debris to batter your house apart, bad in there is no energy dissipating structure in front of you.

Massive structures must be designed to disperse the wave energy by using wedge shapes to create turbulence and froth in the waves striking it. A solid face will receive tremendous impact energy. Successful 'sea-walls' employ a vertically curved face to force the wave up as well as wave front dissipating wedge forms.

It is very difficult to over-estimate the power of a Force 5 Hurricane. 20 foot rise in seal level, with 50 foot waves on top of that. The slope of th sea floor immediately offshore has a large influence on wave height and 'breaking zone. Ideally, the large waves will break offshore, but that takes sand bars offshore.

Don't forget onsite wastewater treatment. Septic tanks pollute coastal environments. We can help with theat

Move your ouse little away from land line and go in ocean..... build a boat itself as your home. No foundation will be needed. Need not worry about sea level rise due to global worming... you will be always floating.

It is my dream home.

nilechamp,

Why? Oh well what does it matter except to you.

Build light, no worries, knowing that no matter the construction your house is going to blow away is only question of when.

So build what suits you and enjoy then build again and again enjoy but have an emergency plan tell everyone about it and use it early.

Don't worry enjoy, just maintain a useable dwelling outside hurricane alley (: don't worry have another pina`colada enjoy

I do not believe that a whole lot has changed in 20 years for foundation design. For non-cohesive sands in shallow groundwater, you still have liquifaction issues. Deep foundation processes like Vibro-replacements, vibro-compaction, rammed-earth, etc require expensive heavy equipment to be mobilized in, and earthen materials that may not be readily available. Driven piles again require specialized equipment, though more common. One option is cast-in-place displacement piles. Another commonly used for smaller residential and commercial buildings is waffle slabs. Or, a combination of piles and waffle slab design.

Thanks to everyone for all the replies.

The house is not actually for me but a client. I have recently finished the construction of my own villa on the island. It is perched on a cliff top so although construction was tricky I have none of the long term problems associated with the new project. After viewing my villa the client asked me to manage design and construction of her project. Consequently I am unable to pinpoint the exact location but suffice to say the island is just 36 sq mls, volcanic but dormant within recorded history and stunningly beautiful. The plot location is on the windward side of the island and totally remote! The remoteness is not a result of previous failed construction attempts but more to do with under development of the island. In fact it is likely that a hotel group are about to purchase adjoining land.

The problems are immense but I believe the nature of the client and the provision of a realistic budget make it both feasible and exciting.

Welderman - travelling back to the UK yesterday I was fortunate enough to sit next to someone on the plane who is connected with Turks and Caicos. They have promised to put me in contact with people on the island.

Guest - Waste water will be treated and used for irrigation. Planning has not yet been granted but initial proposals have been geared to be as environmentally friendly as possible.

HughMattos and Kieth E Bowers - I will research information on historic storm surge levels on the island. I just hope they are localised enough for this project. Rises in sea level resulting from global warming may not be a factor the client will want to consider but I will put it to her. As stated above, the structure will need to be unobtrusive, so sea defences are out. We will need to bend with nature as much as possible rather than fight her. Consequently the use of stilts and indigenous planting will be significant considerations. There are no islands offshore to this particular beach. However, I suspect during a hurricane the sea may be full of debris blown in from other locations.

Replies to this thread appear to reinforce my initial leaning towards stilts. There is another fairly new domestic building on the island using stilts but fortunately it has not yet been 'hurricane tested'.

I am still short on specific foundation design reference material. If anyone has a recommendation, please let me know.

Interesting!

What are the rates for purchase of land? Which is the location. Long / Lat ?

aaaa

Wow, those homes are exceptionally cheap considering most homes within 50 miles of the coast in california run about $100 to $1000 /sqft on a 1/5 ac lot.

The rates quoted are for land only. Construction costs on the island vary between $100 and $300/sqft

Curious, you quoted the cost for floor area. So there is no associated property, just a building pad?

No, the prices quoted in the first part of the reply were for 'green field' plots ie just the land. No buildings, nothing but bush.

In the last paragraph of that reply I referred to a fully constructed villa on the neighbouring island. The sale price of this villa (including the plot upon which it sits) can be equated in a cost per finished foot of liveable space ie roofed 'floor area'. I noted this particular one because it is a staggering $8000/sqft