AmbergrisCaye.com Home Forums The Cayes Ambergris Caye Road Grading North Of The Bridge

For now I'm very happy with it just being navigable. A 40 minute trip yesterday was a 10 minute today...

Yes, I was up the road (or should I say up that creek) last week. I think it took an hour to get up to Grand Caribe. I think the first thing they need to do is add some drainage ditching on both sides of the road. Then add culvert pipes for access to properties. Compaction is also necessary. The water has nowhere to go when it rains!

We know what needs to be done to try and fix the road north, but it is very expensive and requires equipment we do not have, also it is not just the road north that needs major work. Grading is all that can be done at this time. One thing that would help all the roads is if vehicles, like taxi's and heavy trucks would slow down and avoid certain roads during heavy rain. If any one would like to contribute to the cost of road repair please feel free to do so.

If you really want to see crappy roads go for a drive where most of the people on the island live. Those roads make the road up north look like a superhighway.

I think the road north will be more and more used as thats where i see the expansion taking place All you need apart from the grade is a roller, nothing but a dead weight, then the road could be kept in reasonable share. I do agree that cars and trucks need to slow down, especially win heavy rain. Building roads and airfields was my profession, Very willing to mhelp in any way i can

robvee: Are you an engineer? If so perhaps you can give your opinion on Floating Roads. I suggested this technique in one of my posts last year and wanted to do it before all the hardcore was laid down. Have you ever had any experience with this technique which is used extensively in Scotland.

FLOATING ROADS ON PEAT

What is a floating road?
A floating road on peat in its simplest form is a road that is constructed directly on top of the peat relying on the strength of the in-situ peat for its support. The road does not actually "float" on the peat rather an equilibrium builds up between the weight of the road and the in situ strength of the peat whereby the combined system comes into balance.
Modern construction practice generally calls for a geosynthetic layer to be placed on the surface of the peat before the road is constructed to give a working platform for the road and provide a separation layer between the road and the peat below. This layer, however, does not support the road. The road is supported by the peat.


PEAT AS A ROAD FOUNDATION Peat in its normal, unloaded state, is a very weak material on which to build a road but if it can be carefully loaded, allowing time for it to consolidate and increase in strength, it can be transformed into a very useable foundation
Peat is not universally recognized as a foundation on which to build a road and the construction of roads on peat has all too frequently been considered to be a "black art" by some authorities.

As a result many engineers opt for conservative forms of construction such as excavation and displacement techniques to minimize perceived construction risks. These conservative practices are, however, expensive, especially when dealing with deep peat deposits, and ignore the extensive body of experience of floating roads around the world. Excavation and displacement techniques are also primary users of scarce natural resources in times when sustainable construction methods are demanded, and they are only really affordable for the construction of high speed, high volume national roads that demand carriageway surfaces with high tolerances.
The internal road networks of small developments on the other hand do not need to have such high specification routes and can consequently utilize the in situ peat as a serviceable sub grade. These roads can take advantage of the known benefits of floating road construction in deeper peat, such as lower cost and environmental impact than excavated construction, to produce safe and cost effective access routes that are directly suited to their design need.


INITIAL CONSIDERATIONS
The term "peat" can cover a wide range of organic soil types.

The Soil Survey of Scotland defines peat as having a surface horizon greater than 50cm thick with an organic matter content of more than 60 percent. Peat is a natural material and as a result is seldom uniform.

A basic understanding of its properties is therefore necessary before it can be considered as a suitable foundation for a floating road.

Peat forms in a landscape when the natural decay processes fail to keep up with the amount of vegetation being produced. This usually happens on waterlogged land starved of oxygen, where the lack of oxygen prevents the natural micro-organisms from decomposing the dead plant material. Where these conditions occur the dying vegetation does not decay at the end of the growing season as normal but instead accumulates year on year as a layer of peat.
Over thousands of years this slow accumulation of organic material can create a continues deposit over the landscape. In Scotland this takes the form of a "blanket bog." This form of bog typically takes approximately 1000 years to form 0.5 meters of peat.


The most important feature in the peat development scenario is water and in particular the water balance within the peat. For a peat land to survive, the water balance cannot be negative, i.e. the water input must keep up with the water loss.

Within each peat landscape the in situ peat is highly variable due to the way that it has been formed and this gives rise to a range of highly variable characteristics, both horizontally and vertically, in the peat deposit. Such variations are associated with the origins of the peat, the type of plant from which it was derived, the mineral content of the deposit, and the amount of decay or humification that has occurred. This variation (heterogeneity) is particularly noticeable with depth as peat deposits are generally formed in layers, which may differ considerably in their nature.

Fresh fibrous peat tends to occur at the top of a deposit (Acrotelm) while the lower layers (Catotelm) are frequently composed of soft, relatively dense and highly decayed material. Within the catotelm, decayed tree stumps, or peat with a plate-like structure derived from decayed rushes, may be encountered.

The most distinctive characteristic of a virgin peat deposit however is its high water content and most of the basic engineering characteristics of peat as a foundation material result from this simple property.

For example, the shear strength of a peat deposit depends on its water content, degree of decay and mineral content, with water content having a high influence.
Shear strength is a key parameter for floating roads applications and normally the higher the water content of the peat the lower its shear strength, the more fibrous the peat the greater its shear strength, and the higher the degree of decay of the peat the lower its shear strength. The strength of a peat in a deposit will seldom be directly related to depth. Frequently a peat bog will show a decrease in strength with depth due to the changing character of the peat, particularly where it becomes less fibrous and more amorphous with depth, but this is not always the case. Each site will invariably have its own particular characteristics that are a consequence of how the peat was formed. A simple visual classification together with water content can give an early indication of many of the important parameters of interest to the engineer for floating roads, but this should be followed up by a ground investigation to inform the design.

BASIC ENGINEERING PROPERTIES OF PEAT
Peat is generally considered to fall into 3 main groups for engineering purposes: amorphous-granular peat (i.e. well decayed peat),fine fibrous peat and course fibrous peat. The first group of amorphous-granular peats have high colloidal mineral elements and tend to hold their water locked in an adsorbed state around the grain structure much like clay.

The two fibrous peat groups, fine-fibrous and coarse-fibrous peat, are woodier and hold most of their water within the peat mass as free water. These three groups of peat are a direct consequence of how and where the peat deposit grew and, as a result, govern the main engineering properties of the particular peat.

BEHAVIOUR OF PEAT REACTION WHEN LOADED - THE GOOD AND THE BAD
Peat can react in two ways when load is applied to its surface:

A. Slowly, with a steady settlement and volume change as water is forced out of the peat mass. This is the desired method for the construction of a floating road and permits the peat to gradually compress and consolidate allowing time for it to gain in strength and take up the new load. For this to happen the loading phases need to be carefully controlled in order to keep the stresses induced in the peat below the strength of the peat at the time. This is a key consideration for the construction of a stable floating road.


B. Rapidly, accompanied by sudden spread and shear of the peat causing failure. This rapid failure scenario has to be avoided in floating road construction by carefully managing the loading phases of the road. It can however be used as an effective engineering technique ("displacement") where it is intended that the road should be founded on the hard strata below.

It is therefore vitally important that the Designer should have an appreciation of how construction loading rates can affect the consolidation and settlement behaviour of peat in order to avoid a failure on site. Modern site investigation and analysis techniques can quantify such risks so that appropriate measures can be put in place to ensure that the works can be constructed safely.

CONSOLIDATION & SETTLEMENT

In the normal course of events the consolidation and settlement of a peat can be seen to follow two main phases, primary consolidation and secondary compression. There is also an instantaneous elastic phase that happens as the load is initially placed on the peat, but this is generally discounted in the monitoring of consolidation as it is almost impossible to measure.


Peat in its natural state is a highly permeable material and the magnitude of the initial primary consolidation settlement under load is normally fairly large and the period of settlement short, usually days.

During this primary phase the new load is jointly supported by the free water within the peat and the peat vegetal mass. As the vegetal structure takes up the load it compresses, and strengthens, and causes load to be transferred back into the free water increasing the pore water pressures locally.

This pressure in turn releases into the adjacent unloaded peat causing load to be taken up again by peat vegetal structure with further settlement, strength improvement and load transfer.
Normally this primary consolidation process takes place within the time it takes to place the layers of the road and its magnitude is usually dependent on the weight of the road and the thickness of the peat deposit and any other compressible layers. Once the phase has passed, and the primary excess water pressures have dissipated, the settlement under load continues at a much slower �secondary compression rate which is generally accepted to be linear with the logarithm of time.

Secondary compression

In the secondary compression phase the load on the peat continues to transfer from the water within the peat to the internal peat skeleton as the peat continues to respond to the applied load. This is generally accepted to be the result of the loaded plant fragments within the peat mass slipping and re-organizing to form a denser matrix. As these peat fragments come together, and the pore voids close up, the permeability through the peat reduces in response.
This simple 2 phase �primary consolidation and secondary compression scenario does not of course give the full picture of the complex consolidation and strength improvement processes at work in peat, but it does give an indication of the continuous dynamic consolidation process within the loaded peat mass. The amount of primary consolidation that is incurred at a location will vary with type of peat but it can be generally approximated to around 50 per cent of the total settlement over time. For the purposes of design, secondary compression is normally accepted to take place over a period of 30 years.


Summary

Peat should be loaded slowly to allow the underlying peat to respond to the increasing load and be given sufficient time to consolidate and gain strength rather than shear.
If a floated road is placed too quickly so as to approach, or exceed, the in situ strength of the underlying peat then failure can follow. If peat is loaded too quickly, without allowing time for water pressures to be released, the in situ peat will effectively have the shear strength of its water, i.e. zero. This has to be avoided at all costs. Modern design methodologies and risk management strategies can help prevent this but designers should be aware that serious shear stresses can be induced in peat, even by moderate fills, if loadings are not sufficiently controlled. End

By the way Town Council has a small roller. it is currently parked in front of Solitude with a flat tire.

Way over my head but sounds reasonable......you have done a lot for the road north of the bridge......we appreciate your efforts!

Capt.H Im a founder member of the Institute of Asphalt Technology MIAT and an ex Royal Engineer officer. We actually put a rescue road/track into the Cuillin mountains on Skye using mainly heatherinstead of peat, there was peat there , but very wet, Bridge foundations under bridge support columns back in the 16 and 17th centuries were also supported on sacks of wool. and in modern day techniques roads in parts of Scandanavia are built on blocks of polystyrene where permafrost was year round And as you say , geotextile membranes are widely used to construct roads where drainage is difficult . For modern trafficed roads, with high axle loads really onlt the later combined with a correctly designed substrata , base and surface layer, is suitable .
Its a pity the roller is standing unused due to a flat tyre, Mr Macadam and before him the Romans realised a correctly graded stone would interlock and could remain stable for hundreds of yrs , but compaction to consolidate and tighten the material to reduce voids to the minimum is crucial
Robert Vernon

It's unfortunate you weren't around last year when I raised this issue. It might be too late now but I looked into the costing of the geotextile and it would have been a big investment at first, but I think it would have paid off in saved fuel costs and man hours in the long run, not to mention the savings on vehicle repairs. Funding however was not available at the time. I don't know what could be done now as it is not only the heavy vehicles but there seems to be a severe liquifaction problem in certain portions of the road. I am certainly not an expert, but researched it extensively when I was leading the campaign to fix up the road. Now town council has stepped up and has assumed the responsibility.

By the way the roller was just out today and I think they blew the tire on a big rock. They should have it fixed soon.

Id be pleased to help in anyway possible , its my intention to make AC my home. i can be reached on [email protected].
Of course theres also cement stabalisation, but that needs a special machine to be hired in , Mostly made by Wirtgen gmbh who have a main US office in Nashville and are well know to me