How to Constuct Road on Soft Soil/Clay?

I'm not an expert on road construction. Road construction in this country requires much engineering. You just can't lay down gravel over a soft bed and expect it to hold up under a 20-30 ton load whitout it failing. It requires engineering to design a road that will last. Drainage is a big part of it, but also the materials used. Roads here are mostly paved with either asphalt or concrete and can cost upwards of a million dollars per mile to construct. If your country has an abundance of bamboo; that can be used to make some pretty good roads if woven into mats and covered with sand and gravel, but it needs to be placed above the soft sub-strait.

Consider a geotextile fabric under the rock. The fabric keeps the rock and soil from mixing and creates a very stable base. The fabric can complicate grading operations if the fabric is uncovered or torn with the grader.

What is the surrounding area like? Are you going through a swampy area, on a slope, in the bottom of a valley?

It is in swampy area and near beach, and also with very high rainfall rate (heavy rain falls very often, the frequency like one day raining and one day no rain and takes a whole day). I am in south borneo, Indonesia. Another problem is the ditches are easily get shallow.

It is in swampy area and near beach, and also with very high rainfall rate (heavy rain falls very often, the frequency is like one day raining and one day no rain and takes a whole day). I am in south borneo, Indonesia. Another problem is the ditches are easily get shallow (the fines material like mud on the road has been swept easily by rain to the ditches)

Google and read up on the works of "John Loudon McAdam " - best advice.

jt.

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Has nothing to do with the discussion!

Crushed stone with 100% fractured faces is your best friend. This is the best way to stabilize a soft area. Drainage would help but it may not be feasible to drain tight soils, so replace with crushed stone. The deeper the mudhole the bigger the stone. 100% fractured faces is key, bank run or river gravel that is rounded will not work very well. If the soft area is deep, use primary crusher run to bring it up to within a couple of feet, then go with 2 inch minus. You can use geotextile to replace up to a foot and a half or so (40-50 cm) of hard fill.

Ever build a road through a swamp like that?

Never said it would be cheap or easy, but if he has access to crushed stone that is the best way.

Best way or not that is not how it is done if you wish to be successful.

RCE seems to know what he is talking about.

Regards,

I have had situations like the one you are describing. There is a cloth that you can use that 'spans' the soft areas. It looks like the plastic bags that replaced burlap bags. The fabric is made of plastic strands and it comes in rolls 20' wide. Be prepared to spend some money! But if you put this down on a prepared subgrade and then top with limestone 2" you should be able to keep the road's profile.

I have seen it used on a field with no base installed and the fabric was laid, and covered with two inches of stone. It is used now for a sawmill's log storage, large trucks, loaders are on it all day and it doesn't give!

Otherwise you will have to keep pounding stone into the soft ground until you 'find bottom'

One blacktopper told me he would cross a swamp with the cloth, put 5 inches of black top for a road -and guarentee it's use! (and that's a statement)

Good luck,

Thom Rogers/babygrapebooks.com

Your 'blacktopper' must have had a vivid imagination as there is no way the statement was correct.

You would be best served by installing a Geogrid such as a copolymer plastic grid made by Tensar, or an equivalent product, first laid down on the prepared clay soil subgrade, then followed with a fairly thick compacted subbase course of well-graded and drained gravel. IMHO don't just install a geofabric over the clay because it will deflect and possibly tear...eventually you will have severe rutting that mirror images the displacement of the clay subgrade below. Using the Tensar Geogrid acts like a snowshoe helping to disperse (spread out) vehicle wheel loads plus it keeps the subbase materials from migrating into the clay subgrade.

To determine the proper geogrid material as well as the subbase gravel material and thickness is going to take the expertise of a qualified Geotechnical Engineer, who may have to perform field and laboratory soil testing. Please hire the services of such a professional.

Good luck with your road!

Oh by the way Geogrid has huge holes through it so it doesn't stop migration of fines in to the coarser rock, filter fabrics like 140n are tyopically utilied for that purpose. Some Mirafi (Mirafi is more commonly utilized as the industry standard or equivalent) geotextiles can perform as reasonably to provide some minimal filtering capability and provide the tensile strength (500x and such), but Geogrids will only filter object about the size of cobbles. Plus these are only used to replace older process of using a subbase material of sand and gravels graded to perform like a filter and provide stability. A good 1-1/2 inch subbase below the road structural section at 90% relative compaction can provide a reasonable surface to build a road structural section upon, and if graded properly drains well. You need to look at the D85/D15 and D50/D50 gradation relative to the gradation of the clay.

A couple of the Tensar and ARMCO (and few others) geogrids have very little or no openings in them, thereby negating soil migration.....check them out. I've even used open geogrids through swampy areas here in upstate NY, and in LA, MS and up and down the Big Muddy in 3 different USACE Districts (when serving with the USACE) without a fabric such as Mirafi 140N (a good product, but not an end all and be all...usually "punches down" and mirrors the wheel rutting lanes in and under the pavement....also, not the best material for spreading out wheel loadings either....it is best paired with a polypropylene plastic Geogrid with little or no openings in it's Matrix) and could literally walk on the mud and water... migration of stone subbase was absolutely minimal and later in no way detrimental to structural stability of roadways, levees and other structures above it.

Of course all designs were by a Geotech Engineer and not just any engineer "winging it" without actual field and lab testing so as to ascertain the actual site specific Insitu soil conditions, such as Plasticity Index, shear strengths, etc.. Not one design approach nor "what the last guy got away with" approach can be applied to each and every condition encountered, regardless of what one's Engineering experience and credentials are. Everything is, and must be, performance & economically based, with these two parameters balanced based on a good number of important factors as well as good engineering judgement and design experience. That is why I have lots of misgivings and doubts about federal & state DOT mandated "cookbook" approach to soils engineering and building highways, which in many cases can result in short-lived and under-performance (ie life cycle). That approach is sometimes engineering overkill, sometimes not, but always costly to the taxpayer......and in my experience with state DOT's their design philosophy often results in substandard road surface and subbase performance. My God, all you have to do is look at the current state of dismal Interstate conditions, state by state, and you will concur. And the state secondary roadways are even worse!

Enough said. I know that they'll be many here that disagree with my statements and assessments, and then again, many others will agree with me. Let the arguments begin!!! Nothing like a causing a cockfight, eh???!!!!! ***GRINZ***

I would agree and that is why when I started out in Geotechnical and Environmental Engineering, my principals required me to work as afield engineer doing everything the technicians had to do, working on drill rigs logging, forensic investigation of other engineers/contractors failures, and dealing with field changes for encountered conditions during construction. That way when I would write a geotechnical engineering report or a clean closure workplan, or something similar, I was familair with how the testing would be conducted, how investigations data would compare to the conditions encountered during construction and all the problems that develop.

Also, 140n is just a filter fabric not meant for tensile strength, it is typically employed to encapsulate drain rock.

As far as Geogrid, I have a flyer from Tensar here where they have been trying to convince more engineers to spec them instead of mirafi (industry standard). The Geogrid is the plastic straps that are bonded in a perpendicular web, large hole in geogrid. You can bond non-woven or woven geotextile fabrics to the geogrid, we use something similar in asphalt pavements, but this is not the geogrid itself and is a special order above and beyond standard geogrid. I think you are describing geotextile fabrics, which have a much lower transmissivity than filter fabrics, but can retain soils. Geogrid have become the new rage amongst many of the newer geotechnical engineers i deal with on roadways, however, the depth to develop strength and the benefits doesn't usually offest the cost, and i have seen a number of them fail (the engineers typically attribute the failure to installation problems such as excessive lateral pressures when installing fill above the grids. Both the fabric and geogrid depend on building tension to strengthen the soil mass above them, thus they rely on soil interface friction across the weak areas to allow the downward pressures to transmit across the grids as tension (they can not pull out or they fail). Usually it is just cheaper and better too use a aggregate subbase or lime treated subgrade to stabilized the base, and typically cheaper as the materials tend to be cheap and local and the labor is easier and cheaper since it is a simpler process with less likelighood of installation mistake. I had to investigate a $1 million retaining wall where the geogrids mobilized, and once they start moving in clay the thixotropy allows them to slide more rapidly and easily afterwards. As a rule we apply geotextile fabrics here subbase would be way too deep, in areas of localized minor pumping, etc. where we have something stable to attach to through soil interface friction.

GA RCE - someone that has experience with the problem.

I saw a section of road go through a swamp in Trinidad - they excavated deep and did about what you suggest. All flyovers were stabilized with many sheet piles as I remember.

what do you mean by lime treat? Is it cheap method? how much the cost will be if I apply it for 1 km road of 15m wide? Any reading references or link that I can obtain more information for this method?

My family has been widely known for our road building skills for over 150 years. This may not work in your area.So use these posts to learn the questions to ask the guy in your area that does know. Here in claylike, silty soils, we build our roadways across swampy areas much like the Romans, with a high tech twist. We start with woven geotextile fabric followed by a bed of surge, #1(1 1/2"-3") or #357(! 1 1/2"- 4" stone. This will provide a drainage base and spread the load. This should be covered by a layer of #57 (1/2"- 1 1/2") stone and topped with a non graded stone we call #250/Crusher run or #21-A or pug mill. To be stable you must keep the water out as much as possible and elevation is the only way to do it. Build the road on top of not in the swamp. Use material that will spread the load. Anything worthwhile is worth doing right. If you just patch it. You are just pissing your money away and delaying the cost of doing it right at an even higher cost.

You could alway get some Mo-Mats from army surplus. The Army used to use them to make roadways and airfields in swampy areas from WWII through present times.

The classic road over swamps, and still popular in the north, is the corduroy road using local materials (logs). As the wiki says, you can use a structure of this type as a basis for other surfacing - your gravel and so on.

The logs-across-road design provides a foundation for traction and also has some natural drainage characteristics - allows water to drain off the road, and of course, raises it above the swamp level.

nice!.. but how about the decay of the logs?

I guess that depends on the type of log and also the pH and other characteristics of the water and soil. In the northern bogs, spruce wood doesn't break down too fast.

In Italy the European Alder (Red Alder, Alnus glutinosa) was used for various kinds of construction in water, because the wood is very resistant to decay under water.

Local builders' knowledge will tell you whether there is a type of tree in the area that's very suitable for resisting decay in water and in those soft clay soils.

Of course, if you can get the high tech materials, you won't need to worry about decay and your road will be more permanent.

The corduroy roads are good to support traffic for temporary activities (like logging) and when the work is over, the road is left to break down naturally. For long term use, some repairs or replacement will be needed (in our environment) after ten years or so - maybe longer if there's a surface on top. I don't know how long this road would last in a tropical environment.

We are an Australian based company specialising in soil stabilisation especially clay based roads. Our chemical changes the molecular structure of clay to repel water. For more information visit our website www.claycretestabiliser.com

Are you saying it changes the molecular structure of clay minerals. Seriously? This I would have to see (though I susepct that statement is a marketing ploy). Or is it a pozzalanic reaction with the clay, like lime treatments for road bases or the organic stabilizers made from pine tars.