Design of new roads 1

[killswitchengage]

Hello, just wanted to ask even though i know the answer my self
What kind of geotechnical tests do you guys perform on soils for road design , provided that the road is not of major important ? have you ever studied the susceptibility of a given soil to liquefaction in accordance to a road design ?

 

[bridgebuster]

Bearing capacity and settlement analysis.

If the soil is susceptible to liquefaction you'll need to put the road on structure. However, you said the road is not important so it shouldn't matter.

 

[Ron]

Soil classification in the upper 5 feet, potential stability values of layers that will be unimproved, and the location of the water table.

Would not consider liquefaction unless high seismic area and on evacuation route.

 

[killswitchengage]

ehh i am sorry but it seems there is a problem , i stated Road design not the common geotechnical engineering
We usually conduct test pits and identify soils , remodeled samples are then tested through sieve + sand equivalency + Atterberg limits + Proctor and CBR tests
Bridgebuster you are completely false , those are to be chosen for foundation designs
Ron what do you mean by potential stability values

 

[fattdad]

we follow the geotechnical requirements of the FHWA.

f-d

ípapß gordo ainÆt no madre flaca!

 

[killswitchengage]

@fattdad i found this

http://www.fhwa.dot.gov/engineering/geotech/pubs/05037/04a.cfm

Could you please provide me with a resume about the tests you commonly use for new road design ?

 

[Ron]

kse....stability tests would typically be CBR on the subgrade layer.

 

[oldestguy]

Kilswitch:

You have been given a wealth of information, but not all of it will apply. I suggest you contact your local road maintenance organization, such as a State Highway department. They likely have a methodology and a design method that will apply to your site. If you identify your location you may get some pertinent leads from here. Perhaps also you will say "what you already know" so as to minimize the clutter here.

 

[bridgebuster]

Kills,

I worked on several projects that required settlement analyses for the roadway and the structures.

 

[Ron]

OG is correct.....sometimes the first place to go is the DOT in your area. They usually have very good info and pavement design criteria. Some in the US set the pace....Iowa, Illinois, Wisc., Florida, California, Washington, Texas...some have more emphasis on one method over another....check them all. I use empirical methods then I run elastic layer analysis.

As BB noted, sometimes you have to consider settlement of both the roadway and structures. If you have to consider roadway settlement, you're probably trying to build over some pretty bad soil conditions and the fill required for the roadway can induce significant impact on the underlying soils.

To protect your sanity, use several methods of design and cross-check. Think of the many options you have to mitigate poor conditions....cellular concrete fill, geotextiles, beneficiation of soil conditions, combinations of rigid and composite pavement sections.

 

[oldestguy]

KillSwitch:

You apparently are quite well qualified to do the geotech portion of a new roadway project. However, in order to do you any good, I think a much clearer statement of your problem or quandary is needed. It may take attaching or linking to a place where your overall project situation is described. Since you have been involved with settlement studies and probably embankment stability issues that usually are not required on most roadway jobs, it would seem to me that your question is an unusual one and a much clearer description is needed. What sort of an organization do you work for? What is your position there?

 

[killswitchengage]

OK listen up guys
I live in the third world , and i mean that we are literally a million light year behind you ; so slow down. We in Algeria follow French regulations as old as 20 years !!!
Now i know French are following Eurocode 7 for geotechnical studies . When it comes to simple pavement geotechnical tests ( No cuts , no obstacles just a straight line road , no bridges , no culverts nothing ) we conduct the tests i mentioned above (sieve + sand equivalency + Atterberg limits + Proctor and CBR tests) . That being said i feel that this is insufficient , i saw the reports we are making and the Atterberg limits for instance are just mentioned to fill the papers ! . In my last project , we found silty sandy loam as a soil profile and i was concerned about the liquefaction issue .

Here , the highly developed DOT or whatever ; that do exist in America or Canada are completely nonexistence if we are talking about technical advises and expertise . They work as our clients and its our job to design the pavement .

 

[BigH]

Don't get bent out of shape my Algerian friend. I've been involved with a number of 'third world' roads. Geotechnical investigations would vary. As you say there is no cuts - it is a straight road and you said it is "unimportant". I would think the following. A few test pits to identify the soils to a reasonable depth, say 2 to 3 m. Depending on your road length, you would probably take a test pit at 100 m intervals; perhaps 200 if there is no apparent change of stratigraphy.

Take the samples for sure. I would presume that the natural soils would be your subgrade. How much unsuitable material is there? (i.e., topsoil, uncontrolled fill). For laboratory tests, if clays, do the Atterberg, natural moisture content and sieve analysis. I don't think it is so important to obtain the % clay. If the soils are granular, obtain the sieve analysis for classification purposes. You can then go to any older text book and, based on the classification, it will tell you the "general" suitability for the material to be used for road subgrade, fill, etc. This gives you an idea of the overall suitability of your subgrade.

In the upper soils that by judgement you would expect to be acceptable as subgrade, do a Proctor test (yes, even in granular soils as many labs will not have the means of doing relative density (and most everyone does field roadwork using Proctors anyway). At 95% of the MDD, do a CBR (soaked) as you will want something like a CBR of 6 or 8 for subgrade under the subbase.

Field tests, you could try the TRRL miniature dynamic cone test - this could be done at a number of spots and would give you, through rough correlations what the CBR value would be - best if you could calibrate to a couple of locations.

Once you have this data, you would determine if you need an improved subgrade - i.e., select subrade that would take your subgrade soaked CBR value to 12 or more. Knowing this, it is a matter of having data on the type of traffic loading, average daily vehicles and such - you can then go to AASHTO charts to determine your pavement design. (You'll need to know some other environmental things as well - i.e., freeze-thaw; rain-dry.

Sometimes we have put on the select subgrade and then carry out Benkelman beam tests (I'm old) or using other more current deflection methods to confirm your pavement design. - you could do this after laying subbase too; and base course as well before HMA.

I don't see the need for more fancy tests - you could determine the resilient modulus, and all sorts of other parameters and the go to elastic solutions, etc. - but for normal roads the above is the general means that the roads are developed.

Now if you are into mountains, swamps/marshes, soft soils (lacustine lake beds), etc. you will need to use more judgement but the overall steps are basically the same - what I think I am saying, knowing your others posts, is that you don't need to overthink.

Now, gentlemen, hit me with your best shot! (and OG, Ron, fattdad always have great comments that you can learn from - oldest guy from an originator's perspective!, Ron from a forensic perspective and fattdad from just plain great experience)

 

[killswitchengage]

so basically i am right .

 

[oldestguy]

Kill Switch:

Now and then we have a thread situation such as this. They take lots of posts to finally come down to what the real question is. Above I see some 8 replies, not all of use. Finally I see where you are, but not much more detail. In order to answer your question, a clear description of your specific project situation, if provided, may find someone here who will satisfy your needs. I suspect McCoy may have an answer Application of USA methods may apply from areas here of similar climate, etc.

Stay with it and don't hold back details that may not seem important at the start. If Algeria the location was mentioned in first post, you would not see suggestions here that don't apply.

It's like conversing with my wife. Today she talked about a plant in our front yard with blossoms, but phrased her question like it referred to our last location some 100 miles from here. Explains why men and women are different I guess. Mind readers we are not.

 

[fattdad]

It doesn't matter where you live. If you are piling up a bunch of dirt in hopes of making a road, you need to understand the following:

The strength of the fill materials when compacted to the specification requirements.
The location of the the fill materials and variability in the borrow pit.
The character of the subgrade to receive the fill materials - i.e., are undercuts required to prepare the site for the first lift.
The location of the water table.
The imposed load of the fill thickness.
The anticipated settlement from that imposed load.
The global safety factor from the imposed loading, which is ultimately related to the unit weight of the fill, the strength of the fill material and the design sideslope.
The subgrade support value of the newly-formed road bed (i.e., CBR value)
Whether secondary compression or creep will develop during the ensuing decades.

If retaining walls or other critical structures are present, then there are substructure issues. You are asking about a new road. So far, we are not talking about structures.

We struggle with folks designing outside of our requirements, turning the project over to a contractor, building a road and then applying for that private road to be brought into our network for us to maintain. Rarely do folks consider a 75-yr design life however. . .

f-d

ípapß gordo ainÆt no madre flaca!

 

[killswitchengage]

@oldguest : thanks for your suggestion and the funny comparison between men and women
@fattdad could you please explain the water table effect ? and do you mean secondary compression or creep of clays using oedometer test ?

 

[fattdad]

kse, the positon of the water table factors into the determination of effective stress, which factors into the determination of Po when interpreting consolidation data. Change of void ratio without change in effective stress is described as secondary compression in clays. Sand also has long-term strain that follows initial elastic compression.

f-d

ípapß gordo ainÆt no madre flaca!

 

[killswitchengage]

this is weird
when it comes to embankment design of roads , we just use CBR results and a software called Alize which is French. This soft compute with a selected road structure and the load configuration ( as well as yearly traffic and all the gibberish ) all strains and stress that develops in on the base of each layer. Then, we try and improve our design . But nowhere we were asked to study the things you mentioned last fattdad

 

[Ron]

kse....the information I referenced from various departments of transportation in the US is applicable anywhere, depending on the soil conditions. The ones I gave you cover almost any soil imaginable....check them and use the ones with the soil conditions that most closely match yours.

The info is universal and you can apply as necessary to your local conditions. BigH and F-D gave you some terrific information...apply it!