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Geotechnical Interpretative Report 1

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qhtony

Civil/Environmental
Oct 15, 2008
34
Hi guys,

I was recently required to produce a geotech interpretative report on a small scale road widening (about 2km) and interchange upgrade (roundabout upgrade to signalized intersection) project. The road is in an urban area and is slightly on fill (max 2m). Lab testing has been done to the subgrade at the current shoulder and road reserve, which shows a pretty uniform consistency in fill materials.

As there's no similar reports done previously, I was not able to get anything to refer to (i.e. contents, format, etc) and really stuck now. So I'm wondering if anyone here has done such reports on similar jobs and is able to advise me of what to write in the report? It'll be even better if anyone can send me a sample report (tony_qh@live.com). Really appreciated.
 
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So your company does not typically provide geotechnical services? Who will sign off on this report?
My first recommendation is to subcontract the report to a geotech firm, how about the firm that did the testing?

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Barring that, does your local government have a roads department that might provide the minimum requirements
for your roadway report? How about a structures manual?

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Some or all of the following might apply:

Typically, your report should include a detailed description of the proposed impovements
and plans that show the site location and the location of any samples or test borings.

Describe and cite the specifications of the sampling methods. Cite the lab test specs.

Describe the native soils, referencing the local soils book.

Describe the nature, sequence and condition of the subsurface materials found in the test borings,
including existing fill and natural materials.

Provide a visual soil profile (i.e. fence diagram) that shows
elevation of major soil types, groundwater, and proposed roadway elevation.

Discuss the suitability of the exisitng fill for pavement support,
and evaluate in terms of proposed pavement section, if known.
Provide a suitable pavement section if your scope covers that.

I would also characterize the existing fill with regard to expected and observed pavement performance
of the exisitng road, but that might surpass your scope.

Do you need to address the signal poles?
If so, provide geotechnical parameters for lateral support provided by both the exisitng fill and underlying natural materials.

Provide recommendations for site prepartion, fill placement, and pavement subgrade preparation.

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Liberally cover your backside.
Find an experienced geotech to review your report.
 
thanks a lot, escrowe...that really helps!
 
Wrote this yesterday but we lost connections - someone felled a tree on the fibre optic line.[bigsmile]

I guess I'll come from a civil side. Normally on road projects, you would have as a memeber of your team a geotechnical engineer. He would set up a programme of investigation, carry it out under his direction and provide (1) a factual report and (2) an interpretative report.
The designer might take the geotechnical engineer's reports and put together a geotechnical design basis report - identifying the geotechnical requirements of the design work required, i.e., pile foundations rather than shallow foundations, excavation support (open cut or supported), embankment or cut soil/rock design slopes, materials to use for embankment fills and compaction levels required, concerns of sulphate attack on concrete, expansive soils, etc. In effect this summarizes the geotechnical interpretative report so that the designers have a "guide". This could be checked by the team's geotechnical engineer.
The designers, with other design basis reports (such as geometric requirements (vertical and horizontal curves), drainage requirements, etc. would then design the work.
Question - are you doing a geotechnical design basis report? or actually an interpretative report based on boreholes put down (by who?)? If I were you, I wouldn't. Even for a small project.
 
For a road widening project we'd likely have to comply with our state department of transportation requirements. For us (in Virginia) if you widen a road, there's then an implication that there'll be more traffic. So, you'd have to design the pavement section for this new level of traffic.

If you are using asphalt, you'd need CBR values in conjunction with the axle loads. Now it's important to know whether there were any CBR values for the initial road design. If there are, then you may have what you need. Then again, you may just have some "hardball" that was built and it's holding up, but there is really no design.

Just what do you mean by "lab testing done to the subgrade?" Do you have Atterberg limits, CBR, percent sand content, strength data, permeability or other such data? If so, was it obtained by a drilling program?

My state DOT would likely require CBR values every 500 ft. That'd be about 12 CBRs (classification and Proctors too) for the project. If the CBRs are basically for the same soil, we'd use 2/3-rds of the average CBR for the design CBR value. Then I'd make the pavement recommendations for the axle loads. If you had some CBRs of a clay subgrade and another section that's more sandy, then you may use one design CBR for one segment of the design and another CBR for the rest. Hard to tell without data along the alignment.

On the matter of the intersection improvments, You may have to field check the area to see whether it'd be appropriate to add more borings. Sometimes you can also use hand augers to evaluate site preparation and the like (i.e., topsoil thickness/stripping depths).

Write a report that has some introduction, some data presentation and some design recommendations.

Good luck.

f-d

¡papá gordo ain’t no madre flaca!
 
interpretive reports were developed for tunneling projects, but are now increasingly used on other types of underground projects. the fhwa recommends a "one page" summary of the geotechnical conditions. check out:
Publication No. FHWA ED-88-053
August 1988
Revised February 2003
CHECKLIST AND GUIDELINES
FOR REVIEW OF GEOTECHNICAL
REPORTS AND PRELIMINARY PLANS
AND SPECIFICATIONS
 
mudman54 - our company was doing "interpretative reports" up in Canada in the 1960s - and they weren't for tunneling projects. However, geotechnical base-line reports which form a basis of "agreed" to conditions by the owner and engineer was developed for tunneling and with ASCE's fairly recent booklet on the subject are becoming more attractive.
 
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