Converting Modified to Standard Proctor

[moe333]

Does anyone know of a conversion from modified proctor to standard proctor for both dry density and moisture? I usually assume 90 modified = 95 standard, but I need something I can hang my hat on for this particular case, hopefully with a reference. I also assume moisture is a couple percent higher with standard. This is for pretty clean sand SP to SP-SM.

Thanks

 

[Ron]

It varies with the material. There is no direct correlation and the assumption you've made is often wrong.

It would be a lot easier just to spend $150 and run another Proctor...then you'd know and wouldn't have to guess.

 

[BigH]

moe333 - agree with Ron - we have had threads in the past where some have indicated "their region's correlations." In Ontario with the crushed stone, we used, if I remember correclty, 97% Modified = 100% standard.

 

[iandig]

I must agree with the above posts. I have in general found that 100% of the standard proctor (2.5kg rammer) is around the 95% of the modified (heavy/4.5kg rammer) for cohesive soils (medium to high plasticity clays in particular) but I would not use this for design or specification, rather as a check on the material properties and whether or not I believed the results from the lab. I also use this general relationship where the soils become more single-sized/sandy/silty. This is because where the MDD from both tests show less than 5% deviation (i.e. the 97% as indicated by BigH) this is a reflection of the material properties and is an indication of how the material will behave on site, how feasible it will be to achieve less than 5% air voids, the susceptibility of the material to variation in moisture, influence of weather etc... As I say, although in general there is a relationship, you don't rely on that, you compare the variation between the values to assess and interpret the actual material properties and how it will behave, on site, when the real work begins.

 

[jgailla]

There is no theoretical correlation between standard and modified.
You simply don't know what the effect of the additional compaction energy will be for a particular soil.
AS BigH points out, there could be empirical correlations based on long experience with a particular soil type in a particular location.
I would be very suspicious of a geotech telling me there was a specific correlation between standard and modified (unless it was someone very trustworthy, like BigH).

 

[emmgjld]

As I post this, ALL of the above comments and cautions should be incorporated. I do not consider this table to authoritative for comparing Standard & Modified Proctors.
In front of me I have comparative Proctors Ranging from less than 1% for an excellent, prepared Road Base and up to almost 12% for a High Plastic Clay.

ASTM C-1479-07a, Standard Practice for Installation of Pre-cast Concrete Sewer, Storm Drain and Culvert Pipe Using Standard Installations contains an interesting table (Table 3 Equivalent USCS and AASHTO Soil Classifications for Soil Designations) of approximate correlation between the Standard & Modified Proctors.

For Granular, relatively good soils (sands & gravels) the percent compaction differences are 5% between Standard & Modified Proctors.
For Fine Grained, plastic, relatively poor soils (clays & silts) the percent compaction differences are 10% between Standard & Modified Proctors.

This table was probably considered to be rather conservative for the purpose of the Standard. Also note that support of the pipe by the backfill is the ultimate criteria. Every type of construction should carefully consider the specifications with the actual needs.

BigH - this ties in nicely with your find, posted in the Foundations by Terzaghi forum: The Story of Buried Steel Pipes and Tanks, which you may find appropriate to link in this forum.

 

[moe333]

Thanks to all who replied. I know there isn't a great correlation, but wanted to see if there was anything out there. The ASTM reference looks interesting.

 

[BigH]

I've always been fascinated with the history of geotechnical engineering and why we are where we are. My mentor studied under Casagrande and he actually consulted on a number of my mentor's projects. One day, in Toronto, he had come up and a young engineer was showing him the fine details he used for determining the preconsolidation pressure - the Casagrande graphical method . . . Casagrande looked at it - "No, I think it should be about here - and this one there and . . ." When queried, he indicated that he had made up the graphical method as an approximation - had to have something to teach his students how to get in the right ballpark . . . So the story I was told Anyway - on the topic of buried pipes, enjoy:

https://www.steeltank.com/LinkClick.aspx?fileticket=pK9crCD8Z0s=&tabid=94&mid=452

 

[bb29510]

cant convert but there about five pounds different, now that rule of thumb but usually real close to the type material that we have.