Replies

1. 
   brownbagg | Jul 25, 2006 05:35pm | #1

   #200 is the smallest, 200 grids per inch remember pea gravel will be retain on 4.

   #4 and#10 will be the rocks
   #40 and #80 will be sand course and fine
   above 200 silts and below 200 clays

   most of your material wil be passing 4 so small rock almost no rock
   Most will be retain around a 10 and 8% pasiing 200 is very low in clay

   
   

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   Edited 7/25/2006 1:46 pm by brownbagg

1. 
   brownbagg | Jul 25, 2006 08:31pm | #2

   ok I did researchmy computer says its a " poorly graded gravel with silt and sandaashto claims A-1-a material basicaly an underwater backfillTo do the test. you measure a sample , put in flash with solution. wait twenty minutes. measure clay settlement and then the sand settlementsand equivanent = clay reading / sand reading * 100 to nearest whole number.according to the gradation you gave it cannot be caluculated but a test must be run.that is a test we dont do, there is no need for it, no use.

1. 
   brownbagg | Jul 25, 2006 08:45pm | #3

   its how clean the sand is by ratio of clay to sand. if you havd a red sand then it will be higher than a white sand, due to less clay content

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   Catskinner | Jul 25, 2006 09:50pm | #4

   Most totally excellent Mr. 'Bagg.Many thanks.I need to get back out into the field now, I'll tell you more about this project later. I'd like to get a few more opinions from you. So far they have made more sense than everyone else's. <G>

1. 
   dieselpig | Jul 25, 2006 10:12pm | #5

   I barely know what you guys are talking about... but I'm still finding this conversation fascinating.  It's like listening to a foreign language where you pick up a word or two here and there and think you might understand what they're talking about.....but really don't.  ;)View Image

1. 
   brownbagg | Jul 26, 2006 12:15am | #6

   its mainly about the color of sand, but who cares what the color is.

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   Catskinner | Jul 26, 2006 03:31am | #7

   I'll fill in the blanks anywhere you like.Oddly enough, Johnnie is only partly joking with you about the color of sand -- he's half serious and totally right. (The man knows his dirt.)What I am working on is a mix design for a critical application. I need a material that has good load bearing competence, high unrestrained compressive strength (like if the dirt was not contained but compacted how much would it hold), no expansive potential, a plasticity index below 15, and enough cohesive properties to hold it in place even if the surrounding material moves. All easy enough except now I have an engineer who wants it to be impermeable, too.'Bagg is gonna ask me why I didn't just blow this hole full of lean fill (aka controlled low strength, flowable fill, lean fill); two reasons -- cost and it would be tough on the plumbers.For some background; a strong (can handle a load without a shear failure) soil typically consists of well-graded material. Some fines to hold it all together, and an appropriate mixture of other sizes to fill in the gaps from small to large (sand to 3/4" rock). If you can get a fully fractured material of various sizes in there that will lock together, so much the better.Think about a truckload of bowling balls. Full to the top. Add a truck load of golf balls, then a truckload of marbles, shaken, not stirred -- it should all fit into one truck.No expansive potential is because if water gets into this hole after the edifice is constructed, and if there is any appreciable expansive component, the foundation could break.The PI of 15 is easier to understand than it sounds. With some percentage by weight of added water, dirt will start to behave like a plastic. That is the plastic limit. At some higher percentage, it will behave like a liquid. That's the liquid limit. These are also called the Atteberg limits. LL minus PL gives you the PI. Plasticity index is used as a predictive tool of how dirt will behave when wet.Here is where the "color of sand" comes into play.Color is important because it gives you an indication of chemical composition. Clay particles are clay because of the size and shape of the particle. They are sort of like fish scales. Some clays are the result of fractured rock crystals, and because of this, the plates of clay have a polar (like electrostatic sort of)charge. Now if you remember that water has a bond angle of 105 degrees, it is polar, too. So depending upon the chemical composition of that broken sand crystal, you might have good clay and you might have bad clay. Hence the color.I happen to be working in some yellowish-tan stuff that is bordering on evil in its expansive properties, layered with decomposed white stuff that is collapsible.Clay can have various abilities to accept or reject water, anbd will have various reactions when it does. The reaction we are concerned with here is breaking the foundation.OK, back to now. 'Bagg if you are still with this; I can come up with a pretty good mix (and have). It hit a 130.9 Standard Proctor at 7.9% moisture, and has a PI of 6. I made it up out of a few hundred tons of silty sand, a few hundred tons of crusher fines, a bunch of concrete sand, a pinch of 3/8"-minus crushed, and some natural (river) sand.I'm getting densities measured on site (nuclear densometer)of 97% to 105% with very little effort.The good news is rain has no effect on the strength. It percs just short of like beach sand. Bad news is the engineer don't like it. He says he wants more impermeability to moisture.So this is where this morning's question came from. I brought in a bunch of the base course I described to you this morning and blended it with some really good silty sand (no clay whatsoever). Tomorrow I'm going to start bringing in crusher fines.Once I like the feel of the material I will send it for sieve and PI, if it comes back below 15 I will probably go for it.What generated the question that you answered so well for me this morning is how the sand equivalent will have any bearing on what I am trying to do.Here is another question; other than the clay component in the base course I described this morning, can I expect any amount of impermeability from the silt in the silty sand?If I can keep the PI at about 12, keep the material granular enough that high moisture conditions doesn't wreck it but still cohesive (I need the unrestrained compressive strength), include a lot of well-graded fractured up to 3/4", and still have something that will not deform under load, I'm in good shape. What I have now (PI 6 Proctor 130.9 O-Moisture 7.9%) does not have much for unrestrained strength, and is not meeting the impermeability spec.Any thoughts? (Besides get a different engineer; that has already been suggested <G>.)Thanks.

1. 
   dieselpig | Jul 26, 2006 03:40am | #8

   Wow.  And I just call it 'dirt'.  :)

   Thanks for the lesson though... I saved your text and will try to digest it in doses.  I was a natural science major in college with a minor in geology.... for awhile anyway.  This stuff still fascinates me and I often wish I had stuck it out a little longer.  The physics killed me though.  I still have a few of my old texts.  One of my favorites is an early book on plate techtonics called "A New View of the World"... I've pulled it out and read it again a few times since college.  Fascinating stuff, this ground beneath us.View Image

2. 
   Catskinner | Jul 26, 2006 04:07am | #9

   Well, then, could I talk you into digging out a few of those books? I need all the help I can get here.You're right -- it is an art and a science. Most of what we (all of us here) do is so over-built that these prescriptive traditions (everything from wide footings to double 2x12 headers over 3/0 doors) will provide adequate results. Sometimes inefficient, but certainly effective.But when we make unusual demands of our trade, things get interesting.I have nothing but respect for the engineering profession.But right at the moment the engineer is . . . asking a lot.Sometimes it's more art than science.One of the things I want to ask 'Bagg is could a very small amount of clay be a good thing here? (Not enough to push the PI over 15, that is a spec that I have to hit.) And if so, what kind of clay.Every expansive material will have a high PI but not all high PI materials will be expansive.

3. 
   brownbagg | Jul 26, 2006 05:35am | #10

   OK here what we would do down south. a red sand clay. on the real sandy side, here the problem. to get impermable the clay has to swell. you dont want that anywhere. then it starts pumping and wont hold up a load .ORyou could go with your first mix and add a bentnite layer on top. 8 feet of sand with 1 foot of beninite. we dont try to stop the water, we want to water to flow through and move it where we want,like with a french drain. Think of the beach, the wet sand is the hardest, you can drive a truck on itour heavyiest red sand clay run about 125 lbs modified proctor and is non plastic. that means the liquid limit is lower than the plastic limits. and I want to go on the record, I hate Mr atterberg and his whole family. most red sand clays are about 11% clay.permable clays are going to swell, permable clays are going have a LL around 55+ most around 85. I have a problem with the permable part, that is only used in landfill covers. anything holding a load needs to be coarse sand type. not sugar sand but mortar sand. that way water will pass.another lesson material retain on 4 and above gravels. 10-100 retain sand 100 passing- 200 retain silt. passing 200 clays.PI plastic index, liquid limit minus plastic limitsand has no plastic limit, if plastic is higher than liquid then its a non plastic material. a zero PIa pi up to 20 is no big deal, little higher it start sticking to your feet, around 30 you start growing in heightI,m sorry I cannot picture what you are trying to do.

4. 
   Catskinner | Jul 26, 2006 05:57am | #12

   <<we dont try to stop the water, we want to water to flow through and move it where we want,like with a french drain. Think of the beach, the wet sand is the hardest, you can drive a truck on it>>That's how it struck me, too.<<and I want to go on the record, I hate Mr atterberg and his whole family.>>ROAR!!<<another lesson material retain on 4 and above gravels. 10-100 retain sand 100 passing- 200 retain silt. passing 200 clays.>>OK, now we are getting somewhere.The material that you do the PI test with -- What size sieve does it pass?<<a pi up to 20 is no big deal, little higher it start sticking to your feet, around 30 you start growing in height>>Beautiful. So that is why the PI 6 mix I made up doesn't stick to anything.<<I,m sorry I cannot picture what you are trying to do.>>You have no idea how happy I am to hear that. It didn't make any sense to me either, but I really am a "get along/go along" kind of guy so I thought I would try to comply with the engineer's request.A friend of mine (also a dirt guy) just decided the engineer was having one of those "first day with the new crack pipe" kind of days.OK so let me try it another way -- how do I get unrestrained compressive strength with a PI below 15?Man, thank you for taking the time for me here. This is seriously educational.

5. 
   brownbagg | Jul 26, 2006 06:31am | #14

   The material that you do the PI test with -- What size sieve does it pass?cant do any atterberg on material retain on a 40. everything passing 40how do I get unrestrained compressive strength with a PI below 15?You can hold up the world on compacted sand. sand has a bearing ratio of about 2000 psf, red sand clay about 3000 psfunrestrained compressive strength, no such thing, its not concrete, you looking for load bearing ratio. how much load it will hold before settlement.

6. 
   Catskinner | Jul 26, 2006 06:37am | #15

   <<The material that you do the PI test with -- What size sieve does it pass?cant do any atterberg on material retain on a 40. everything passing 40>>Cool. Thanks.<<you looking for load bearing ratio. how much load it will hold before settlement.>>Besides hitting 95% or better on the compaction test, what are the other factors that govern load bearing ratio?

7. 
   brownbagg | Jul 26, 2006 05:38am | #11

   I need a material that has good load bearing competence, high unrestrained compressive strength (like if the dirt was not contained but compacted how much would it hold), no expansive potential, a plasticity index below 15, and enough cohesive properties to hold it in place even if the surrounding material moves.red sand clay All easy enough except now I have an engineer who wants it to be impermeable, too. cant be done

8. 
   Catskinner | Jul 26, 2006 05:58am | #13

   <<I need a material that has good load bearing competence, high unrestrained compressive strength (like if the dirt was not contained but compacted how much would it hold), no expansive potential, a plasticity index below 15, and enough cohesive properties to hold it in place even if the surrounding material moves.red sand clayAll easy enough except now I have an engineer who wants it to be impermeable, too.cant be done>>THANK YOU! <G>