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  1. ocgeo

    Temporary Shoring and Seismic Lateral Earth Pressure

    For California (Los Angeles City) temporary cantilevered shoring wall exceeding 6 feet in height, is there a requirement that the shoring engineer must use a seismic increment in addition to the active pressure?
  2. ocgeo

    Drywell under a 10 story building

    Do something seems incorrect with funneling 7,500cubic feet of water (major storm event) and all other site water into a drywell directly beneath a 7 to 8 story building at a depth of about 50 feet. The site is underlain by an alluvial deposit with varying soil layers of silt, sand, cobbles...
  3. ocgeo

    Infiltration Systems near Moisture Sensitive Structure Bearing Soils

    That is a good point with loess (silts) and piping. That is a concern with the levees in Sacramento. The roots, active or dead, create a piping potential. BigH, I also have had many issues with trees (I think the PTI has a lot of info on the soil moisture gain/loss potential in expansive...
  4. ocgeo

    Infiltration Systems near Moisture Sensitive Structure Bearing Soils

    Good points, if the soil cannot densify, and has the overburden to resist expansion, that would help. I would be concerned about collapsible soil at depths that were not overexcavated and reprocessed, or (to relate to dam terms) 'piping' vertically into a non-natural open graded soil filter...
  5. ocgeo

    Soil Bearing Capacity Based on Settlement (Bowles)

    There is an existing 10 story building with 10'x10' footings (36 total on square grid) with pressures of 7 to 10 ksf, with the concrete building built 100 years ago, and showing some settlement/stress, but not much. Too bad we couldn't study that building/bearing soils to back calculate an E.
  6. ocgeo

    Infiltration Systems near Moisture Sensitive Structure Bearing Soils

    Here is an interesting topic. Where can water be infiltrated into the building load bearing moisture sensitive soils? My thought is that the load extends at a 1:1 (+ or - with soil type) from the bottom of the footing, so not a great idea to introduce water within this area, until you get to a...
  7. ocgeo

    Soil Bearing Capacity Based on Settlement (Bowles)

    I am using the Terzaghi and Peck 1967 researched theory (Modified by Bowles), which is: [N55/F}((B+F2)/B)^2(K) where F and F2 are 'factors' which were derived from the research and testing, and varies with B (width of square footing). The Es, I believe, is a function of the F factors. K is...
  8. ocgeo

    Soil Bearing Capacity Based on Settlement (Bowles)

    I tend to agree with the Schmertmann analysis (Elasticity), but like to explore all relevant research data. For instance the Bowles analysis (modification to the Terzhagi and Peck), with N55 of 31, calculates to 10,200 psf for 1 inch settlement. In that case I would use an average bearing...
  9. ocgeo

    Soil Bearing Capacity Based on Settlement (Bowles)

    We have a clean sand site with average blow counts in the upper 2B (B = 12 ft. square = width of footing) of 30. I calculate a bearing capacity of about 10,200 psf for a settlement of 1 inch per the analysis in Bowles Foundation Design (base don Terzhagi and Peck 1967). We have column loads of...
  10. ocgeo

    Pressure Under a Mat Foundation

    It seems that for a large mat foundation say 100ft x 100ft, Westergaard and Boussinesq theories may be very conservative, as the soil pressures will tend to 'travel' more laterally with great depths, creating a bridging effect. There must be research on pressure cells at various depths, say at...
  11. ocgeo

    90% Soil Compaction with Tracks of a Tractor

    Agree, I also saw a thread about getting compaction above 100%, which of course is achievable, the reason the Modified Proctor evolved from the Standard Proctor, as the equipment became more capable of better compaction. It was amazing to see an aggregate base turn to what almost looked like...
  12. ocgeo

    90% Soil Compaction with Tracks of a Tractor

    We only use the modified here in CA. It is a 25 ton tractor, and has a 3.5 yd loaded bucket, so the tracks contact pressure is about 20 psi (about 3000 psf), very low. Normal pneumatic tires exert the pressure of the tire, about 35 to 100 psi. A sheepsfoot knob exerts about 300 to 1000 psi...
  13. ocgeo

    90% Soil Compaction with Tracks of a Tractor

    Actually it is 90 percent relative compaction based on the modified proctor, we are getting about 120 to 125 lb/ft3 dry density, so I would estimate the relative density about 70 to 80 percent, but does have some fines.
  14. ocgeo

    90% Soil Compaction with Tracks of a Tractor

    A site with sandy clay to clayey sand, trace gravel, has obtained 90 percent relative compaction up to almost 20 feet in depth, with the tracks of a 25 ton tractor, using enough passes, a loaded front bucket, and 8 inch thick loose lifts. It can be done, more to come if interested (track width...
  15. ocgeo

    Geotechnical Engineer Exam

    Coduto has new theories on filter design, so if you use the wrong reference you get it wrong. Are you supposed to use the new or the old. There are a lot of really good questions, and some that are really poor. It needs more funding to develop a better study guide than a list of 21...
  16. ocgeo

    Peat Ground Improements - Site Class E to C?

    Thanks for the responses, ideas, and clarifications. EireChch, The piles planned are a mixture of aggregate and grout. A hollow steel casing is inserted to depth, displacing the peat, with aggregate and grout placed and compacted in lifts to the surface, creating 24 inch columns. We plan to...
  17. ocgeo

    Peat Ground Improements - Site Class E to C?

    That is interesting, I think also the weaker soil has a longer period which if it is similar to the building will cause a lot of damage. I thought also based on the stiffness comment that the ground improvements stiffen the soil, however I am not sure how or if you can quantify that. Thanks...
  18. ocgeo

    Peat Ground Improements - Site Class E to C?

    Hi, we have a site with 30 feet of peat over 70 feet of 100 blow count till. We are at a Site Class E due to the peat with a thickness of 10 feet and M%>40; PI>20, Su<500psf per the code. However when we install grouted rock piles through the peat on a 10' x 10' grid, and no longer have a...
  19. ocgeo

    California Geotechnical Engineer (GE) license

    Let me know how it goes, I have taken it 3 times, and prepared several months, about 1 to 2 hours per weekday, before each exam. I used the CalGeo videos (it will take you hours just to organize the pdf handout from CalGeo, and for me was not helpful), and many of the references the Board. The...
  20. ocgeo

    Liquefaction Analysis

    Great paper and summary of the 3 studies I am somewhat familiar with, mostly use the Bray and Sancio. It would be nice to have a 'formula' to follow which it seems is the attempt, however I think each 'borderline' soil must be looked at individually with engineering judgment. Failure modes...

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