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  1. nbr1

    Pore Pressures - Staged Construction

    1. If an undrained sloped stability evaluation indicates acceptable safety factors for full loading, would measurement of pore pressures beneath an embankment over soft clay be necessary (from a theoretical perspective) to avoid high PWP buildup leading to a failure? 2. What is a good...
  2. nbr1

    Slab On-Grade, Over Bedrock

    Assuming no freeze/thaw or expansion of bedrock issues, is there any issue with placing a slab on-grade directely on a granular bed of 4-inches directly over limestone bedrock. Assuming the bedrock is relatively level. Intuitively, I can't envision there being an issue with this; but would...
  3. nbr1

    Mechanical Excavation vs Blasting

    I don't think blasting would be an issue. It's a relatively remote area (more remote than I've seen blasted in the past). I'm more concerned that it won't be allowed (for whatever reason the Owner provides) and change orders follow; due to contractor claims of difficult 'mechanical excavation'.
  4. nbr1

    Mechanical Excavation vs Blasting

    I am involved in a project where the Owner would like to omit drilling and blasting as a method for rock excavation; however, rock excavation will be required for foundations and utilities for numerous(>30)residential structures on shallow foundations (no basements). The site is relatively...
  5. nbr1

    Driven Piles - Skin Friction

    Is there a way to utilize unit skin friction values (calculated from a load test on H-Piles) for use in pipe pile design? Seems to me that this would not be possible due to the skin-soil-skin-soil (assumed plugged) behavious of an H-Pile; but wanted to hear from others on this.
  6. nbr1

    Foundation Settlement based on DMT Modulus vs Traditional Oedometer Approach

    When calculating foundation settlement in moist (unsaturated) clay, do DMT methods (eg. Schmertmann, 1986) consider the effects of possible future saturation?
  7. nbr1

    CBR Results Valid??

    We received a CBR test report indicating a CBR of 92 (0.1 in. penetration) for a silty sand (Max. Dry Density 132.1 pcf) with no gravel. The reported Dry Density Before and After Soaking was 129.4 and 129.6 pcf, respectively. The uncorrected CBR was around 40 (0.1 inch penetration) and after...
  8. nbr1

    Undrained Shear Strength - Granular Soils

    I understand which value would be used in the analysis. I'm just trying to figure out the proper protocol for reporting strength values. So, if you reported an undrained strength the same as the drained strength.....would that technically be correct? Or should you just not report an undrained...
  9. nbr1

    Undrained Shear Strength - Granular Soils

    For the purposes of a slope stability analysis (static case only), would a free draining material (eg. clean gravel and/or sand) have an undrained strength? I often see in reports that the undrained strength is equal to the drained strength. For example, the following values may be reported...
  10. nbr1

    Vertical Uplift Gradient and Phreatic Surface

    Typically, average vertical 'uplift' gradients are limited to about 0.5 near the landside toe of an embankment levee or dam; and where the phreatic surface exits to the ground surface. What is the protocol for determining exit gradient if phreatic surface is buried; such that it can be compared...
  11. nbr1

    CD vs CU(bar) Triaxial Testing

    A soils testing firm is suggesting that CD testing is not required for a stability analysis of a silty clay compacted embankment soil; rather just CU(bar). Indicating that CD testing is rarely performed. Is there a justification for not performing CD testing for drained conditions on compacted...
  12. nbr1

    Engineering News Formula - Timber Pile

    Looks like there are several versions of the ENR formula. Some which calculate Qu and some which calculate a 'safe load' which I assume is Qu. What does the original formula calculate?
  13. nbr1

    Engineering News Formula - Timber Pile

    An old dwg prepared by USACE references the following: 'Min. length of round timber piles 30-ft; or driven to a firm bearing so as to support a load of 25 Tons, calculated by the Engineering News Formula.' My question is whether or not the pile load referenced is allowable or ultimate. My...
  14. nbr1

    Levee Underseepage

    Assuming a clay levee over an impervious top stratum overlying sand and fully loaded; is there a difference between the factor of safety against piping (FS=ic/i) at the levee toe (landside) versus the factor of safety against uplift (landside toe)? Are these terms essentially the same phenomenon?
  15. nbr1

    Void Ratio from CPT

    Are there any methodologies for estimating void ratio (for a sand) from CPT data? Any references would be appreciated.
  16. nbr1

    liquefaction/cyclic softening of fine-grained soils

    Suggest you evaluate the fine grain soils with CPTu testing; and the proposed CPT method attached which uses Ic and Bq parameters.http://files.engineering.com/getfile.aspx?folder=bdf81734-2823-429f-8b22-1b317faae377&file=CPT.pdf
  17. nbr1

    CU Triaxial and CD Triaxial - Effective Parameters

    I am trying to determine effective stress parameters for a foundation soil and have been provided the following information (which is the only information available at present): The material is a slightly silty clay (CL); having a PI ~20 and moisture content of 20%. Lab Test Phi...
  18. nbr1

    Levee Stability - Riverside or Landside Excavation

    Just to clarify, this is not a homework problem; nor is it a specific project....it's just conceptual, so no need to be get too precise. I'm just curious as to which side of a levee would be more favorable (in terms of stability/seepage concerns) for an excavation; say for a large pit or quarry...
  19. nbr1

    Levee Stability - Riverside or Landside Excavation

    Which would produce the least favorable conditions for slope stability and/or seepage (see attached); assuming all reasonable loading considerations with the exception of earthquakes and all other things considered equal? - a riverside excavation OR a landside excavation near a levee toe
  20. nbr1

    SPT N values

    The N-Value is the sum of the last 2 blow counts, which in your example (25-30-50/0mm) would be N=80 if you stopped after 50 blows with no advance on the last spoon...which most would. As Mike indicated, you could report as 80/150mm assuming no advance on last spoon. If last spoon did advance...

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