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  1. SmokeyBear

    Use of polymers to improve soil subgrades

    Thanks for the responses. I feel "snake oil" is appropriate, but I should have asked if anyone knows of testing such as CBR, Atterberg Limits or UCS over a period of time which indicates the improvement, or lack thereof, when using polymers with and without traditional additives such as lime or...
  2. SmokeyBear

    Use of polymers to improve soil subgrades

    We are looking at an "ionic polymerisation" additive to stabilise and "waterproof" soil subgrade materials. The distributor claims the polymer links together and forms a bond which increases the density of the material, while reducing the porosity of the soil matrix making it resistant to water...
  3. SmokeyBear

    Colloidal Grouts for Anchoring and Deep Soil Mixing

    Thanks for responses. born2drill and PEinc, Using an Obermann 600 and agree completely re bells and whistles and that it's not a colloidal mixer. I should have added that we are using a high speed shear mixer in the agitator tank after batching in the Obermann. For anchors I'm not concerned...
  4. SmokeyBear

    Colloidal Grouts for Anchoring and Deep Soil Mixing

    We are engaged in heated discussions about the need, or otherwise, of using true colloidal grouts (cement and water) for grouting soil or rock anchors and for deep mixing in soils. One view is that it is not necessary, the opposing view is that it is essential.We are using an Obermann twin bowl...
  5. SmokeyBear

    Shaft Adhesion in Bored Piles of Different Diameters.

    Rockmynci: the piles were drilled in very stiff to hard residual clays of medium plasticity, grading to weathered rock at depth. The rock is a slightly metamorphosed sandstone/siltstone, varying from extremely low to low strength. Typically all piles were founded above the water table.
  6. SmokeyBear

    Shaft Adhesion in Bored Piles of Different Diameters.

    Rockmynci; thanks for the information. I tend to agree with BigH. However, one should certainly consider time to drill and time to pour. Over many years, I have found that for bored piles, 600 and 750mm diameter holes are the quickest to drill, 9oo next, then 600 and less; with 1200 diameter...
  7. SmokeyBear

    Shaft Adhesion in Bored Piles of Different Diameters.

    Big H and PSlem, Thanks for the comments. I await with bated breathe further posts. My collegue mumbled something about Poisson's ratio, but I have my doubts. PSlem, could you elucidate? Do you mean that you noted very little differece for various diameters? This seems counter intuitive.
  8. SmokeyBear

    Shaft Adhesion in Bored Piles of Different Diameters.

    Has anyone observed a reduction in shaft adhesion for increasing diameters of bored piles in similar subsurface condition? In a recent project, shaft adhesions were developed from in-situ and laboratory testing. These values were confirmed/modified based on a number of CAPWAP analyses undertaken...
  9. SmokeyBear

    young's modulus of soft clays

    For normally consolidated or slightly overconsolidated alluvial soft/very soft clays, Eu is approximately 250 times Su.
  10. SmokeyBear

    Shear Strength for Temporary Support of Excavation

    DirtPlayer, Assumming we are not looking at partially saturated soils, which seems to be a new kid on the block, low strength cohesive materials are probably best considered as undrained for "normal" construction times. We tend to use vane shears to assess Su, applying Bjerrum's correction for...
  11. SmokeyBear

    phi angle for silty or clayey sands

    Some late thoughts... Probably the best method of assessing residual strength is to use a ring shear device. I would guess around 22-25 deg with c'=0. I don't think there is anyway to get "better" values. Residual strength is residual strength. However, the method of testing will certainly...
  12. SmokeyBear

    PY Wall Deflections

    PEinc, Agreed - apparent pressure diagrams are conservative envelopes, widely used before PCs. Soil-structure interaction analyses must be carried out for multi-propped walls and should be used for single props. You commented "..people who specialize in the design and building of shoring walls...
  13. SmokeyBear

    Open question: Are we doing less lab testing?

    We do a lot of work in soft clays and over the past 25 years a large testing data base has been collected. It suggests Su ranges from around 10 to 30kPa, phi' between 20 to 28 deg and c' between 1 and 5 kPa. While I agree with dgilllete et. al. that for "stronger" soils, the difference between...
  14. SmokeyBear

    CPT pwp dissapation rate

    geodan, a very good reference is Cone Penetration Testing in Geotechnical Practice, T. Lunne, P.K. Robertson and J.J.M. Powell, 1997, reprinted by Routledge in the USA and Canada. Two warning comments:- Prediction of Cv only within one order of magnitude. Permeability from CPT dissapation is...
  15. SmokeyBear

    Open question: Are we doing less lab testing?

    A very late reply; but...I do not understand how you can:- calculate settlements without some knowledge of stress history assess overburden pressure without densities, assess c' and phi' without strength testing, classify soils (to the extent that different people logging the soils, call them...
  16. SmokeyBear

    Cleaning holes for end-bearing piles

    worldofmud correct.Provided accurate depth of drilling is measured, so you know where you actually drilled to, a good clean-out bucket can remove all but a handfull of spoil. You can visually check base cleanliness using a torch. In other than rock, you can actually "drill" a little with the...
  17. SmokeyBear

    Pile Construction in Porous Rock

    A dual-head drilling system, where the casing and the auger are counter-rotated would seem the way to go. If you use a CFA method (recommended) the hole will stay relatively dry and the concrete will be tremmied into the base of the hole during extraction. A hard/soft system would seem best -...
  18. SmokeyBear

    Pile Design based on CPT Data

    Greetings from the Antipodes. Does anyone have a contact, or knowledge of the Lousiana DOT program for pile design based on CPT data. The L-DOT site doesn't seem to mention it and I have made fruitless searches of FHWA, COE etc. Details of the program are given in Fred Spinks excellent software...
  19. SmokeyBear

    Grouted Soil Anchor Design References

    The British Standard BS 8081-1989 "Soil and Rock Anchors" is an excellent reference. Your query on cover is explained and the standard has a good bibliography. Good Luck
  20. SmokeyBear

    Chisel Design for Excavation of Cut-off-wall

    I agree with PSlem on the need for a good an edge as possible. Have you tried increasing the weight of the sinker bar. More weight = more energy at the bit.

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