Pile suitable for bouldery, gravelly soil
Pile suitable for bouldery, gravelly soil
(OP)
I’m one of the structural engineers for a project in California, where piles are needed to anchor a concrete “protective structure” subject to large, somewhat dynamic lateral loads on the order of hundreds of kips due to mudslide. I have a soil boring that shows bouldery, gravelly silt conditions, but I’ve been told by the folk who bid the job that there will be no budget for a geotechnical consultant. I have 2 weeks to come up with a design, and I have limited experience with pile supported structures.
Since this is an extremely affluent, densely populated area, I suspect that the noise and vibration of driven piles could open a political can of worms, and I’m sure the bouldery soil would preclude them anyways.
Can anyone recommend a type of pile with high lateral resistance, constructible in these soil conditions, and without high levels of noise and vibration that the local residents will tolerate?
Since this is an extremely affluent, densely populated area, I suspect that the noise and vibration of driven piles could open a political can of worms, and I’m sure the bouldery soil would preclude them anyways.
Can anyone recommend a type of pile with high lateral resistance, constructible in these soil conditions, and without high levels of noise and vibration that the local residents will tolerate?





RE: Pile suitable for bouldery, gravelly soil
RE: Pile suitable for bouldery, gravelly soil
RE: Pile suitable for bouldery, gravelly soil
RE: Pile suitable for bouldery, gravelly soil
1) If conditions are as bad as you assume... doubt a typical boring could have been made. Maybe a few question about the field details encountered during the boring would shed more light on soil conditions.
2) I disagree with using "noise level" as the primary criteria to dictate design. As a former bridge contractor, sometime driving piling in residential areas, I can tell you first-hand that "noise" is only one factor... probably NOT the most important one, either.
Time of day for the "noise" is important. Say 9am to 5pm, as apposed to sunup to sundown.
Which days of the week, too. Monday thru Friday, ok. Weekends, no.
The most important is duration of the work. If the Contractor gets "in" and "out" on schedule - great. The worst is to have work "drag" on for what seems like a long, long time.
If driven pile are "best" (IMHO, probably are considering the description), there are steps that can be taken to minimize pile driving noise. You will have to work with a qualified pile driver to determine the details, but the following is possible:
A. Select a type pile hammer that is optimum for the piling and condition.
B. Within that type hammer, select one with optimum energy rating AND geometry.
As an example, say that a single-acting impact hammer is determined to be best. Also, an energy rating of 22,000 to 25,000 foot-pounds is optimum. Then, select, perhaps, a Vulcan 0 (24,400 ft-lb) versus a MKT DE-30 (22,400 ft-lb). The deciding factor (to reduce noise) is the impact velocity of the ram on the anvil (pile). A Vulcan 0 has a 7500 lb ram falling 39 inches. The MKT DE-30, 2800 lb, ram falling 96 inches. Lower impact velocity for the Vulcan.
The lower the impact velocity the more efficient energy is transferred from the ram to the pile... more efficient, less noise.
Use a proper size hammer... more efficient advancing the pile rather than "bouncing" the pile of the rock and rebounding the ram... advance the pile, less noise.
The funny thing is, with this level of attention to detail, the pile driving (if it is appropriate for this project) will go more smoothly, quickly, (relatively) quietly and cost effectively.
If you do decide to go with driven piling, after the pile driver has mobilized, have them drive a few "index piling" to determine if the proper hammer has been selected... sort of a DIY geotechnical investigation for a pile driver.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Pile suitable for bouldery, gravelly soil
SRE - I certainly will be pressing for more information in the coming week. I wasn’t on the original proposal team and I’m just joining on now from another office on the east coast. I’ve seen one site photo which was taken post-mudslide, and visually it looks to be 50% boulders and cobbles and 50% dirt. If steel piles are feasible from a constructabilty standpoint, then I won’t disqualify them solely based on my cynical concerns about the neighbors.
RE: Pile suitable for bouldery, gravelly soil
RE: Pile suitable for bouldery, gravelly soil
See if the plans and possibly some construction records for the existing bridge are available (probably are if it is a DOT bridge). That information will give a good idea what is possible on this site.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Pile suitable for bouldery, gravelly soil
Have you explained to your client that it is s very bad idea to not hire a geotechnical consultant?
It surprises me that you would be ok taking on this liability in a field you're not knowledgeable in. I have some experience in deep foundation design but would never go along with no geotechnical study scenario. If anything were to go wrong and everybody got sued, you would be the first one to loose the case and most likely your license.
I would advise you to press harder for a geotechnical study to be done and document that you did.
Good luck.
RE: Pile suitable for bouldery, gravelly soil
RE: Pile suitable for bouldery, gravelly soil
The other ting (which I believe you are doing) is to built a large safety factor into the design and have the client pay the price. It always amazes me that the owners/developers or what not are willing to save a few bucks but not paying a geotech but don't realize they may be paying much more for their foundation system.
I am a big proponent of always involving a geotechnical engineer, worth the money most every time...(And I don't say it only because I am married to one :))
RE: Pile suitable for bouldery, gravelly soil
RE: Pile suitable for bouldery, gravelly soil
www.PeirceEngineering.com
RE: Pile suitable for bouldery, gravelly soil
Thanks.
RE: Pile suitable for bouldery, gravelly soil
BUGGAR - It is in the Santa Barbara area.
RE: Pile suitable for bouldery, gravelly soil
RE: Pile suitable for bouldery, gravelly soil
www.PeirceEngineering.com
RE: Pile suitable for bouldery, gravelly soil
Recent weather related geological events in this area render it highly unlikely the job will proceed without a geotech. We have pockets of corrosive soils up there as well.
RE: Pile suitable for bouldery, gravelly soil
Yes, those weather related geological events are the reason for this project. The decision not to have a geotech on board is out of my control. I'm not stamping the drawings and have no intention of taking on the responsibility of the geotech portion of the design.
My scope is to help design the superstructure, so I'm just trying to determine what type of pile/caisson/tie-down is feasible in these soil conditions and get some ballpark capacities so I can layout and design the rest of the structure accordingly. The client wants shovels in the ground next week and I'm still doing conceptual design.
RE: Pile suitable for bouldery, gravelly soil
Thank you.
RE: Pile suitable for bouldery, gravelly soil
If you feel you must come up with something, I'll second Okiryu's suggestion to consider prebored and grouted piles. That, or just regular drilled shafts would solve the noise issue. If you have info on the depth of the slide and the soil properties, you can estimate the soil pressures. I would recommend being very conservative with that estimate. Just as an example, we had one of those consultants who specializes in slope stability and slide mitigation recently use a value of 5 times the passive resistance coefficient, Kp to estimate loads for a drilled shaft group (coupled using a CIP concrete cap) protecting bridge piers in a slide area. If you have enough information to estimate the loads, a program such as Lpile or Allpile can analyze the lateral geotechnical resistance and bending moment.
RE: Pile suitable for bouldery, gravelly soil
In general, I agree with everyone's advice about not designing a specialized structure without having the requisite specific experience. I was brought on to this job mainly to perform dynamic impact analysis, which I do have a fair amount of experience with. A pile/anchor type had not been selected for the conceptual design, which I needed to include in the model to try to capture the overall force-displacement behavior. Since I was told there would be no geotechnical assistance, I posed my question here in hopes of at least narrowing down the most feasible type of pile.
I had initially looked at driven H-piles, generated p-y curves in L-PILE based on sand (conservative for displacement) and had reasonable looking results in the dynamic analysis. My hope was to take that proof-of-concept analysis and refine it with geotech-provided parameters at a later date, or if that never happened, put huge disclaimers on the results and let my management take it for what it's worth.
RE: Pile suitable for bouldery, gravelly soil
Seismic conditions....mudslide...I think that your company has to solve this issue (not having a geotech on board) before start thinking on the type of piles that may be required for this project...
Just curious to know: what is the reason why you do not have a geotech on board for this geotechnical issue?
RE: Pile suitable for bouldery, gravelly soil
RE: Pile suitable for bouldery, gravelly soil