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Steel Pipe Piles

Steel Pipe Piles

Steel Pipe Piles

Given that 10" concrete filled reinforced steel pipe piles with an axial design load of 75 tons are the design requirment for a building foundation, and that the piles are closed end and driven to a depth of an average of 47', How does one calculate the required pipe wall thickness in order to resist any significant distortion (less than 10% of pipe diameter change.  The soil is described as creamy, loose to dense, water logged, calcareous, gravelly silty sand limestone formation 'marl'.  The SPT rod sank 2' with one blow.  The underlying bedrock formation is a uneven, pitted, fractured coralline limestone.  The ground water has also has high quantities of sulfates and chlorides.  As a result, the design corrosion rate of the piles is estimated at 0.08 mm/year.  The design calls for a minimum pipe wall thickness of 0.365 inches.  Is this adequate?   

RE: Steel Pipe Piles

W/O detailed calculation and based on your soil condition, I would recommend an open-end pipe pile for you project. You might break your pile during driving if it is closed-end. For 50-year design life you might looking at 0.2-in thickness just for corrosion. 0.365 or 0.5-in, how much you can save? Your "I" to resist lateral force might control!!

RE: Steel Pipe Piles

I have designed and observed a large number of driven pipe piling for end bearing conditions. Many of our soils are very soft (SPT <2/12) under the water table and the bearing formation is a hard shale (SPT >100/12).  For light to medium loads (up to 100 tons) we usually use 10" or 12", closed ended pipe piling. The wall thickness are 0.25" or thicker if driving into cobbles, large loads and/or if the piles are long (over 90'). The piling are concrete filled after driving. I deals with large amounts of sulfate salts.

The pipe piling are normally designed with little or no contributions from the surrounding soil (similar to coastal conditions of docks).  The concrete filling is not used to determine the ultimate pile capacity. The pipe are designed similar to columns and extra thickness may be added if excessive corrosion is anticiapted.  As our soils are usually basic, instead of acidic, the high sulfates are not as much of a problem.

Visitor mentioned the problem of 'breaking'. I have experienced some buckling, usually when the hammer is too 'heavy'. Proper selection of the driving equipment proper selection of the final drive or 'set' will usually minimize damage to the piling.

RE: Steel Pipe Piles

The first question is do you intend to use the steel shell to carry any of the load. If you do, you should be concerned about corrosion. At .08mm/yr, the shell would be reduced to .25 inches of shell thickness in approx. 40 years, which may be the limit of the design life. However if you figure just the concrete, the 75 tons applies 2000 psi stress to the concrete. (P/Ag). Note that a load test  to 2x Design will impose a higher stress, although the shell could participate, so that the load in the concrete would be less than 4000 psi.

The next consideration is the pile driving. Driving pipes closed end is not a problem, however I have not driven pipes less than 12" There is not a big difference between driving open or closed pipes. Usually the pipe will plug tightly and act as a closed end. If you plan to fill the piles, the really should be closed end as you will never do a good job of cleaning out the pipe prior to placing the concrete. Often a flat plate is welded to the bottom of the pile, although conical points are available. I would strongly recomend a WEAP analysis in  the design phase for your project due the unusual soil conditions in your project. I would use a Vulcan 01 air hammer with an aluminum mcarta cushion and see what the driving stresses and final blow count look like.

Which segways into my third consideration, the soil/rock profile. The soft soil deposits may not sufficantly brace the piles. To have a rod sink 2 feet in one blow is pretty soft. Also since the soil is so soft pile alignment will be a problem. You should expect significant out of location on these piles. Also these piles may not have good lateral stability. If that is an issue, you may want to consider batter piles. The limestone can have soft zones underlying competent rock. If this is the case, then you could have serious questions abut the bearing capacity of the rock.

Depending on the field conditions, you could get 10 inch piles to work, although I would consider 12 to lower the stress. I would not figure the cpacity of the shell into the capacity of the pile. I would be concerned about lateral support and unbraced length. I would also be concerned about pile alignment and driving stresses. I would also closely look at the bearing capacity of the limestone. As a final thought, I would consider 10 inch drilled in mini-piles that were socketed at least 5 feet into the rock. This could solve a lot of problems, including the alignment, the bearing and the driving stresses. A conversation with a local pile driver and a local mini pile installer could give you a wealth of information.
Good luck and let us know how you make out!

RE: Steel Pipe Piles

Pile thicknesses are actually made up from
* thickness for pile dia./driver/soil combination without buckling- mills and local contractors are a good guide in the absence of a detailed analysis
* an allowance for corrossion based on the chemical analysis of the soil/water
* the 0.08mm/year allowance is normally lower end for the tropics, ranges are 0.08~0.16mm/year

In the discussions, hope the point was not missed that advised corrossion allowances are actually per side of the pile


RE: Steel Pipe Piles

I normaly run the weap analysis and determine the drivability stresses/depth using various hammers. An open ended 10"d pile would plug between 15d to 30d and u may need to clean out pile. I would weld a driving plate at tip and reinforce top if driving stress are larger than 80% yield. Then I would use min A253 Gr3 or 70 ksi steel say 5/16" thickness, min. You only need this for driving and not for anything else because these are cip anyway using good quality mix and even coated bars/spirals.

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