ITEM 506  STATIC LOAD TEST

506.01  Description

506.02  General

506.03  Test Procedure

506.04  Basis of Payment

 

506.01  Description.  This work consists of applying a static load to a driven pile and furnishing instruments and facilities to obtain load-displacement data required to determine the ultimate bearing value of the pile.  When subsequent static load tests are specified, the Office of Structural Engineering will determine whether subsequent static load tests are to be performed and the location of all piles to be tested.

506.02  General.  Perform the static load test according to ASTM D1143, Procedure A: Quick Test, except as modified below.

Use the hammer selected for driving the test pile to drive all piles represented by the test.  If the Contractor finds it necessary to use a different hammer, the Office of Structural Engineering will determine if an additional static load test is necessary.

If using anchor piles to apply the load to the test pile, locate the anchor piles to provide a minimum clear distance of 8 feet (2.5 m) from the test pile.  The Contractor may use battered piles as anchor piles, provided the horizontal forces in the anchor system are balanced and excessive bending stresses are not induced in the piles.  The Contractor may also use bearing piles meeting these requirements as anchor piles.  After the test has been completed, remove or cut off at least 1 foot (0.3 m) below the bottom of the footing or finished surface of the ground all anchor piles outside the limits of the footing.  Cut off anchor piles, other than bearing piles, within the limits of the footing 3 inches (75 mm) above the bottom of the footing.  Redrive all bearing piles used as anchor piles that are displaced upward during the application of the test load according to the plan requirements.

For the duration of the test, provide adequate facilities to record load and displacement readings.  To avoid column buckling of the pile, ensure that tested piles are substantially vertical and that the load is applied to the pile at a point as near the ground surface as possible.

Provide equipment and loading apparatus to apply a maximum test load of twice the ultimate bearing value.  Have a Registered Engineer design the loading apparatus.  Determine if piles on the plan order list for cast-in-place reinforced concrete piles have a pile wall thick enough to support the maximum test load of twice the ultimate bearing value.  The minimum pile wall thickness to support twice the ultimate bearing value is:

t (inch) =

2 R (lb)

 

t (mm) =

2 R (N)

113,000 D (inch)

 

780 D (mm)

 

Where:

                       t = pile wall thickness in inches (mm)

                      R = ultimate bearing value in pounds (N)

                      D = diameter of pile in inches (mm)

 

If the pile wall thickness for the test pile is less than t, before performing the static load test, either drive a test pile with a thicker pile wall, or fill the pile with concrete and allow the concrete to cure for 5 days.  The static load test is unacceptable if the pile fails internally during the test due to improper installation or procedure by the Contractor.

506.03  Test Procedure.  Apply the load at least 5 days after placing concrete in the pile or 72 hours after driving both the test pile and the anchor piles.

Use displacement indicators as the primary system to measure axial movement of the test pile top, with a redundant secondary system as described in ASTM D1143.

Apply the test load in increments of approximately one-tenth the ultimate bearing value.  Between each load increment, keep the test load constant for 15 minutes.  Add load increments until the test load reaches twice the ultimate bearing value or until continuous jacking is required to maintain the test load.  Remove the test load in five approximately equal decrements, keeping the test load constant for 15 minutes between decrements.  If it is necessary to remove and reapply the load during the test, use the same loading procedure to reapply the test load.

Record test readings taken at 1, 2, 4, 8, and 15 minutes after completing application of each load increment.  Record test readings taken at 1 and 15 minutes after each load decrement and after removing all load from the test pile.

Determine the load test ultimate bearing value (Qf) using the Davisson criteria.  First plot the displacement versus load on the pile (Q).  Next, draw a line representing the theoretical elastic deformation of the pile, using the following equation.

d =

Q L

A E

Where:

                          d =  Elastic deformation of pile in inches (mm)

                         Q =  Test load in pounds (N)

                          L =  Length of pile in inches (mm)

                          A =  cross-sectional area of pile in square inches (mm)

                          E =  Elastic modulus of pile in lb/in (MPa)
for steel E=29,000,000 lb/in (200,000 MPa)

 

Draw the Davisson criteria line parallel to the theoretical elastic deformation but offset by the following formula:

0.15 inch + 0.008D   (3.8 mm + 0.008D)

Where:

                         D =  Diameter or width of the pile in inches (mm). 

 

The test load ultimate bearing value (Qf) is the load corresponding to where the Davisson criteria line crosses the load-displacement curve. See the figure below.

Within four days of completing the static load test, submit a report to the Engineer which contains the information required according to ASTM D 1143 and the load displacement graph described above.

506.04  Basis of Payment.  If the Contractor subsequently finds it necessary to use a different hammer, the Office of Structural Engineering will determine if an additional static load test is necessary; the Contractor shall complete any such additional test at no additional cost to the Department.

The cost of furnishing test piles with thicker pile walls is included under Static Load Test.

The Department will pay for accepted quantities at the contract prices as follows:

Item           Unit                                Description

506             Lump Sum                      Static Load Test

506             Each                                Subsequent Static Load Test