Difficulties Encountered in Pile Driving

Various defects are encountered in working with piles. Some of the common defects the inspector may encounter in wood and concrete piles are covered next.

WOOD PILES. - The inspector must be alert to detect and take steps to correct deficiencies in equipment and methods which may damage wood piles. The inspector must learn to recognize the indications of such failures and require that the methods be modified, if necessary. Overdriving is usually indicated by bending or staggering the hammer. Breaking or shearing is indicated by sudden resumption of easy driving after the pile has apparently been driven to practical refusal. Similar behavior may occur when the pile breaks through a hard crust into a softer stratum. Sudden hard driving may indicate that the pile has struck a boulder. Sudden change of direction may indicate that the pile has sheared or broken or that the pile has glanced off a boulder. The inspector should inform the superior when such difficulties recur and that there is doubt as to the cause and should recognize that damaged piles may endanger the safety of the structure supported by them.

CONCRETE PILES. - Common failures that may occur in precast concrete piles are cracking and spalling or shattering of the head.

Cracking may occur as a result of faulty mixes or curing, but it usually results from carelessness or improper rigging in handling. Piles should be inspected frequently and minutely during driving to make sure cracks do not exist. They are particularly dangerous in the portion above the mud line where they may permit corrosion of the reinforcement to occur. When numerous cracks occur, report the situation to your superior so that a fill-engineering investigation can be made and the causes corrected.

Spalling or shattering of the heads usually occurs in precast concrete piles, because the proper followers and driving blocks are not used. The equipment should be modified if these troubles develop consistently. Piles with badly shattered heads cannot be repaired effectively so that they can be driven with assurance that fill-bearing capacity is obtained. It may, in extreme cases, be necessary to remove and replace the pile. If the pile is not damaged badly enough to warrant rejection, the inspector should require the removal of all unsound concrete and building up to the finished cutoff.

With cast-in-place piles, difficulties are sometimes experienced through tearing of the shells or partial collapse after the mandrel is removed. A customary emergency measure is to drive a second shell inside the damaged shell. All shells should be inspected by throwing a beam of light down the shaft with a mirror and determining that they are sound, intact, and tight. Piles that are rejected as defective must be filled with concrete to eliminate a hole in the ground that could subsequently decrease the bearing capacity of adjacent piles.

The main difficulties with steel piles are twisting and distortion of the heads. Take special care to see that caps of proper design are provided to prevent this action.

TIMBER CONSTRUCTION

This section relates primarily to the inspection of the field construction of timber structures. Some of the major items to be covered in the inspection are given below.

Delivery and Storage

When timber is delivered to the site of the work for incorporation into the structure being constructed, the inspector must make sure that it has been inspected and grade-marked as required by the specifications or as approved by proper authority and that inspection certificates have been furnished by the inspecting agency. These certificates must be properly identified as pertaining to the material delivered, and the tally of material delivered must be correct. If it is treated material, the inspector must make sure that the inspection reports of treatment are received, identified, and indicate that the treatment complies with requirements. If inspection before delivery has been waived for any reason, the inspector must make sure that the timber conforms in species, dimensions, and quality to the requirements of the specifications.

The inspector must make sure that all timber is unloaded with reasonable care so that it is not damaged in handling. Exercise special care when handling timber treated with creosote or other preservatives to preclude damage penetrating the more heavily treated surface layer.

The inspector must require that timber be stored in a well-drained area so that it will be clear of the ground; that it be stacked so that there is good circulation of air through the pile; that in stacking, one end be raised so