Texas State Board of Registration for Professional Engineers
Date: May 17, 1989
From: H. Edwin Crow, P.E.
To: Kenneth R. Wood
This note is in response to the question asked in the last paragraph of Joan S. Pierson’s letter dated April 14, 1989. You have asked about the suitability of the Perma-Pile method for foundation repair for use in the soil of Southeast Texas. The TSBRPE does not have the resources to evaluate engineering innovations nor engineering solutions to problems; however, a brief review of the literature that you enclosed raised several questions that should be answered before an opinion could be formulated. Some of these question and concerns are:
- The Literature indicated that the Perm-Pile System minimizes the dependence on the exact knowledge of the soil. This statement is contrary to accepted engineering practices. The constituents and the physical characteristics of the soil are necessary to establish the load-bearing capability, permeability, potential vertical rise and other engineering aspects of the soil.
- Since the pile to be driven must be slanted in order to get under the grade beam, how can the alignment be controlled during the driving process, particularly if an underground obstruction (such as a stump, pipe, etc.) is struck by the pile?
- Since larger section of concrete blocks are placed on top of the pile, and apparently are not attached to the pile, what keeps the expansive soil from pushing those blocks up when expansion occurs? (along with the foundation)
- There is no reinforcing steel indicated for the pre-cast piles in the sketch attached to your letter. What holds the pile together during the driving process and how can the pile sustain its load-bearing capability without having reinforcing steel in it?
- In paragraph (e) of the sketch how can the strength of the concrete be verified during installation? (If it breaks, drive another pile?)
- No mention is made of possible heaving of the soil under the interior part of a slab during the driving of the piles. How does Perm-Pile suggest controlling this distinct possibility?
MORE POINTS FROM ENGINEERS AT TEXAS A & M UNIVERSITY
Mr. M. Lewis Coody, P.E.
Mr. Ronald J. Kruhl, P.E.
- The Press Pile System, therefore, will not be capable of supporting the maximum combination of dead load and live load as stated in the specifications without excessive settlement.
- Furthermore, since only the dead load and existing live load at the time of installation are used in resisting the jacking force no factor of safety can be incorporated.
- Settlement can occur in varying amounts after the piles are pressed into saturated expansive clay soil because friction resistance will be lost when the soil loses moisture and pulls away from the pile.
- Furthermore, there is no assurance that the Press Pile System will be driven straight or what the effective length of the pile will be in soft saturated plastic clays. If one portion of the tip section encounters a foreign object such as a rock or tree root it may skew off to one side. This tip section may in turn cause other sections of the pile to skew off as well. This, of course, could not be detected by the installer. Althought a large number of sections may be jacked into the ground there is no guarantee that the pile is deep and that adequate long term capacity will be sustained.
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