* In response to “Subway Tunnel Walls Thinner Than Designed,” Aug. 29:
For more than 25 years, before coming to academia in 1971, I worked as an engineer on major highway and bridge construction projects, both in the field and on design.
I find reports in The Times of deficiencies in the thickness of the Red Line subway tunnel walls incredible. Public projects of this type have expensive engineering supervision that carefully controls every phase of the contractors’ operations.
From my own experience I find it incredible that any part of critical structural elements, in this case the tunnel walls, could have been built deficiently. Apparently in lieu of the 12 inches of structural concrete called for on the plans, the tunnel was built throughout its length with thicknesses varying between six inches and 12 inches. It seems to me that construction tolerances for such elements would be limited to less than one-half inch.
If six inches of concrete was sufficient, why did the design engineers specify a 12-inch wall thickness, for which the contractor is generally paid on a cubic yard basis? What happened to the location of the reinforcing steel in the deficient sections? The whole matter smacks to me of a potentially scandalous situation for which the public has the right to demand competent professional answers.
Professor of Civil Engineering
Cal State Los Angeles
* It should be a cut-and-dried situation. Construction documents should state the materials, measurements and methods of installation. These are the documents that the contractor submitted his bid on. This is what the contractor should furnish, period.
If the responsible project administration inspector determines that there’s inadequate thickness of concrete, etc., according to project specifications, then the contractor must be made to make the corrections at his expense unless there is documented authorization to vary from the construction documents.
Left unchecked, these reported structural deficiencies can cause havoc with the subway system years from now or any time there is an earth movement of less magnitude than the engineer’s seismic design of the tunnel.
* Fact: The contractor did not pour concrete as per the design. Fact: The inspectors allowed the pour.
* In response to your editorial on Metro Rail tunnel concrete thickness, Aug. 31:
Before making any negative assessment of Metro Rail construction please consider the following:
Obviously it would be wonderful had the Metro Rail contractor built the concrete tunnels exactly as designed; however, this was not the case here and, in practice, it is the exception. Frequently, the real world forces us to consider alternatives, just as Metro Rail designers did when they reviewed and corrected tunnels by reinforcing them with steel plates. To doubt their solution undermines the Metro Rail system as well as the entire construction industry.
Consider the added time involved, as the Metropolitan Transit Authority surely did, of forcing the contractor to remove and rebuild thin concrete tunnel walls. Metro Rail construction already takes forever and the adjacent businesses take a beating in lost business because of it. If redesigning rather than rebuilding tunnels is a more effective solution, what is wrong with that?
Furthermore, the federal government agrees to fund the Los Angeles Metro Rail construction because we do not meet the current federal air quality standards. This is a serious problem that not only affects our quality of life but also hampers future growth. Los Angeles cannot continue to grow until we take steps to improve air quality. Assuming mass transit has an impact, the sooner they complete the construction the better.