Iano's backfill

Construction Site Safety

Engineer Had No Duty to Warn General Contractor’s Employee of Danger, ConstructionRisk.com Report, Vol. 6, No. 2, Feb 04, discusses a recent Mississippi court case in which a structural engineer was sued by the family of a construction worker who died as a result of an accident during construction. The worker's estate charged that the engineer's design was defective, and that the engineer had not performed his duty to warn the worker of dangers posed by the design.

For design professionals whose work takes them into the field, this article is a good reminder concerning who is responsible for construction site safety (the general contractor), and how the design professional should conduct themselves in the field so as to avoid assuming responsibility for such matters.

According to the article, the engineer's role during construction was limited to "monitoring the progress of the construction work" for general compliance with the design documents. The engineer was not authorized to stop work, or issue change orders. Resposibility for site safety was also assigned to the general contractor by its contract for construction. Based on these facts, and a lack of evidence of any deficiencies in the design, the court sided with the engineer.

The article goes on to summarize actions that courts are likely to consider in assigning responsibility for site safety, including for example:

• Supervision and control of the work
• Constant participation in construction site activities
• Supervision of subcontractors
• Assumption of responsibility for safety practices
• Assuming authority to issue change orders or to stop work

Pop Quiz!

The accompanying photo shows a reinforced concrete masonry wall under construction. When the author observed this wall during a recent site visit, he immediately instructed the contractor to take corrective action.

Can you identify the problem and what corrective action was required? Use the comment link below to submit your answer.

Hints: No work is currently taking place on the wall. The problem is nonstructural, and does not relate to temporary bracing.

Falling Water Restoration

Restoration wrapping up at Fallingwater, Fine Homebuilding January 2004, reports that the structural portion of the $11.5 million restoration started in 1996 is coming to a close.

VSL, the concrete restoration company hired to implement the repairs, provides additional details regarding the structural repairs on their web site, including:
--Explanation and diagrams of the posttensioning reinforcement of the main cantilevers, consisting of bundles of 13 1/2-inch steel cables
--Project background and description of structural steel channels and fiber reinforced polymer bars used to reinforce other parts of the structure.

Future restoration includes waterproofing, finishes, furnishings, and landscaping.

More information:
The textbook discusses posttension and other prestressing concepts on pages 493 - 499.
VSL Falling Water Media Coverage provides additional links to articles and media coverage of the Falling Water Repair project.
Western Pennsylvania Conservancy provides information about the building, and visiting Falling Water.
The Frank Lloyd Wright Building Conservancy provides information about conservation efforts related to all of Frank Lloyd Wright's projects.

Bentonite Foundation Waterproofing

The following are images, with accompanying explanation, taken during several site visits to a bentonite waterproofing installation. More background on this type of waterproofing can be found in the textbook, Chapter 2, Foundations, Waterproofing and Drainage, or on a manufacturer's web site.

[Click on images to enlarge.] The foundation is cast-in-place concrete. The geotechnical report indicates a high likelihood of groundwater around the foundation, especially during wetter times of the year. The interior of the basement includes fully finished spaces. Due to the severity of the groundwater conditions, and the sensitivity of the interior spaces, waterproofing and a drainage system are being provided both around the foundation walls and under the basement slab on grade. This article will look at the waterproofing applied to walls, with special attention to the treatment of penetrations in the wall.

In this view, one side of the concrete wall formwork has been erected. Steel reinforcing and form ties are in place, and a collection of PVC pipe sleeves have been installed. These sleeves will be cast into the wall. Later, utility lines of various types (water service, waste, gas, power, etc.) will be installed through the openings created by these sleeves.

The ends of the sleeves are taped off with duct tape to prevent concrete from leaking into the pipes during the pour. Around the middle of each pipe is a bentonite mastic waterstop. These will be cast into the concrete and create a waterproof seal between the concrete and the outside of the PVC pipe.

Here are the sleeves after the concrete has been poured and the forms stripped. Note the rough concrete edges around the outside of the PVC pipes. It's easy to imagine water seeping through this juncture if there wasn't a waterstop part-way in to stop it.

Here is another example of the use of the bentonite waterstop. On this project, waterstops are to be applied at all "cold" joints (where new concrete is cast directly against previously poured concrete) throughout the foundation work, to prevent leakage across these vulnerable locations. Note however that bentonite waterstops are not suitable for use at moving joints.

This view, from the inside of the foundation, shows a short length of utility pipe installed through the PVC sleeve. The outer sleeve can be seen, its face flush with the concrete wall. The inner pipe, which projects beyond the surface of the wall, is the actual utility service line (the continuation of the pipe will be installed later). In between is a mechanical gasket, which when tightened, forms a waterproof seal in the space between the sleeve and the utility pipe.

Here is another view of a partially installed utility line, this time taken from the outside of the foundation wall. Bentonite panels have been partially installed around the pipe penetration. Note the additional layers of waterproofing and mastic applied around this penetration to provide additional protection against leakage.

This image shows an interesting detail at the foot of the concrete wall where it meets the spread footing. Additional bentonite granules contained in a plastic "sausage" are inserted behind the panel. The plastic will dissolve when it first comes in contact with water, depositing a thick extra layer of bentonite at this vulnerable juncture.

This final images shows a section of wall with the waterproofing work almost complete--the top edge of the waterproofing is set to come within six inches or less of finished grade. Drainage panel installation is still in progress, with the upper half of waterproofing yet to be covered. In addition to relieving water pressure against the foundation wall, these panels will also provide physical protection to the waterproofing as the foundation is backfilled. Note the filter fabric facing on the drainage panels. This material prevents soil particles from being carried into and eventually clogging the panel. Note the fasteners used to attach the bentonite and drainage panels to the wall. These powder-actuated fasteners penetrate through both panels into the concrete. When the bentonite first gets wet and swells, it will form a tight seal around these penetrations. Also partially visible at the bottom right of this photo is the trench along the sides of the spread footing, ready to receive perimeter footing drains.
(c) Joe Iano 2003