Residential Structure Investigations for Vibrations from Subsurface Drilling

CA investigated whether the alleged distress at 28 residences located in Peñitas, Texas was the result of drilling operations which occurred in the area between 2007 and 2011. The investigation included a detailed condition survey of each residence as well as an elevation survey of each residence’s slab-on-grade foundation. CA reviewed applicable industry standards and relevant published literature regarding ground vibrations and damage to existing structures. The investigation did not produce any evidence to support the conclusion that the alleged distress in the residences was the result of ground vibrations from the drilling operations. CA determined that the observed distress in the residences was most likely caused by one or a combination of the following: dimensional movement of the structure due to temperature and humidity cycles, drying shrinkage stresses, foundation movement, and/or deficient construction.

Cold Weather Concrete, Post-Tensioned Slab Blowout

CA investigated allegations that the characteristics of the concrete mixture and properties of the as-delivered concrete caused numerous post-tensioning blowouts and delays during construction of a seven-level parking garage. CA’s investigation focused on investigating the concrete mixture design’s conformance with the design requirements, the quality and suitability of the as‐delivered concrete for its intended purpose, and if the concrete caused and/or contributed to the alleged delays and blowouts experienced during construction. CA determined that the ready-mix supplier’s concrete mix design submittal was in compliance with the design requirements for the construction of the parking garage and was approved by the engineer of record. CA’s investigation into the materials, proportioning, production, mixing, and delivery of the fresh concrete and its characteristics and performance did not reveal any evidence to support the allegation that the concrete produced and delivered was the cause of or a contributing factor to the alleged delays and blowouts during post‐tensioning. CA found that the blowouts were the result of any one or a combination of the following deficiencies within the responsibilities of the general contractor: in‐place concrete early‐age protection and curing during cold weather, curing and handling of field‐cured cylinders, concrete placement quality, and installation of reinforcement.

Municipal Water Tank Roof Failure

CA investigated the structural integrity of a 275,000 gallon municipal water tank in Vermont. The water tank consisted of a cast-in-place concrete foundation slab, cast-in-place concrete walls, and a precast, hollow-core plank roof with a continuous cast-in-place concrete topping slab over the planks. After only about ten years in service, distress was noted on the underside of the precast, hollow-core planks in the form of cracking and fractured and fallen sections of concrete. CA investigated the distress and alleged failure of the water tank. CA focused on the structural system, construction, and condition of the water tank as well as determining the cause(s) of the observed distress. CA reviewed construction documents, construction specifications, previous engineering and petrographic summary reports, and relevant published literature and industry standards. CA’s field observations, sampling, and petrographic examination revealed that the overall tank structure was in good condition and that the distress in the roof structure was due to an internal sulfate attack mechanism. CA determined that the distress mechanism emanated from planks’ manufacturing process.

As-Built Construction Investigation of Concrete Water-Retaining Structures

Carrasquillo Associates investigated leaking and cracking in multiple concrete structures which occurred several months after construction of a municipal drinking water treatment plant. CA’s investigation focused on determining if the distress observed in the concrete structures resulted from deficiencies in the installation of the steel reinforcement, as well as evaluating the findings and recommendations of the investigations performed by other parties.

Pavement Construction and Possible Overload Investigation

Several new structures for an oil-field equipment servicing company were constructed in 2012 in Houston, TX.  The structures were surrounded by three large reinforced concrete drive lanes utilized for delivery and pick-up of the large-size oil equipment parts.  Shortly after construction, the reinforced concrete pavement exhibited distress in form of spalled joints at dowel locations, pumping, and localized panel failures.  CA was retained to determine the cause(s) of the distress and provide repair recommendations.  CA’s field work included soil sampling and testing, non-destructive testing of the concrete pavement, including the use of ground penetrating radar, and relative elevation surveys to verify surface drainage patterns.  In addition to the field work, CA also performed an analysis of the pavement design to determine its structural adequacy as-designed considering the actual forklift and truck traffic.  CA’s investigation revealed numerous design deficiencies relating to the base material and pavement thickness considering the actual pavement loads. Certain construction deficiencies exacerbated the observed distress as well. CA provided a repair plan for the pavement.

Burnished Concrete Floor Finish Investigation

Carrasquillo Associates reviewed a 150,000 square foot interior slab-on-ground for a big box retailer in Cibolo, TX. The project specifications for the slab-on-ground finish incorporated strict aesthetic requirements.  Shortly after burnishing and cleaning the finished floor surface, the contractor was notified that the floor was unacceptable due to various aesthetic issues on the surface of the floor. CA extracted concrete core samples for petrographic examination of the concrete and finished surface. CA determined that the concrete floor was structurally adequate, but identified various deficiencies in the burnishing and/or cleaning operations which affected the initial hard trowel finish leaving a dull appearance and exposed aggregate at localized areas.

Progressive Distress Mechanism in Industrial Concrete Pavement

Carrasquillo Associates investigated distress in a 1,000,000 square foot concrete trucking pavement. CA’s investigation revealed two key findings. First, CA’s periodic condition surveys utilizing ASTM and FHWA practices provided clear evidence of a progressive distress mechanism. This distress mechanism began with joint sealant degradation and proceeded to water penetration, pumping, corner breaks, loss of support and faulting, and finally a completely broken pavement section. Second, CA determined that the rigid base which utilized on-site materials was mischaracterized as limestone during construction. In actuality, the base material was marl, which has a strength and appearance similar to limestone, but is moisture-sensitive, meaning strength is lost when the moisture content increases. In summary, CA’s investigation revealed that the failure to perform maintenance at the first manifestation of distress caused the premature pavement failures as a result of an improper base material

Construction Vibration Investigation

The project consisted of two residential structures, eight- and four-stories high, both supported by deep foundations with superstructures comprised of reinforced concrete and CMU block. The building between the two structures was demolished and construction of a new building, as well as some roadway construction, commenced. CA was retained to investigate allegations that this construction caused vibration-induced damage in the two residential structures.  CA’s activities included performing a condition survey of the exterior and reviewing established literature regarding distress on structures due to vibrations resulting from construction activities. CA determined there was no technically justifiable evidence to support that any of the alleged distress at the residential structures was caused by or affected by ground vibrations resulting from the construction activities.

Cementitious Underlayment Deficiencies in Hospital Operating Rooms

CA investigated the quality of a cementitious underlayment installed as part of the finish out of the 11th and 12th floors of an existing 33-story hospital building. The elevated concrete structural slabs of these floors were covered with a variable thickness cementitious underlayment material, with the intent to achieve an adequate floor surface that would later receive final floor finishes such as tile or carpet. The owner observed that this underlayment exhibited an inconsistent appearance, variable color, a dusty/powdery surface, and a poor bond with the finished flooring. CA evaluated the underlayment and assessed the expected performance of the floor, specifically its integrity and ability to resist wear due to long-term loading from wheeled medical equipment. CA’s investigation included a walk-through, visual condition assessment, core sampling, petrographic examination, and bond pull-off testing. CA’s analysis resulted in the removal and replacement of the underlayment to ensure a quality long-term floor system in the operating rooms and associated support rooms.

Post-Tensioned Slab Blowout

CA investigated a large post-tensioning blowout which occurred during construction of a complicated, unique portion of a 30-story residential tower. CA’s investigation was focused on reviewing the design and construction of the Project, specifically the post-tensioned slabs, as well as documenting and analyzing the conditions and circumstances associated with the post-tensioning blowout and subsequent repair. CA determined that the structural design did not consider the complexity of the blowout location. No direction was provided regarding the anchorage placement with regard to the curved slab edge and the close proximity of the distributed and banded tendons. CA performed a finite element analysis which showed that the blowout location experienced overlapping bursting stresses from distributed tendons and the banded tendons. This, combined with restraint and an upward post-tensioning force, resulted in a localized region of amplified tensile stresses. These amplified stresses made the section susceptible to a post-tensioning blowout failure during construction. The repair of the blowout area incorporated numerous modifications as compared to the original design, including the relocation of the distributed tendons away from the banded tendon anchorages. During the repair, the blowout did not re-occur, confirming that the cause and/or contributing factors related to the design had been eliminated and addressed.