Engineer: Jack’s wall was doomed to failure

“The integrity of the wall was tarnished at the time of construction. From Day One its integrity was compromised.”{{more}}

This was the response of Trinidadian civil engineer Kelvin Burgess, as he was crossed examined by attorney Samuel Commissiong at the Serious Offences Court on September 1, 2009.

Burgess, a key witness in the coroner’s inquest into the death of Patsy Bowman, revealed in court that many factors, including the structure of the wall, had contributed to its failure.

Patsy Bowman, 67, was killed on September 19, 2009, when the retaining wall surrounding the property owned by Alex Jack, of Ratho Mill, collapsed and crushed her in her car. The wall, construction of which began in 1994, collapsed after three days of continuous rain.

According to Burgess, additional problems impacting on the strength of the wall included the hydrologic conductivity (ability of soil to retain water) of the soil behind the wall, the thickness of the steel used to reinforce it and the drainage system employed.

Burgess stated that the stone masonry material used to build the wall was inappropriate as stone is “subject to high bending stresses”. The stone masonry material, which is a combination of stone and water, would not work as a solid homogenous material, he said, and would have been more susceptible to collapsing.

He added that using steel reinforcement with stone masonry, as used in the construction of Jack’s wall, would not completely ensure that a wall would stand strong.

“The idea that you can reinforce (stone masonry) material and expect it to act as a reinforced concrete section is a flawed concept to begin with,” he said.

Burgess added that a concrete wall would have held stronger as it is made of a number of materials that act together as one homogenous structure. The engineer also told the court that the steel reinforcement used was not enough to support a wall of such thickness.

The water-retaining capacity of the soil behind the wall also played a part in its collapse, he added. Burgess, who inspected the soil behind the collapsed segment, noted that the soil was a sandy material, which did not have the ability to retain large quantities of water. The heavy rainfall that occurred, combined with the low water-retaining capability and the deficient structure of the wall, caused it to become stressed, eventually leading to its failure.

The inquest was scheduled to be completed last Tuesday, but has now been extended until September 16, when civil engineer Glenford Stewart will be crossexamined. (OS)