engineering assignment

BACKGROUND

Trench digging is one of the oldest types of construction work documented in history. Prior to World War II, trenches were dug by hand. As workers dug trenches deeper, the sides of the trench had to be shored, or supported, to keep the walls of the trench from collapsing. Following the war, innovations were made in cable backhoes, and trench digging disappeared as an established profession. By the 1950's, hydraulic backhoes were developed, making it possible to rapidly dig very deep trenches. As a result of backhoe innovations, and because there were no workers inside the trenches during digging, trench walls were no longer shored.

All trenches have what is known as a stand-up time. The stand-up time is the time that elapses from the time the trench is dug until the trench walls start collapsing. Stand-up time is dependent on many factors, including soil type, water content, trench depth, weather conditions, and whether or not the soil has been previously disturbed. Stand-up times can be as short as zero seconds or as long as several months, and are difficult to predict. Before trenches are dug, someone can take soil samples as a means of estimating stand-up time; however, soil conditions can be dramatically disparate only a few feet from where the soil sample was taken.

After a trench is dug, workers go down into the trench, performing whatever work is necessary, such as laying pipe or telephone lines, welding pipe, or installing valves. If the walls of the trench are not supported, there is the possibility that the walls will collapse and trap the workers in the trench (see view of trench contained on the following page). Historically, there have been between 100 and 300 people killed in the United States every year due to trench collapses. The state of Texas usually leads the nation in this statistic.

A trench box (also called a trench shield) may be placed in the trench to prevent trench failures from injuring workers. A trench box consists of two large plates, usually made of steel, which are parallel to the walls of the trench, and horizontal cross-members that hold the two plates apart. The lower edge of the box rests on the bottom of the trench, and the top edge extends above the top of the trench. The workers stay between the plates of the trench box, so that if the wall of the trench collapses, the trench box will stop the dirt from falling on the workers. As work progresses, the trench box is pulled along the trench with a backhoe.

Due to the added expense of using the trench box, many contractors are reluctant to use them. They know that if a worker is killed or injured in a trench wall collapse, Workman's Compensation will cover all medical expenses and reimburse the families of the deceased workers. The contractors cannot be sued civilly for negligence or wrongful death by the works or their families.

When a construction project requires a large excavation, such as digging the foundation for a tall building, the support structure for the excavated walls is specified in the plans. The main problem involving nonuse of trench boxes occurs in cities, when water or sewer lines are being installed or repaired. The engineer usually does not specify the support structure for the trench on the plans, but leaves that to the contractor.

SPECIFIC STATUTORY AND REGULATORY LAW

In September 1987, a statute was enacted in Texas that required the following: plans for city projects had to include the support structure on the plans, the support structure (or trench box) had to be included in the bid for the project, and the contractor had to install the trench box in the trench. In 1987, before the bill was passed, 18 people died in Texas due to trench wall collapses. In 1988, only two people were killed, and both of these deaths were not the result of a trench box inadequacy. Over the years, the success of this statute in preventing death and serious injury in trench-related accidents has become widely known in the geotechnical and soils engineering fields.

California does NOT have a statute similar to the one in Texas.

Under federal law applicable to all states, plans are only required to show trench support on the plans, not the actual design of the support system itself. It is up to the contractor to provide a suitable support system for the trench. The OSHA regulation gives the following four ways of providing for proper trench support:

1. Slope the sides of the trench to a specified angle, thus eliminating the need for all support.

2. Look at the soil and determine the type of support required from the tables provided in the OSHA regulation.

3. Hire an engineer to design a suitable support system.

4. Go to a trench wall manufacturer and use their tables for determining the proper support system.

FACTS

The contractor, Cal Trons Corporation, followed the OSHA regulation by hiring Arthur Haverley, a young soils engineer, to design a suitable support system. Haverley relied on the geotechnical report prepared by Mega Engineers from 1998 when the sewer line was first installed. The Mega report concluded that soil collapse in this sector was highly unlikely and did not recommend any specific form of trench support. No trench support was used at the time of the original installation of the pipe, because the installation was entirely done by mechanical equipment and the only time anyone was in the trench was when a worker in a harness was lowered into the trench to check the fittings. However, information about the installation method used was not contained in the Mega report. Haverley advised the contractor that no specific trench support was required under the circumstances. Cal Trons therefore chose and used the least expensive, movable small area trench support system made by Dirtco, Inc.

On April 1, 2005, Uka Maku, an entrepreneur, was buried alive when a narrow trench that was excavated eight feet deep with a backhoe to repair a sewer line, suddenly collapsed on him. By the time the soil was cleared, he was dead. Maku jumped into the trench to retrieve critically important notes on a new cell phone (the iPhoney) designed to compete with Apple that blew out of his hands by a sudden gust of wind. The Dirtco trench support was two feet to the right of where Maku was killed. Cal Trons had posted a sign “DANGER – OPEN TRENCH” and completely fenced off the work area when workers were not present.

Maku’s wife sues Haverley for professional negligence and Cal Trons for negligence for Maku’s death. Cal Trons is dismissed from the case on a motion for summary judgment. Plaintiff’s EGR 4050: Role of Design Professionals in Society 3/3 EGR 4050 expert witness, Sue Perior, testifies that Haverley should have conducted a new soils analysis and then recommended and designed a trench box appropriate for the soil. Haverley’s expert, Dee Nye, counters that a trench box was not required under California law and that under federal law a suitable system can mean that no system is actually required under the circumstances. Plaintiffs’ expert rebuts by testifying that the OSHA regulation presumes that some form of trench support is always required even if a specific type is not and that any soils engineer must consider the statute. Nye rebuts by saying that there was a trench support system chosen by the contractor and that the statute applies only to the contractor.

The jury will receive the following California Bench Approved Jury Instruction (BAJI, 1986) from the judge regarding the standard of care:

“In performing professional services for a client, a design engineer has the duty to have that degree of learning and skill ordinarily possessed by reputable design engineer in the same field of expertise practicing in the same or similar locality and under similar circumstances. It is the design engineer's further duty to use the care and skill ordinarily used in like cases by reputable members of the soils engineering profession practicing in the same or similar locality under similar circumstances, and to use reasonable diligence and the soil engineer's best judgment in the exercise of professional skill and in the application of learning, in an effort to accomplish the purpose for which the soil engineer was employed.”

The jury is further instructed that a failure to fulfill any legal duty is negligence if causation (both actual and legal) can be established between a breach of the legal duty and the injury claimed. Actual cause and legal (proximate) cause are as described in your notes.