I am sure University of Washington Professor Kamran M. Nemati would label this a temporary structure of the earth restraining type. It is placed in a trench which houses a city water main with the primary function of preventing a suffocating, life ending, cave in.
The picture you see below is a protective system seen in many trenching and excavation construction operations. It is designed to hold back the earth and prevent collapse. Despite the numerous OSHA enforced safety standards, hazards including falls, falling loads, hazardous atmospheres, and incidents involving mobile equipment take the lives of many construction workers annually. Trench collapses are responsible for more fatalities than any of the items in the list. A young man, home for summer break from college, was buried alive in trench apparently because of trench cave-in caused by heavy equipment near edge of trench. His death was an agonizing one as his coworkers could hear his muffled screams for help, but had no way of digging him out prior to him asphyxiating on soil.
In some cases the worker will move outside the protection of the shoring system which are like the temporary walls with bracing you see in the picture below. This is what happened in the 11 foot deep trench that interred Michael Casey Holland of Portland, Oregon. RIP
The pic below shows 5-6 foot deep trench along Union Avenue in Roswell,NM. That plywood does not look strong enough to stop a cave-in to me.