This type of shovel is often referred to as a "clean out" shovel as well as a trench shovel. This is because they are designed to help you scoop up any loose soil in your trench after it has been cut. The cut can be completed by hand or by using a powered trencher.
The most important thing to remember is that the trench shovel is not designed to cut down into the soil. If you look at the design of this type of shovel, you can see that the blade is not really wide enough for you to get your foot on it.
This, in turn, means you will not be able to put enough downward pressure on the shovel for it to cut through anything but loose soil. However, the narrow design makes it the perfect shovel for cleaning out trenches that are both narrow and deep.
With this in mind, you may want to consider using a tile or drain spade to cut the sides of the trench and loosen the soil before using a trenching shovel to remove the soil and to finish shaping the trench.