Final answer:
The claim that tension cracks are rarely a sign of imminent trench failure is false. Tension cracks can signify soil instability and potential trench collapse, much like how mudcracks and thermal stress illustrate the significant effects of tension on structures.
Step-by-step explanation:
The statement that tension cracks are rarely a sign of imminent trench failure is Option 2: False. Tension is indeed the result of opposite forces that pull each point of a connector apart in a direction parallel to the length of the connector, leading to various types of structural responses, including the potential for failure. In the context of a trench, the appearance of tension cracks can indicate that the soil is beginning to pull apart, which is a sign of instability. Similar to mudcracks that are wider at the top, tension cracks in the soil around a trench can indicate that the upper parts are moving, which may lead to a collapse. Factors like thermal stress show the profound effects tension can have on materials, demonstrating that such forces and pressures need to be carefully considered to ensure the integrity of structures.