For a simple sloping system in Type C soil (and no engineering), the maximum allowable slope is approximately:

解析

Type C takes the flattest cut in the table, 1.5 horizontal to 1 vertical, about 34 degrees from horizontal, because it is the least stable classification - granular soil, submerged soil, or soil in a layer that dips into the excavation. Every wrong option is a real figure from the same table attached to the wrong soil and is therefore too steep to hold Type C: 1:1 is Type B, 3/4:1 is Type A, and 1/2:1 is the short-term exception Appendix B allows in Type A for excavations open 24 hours or less and 12 feet or less deep. Past 20 feet the table stops applying altogether and the system must be designed by a registered professional engineer.