Soil samples are collected at various levels. The biggest advantage of this method is that soil strata can be inspected in their natural condition and samples (disturbed or undisturbed) can be conveniently taken. A typical trial pit is shown in Fig. 2.11.
FIG. 2.11. TRIAL PIT
The method is generally considered suitable for shallow depths, say upto 3 m. The cost of open excavation increases rapidly with depth. For greater depths and for excavation below ground water table, specially in pervious soils, measures for lateral support and ground water lowering becomes necessary.