OPEN EXCAVATION (OPEN TRIAL PITS) - SITE EXPLORATION.

Trial pits are tho cheapest method of exploration in shallow deposits, since these can be used in all types of soils. In this method, pits are excavated at the site, exposing the sub-soil surface thoroughly.

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.