In most cases, the evaluation consists of opening trenches at regular distances to enable the archaeologist to estimate whether there are archaeological structures or not. The number and the size of the trenches opened are dependent on the area to be tested. As a general rule, a trench from 1.30m to 3m wide (corresponding to the width of the bucket of the digger), of variable length is opened. When archaeological deposits appear, it is sometimes useful to widen the trenches so as to better understand how the structures are organised (e.g. post holes forming a building). The depth depends on the level at which the deposits are buried, which can vary from 30cm below the present surface level to more that 4m, in particular for earlier periods.
The trench is dug as follows: an archaeologist stands in front of the bucket of the hydraulic digger at a safe distance and guides the driver. The soil is removed horizontally until the deposits are reached. The different colours or textures which could correspond to wall foundations, rubbish pits, graves, etc. are noted Partial excavation helps to date the human occupation of the site and verify the state of conservation and nature of the deposits. The archaeologist locates the structures on a plan. Several different periods can be present on the same site.