PROBLEMS - Hydrogeology: Objectives, Methods, Applications - page 336

A survey was undertaken of the area around residence A, with the help
of a penetrometer (soil engineering apparatus measuring the resistance of
the soil: a weight strikes a vertical rod equipped with a calibrated point, and
the number of strikes needed per unit of length to sink the rod is counted).
This investigation gave the following results (see table):

Table 9 Results of the penetrometer survey.

Depth
in cm

0-20 20-40 40-60 60-80 80-100 100-120 120-140 140-160 160-180

S1 1 1 9 45 60 no

passage

S2 1 1 2 10 24 20 42 72 120 no

passage

S3 1 1 2 19 70 89 92

S4 2 3 1 3 24 36 98

The geologist then studied the area and made the following observations
(Figure 11).
The two residences are built on andesite. Residence A is old, with
superfi cial foundations. It rests on an andesite weathering mantle. Uphill,
the residence is protected by a drain, directing groundwater towards an
old infi ltration well. This well also collects part of the water drained from
the rooftops.

Figure 11 Schematic cross-section of the two residences.

Residence B is founded on piles driven into the andesitic bedrock.
Downhill, an old well contains water. The construction required the creation
of a 2 m talus along the property line. This talus was reinforced with a
concrete wall described in Figure 12.