5 Geotechnical investigation

5.1 General

5.1.1 The general investigation shall fulfil the requirements of EN 1997–1.

5.1.2 The geotechnical investigation report shall be available in time, to allow for reliable design and execution of the special geotechnical works (micropiles).

5.1.3 The geotechnical investigation shall be checked to see whether it is sufficient for the design and execution of the special geotechnical works (micropiles).

5.1.4 If the geotechnical investigations are not sufficient, a supplementary investigation shall be conducted.

5.2 Specific requirements

5.2.1 When determining the extent of geotechnical investigation, relevant experience which has been collected during the execution of comparable foundation works under similar conditions and/or at adjacent sites shall be taken into account.

NOTE Reference to relevant experience in this matter is acceptable if appropriate means of verification are taken (e.g. by penetration tests, pressuremeter or other tests).

5.2.2 The soil characteristics shall be determined by in situ tests and/or laboratory tests over the depth of the micropiles and to a depth beneath the base depending on the nature of the ground and on the type of the micropile (end bearing and/or friction bearing).

5.2.3 The geotechnical investigation shall demonstrate for end bearing micropiles that any competent foundation stratum is not immediately underlain by a soft stratum with a possibility of a punching failure or unacceptable settlements.

5.2.4 The following information, when relevant for the execution of micropiles, shall be given in the geotechnical investigation report:

a) piezometric levels of all water–tables of the soil and rock layers. Where appropriate, the piezometric levels in the various water–tables existing on the site should be monitored separately and over a sufficient period of time to estimate the highest piezometric levels which may occur during the installation of the micropiles. Particular attention shall be paid to artesian conditions and rapid underground water flows;
b) presence of coarse highly permeable soils or cavities (natural or artificial) which may cause sudden losses of drilling fluid and instability of the borehole, and thus may require special measures;
c) presence, strength and deformation characteristics of soft layers, such as very soft clay or peat, which may cause difficulties during execution or loading of micropiles (deformation or instability of the borehole, risk of buckling);
d) presence of cobbles and boulders or other underground obstructions which may cause difficulties for the installation and thus may require special methods or tools for penetration (passing through) or removal;
e) the level and the slope of rock surface, the thickness and extent of any existing weathered rock, the presence of fissures or cavities;

NOTE In some cases it may also be necessary to determine the strength or hardness of the rock.

f) chemical aggressiveness of groundwater, soil or rock that can affect the properties of grout, mortar or concrete and steel;
g) presence, extent, thickness and nature of contaminated soil or waste that can influence the disposal of the spoil generated and that may require special measures for the protection and safety of the work force;
h) degradation of soil or rock properties when in contact with water.