4.3 Checking ground conditions
4.3.1 Soil and rock
(1)P The descriptions and geotechnical properties of the soils and rocks in or on which the structure is founded or located shall be checked during construction.
(2) For Geotechnical Category 1, the descriptions of the soils and rocks should be checked by:
- inspecting the site;
- determining the types of soil and rock within the zone of influence of the structure;
- recording descriptions of the soil and rock exposed in excavations.
(3) For Geotechnical Category 2, the geotechnical properties of the soil or rock in or on which the structure is founded or located should also be checked. Additional site investigation may be needed. Representative samples should be recovered and tested to determine the index properties, strength and deformability.
(4) For Geotechnical Category 3, additional requirements should include further investigations and examination of details of the ground or fill conditions, which may have important consequences for the design.
(5) Indirect evidence of the geotechnical properties of the ground (for example, from pile driving records) should be recorded and used to assist in interpreting the ground conditions.
(6)P Deviations from the ground type and properties assumed in the design shall be reported without delay.
NOTE Normally these deviations are reported to the designer.
(7)P The principles used in design shall be checked to ensure that they are appropriate for the geotechnical features of the ground, which are encountered.
(1)P As appropriate, the ground-water levels, pore-water pressures and ground-water chemistry encountered during execution shall be compared with those assumed in the design.
(2) More thorough checks should be performed for sites on which significant variations of ground type and permeability are known or believed to exist.
(3) For Geotechnical Category 1, checks should usually be based on previously documented experience in the area or on indirect evidence.
(4) For Geotechnical Categories 2 and 3, direct observations should normally be made of the ground-water conditions if these greatly affect either the method of construction or the performance of the structure.
(5) Ground-water flow characteristics and the pore-water pressure regime should be obtained by means of piezometers, which preferably should be installed before the start of construction operations. It may sometimes be necessary to install piezometers at large distances from the site as part of the monitoring system.
(6) If pore-water pressure changes occur during construction that may affect the performance of the structure, pore-water pressures should be monitored until construction is complete or until the pore-water pressures have dissipated to safe values.
(7) For structures below ground-water level, which may be subject to uplift, pore-water pressures should be monitored until the weight of the structure is sufficient to rule out the possibility of uplift.
(8) Chemical analysis of mobile water should be performed when any part of the permanent or temporary works may be significantly affected by chemical attack.
(9)P The effect of construction operations (including processes such as dewatering, grouting and tunnelling) on the ground-water regime shall be checked.
(10)P Deviations from the ground-water features assumed in the design shall be reported without delay.
(11)P The principles used in design shall be checked to ensure that they are appropriate for the ground-water features, which are encountered.