5 Fill, dewatering, ground improvement and reinforcement
(1)P The provisions in this Section shall apply where adequate ground conditions are achieved by:
- placing natural soil, crushed rock, blasted stone or certain waste products;
- treating ground;
- reinforcing ground.
NOTE 1 Situations where soil or granular material is placed for engineering purposes include:
- fills beneath foundations and ground slabs;
- backfill to excavations and retaining structures;
- general landfill including hydraulic fill, landscape mounds and spoil heaps;
- embankments, small dams and infrastructure.
NOTE 2 Dewatering of ground may be temporary or permanent.
NOTE 3 Ground, which is treated to improve its properties may be either natural ground or fill. The ground improvement may be either temporary or permanent.
5.2 Fundamental requirements
(1)P Fill and dewatered, improved or reinforced ground shall be capable of sustaining the actions arising from its function and from its environment.
(2)P These fundamental requirements shall also be satisfied for the ground on which the fill is placed.
5.3 Fill construction
(1)P When designing fill constructions it shall be considered that the adequacy of the fill depends on the following:
- good material handling properties,
- adequate engineering properties after compaction.
(2) Transport and placement of the fill should be considered in the design.
5.3.2 Selection of fill material
(1)P The criteria for specifying material as suitable for use as fill shall be based on achieving adequate strength, stiffness, durability and permeability after compaction. These criteria shall take account of the purpose of the fill and the requirements of any structure to be placed on it.
(2) Suitable fill materials may include most graded natural granular materials and certain waste products such as selected colliery waste and pulverised fuel ash. Some manufactured materials, such as light aggregate, may also be used in some circumstances. Some cohesive materials may be suitable but require particular care.
(3)P The following aspects shall be taken into account when specifying a fill material:
- resistance to crushing;
- strength of underlying ground;
- organic content;
- chemical aggression;
- pollution effects;
- susceptibility to volume changes (swelling clays and collapsible materials);
- low temperature and frost susceptibility;
- resistance to weathering;
- effect of excavation, transportation and placement;
- possibility of cementation occurring after placement (e.g. blast furnace slags).
(4) If local materials in their natural state are not suitable for use as fill, it can be necessary to adopt one of the following procedures:
- adjust the water content;
- mix with cement, lime or other materials;
- crush, sieve or wash;
- protect with appropriate material;
- use drainage layers.
(5) Frozen, expansive or soluble soils should not normally be used as fill material.
(6)P When the selected material contains potentially aggressive or polluting chemicals, adequate provisions shall be adopted to prevent it from attacking structures or services or polluting the ground-water. Such materials shall only be used in large amounts in permanently monitored locations.
(7)P In case of doubt, the fill material shall be tested at source to ensure that it is suitable for its intended purpose. The type, number and frequency of the tests shall be selected according to the type and heterogeneity of the material and the nature of the project.
(8) In Geotechnical Category 1, inspection of the material may often be sufficient.
(9)P Material used for fill with specified severe requirements regarding bearing resistance, settlement and stability shall not contain matter such as snow, ice or peat in any significant amount.
(10) In fills with no specified requirements for bearing resistance, settlement or stability, the fill material may contain small amounts of snow, ice or peat.