Earthworks and Foundation Structures. Methods to Improve the Load-bearing Capacity of the Site

Technical investigations of the ground should provide sufficient data for efficient construction planning and execution of the building work. Depending on the construction type, the ground is evaluated either as building (for foundations), or as building material (for earth works). Building structures are planned (if legally possible and with local approval), according to expert assessment (i.e. avoiding marshy areas, landfill, etc.).

The building construction type and the prevailing ground conditions affect the design of the foundations, e.g. individual footings – (7), strip foundations - (8), raft foundations - (9), or if the ground strata are only able to carry the load structure at greater depth, pile foundations – (10). Pressure distribution must not extend over 45° in masonry, or 60° in concrete. Masonry foundations are seldom used, due to high cost.

Unreinforced concrete foundations are used when the load spreading area is relatively small, e.g. for smaller building structures. Steel reinforced concrete foundations are used for larger spans and at higher ground compression; they contain reinforcement to withstand the tensile loads (11) + (12). Reinforced, instead of mass, concrete is used to reduce foundation height, weight and excavation depth. For flexible joints and near to existing structures or boundaries – (13). For cross-sections of raft foundations (14) - used when load-bearing capacity is lower, or if individual footings or strip foundations are inadequate for the imposed load. Frost-free depth for base > 0.80m, for engineering structures 1.0-1.5m deep.

Methods to improve the load-bearing capacity of the site. Vibratory pressure process, with vibrator, compact in a radius of 2.3-3m; separation of the vibration cores approx. 1.5m; the area is thus filled; improvement depends on the granulation and original strata. Ground compression piles: core is filled up with aggregate of varied grain size without bonding agent. Solidification and compression of the ground: pressure injection of cement grout; not applicable to cohesive ground and ground which is aggressive to cement; only applicable in quartzous ground (gravel, sand and loose stone); injection of chemicals (silicic acid solution, calcium chloride); immediate and lasting petrifaction.

Building and Site Drainage. External underground drains are understood to be those which are laid outside the plan area of the building. Drains underneath cellar areas are taken as interior drains. Depending on topography, the depths required are 0.80m, 1.00m and 1.20m. In severe climates, measures must be taken to protect against frost.

Changes in direction of main drains must be constructed only with prefabricated bend fittings and no individual bend should be greater than 45°. If a junction of drains cannot be formed with prefabricated fittings, then a manhole must be constructed. Inaccessible double junctions are not permitted and a drain must not be reduced by connection into a narrower pipe in the direction of flow (with the exception of rainwater drainage outside buildings).