Construction pit
The construction pit is the space that is dug below the surface of the site, for example to found a structure , to build traffic systems or to lay supply lines . In addition to the structure being built, the base of the excavation must accommodate the required lateral working space all around. The work area is surrounded by the construction pit enclosure, which can be designed as an embankment or as a construction pit sheeting. At the upper edge, the construction pit protection prevents accidental falls into the pit.
The water conditions are also decisive for the formation of a construction pit. The type of construction pit enclosure, the formation of the construction pit base and the water retention and drainage are significantly influenced by the groundwater or strata water .
Construction pit enclosure
working space
Depending on the selected construction pit enclosure, it must be ensured that there is a clear working space of at least 0.5 meters between the slope toe and the outside of the building being built, or a clear working space of at least 0.6 meters between the edge of the building pit lining and the outside of the building being built must be present. Any existing formwork , scaffolding or the like must not restrict this work area. If the room conditions are favorable and laborious work is to be expected on the outside wall of the building, e.g. the application of a thick bitumen coating , a working space of 1.0 to 1.5 meters is recommended.
Sloped excavation
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If there is sufficient space, the side surfaces of the construction pit can be bevelled to form an embankment . If large amounts of slope or surface water are not expected to run in, they do not need any further protection.
The embankment must be created in accordance with the requirements of DIN 4124 and the regulations of the professional association. In particular, the angle of repose must be adapted to the soil and water conditions. A 0.6 meter wide strip of loads (building materials or excavated material) must be kept free above the embankment in order to prevent the embankment edge from slipping.
In the case of high excavation slopes, berms are to be provided as steps. They serve to catch material that slips down and should be put on after every 3 meters of altitude. If they are only used for walking, a width of 60 cm or more is sufficient, otherwise 1.5 meters are required.
If there is no separate proof of stability, the following slope angles apply:
- for non-cohesive or soft cohesive soils 45 °
- for stiff or semi-firm cohesive soils 60 °
- on rocky soils 80 °
The stability of the slope must be proven in accordance with DIN 4124 if:
- the embankment is higher than 5.0 meters
- the abovementioned slope angles should be exceeded
- difficult soil and water conditions exist
- existing structures could be endangered
- the upper edge of the embankment is loaded with loads greater than 10 kN / m²
- the surface of the terrain outside the excavation is more than 1:10 inclined
- the top edge of the embankment is driven on with vehicles at a distance of less than one meter.
Construction pit lining
If there is limited space, such as in a vacant lot , or if the soil and water conditions do not allow a sloped construction pit, a construction pit must be built . It prevents the pit walls from collapsing due to soil sliding in or penetrating water, as well as the subsidence of neighboring areas. The execution and stability of the shoring are the subject constructional he evidence and regulated by applicable norms.
According to their flexibility, a distinction is made:
- Soft types of shoring that deform due to the earth pressure created during excavation (e.g. girder pile shoring and sheet pile walls ) but are usually cheaper
- Rigid, low-deformation shoring types (e.g. bored pile walls and diaphragm walls ), which are to be used in surroundings that are sensitive to settlement (neighboring buildings, sensitive traffic routes such as railways).
According to reusability, the following are decided:
- temporary installed, which, after being used again dismantled or out of the building to be removed
- permanent structures that remain in function after completion of the construction project and possibly become part of a structure, e.g. B. as a retaining wall , slope protection, embankment wall or cut-off wall .
In contrast to trench sheeting , in which the securing walls running next to one another can usually be supported against each other, the excavation sheeting must be secured in a different way:
- Back anchoring through ground anchors
- Reinforcements to the base of the excavation or across corners
- Restraint in the ground
- Lid construction with mutual support of the retaining walls, the z. B. is used in tunneling .
Excavation base
The base of the excavation forms the lower end of the excavation and serves as a foundation level for the structure to be constructed. Certain requirements are placed on them in terms of evenness and load-bearing capacity. There must also be sufficient security against ground breakage or sole breakage. It must be protected from being soaked through or loosening, as otherwise damage to the building may result later from subsidence. If the excavation is embedded in the groundwater, the foundation of the excavation can be sealed with injection layers or underwater concrete floors.
Excavation
Excavation is a part of earthworks and is usually carried out with excavators , wheel loaders and crawler loaders . First of all, the topsoil ( topsoil ) must be removed and stored separately.
For the computational determination of the excavation volume, the procurement and contract regulations for construction services (VOB / B) allow the use of approximation methods. A method that leads to relatively precise results is the prism method. This method is described in the regulations for electronic construction accounting (REB) No. 22.013 of the Joint Committee for Electronics in Construction (GAEB).
See also
Norms and standards
- DIN 4124 - Construction pits and trenches; Embankments, shoring, working area widths
- DIN 4084 - subsoil; Land and slope failure calculations
- Recommendations of the excavation work group (EAB)
Individual evidence
- ^ Rudolf Floss: ZTVE - Commentary with compendium earthworks and rock construction . Kirschbaum Verlag, Bonn 1997, ISBN 3-7812-1430-3 , p. 304 .
- ↑ Balder Batran: Basic knowledge of construction . Handwerk und Technik Verlag, Stuttgart 2003, ISBN 3-582-03500-X , p. 49 .
- ↑ a b Konrad Zilch: Handbook for civil engineers . Springer Verlag, Berlin 2002, ISBN 3-540-65760-6 , pp. Chapter 4 - page 120 .
