Construction surveying: setting out, site support, monitoring

Engineering surveying supports the planning, construction and operation of buildings and installations, mostly for larger projects in building construction, civil engineering and hydraulic engineering. It includes the site control network for position and height, setting out, surveys of existing conditions, monitoring of structures and surveys of profiles, longitudinal and cross sections. Typical are high accuracy requirements under difficult conditions.

Whenever construction work can cause movement in the ground or in neighbouring structures. For example, excavations next to existing buildings, lowering of groundwater, piling and vibration work, and retaining walls and bridges. We measure at agreed intervals and compare with an initial measurement made before construction starts. The structural engineer and the soil expert set the permitted values and the reporting route. We report any exceedance immediately.

The required accuracy follows from the task and from the permitted tolerances of the structure, in building construction for example from DIN 18202. Where the highest precision is required, we work with precise levelling and our own control networks.

Before the first dig, we document the condition of neighbouring buildings, roads and installations. We make an initial height measurement and take photos of any existing cracks. If there is a dispute later about settlement or cracks, there is a reliable basis for comparison. This protects clients and construction companies alike against unfounded claims.

Usually the official position and height reference system, connected via the satellite positioning service or via official control points. For larger projects we also set up a separate site control network for position and height. It lies outside the area affected by the construction work and is checked regularly. Note that distances from official UTM coordinates are slightly distorted compared with reality. We take this into account when setting out.

The setting-out plan (Absteckungsplan) documents the setting out: which points and axes were set out, how they are marked on site and which height reference points apply. We check the setting out and hand the plan to the client and the construction company. It is the common basis if questions about position come up later.

We supply the site control network for position and height, the connection to the official control point network, all kinds of setting out, monitoring of structures, deformation and settlement measurements with a report, and surveys of profiles, longitudinal and cross sections.

A digital terrain model (DGM) describes the ground surface without buildings and without plants. It consists of height points and of break lines such as slopes, ditches and kerbs. From it you can derive contour lines, profiles and earthwork volumes, for example for development plans, route planning and drainage.

For a first assessment and for large areas it is usually enough. For detailed design, drainage or a volume calculation it is usually too coarse. Kerbs, slope edges and ditches disappear in the grid, and the data can be several years old. We check how current it is and add a survey on site where needed.

Depending on size and accuracy, we measure with GNSS and total station, fly over the area with a drone or record it by laser scanning. Often we combine these methods. What matters is less the number of points than a clean record of the break lines. Without them, the model smooths out reality and the volumes are wrong.

The standard is the official height system DHHN2016 with heights above standard height zero (Normalhöhennull), and for position the system ETRS89/UTM in zone 33. Older documents in Mecklenburg-Vorpommern often still contain heights from earlier systems. If old and new data are mixed without noticing, errors in the range of decimetres occur. So we check the height reference before we use other people's data and convert it into the official system.

Common are DXF and DWG, REB data types and simple point lists. Which format makes sense depends on the software of your planner or specialist office. We agree this in advance and supply a test file if needed. You usually also receive a site plan as PDF showing the surveyed ground.

We supply the ground survey on site, the finished terrain model with break lines, contour lines and profiles, and a site plan as PDF. It shows the surveyed ground and states date, reference system and accuracy.

The basis is two terrain models that are compared, for example the original ground and the bottom of the excavation. With surveys in between, soil areas with different contamination can also be calculated separately. For excavations and stockpiles we calculate by area with prisms, for roads, ditches and other linear structures via cross sections. The methods follow the rules for electronic billing of construction work (REB), so both parties to the contract can follow the result.

Once the topsoil has been removed, the original condition can no longer be reconstructed. Without this initial survey, only an estimate remains at the end, and this is where most disputes about quantities come from. Ideally the appointment takes place together with the client and the construction company.

The volume calculated from the terrain model is the undisturbed, solid soil. When it is dug out, the soil loosens a lot depending on its type, so the volume transported is larger than the volume calculated. Billing is usually based on the excavated volume in solid state. But your construction contract always decides.

For large, open areas and for stockpiles, the drone is fast and gives a complete picture. For small excavations, under plants and where single points matter, measurement with GNSS and total station is more accurate. We often combine both and check the result.

This includes the survey data with date and height reference, the calculation method used, the calculation record and plans of the cut and fill areas. For construction contracts under VOB, the client requires billing that can be checked, with the quantity calculations and drawings. Survey sheets signed by both sides save discussions later.

We supply the survey of the original ground before construction starts, interim and final surveys, the volume calculation according to REB, plans and records for billing, and the survey of stockpiles by drone.