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WHAT-WE-DO: Mull & Partner Ingenieurgesellschaft Hannover operates its own soil mechanics laboratory for analysing soil material in connection with subsoil investigations. The laboratory tests are used to assess and evaluate soil properties and to answer construction-related questions in the fields of geotechnics and water management. They form the basis for static soil calculations for construction planning and modelling for dewatering.
The in-house laboratory allows for particularly time and cost-optimised project management, as the soil samples taken in the field usually arrive in the laboratory and can be processed on the same day. In addition, retained samples are stored for at least 6 months so that any questions that arise can be answered flexibly.
The following tests are carried out by M&P:
- Determination of particle size distribution according to DIN 18123 by sieve analyses and combined sieve/slurry analyses
Depending on the particle size, sieve (d ≥ 63 µm), slurry (d < 63 µm) or combined analyses are carried out to determine the particle size distribution.
In sieve analysis, the sample dried at 105 °C is placed in a sieve tower with mesh sizes decreasing from top to bottom. After separation into individual fractions using a vibrator, the residue on the individual sieves is weighed to determine the particle size distribution.
In slurry analysis, the soil sample is stirred in a cylinder with water to form a suspension. A dispersing agent is added to prevent coagulation. A hydrometer is then immersed free-floating. The hydrometer is read after 30 seconds, then after 1, 2, 5, 15 and 45 minutes and after 2, 6 and 24 hours. The temperature is measured at the same time. The results are analysed using the nomogram of Stokes' law according to Casagrande.
For a combined sieve/sludge analysis, the entire soil sample is first separated into fine and coarse fractions by wet sieving. This is followed by a separate sieve or sludge analysis as described.
- Determination of the water content according to DIN 18121
The water content is calculated from the ratio of the mass of water present in the soil mw to the mass of the dry sample md determined. w = mw / md [The soil sample is weighed both before and after drying in the oven at 105 °C, the difference gives the water present in the soil mw.
- Determination of the consistency limits according to Atterberg or DIN 18122
The state form (consistency) of cohesive soils depends on the water content w of the soil. With decreasing water content, a cohesive soil changes from a liquid to a plastic, then to a semi-solid and finally to a solid state. These transitions have been defined by Atterberg and are called: yield point wL, roll-out limit wP and shrinkage limit wS. The Casagrande yield point device with furrow opener is used for the respective tests.
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