„SEBRO – Strukturempflindliche Böden Rosenheim“

Civil engineers are faced with limitations using conventional methods in muddy basin sediments, which are frequently encountered in the lake regions of Southern Bavaria. Through unique field experiments and novel modeling approaches, essential foundations for a sustainable design of foundations in these particular soils are to be established.

Structurally sensitive fine-grained lacustrine soils, colloquially known as lacustrine clays, exhibit the peculiarity of significantly losing their already relatively low shear strength when disturbed from their natural state. Compared to other soft soils, lacustrine clays are particularly challenging: this applies both to exploration and soil mechanical characterization, as well as to the load-carrying behavior of foundations, which is significantly influenced by the intensity of construction-related interference.

Common field and laboratory methods, as well as modeling approaches that form the basis of foundation design, reach their limits. The functionality of foundation systems successfully applied in soft soils with high structural sensitivity cannot be assumed. This complicates the implementation of construction projects and can even call their feasibility into question.

In the past, in Southern Bavaria, the construction use of areas with such high ground construction risk could often be avoided. However, the demand for infrastructure for mobility, as well as the development of sites for commercial and residential use, makes sustainable utilization of all available areas, considering ecological, economic, and social aspects, unavoidable in the future.

On a test site of around 6,000 m² in Kolbermoor near Rosenheim, large-scale load tests will be carried out on twelve foundation systems and an additional shallow foundation which is unique in terms of design and scope worldwide. The results of the load tests and the accompanying advanced field and laboratory tests are used to validate novel modeling approaches. Subsequently, the efficiency and sustainability of the considered foundation methods concerning region-specific soils will be evaluated. The ecological footprint will be considered from the production to the possible dismantling of the foundation.

Current Status – May/June 2026:

Building on the geosynthetic tests, individual element and group loading tests are being conducted in parallel, each with at least two test fields. The dead loads and 5 m x 5 m mobile foundations are being loaded step-by-step by BKL  through loading, unloading, and reloading phases of the foundations, with a maximum of approximately 640 tons each. For all 12+1 test fields (including one test field for lifting injections to investigate remediation options in case of serviceability issues), a total of approximately 4,000 running meters of vertical drains were installed in advance by Menard.

The first two test fields—shallow foundations (TUM Geotechnical Center) and the mill-mix method (Kemroc)—were already subjected to gradual loading in 2024 over a period of approximately six months each. The subsequent unloading cycle coincides with the loading of the next test fields. The loading cycles for the subsequent test fields—the Ductile Driven Pile system (Kurt Motz with Tiroler Rohre) and the Atlas pile system (Porr Group, specializing in deep foundation engineering)—have also been completed. The systems—CSV dry mortar stabilization columns (Laumer company) and CMC® wet mortar columns (Menard)—are in the unloading phase and are nearing completion, with each now loaded only by the dead load of the foundation slabs, approximately 32 tons. 

The subsequent test fields—the TITAN micropile system (Laumer) and the Centrum precast reinforced concrete pile (Aarsleff-Spezialtiefbau)  —were constructed by July 2025 and are currently in the unloading phase, while the subsequent procedures—vibro-compaction with a vibrating rammer and concrete rammed columns—by Keller Grundbau are being tested in stages up to the maximum load of approximately 640 tons of dead load (average base pressure approximately 250 kPa).

Starting in January 2026, the construction-induced effects on the test sections under load were investigated using the following methods:

Vibro-compaction with a vibrating hammer ((Keller Grundbau company) – January/February 2026

Concrete pile columns ((Keller Grundbau company) – January/February 2026

Finally, in Q3 2026, the last test fields will be constructed using the following methods and subsequently subjected to load tests:

vibratory compaction with a vibratory pipe and additional vibrator (Bauer Spezialtiefbau company)

Hybridinjection® (Uretek) 

Measurement Technology for Each Test Field – With the support of cooperation partners Glötzl and Solexperts:

• Extensometer in several depth steps
• Sliding deformeter
• Inclinometers for measuring horizontal deformations and for seismic cross-hole tests
• Earth pressure and pore water pressure sensors at several depth steps
• Hose level sensors for settlement and inclination measurement, both below and at the foundation edges
• Geodetic measuring bolts
• Surface seismics
• Concrete deformation device
• Fiber optics DFOS (distributed fiber optic sensors)

Site Investigation – Conducted and supported by cooperation partners Geo-Bohrtechnik and Mull & Partner:

For more than two years, various geotechnical investigation campaigns have been continuously conducted and evaluated. The field tests (in-situ) include, among other things:

• Plate loading tests (static & dynamic)
• Pressure soundings with measurement of pore water pressure (CPTu)
• Seismic pressure soundings (SCPT)
• Vane shear tests
• Cross-hole tests
• Self-boring pressure meter (Novel test in Germany)
• Menard Pressureometer
• Marchetti Medusa / SDMT
• Tomographic measurement

These field trials are accompanied by extensive and novel laboratory experiments (Bender Element, P-Rat, etc.) in addition to index trials.

Within the framework of the research project, theses are currently being prepared on numerical simulations of settlement prediction, on the classification of marine clay using advanced laboratory experiments, and on the sustainability assessment of foundation systems.

Current Status – May / June 2026:

• Vibro compaction with vibratory pipe and vibratory attachment ( Bauer Spezialtiefbau company) - individual load tests from approximately August 2026
• Hybridinjection® ( Uretek ) - Individual load tests from approximately August 2026

Preparations and implementation:

Based on two preliminary tensile tests conducted independently on the test site using ductile driven piles from Kurt Motz with Tiroler Rohre , the load-bearing capacities of the foundation variants implemented in the research project were estimated for their individual load tests. These are subjected to individual element load tests at conventional intervals after construction, in parallel with the group load tests. For each method, a total of three individual load tests are performed, some with varying boundary conditions of the manufacturing parameters, and loaded to the ultimate limit state (ULS). 

• Atlas pile (Porr Spezialtiefbau ) - Individual load tests completed October/November 2024
• Ductile iron driven pile ( Kurt Motz company with Tiroler Rohre ) - individual load tests completed October/November 2024
• Dry mortar stabilization columns CSV ( Laumer company ) - individual load tests completed April 2025
• Wet mortar columns CMC® ( Menard ) - Individual load tests completed April/May 2025
• Micropile TITAN ( Ischebeck company ) - Individual load tests completed September 2025
• Centrum - precast reinforced concrete pile ( Aarsleff Special Foundations ) - individual load tests completed December 2025
• Concrete pile columns (Keller Grundbau company) - Individual load tests completed in April 2026

Test field and preparation – with the support of partners Zosseder und Naue

Prior to the load tests, geosynthetic tests were carried out in cooperation with the company Naue using trucks with stable tracks. Among other things, these serve to specifically examine the dimensioning of reinforced base layers.

• Geosynthetic overrun tests completed
• Geosynthetic tests to investigate the effects of manufacturing-induced dynamic stress caused by construction equipment completed
• Geosynthetic tests to investigate reinforced base layers under quasi-static crane loads - t.b.d.