Leon A. van Paassen

Microbial Carbonate Precipitation as a Soil Improvement Technique

In order to evaluate MCP as a soil strengthening process, a five meter sand column was treated with bacteria and reagents under conditions that were realistic for field applications. The injection and reaction parameters were monitored during the process and both bacteria and process reagents could be injected over the full column length at low pressures (hydraulic gradient < 1; a flow rate of approximately 7 m/day) without resulting in clogging of the material. After treatment, the column was subjected to mechanical testing, which indicated a significant improvement of strength and stiffness over several meters. Calcium carbonate was precipitated over the entire five meter treatment length. Improvement of the load bearing capacity of the soil without making the soil impermeable to fluids was shown with microbial carbonate precipitation, and this is a unique property compared to alternative soil treatment methods that are currently available for use in the subsurface.

Quantifying Biomediated Ground Improvement by Ureolysis: Large-Scale Biogrout Experiment

Biogrouting is a biological ground improvement method, in which microorganisms are used to induce carbonate precipitation in the subsurface in order to increase the strength and stiffness of granular soils. In this paper the results of a large-scale experiment ( 100  m3 ) are presented, in which the feasibility of biogrouting as a ground improvement method is investigated using techniques and equipment similar to those used in potential applications. In situ geophysical measurements were used to monitor the biogrouting process during treatment and indicated that the stiffness had increased significantly after one day of treatment. The results of unconfined compressive strength tests on samples which were excavated after treatment were used to assess the distribution of mechanical properties throughout the cemented sand body, which correlated quite well with the results of the in situ geophysical measurements. The stiffness increase could be quantified as a function of the injected volume of grouting agent...

Use of Waste Streams and Microbes for in situ Transformation of Sand Into Sandstone

In the BioGrout process, sand is strengthened to sandstone with a strength, which is controllable from 0.3 to 30MPa (unconfined compressive strength) using bio- based methods in which calcium carbonate (calcite) is precipitated in situ .T he spectacular increase in strength, coupled to a limited reduction in porosity and permeability, makes the method a promising alternative to chemical grouting methods. The product is appli- cable in many geo- and civil-engineering applications, like strengthening of dykes, the production of underwater reefs or reducing risk of piping. A first generation of the process based on the hydrolysis of urea has been applied on a 100m3 scale. Denitrification is one of the microbial processes which can be used as a BioGrout pro- cess. In this process, calcium nitrate and calcium-fatty acids are converted to form calcite by denitrifying microbes. These organisms are already present in the subsoil in low num- bers, but are selectively enriched upon addition of the substrates the required substrates can be produced from chalk, manure and waste streams from food industries or tanneries. When nitrate is completely reduced, nitrogen gas is the only side product, emphasizing the sustainability of this new ground improvement method. In this contribution, the governing principles behind the method are elucidated and applications are discussed.

Gas Bubble Migration and Trapping in Porous Media: Pore‐Scale Simulation

This work was supported by the research fund of Hanyang University (HY-201700000002411). The data presented in this study are available at http://jwjang1977.wixsite.com/mysite/data.

Investigating the susceptibility of iron ore to liquefaction

Liquefaction of cargo in a bulk carrier can cause the cargo to shift, which in turn can cause a ship to list and eventually can cause the ship to capsize. When liquefaction occurs, a material undergoes a transition from a solid to a liquid state and, in general, it is caused by the pore water pressure increasing above the total stress and overcoming the effects of cohesion, i.e. shear strength becomes negligible. In this paper, a number of iron ore samples, representing loosely the range of iron ore cargos from around the world, are characterised and tested. The grain size distribution and particle density were determined along with the tests which are prescribed by the International Maritime Solid Bulk Cargoes (IMSBC) code to assess the liquefaction potential: the Proctor/Fagerberg test, the penetration test and the flow table test. It is found that the results from these test methods correspond reasonably well, however they are not applicable for all ore types and the conditions at which the tests are performed do not correspond with the conditions encountered in the ship. Therefore one cannot quantify the risk of liquefaction based on the results of these tests alone, and further investigations on the liquefaction mechanism and the factors which influence this process are required. Part of these investigations have shown that the liquefaction behaviour is strongly linked to the grain size distribution, both in terms of particle size and grading. It is anticipated that the permeability, compaction and water retention behaviour are also of influence in determining liquefaction potential and are governed, in part, by the grain size distribution. Examples of these properties are presented, although the experimental programme is still ongoing.