The waste management center was according to the waste management plan from 2017-2022 year, defined as a building of national importance, which brings the Republic of Croatia (hereinafter referred to as the RC) closer to the regulations of the Waste Directive (2008/98/EZ). To date, there are two County Waste Management Centers in the RC that process waste using mechanical and biological processes, and which, as one of the waste streams, have a so-called methanogenic fraction suitable for disposal at a bioreactor landfill. A bioreactor landfill implies, after filling the capacity of the landfill space, moistening the embedded waste material and recirculating leachate (the so-called filtrate) with the aim of encouraging the microbiological decomposition of the organic component of the waste and the production of biogas. Obviously, from a geotechnical point of view, the design of bioreactor landfills is a complex problem. Experimental data on the geotechnical parameters of the methanogenic waste fraction are necessary for the proper design and management of a bioreactor landfill. For this reason, as part of this doctoral dissertation, an extensive laboratory test of the geotechnical parameters of the methanogenic waste fraction was conducted. Since the research was conducted on material produced in the County Waste Management Center Marišćina, which is located in the Primorje-Gorski Kotar County, due to the possible impact of the tourist season, the examined material was sampled outside and inside the tourist season. Tests on material sampled outside the tourist season (material A) and inside the tourist season (material B) were done separately to examine the influence of seasonal variations on the composition and mechanical parameters of the waste material. In the first place, the basic characteristics and basic geotechnical parameters of the waste were determined: the average composition of the examined waste by individual components, the composition of the waste according to the particle sizes 0D, 1D, 2D and 3D, granulometric analysis, the organic matter content and the moisture content were determined. The obtained results of these tests served for a preliminary assessment of the characteristics of the tested material. It was found that the maximum grain size in more than 90% of the examined material is less than 25 mm, and that the granulometric curves fit well with similar results of other researchers. The high proportion of organic matter, more than 50% for material A and B, suggests a great potential for biogas production. The moisture content found after the treatment process was less than 20% (relative to the total mass), which makes it suitable for disposal in a bioreactor landfill due to reduced microbiological activity. Since larger settlements are expected in the bioreactor landfill, the possibility of its prediction implies accurate knowledge of the density of solid particles 𝜌𝑠, the necessary parameter for determining the initial void ratio 𝑒0. For this reason, the solid particle density of the methanogenic fraction 𝜌𝑠 was measured, with the help of a gas pycnometer composed exclusively of laboratory devices that are typically found in geotechnical laboratories. The solid particles density is one of the basic properties of materials and is very often used in design calculations and for predicting the mechanical behavior of materials. The solid particle density results were compared with several parameters such as the void ratio, porosity, dry density, and their mutual dependence was established. In addition to the gas pycnometer, the solid particle density was also determined with the help of a large water pycnometer, and the results were mutually compared and with the results published in the literature. The method of measuring the solid particle density with a gas pycnometer proved to be an easily accessible, cost-effective and quick solution. Since the method is non-destructive, the tested samples can be saved for further analyses. By installing the methanogenic fraction into the bioreactor landfill body in a dry state and subsequent wetting, it is necessary to know the dependence of the dry density 𝜌𝑑 on the moisture content of the material. For this purpose, the possibility of compacting the methanogenic fraction with a vibro plate and standard and modified Proctor's test in dry and wet state of the material was tested. Tests have established that by increasing the moisture content to a certain limit, the dry density of the material 𝜌𝑑 increases to its maximum value 𝜌𝑑,𝑚𝑎𝑥, after which, with a further increase in moisture, the value of the dry density decreases, regardless of the applied test method. Also, for both materials, the values of the optimal moisture content 𝑤𝑜𝑝𝑡, at which the maximum dry density 𝜌𝑑,𝑚𝑎𝑥 is achieved, were determined. In addition to the maximum dry density, the minimum dry density 𝜌𝑑,𝑚𝑖𝑛 was determined on material A by pouring the material into a mold of standard volume under atmospheric pressure. Furthermore, the corresponding void ratios were determined, i.e., at the minimum dry density 𝜌𝑑,𝑚𝑖𝑛 the maximum void ratio 𝑒 𝑚𝑎𝑥 was calculated, while at the maximum dry density 𝜌𝑑,𝑚𝑎𝑥the corresponding minimum void ratio 𝑒 𝑚𝑖𝑛 which determined the possible compaction range of the considered material. In a functional bioreactor landfill, as a result of wetting the waste, the unit weight of the waste increases, while the effective stresses decrease. In relation to the method of installing the methanogenic fraction into the landfill body, as well as the expected settlement after wetting the material, for quality management of the bioreactor landfill it is necessary to know the compressibility properties of the methanogenic fraction in dry and wet conditions. For this purpose, an oedometer experiment was carried out for several states of the material: for a dry state, for a wet state, for an initially dry state up to a certain stress, after which the material's moisture was changed and a long-term oedometer experiment was carried out in which the settlements caused by biodegradation were measured, with continuous monitoring of the temperature of the sample and the percentage of landfill gases generated. The oedometer test results determined the compressibility parameters, relative deformation of the material in each of the mentioned states and confirmed the collapsible behavior of the methanogenic fraction of biodried waste.