A Passive House (PH) system is not only an opportunity but also a necessity for the further development of sustainable eco-buildings. Construction of the foundation in energy-efficient houses is the key to maintaining low energy losses. The appropriate selection of building materials requires considering the thermal conditions of the environment, including its location and the zero isotherms in the ground. The main objective of this work is to analyze the possibilities of designing foundations for PHs in Poland, according to the current methodological data. In order to realize the basic aims, the work was divided into the following materials and methods: (I) literature review; (II) database of PH in Central Europe; (III) method of depth of ground freezing determination; (IV) selection of the joint of slab-on-ground foundation and external wall to analysis; (V) description and validation of the heat-transfer model. The result of the research work is: (i) analysis of the foundation under the conditions of freezing of the ground in Poland; (ii) description and validation of the heat-transfer model. The research has revealed that in the Polish climate zone, the most efficient solution for passive buildings is to build them on a foundation slab. The foundation of a building below the latest specified ground frost depths in Poland is inefficient in terms of, for example, thermal insulation, economics, and the idea of PH.

The article presents the preliminary results concerning the use of miniature magnetic linear encoders for the measurement of displacements at small strains in triaxial soil tests. Presented are: the main principle of operation of this type of sensors, their advantages, and how they have been implemented in a standard triaxial test stand to the existing equipment. Finally, the test results obtained for a soil sample are used to highlight the difference in results obtained with the new sensors compared to linear variable differential transformer transducers.

Typical ranges of variability of basic soil parameters are relatively well known. Such knowledge is important to aid engineers in the selection of characteristic values for design or as a basis for conducting sensitivity analyses for more complex soil-structure interaction problems. However, for application of advanced non-linear constitutive models, which often are defined by model-specific parameters, such variability is rarely known. To improve parameter estimation, as well as to provide a basis for the choice of realistic variability range, a database of high quality laboratory tests can be used. The paper presents the results of preliminary assessment of variability of selected Hardening Soils model parameters for overconsolidated glacial tills and clays from Poland, based on a local database of triaxial test results.

The requirement for implementing local measurements at small strains is well known. Without this type of measurement, it is not possible to accurately identify the soil stiffness characteristics over the entire stiffness degradation curve. The paper presents the results of the use of new sensor based on miniature magnetic encoders for axial and radial deformation measurements in triaxial soil test. Presented results include two types of measurement techniques for radial direction and one for axial deformation.

Based on the Frictional State Concept (FSC), the stress–dilatancy behavior of alluvial sands in drained triaxial compression was investigated. The dilatant failure state is equivalent to the minimum plastic dilatancy state for sands. The dilatant failure state slightly precedes the failure state. The straight line approximating dilatant failure states in the stress ratio–plastic dilatancy plane defines the slope of the critical frictional state line in the q-p’ plane, i.e., the critical frictional state angle. The stress ratio–plastic dilatancy relationship, obtained from the FSC, defines the sand shear angle as a function of the critical frictional state angle and plastic dilatancy. The shear angle of the tested sand is a maximum of 2° greater than that obtained from Bolton’s formula. According to the authors, these differences are affected by the transverse anisotropy of sand in the tested samples and the difference between the dilatant failure state and the failure state.