This study concerns the creep impact on strength parameters of the selected very cohesive soils (PI = 30–70%). The analysis refers to Neogene clays characterized by a complex structure, resulting directly from a complicated load history in the geological time scale and identified glacitectonic deformations. In the process of samples’ preparation for strength tests as well as during the interpretation of the post-failure state, particular attention was paid to the soil structure. The imaging methods (X-ray densitometry and computer microtomography) enabled the comparison of the soil structure and the selection of samples with similar characteristics. The completed program of strength tests consisted of two series of tests in the triaxial stress state, differentiated by the occurrence of the initial creep stage, preceding the typical strength test scheme under undrained conditions. This study allowed to obtain a quantitative assessment of the influence of the creep process on the strength parameters of tested soils. Constant stress lower than 60% of the shear stress deviator leads to the deceleration creep course (m parameter 0.64–0.89). As a result, higher values of internal friction angle (20% increase comparing to triaxial tests without creep stage) and cohesion reduction are obtained from triaxial creep tests. Creep parameter m is found to be a valuable indicator for differentiation of landslide activity trend. The tests proved low values of axial strains (1–5%) at failure, which was associated with lithogenesis. By the implementation of obtained strength parameters into the 3D finite element model of the slope, the potential influence of the creep process on the stability of an exemplary cross section of the Warsaw slope could be determined.

1 Uni ver sity of War saw, Fac ulty of Ge ol ogy, ¯wirki i Wigury 93, 02-089 Warszawa, Po land 2 Cra cow Uni ver sity of Tech nol ogy, Fac ulty of En vi ron men tal En gi neer ing, Warszawska 24, 30-155 Kraków, Po land Dobak, P., Gaszyñski, J., 2015. Eval u a tion of soil per me abil ity from con sol i da tion anal y sis based on Terzaghi's and Biot's theories. Geo log i cal Quar terly, 59 (2): 373-381, doi: 10.7306/gq.1197Proper eval u a tion of per me abil ity pa ram e ters has a cru cial sig ni fi ca tion in multi-scale pre dic tion of con sol i da tion. Drain age path is con nected with the time of one-di men sional con sol i da tion in Terzaghi's the ory and nu mer ous later so lu tions. That is why the eval u a tion of per me abil ity fac tor al lows to model the set tle ment's time of geo log i cal lay ers based on re sults ob tained on a lab o ra tory scale. Nu mer ous tests show a dif fer ence of the con sol i da tion de gree ob tained from one-di men sional strain course and pore pres sure dis tri bu tion. Eval u a tion of con sol i da tion co ef fi cient c v based on a newly pro posed method al lows better un der stand ing of the ba sic rea sons of un con ven tional be hav iour of tested soils. Un paral lel char ac ter is tics of strain and pore pres sure dis tri bu tion show im por tant role of soil's skel e ton creep and its re la tion to per me abil ity as pects. So lu tions pro posed by Biot's the ory al low ana lys ing the dif fer ent ve loc ity of strain and pore pres sure dis tri bu tion. The ar ti cle pres ents a new ap prox i mated method based on Terzaghi's the ory and eval u a tion of pa ram e ters which are nec es sary in ap pli ca tion of Biot's one-di men sional so lu tion. These pa ram e ters are con nected with com press ibil ity and co ef fi cient of per me abil ity. The goal of pre sented meth od olog i cal stud ies is com par i son be tween per me abil ity ob tained from ap pli ca tion of Terzaghi's and Biot's theories. It al lows try ing to ex plain phys i cal rea sons of dif fer ences be tween ap plied mod els and test ing re sults, and improv ing the meth od ol ogy of one-di men sional con sol i da tions tests. Key words: con sol i da tion, co he sive soils, Terzaghi's the ory, Biot's the ory, per me abil ity, geo log i cal bar ri ers, in su la tion proper ties.

Soil creep deformation refers to phenomena which take place in many areas and research in this field of science is rich and constantly developing. The article presents an analysis of the literature on soil creep phenomena. In light of the complexity of the issues involved and the wide variety of perspectives taken, this attempt at systematization seeks to provide a reliable review of current theories and practical approaches concerning creep deformation. The paper deals with subjects such as definition of creep, creep genesis, basic description of soil creep dynamics deformation, estimation of creep capabilities, various fields of creep occurrence, and an introduction to creep modeling. Furthermore, based on this analysis, a new direction for research is proposed.

Localised landslide activity has been observed in the area of the plateau slope analysed, in the vicinity of the planned Warsaw Southern Ring Road. Using calculation models quantitative and qualitative evaluations of the impact of natural and anthropogenic load factors on slope stability (and hence, safety) are made. The present paper defines six stages of slope stability analysis, leading to an indication of optimum slope design in relation to the development planned. The proposed procedure produces a ranking of factors that affect slope stability. In the engineering geological conditions under consideration, the greatest factors impacting degradation and failure of slope stability are changes in soil strength due to local, periodic yielding and the presence of dynamic loads generated by intensification of road traffic. Calculation models were used to assess the impact of destabilisation factors and to obtain mutual equivalence with 3D-visualisation relations. Based on this methodology, various scenarios dedicated to specific engineering geological conditions can be developed and rapid stability evaluations of changing slope loads can be performed.

Abstract:The study concerns soil creep deformation in multistage triaxial stress tests under drained conditions. High resolution X-ray computed microtomography (XμCT) was involved in structure recognition before and after triaxial tests. Undisturbed Neogene clay samples, which are widespread in central Poland, were used in this study. XμCT was used to identify representative sample series and informed the detection and rejection of unreliable ones. Maximum deviatoric stress for in situ stress confining condition was equal 95.1 kPa. This result helped in the design of further multistage investigations. The study identified the rheological strain course, which can be broken down into three characterizations: decreasing creep strain rate, transitional constant creep velocity, and accelerating creep deformation. The study found that due to multistage creep loading, the samples were strengthened. Furthermore, there is a visibly "brittle" character of failure, which may be the consequence of the microstructure transformation as a function of time as well as collapse of voids. Due to the glacial tectonic history of the analyzed samples, the reactivation of microcracks might also serve as an explanation. The number of the various sizes of shear planes after failure is confirmed by XμCT overexposure.