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The construction of high-rise building and structures has been widely developed recently in Vietnam. Pile foundations are considered one of the most suitable solutions when choosing the foundations for their construction, especially in difficult geological conditions, including seismic areas. According to many researches, geological conditions of Ho Chi Minh City are generally difficult. The occurrence of earthquakes there influences the conditions for the construction. Besides, many historical cases have shown that soil liquefaction is often manifested, negatively affecting the underground structures and foundation working. With an increase in investments of international construction companies and organizations in Vietnam, pile foundations can be designed according to domestic or foreign normative documents. Therefore, at present, a better understanding and detailed analysis of various existing normative documents and methods for designing pile foundations are required, especially when the influence of soil liquefaction is taken into account. This paper presents a review of various normative documents, including Russian, Vietnamese, American and Eurocode. The different methods in these normative documents for calculating the piles' bearing capacity are considered in 2 cases: with and without taking into account the soil liquefaction based on the hypothesis that the additional downward loads due to self-compaction of liquefiable soils affect piles. Finally, a comparison of the calculation results is presented. The comparison shows how these considering methods in these normative documents differ from each other and how much the pile's bearing capacity can be reduced when considering the soil liquefaction in calculations.

Construction of industrial and civil buildings, taking into account the dynamic effects on the foundations, requires special experiments on the mechanical properties of soils. This article presents the results of studying the dynamic properties of coarse gravelly soils using the resonant column method. These studies are relevant, since the determination of the dynamic properties of coarse-grained soils under laboratory conditions is associated with a restriction on the size of the fractions in the sample volume. This circumstance leads to the fact that at the moment most of the laboratory tests of the dynamic properties of coarse-grained soils are performed on smaller aggregate fractions, which, in general, significantly reduces the resulting mechanical properties of soils. It does not reflect the real operation of the foundation of buildings during dynamic effects. This paper presents a description of the available laboratory equipment, the sequence of preparation of samples of coarse grained crushed stone soil and sample assembly in the working chamber of the installation. The article contains the main graphs characterizing the change in shear modulus and damping coefficient depending on shear deformations. It is noted that the results obtained are particularly relevant for modeling the dynamic effects of natural and man-made character on the foundations of industrial and civil buildings, the bases of which are composed of coarse-grained soils. Dynamic parameters considered in this paper, can and must be used in numerical calculations by finite element method with the use of modern groundwater models in geotechnical software systems.

In this paper, we determine the characteristics of the physical damping of sand and clay soil by the results of special laboratory tests. The transition from parameters obtained directly from the results of triaxial dynamic tests to parameters of mathematical models of soils used in modern software complexes is shown. The solution of several dynamic FEM problems is exemplified by PLAXIS PC taking into account different damping characteristics of the ground base of a multi-storey building with a developed underground part. Recommendations are given for selecting a soil model for dynamic impact and dynamic soil parameters, and an analysis of the solutions obtained.

The construction of buildings and structures in seismically hazardous areas is closely connected with the solution of the question of the dynamic stability of the soil base. World experience shows that the most destructive effect of seismic action is dynamic liquefaction. The probability of occurrence and intensity of this process are determined by the geological and hydrogeological structure of the soil massif. Based on the results of special laboratory and field dynamic tests of soils, it is not always possible to completely exclude the possibility of developing this extremely negative process. In this paper, the main stages of the analysis of the dynamic stability of the soil of the foundations of buildings and structures in complex engineering-geological conditions are presented. A brief review of existing domestic and foreign measures for the protection of buildings and structures from the dynamic dilution of soils is given. Information is provided on the applicability and comparative effectiveness of the methods in question.

Dynamic loading causes (1) a substantial change in the strength and deformation parameters of sandy soil and (2) excessive viscoplastic deformation. The goal of this study is to create a new analytical solution to the problem of the settlement of (1) the foundation that is the source of dynamic loading, and (2) a nearby foundation, taking into account the rheological properties of sandy soil subjected to vibration, given that these rheological properties depend on shear stresses. The proposed solution allows the progress of deformation over time to be described. The present paper states and provides an analytical solution for the problem of evaluating the settlement of a single foundation that transmits static and dynamic harmonic pressure to the base. The authors also analyze the settlement of another foundation located at some distance from the transmitting foundation. The second foundation transmits static pressure to the base. The dependence of the viscosity coefficient on the shear stress intensity and vibration intensity, as well as the vibrocreep decay over time, are based on the exponential and homographic dependencies previously identified by two of the authors (A.Z. Ter-Martirosyan and E.S. Sobolev). The solution to the problem is obtained by numerical integration in the Mathcad program of an analytical expression for nonlinear viscoplastic deformations. As a result of the research, the authors have found that the dynamic viscoplastic component makes the greatest contribution to foundation settlement. The settlement of the transmitting foundation increases along with increasing static and dynamic pressure transmitted to the base. The settlement of the nearby foundation increases when the pressure increases under the foundation, but it reduces when static pressure from the transmitting foundation, the depth of the foundation, and the distance between the foundations increase. General analytical dependencies obtained by the authors comply with the results of laboratory and field experiments performed by other researchers. These dependencies can be used to predict the settlement of foundations in whose unsaturated sandy bases mechanical vibrations propagate. [ABSTRACT FROM AUTHOR]

The first ichthyosaurian specimens discovered from the Upper Triassic of the Russian Arctic (Kotelny Island, New Siberian Islands) are described herein. They include the remains of large- to small-bodied ichthyosaurians originating from six stratigraphic levels spanning the lower Carnian to middle Norian. The material is mostly represented by isolated vertebrae and ribs, which are not possible to accurately diagnose, but also includes specimens comprising associated vertebrae and a fragmentary skeleton that preserves cranial remains (parabasisphenoid, fragmentary quadrate, partial mandible and hyoids). Based on vertebral and rib morphology, we identify the specimens as representatives of the following taxonomic groups: large-bodied shastasaurids, medium-sized indeterminate ichthyosaurians with a single rib facet in the presacral centra, and small euichthyosaurians with double rib facets present throughout the presacral vertebrae that likely represent toretocnemids and/or basal parvipelvians. In addition, the cranial and mandibular remains preserved in one of the specimens, ZIN PH 5/250, were studied using micro-computed tomography. Its mandible is highly similar to that of toretocnemids, whereas the parabasisphenoid demonstrates a peculiar combination of both plesiomorphic and derived character states, providing the first detailed data on this cranial element in a Late Triassic ichthyosaurian. Furthermore, the specimen also demonstrates a distinctive condition of rib articulation in the anteriormost presacral (cervical) vertebrae, which together with other features allows for the erection of a new taxon – Auroroborealia incognita gen. et sp. nov. Although the phylogenetic position of this taxon is uncertain due to its fragmentary nature, its anatomy, indicating toretocnemid or parvipelvian affinities, further supports the previously hypothesised sister-group relationships between these two clades. The morphology of the parabasisphenoid and vertebral column of the new taxon is discussed in broader contexts of the patterns of evolution of these skeletal regions in ichthyosaurs. [ABSTRACT FROM AUTHOR]