Showing papers in "Soil Mechanics and Foundation Engineering in 2016"

Long-Term Settlement of Buildings Erected on Driven Cast-In-Situ Piles in Loess Soil

Abstract: Results are presented for long-term geodetic observations of the settlement of residential buildings erected on driven cast-in-situ piles that are part of foundation frames on loess soil. Stabilized deformations of building foundation beds are compared to the results of analysis using normative methods and simulation of the stress-strain state of the system using two- and three-dimensional versions of the finite element method and a plasticelastic soil model.

A New Model for Determining Slope Stability Based on Seismic Motion Performance

Abstract: The factor of safety is one of the major aspects for designing specific structures like embankment, landslide, and artificial slopes. In this context, some huge damages are particularly reported due to the effect of earthquakes. In this paper, 700 slopes were designed based on the limit equilibrium method, and relevant factor of safety values were obtained. In the modelling process, the parameters with the greatest effect (slope height, slope degree, soil cohesion, and internal angle of friction with peak ground acceleration), were considered as predictors or model inputs. As a result, the factor of safety under the impact of seismic motion is significantly reduced when the peak ground acceleration increases. A multiple regression model was developed. Coefficients of determination for the training and testing datasets indicate the excellent ability of the proposed model to estimate the seismic factor of safety. Peak ground acceleration and soil cohesion were obtained as the parameters with the most and least effect on the factor of safety, respectively.

Laws of Shear Interaction at Contact Surfaces Between Solid Bodies and Soil

Abstract: Nonlinear relations based on Winkler-like and Coulomb laws are proposed to describe the process of shear interaction between structures and soil. Their advantages and shortcomings are illustrated, along with the suitability of experimental results.

Strength and Deformability of Clay Soil Under Different Triaxial Load Regimes that Consider Crack Formation

Abstract: A spatial model of dilatating soil under triaxial load conditions with different regimes are described on the basis of a hypothesis that the Coulomb dry friction force acts in the plane of tangential particle shear. Spatial soil deformation over time is described in accordance with the theory of inherited creep in the form of the sum of deformations due to changes in volume and shape, with due regard for their interrelation.

Ultrasound Study of Limestone Rock Physical and Mechanical Properties

Abstract: Regressive analysis was used to determine empirical correlations between the velocity of an elastic P-wave (compressional pulse) and a number of physical, strength, and deformation characteristics of limestone rock collected at quarries in Turkey. The results may be used to determine the properties of limestone rock formations for engineering purposes.

Aspects of the Joint Operation of a Ring Foundation and a Soil Bed with Zones of Inhomogeneity Present

Abstract: Maximum allowable tank bed settlement values are determined with due regard for structural steel metalwork stiffness when an inhomogeneous zone is present in the bed. A Drucker-Prager model for linear elastic-plastic materials is used in the article to simulate an inhomogeneous zone, and is implemented in the ANSYS finite-element model program package.

Seismic Behavior of Underground Polymer Piping with Variable Interaction Coefficients

Abstract: The dependence of the coefficient of interaction between a polymer pipe and soil on soil moisture is determined experimentally. Variable coefficients corresponding to certain cases of moisture distribution are approximated. Based on variable coefficients, the longitudinal oscillations of underground polymer piping is studied in response to seismic loads. An algorithm and program were developed for calculating seismic stability.

Mechanical Behavior of Loose Sand Reinforced with Synthetic Fibers

Abstract: This work describes an experimental study about the effects the addition of randomly oriented polypropylene fibers have on the behavior of an alluvial fine to medium sand in a loose state. The study is focused on the characterization of the influence the fiber addition has on the shear strength and on the deformational modulus corresponding to low, medium, and large strain levels of the reinforced sand. The effect of the type (smooth and meshed), length, and fiber content, is analyzed by means of drained triaxial, direct shear, and shear wave velocity tests.

Evaluation of Freezing-Thawing Cycles for Foundation Soil Stabilization

Abstract: Freezing-thawing cycles in soils reduce considerably the foundation capacity of buildings and infrastructure. In recent years, development of nontraditional stabilizers has created hundreds of new products for soil stabilization. Fiber portions of biomass (such as lignin) can be considered as byproducts of the conversion process, and these byproducts are generally used to produce octane booster fuels, bio-based products, and other chemical products. The use of lignin-based biofuel co-products (BCPs) to stabilize pavement subgrade soil is an innovative idea and satisfies the needs of sustainable development in construction. A series of laboratory tests, including unconsolidated undrained direct shear test, freeze-thaw durability test, and scanning electron microscope tests, was conducted to evaluate the effect of BCP addition on shear strength performance for four different soils encountered in Iowa. The results of this study indicate that BCPs are beneficial in the soil stabilization of low-quality materials for use in road construction.

Evaluation of Vacuum Preloading with Vertical Drains as a Soft Soil Improvement Measure

Abstract: Site condition and construction technology are described in detail, as well as the solutions to common problems encountered during the construction phase of such a project. A numerical model is established based on the case study and validated by the actual field measurements. The differences between modeled results and field measurements were 2.4-49.4%, which validate the accuracy of the numerical model. Settlement at the surface of soft soils was found to increase when the length and permeability coefficient of prefabricated vertical drains were increased, and decreased as the spacing increased. The estimated degree of consolidation at the final stage of vacuum preloading was 93.4% based on the degree of settlement, and 88.3% based on pore water pressure measurements. Thus, vacuum preloading with vertical drains was found to be an effective method by which to improve the strength of soft soils prior to construction on them.

A Numerical Study of the Active Earth Pressure on a Rigid Retaining Wall for Various Modes of Movements

Abstract: The magnitude and the application point of the resultant active earth pressure are two key problems in the design of a variety of civil engineering structures. Experimental results indicate that these parameters are affected by the wall movements. In this paper, series of two- dimensional finite difference analyses have been carried out using the code FLAC (Fast Lagrangian Analyses of Continua) to study the active earth pressure distribution behind a retaining wall under horizontal translation, rotation about the bottom, and rotation about the top modes of wall displacements. The computation results show remarkable similarity to experimental results available in the literature indicating that the active earth pressure distribution is nonlinear due to the arching effect. It is found that, for a wall under translational and base rotation modes, the active earth pressure is substantially hydrostatic except at the wall base where curvature was observed. These two wall modes are in good agreement with classical solutions. However, the earth pressure distribution due to rotation about the top is found far from the hydrostatic distribution and is highly affected by the arching effect.

Experience in Preserving Adjacent Buildings During Excavation of Large Foundation Pits Under Conditions of Dense Development

Abstract: This article considers the successful implementation of a deep foundation pit next to existing buildings, which experiences settlement and damage to load-bearing structure during the course of its excavation. An analysis is presented of the causes of building settlement and deformation. Steps are described to stabilize settlement and to reinforce foundation beds in damaged buildings. Additional settlements in adjacent buildings, calculated using the finite-element method, are compared to monitoring results upon final completion of the foundation pit.

Interaction of Compaction Piles with Surrounding Soil with Due Regard for Pile Diameter Expansion

Abstract: Analytical and numerical solutions are provided for the problem of the interaction between compaction piles and a foundation slab and a surrounding soil cylinder that rests on an incompressible bed, with due regard for the potential expansion of the pile shaft. Closed solutions are obtained for determining stresses in the pile shaft and the soil under a foundation slab in an end bearing pile scheme. This issue is most immediate for transforming beds using drain piles composed of a sand-gravel mixture.

Compression Ratio Design and Research on Lower Coal Seams in Solid Backfilling Mining Under Urban Areas

Abstract: Large coal resources occur under buildings in the Iron Third District of Tangshan Mine, which not only greatly reduces the service life of the coal mine, but also wastes the coal resources. To ensure the safety of ground buildings and maximize exploitation of the coal resources, solid backfill mining technology is proposed. This paper studies the compression ratio of the coal seam during backfill mining with a global numerical model based on the finite difference software, FLAC3D. The compression ratio of the coal seam was also similarly studied based on theoretical analysis and the local model.

Strength of a Roller Compacted Rockfill Sandstone from In-Situ Direct Shear Test

Abstract: A simplified in-situ direct shear test suggested to determine the shear strength of roller compacted rockfill material, was conducted on a concrete-face rock-fill dam (CFRD) under construction. The strength of the roller compacted rockfill sandstone, was determined by a simplified in-situ direct shear test. The vertical load applied on the upper surface of the specimen before shearing, was supplied by stacking many soil pockets with equal weight. The horizontal shear load, which was applied on the steel shear box, was provided by exerting a horizontal drawing force on the shear box step by step. The real normal stress and shear stress acting on the shear plane were precisely measured, and the shear strength of the tested material was obtained.

Soil Arching Effect in Sand Reinforced with Micropiles Under Lateral Load

Abstract: The mechanics of the mobilization of resistance from passive pile groups subjected to lateral soil movement is discussed from the standpoint of the arching effect. An innovative approach has been attempted to study the effect of introducing multiple rows arrangement of micropiles in sand at varying ground densities (30% and 80%). Similarly, parametric study focusing on the effect of the reinforcing rods cross sections (10 × 10 mm square and 3 mm in diameter piles) was also considered in terms of their pressure resistance. The results reveal that the formation and shape of the arching zone are functions of pile arrangement and pile shape. Group effects in multiple rows of piles are significant, but no significant effect under lateral soil movement (passive loading) for single row of piles was observed in sand.

On the Use of Numerical Methods to Analyze Bed Deformations

Abstract: The results of numerical studies examining the interaction between a foundation slab and a uniform bed are examined. A comparison is presented of foundation settling according to the way in which the bed and foundation are modeled.

Analysis of the Maximum Dynamic Shear Modulus and Particle Arrangement Properties of Saturated Soft Clay Soils

Abstract: In this paper, using the resonant column test, electron microscope observation, and microscopic structure analysis, the relationship between the maximum dynamic shear modulus and the microscopic particles arrangement of remolded clay soil was examined. Focusing on the soil microstructure, this study found that, as the effective consolidation stress increases, the soil particles are rearranged in an orientation parallel to the direction of maximum principal stress and maximum shear stress. The probabilistic entropy of the soil particle arrangement decreases, the mechanical wave velocity in the continuous medium of the soil particles increases, and the maximum dynamic shear modulus increases.

Numerical Modelling of the Consolidation Behavior of Peat Soil Improved by Sand Columns

Abstract: This paper presents a ground improvement method using sand as material in columnar inclusion. The main focus of the study is to model the consolidation behavior of peat soil reinforced by sand columns. The effects of sand column length and column diameter were determined using numerical analysis. It was revealed that the final settlement strongly depends on the area replacement ratio. The numerical results showed that the installation of larger-diameter, fully penetrated columns reduced soil settlement. The settlement reduction results of our numerical analysis are in good agreement with the experimental results. In order to improve the confining stresses of sand, an alternative approach utilizing geogrid encasement was examined numerically. The increasing stiffness of geogrid effectively increased the load carrying capacity of the sand column. Based on the results, geogrid performs better in smaller-diameter columns.

Seismic Stability of Tunnels at the Kapchagai Hydropower Plant

Abstract: Results are presented of a full-scale study to assess the seismic stability of the spillway tunnels at the Kapchagai HPP in connection with an increase in the seismic rating of the site. Tests of the concrete used in the tunnel lining and of the surrounding rock determined the physical and mechanical properties of the materials and calculations were carried out for an earthquake load of intensity 8 on the facility. Calculations were carried out using the Tunnel' program package (developed by the authors) and ANSYS program package. Zones were identified in the tunnel lining where hazardous tensile stresses may potentially occur. It is shown that the existing spillway tunnels are seismically stable.

Influence of Local Wetting of Loess Soil on the Redistribution of Reactive Pressures Under Foundations

Abstract: An experimental-theoretical method is presented for tracking reactive soil pressures in a local wetted zone when solving problems of plate bending on an elastic bed with due regard for incomplete contact.

Experience in Applying Pile Static Testing Methods at the Expo 2017 Construction Site

Abstract: Results of static pile tests using the static cycling quick-load test (SCQLT) and Osterberg (O-Cell) methods are presented.

Slope Monitoring Study Using Soil Mechanics Properties and 4-D Electrical Resistivity Tomography Methods

Abstract: In past applications of electrical resistivity survey, users commonly focussed on the Earth's subsurface to locate water table, bedrock, etc. Nowadays, this electrical resistivity method is used by engineers for shallow subsurface investigations. This paper presents the integration of soil mechanics properties with electrical resistivity tomography methods and recommends the proper selection of resistivity array (survey planning) and appropriate inversion constraint parameters (data processing) that are able to deliver optimum resistivity tomography model results. This study identifies the empirical correlations of the soil's properties such as shear strength parameters, moisture content, void ratio, porosity, saturation degree, and Atterberg's limits with the electrical resistivity values (resistivity tomography models). A total of 11 undisturbed clayey sand soil samples was collected at different distances, depths, and times and were tested under both infield and laboratory conditions during the slope monitoring period. The soil mechanics properties of the soil samples were obtained right after the electrical resistivity survey was made. It is shown that the electrical resistivity values are greatly influenced by the soil mechanics properties. Thus, the electrical resistivity (4-D) survey using the optimized Wenner-Schlumberger array (high data density) is capable of reliably enhancing the conventional outcome of the Earth's subsurface investigation.

Physical and Mechanical Conditions for Primary Frost Crack Formation

Abstract: An idea of B.N. Dostovalov’s to represent a mass of frozen soil, prior to its failure, as an elastic brittle body is considered. An analytical estimate is provided of the temperature field and thermoelastic stresses occurring in the near-surface layer as a result of sudden atmospheric cooling. The principal parameters of primary frost cracks are calculated. An analysis is presented of their dependence on mechanical and thermophysical soil properties and baseline data.

Estimate of Rotational Components of Seismic Ground Motion

Abstract: A method for the simultaneous calculation of three rotational components using available translational motion accelerograms is examined, allowing a universal analytical relationship to be obtained between Fourier coefficients for rotational and translational motion. The method has been implemented in Eurosoft Odyssey software (published by JSC Eurosoft) and verified by carrying out seismic calculations at the Kurchenko Central Scientific-Research Institute of Structural Engineering.

Propagation Conditions of Rayleigh Waves in Nonhomogeneous Saturated Porous Media

Abstract: Based on Biot’s theory of saturated porous media, the propagation of Rayleigh waves in nonhomogeneous saturated porous media is studied. The frequency equation of Rayleigh waves in inhomogeneous saturated porous media is derived in which the variation of shear modulus is taken into account, and the existence conditions are also given. It is pointed out that the shear modulus of the material parameters is a function of depth via a theoretical derivation, and the final expression of the solid skeleton and fluid displacement in the medium is obtained.

Development of Correlation Between Standard Penetration Test and Pressuremeter Test for Clayey Sand and Sandy Soil

Abstract: The standard penetration test (SPT) and Menard’s pressuremeter test (PMT) are among the available in-situ techniques. This research has been carried out with the aim to develop correlations among the in-situ parameters obtained by both methods.

Determining Tilt in Tanks Used to Store Oil and Oil Products During Hydraulic Testing and Operation

Abstract: Requirements stated in regulatory documents are discussed with respect to determining deformations in beds of vertical steel cylindrical tanks used to store oil and oil products. A procedure is proposed for determining tilt in the foundation and the tank proper, based on the aggregate settlement of deformation markings on the foundation and points along the bottom edge. A computer program was developed to calculate tilt. An example is presented of determining settlement and tilt for a pile foundation of a vertical steel tank after 5 years of operation.

Engineering Analysis of Foundation Slab Settlement and Deformation for a High-Rise Building on a Nonuniform Rock Bed

Abstract: The development of a Gersevanov Institute procedure is given for analyzing bed settlement under a slab foundation, with consideration of the foundation shape, uneven load, and bed nonuniformity. In the proposed procedure alternative, which has been adapted for the analysis of foundation slabs on a nonuniform rock bed, the load distribution under the slab bottom is taken from the results of a finite-element analysis of a building structure on a base assumed to be absolutely inelastic. Implementation of the analytical procedure is shown using the example of calculating the settlement and deformation of a high-rise building slab, for which a "weakened" area was identified in the bed during surveys. Stochastic simulation of additional "columns" of geological engineering boreholes is carried out to estimate the impact of insufficiently complete information on the properties of the rock mass. The impact of bed nonuniformity on the results of analyzing settlement, slab tilt, and forces within the slab are analyzed.

Collapse Characteristics of High-Density Silt Under Principal Stress Rotation

Abstract: To study the collapse characteristics of high-density silt under complex loads, three series of hollow-cylinder tests were conducted on high-density saturated silt samples taken from the sea entrance of the Yangtze River. In the first series of tests, samples with high density were isotropically consolidated and then sheared under undrained triaxial loads. In subsequent tests, samples with low and high densities were isotropically consolidated and then cyclically sheared by principal stress rotation of 0-180°. Collapse and liquefaction were clearly observed in all the samples tested under cyclic principal stress rotation when the pore water pressure was equal to the initial effective confining pressure. Two critical points, the graded phase transformation point and the cataclysmic phase transformation point (collapse point), were observed for the high-density samples before liquefaction; these divided the buildup of the pore water pressure into three or two stages depending the shear stress level. At low shear stresses, the characteristics of the transformation points were hardly influenced by load frequency. The isotropic consolidated high-density silt and low-density silt expressed similar behaviors. However, in the high-density silt, the strain development could be divided into two stages by the collapse point, which corresponds to the cataclysmic phase transformation point of the pore water pressure representing the state of structure collapse. The deviator strains were limited within a narrow range of 0.2-0.4% at the collapse state. The stress state of collapse can be normalized by the quasi-unstable line in the p'-q space. Finally, we introduce the modified Seed model to successfully estimate the development of pore water pressure in high-density silt.