Geotechnical Practice Research Articles

Assessment of liquefaction potential of soil based on standard penetration test for the upper Benue region in Nigeria

Determining a specific site ‘s geotechnical parameters is a crucial step in geotechnical analyses and designs in a seismically active area. In recent years, many parts of Nigeria have been subjected to several earthquakes; therefore, subsurface description has been a challenging task in geotechnical practice in this region. This paper aims to evaluate subsurface formation for soil liquefaction analysis at a sugar plant site located in Nigeria ‘s Upper Benue region. The study used data from the standard penetration test (SPT) measured at 28 boreholes and soil samples ‘ laboratory analysis. The liquefaction parameters were derived according to the procedure in Idriss and Boulanger (2014). Soil liquefaction has been evaluated, assuming an earthquake scenario of 7.5 Mw with a peak horizontal acceleration (amax) of 0.15 g. Results showed that the subsurface formation between 1.5 and 4.5 m is saturated loose to medium-dense sandy, silty clayey soil, and the liquefaction safety factor is less than 1. The Formation at a depth deeper than 4.5 m comprises very densely to stiff clayey sands with a safety factor higher than 1. The applied approach has been proved to be a rapid and reliable method for investigating sandy soil’s liquefaction under the effect of earthquakes.

Three-dimensional subsurface modeling using Geotechnical Lasso

This study develops a least absolute shrinkage selection operator (lasso) for realistic three-dimensional (3D) geotechnical problems. We propose a lasso-based method specialized for subsurface modeling considering the difference between the vertical and horizontal correlations of soil properties. The straightforward computational implementation of this geotechnical lasso (GLasso) is not feasible in 3D problems because of significant runtime and memory exceedance. To address this problem, we propose an efficient implementation of the alternating direction method of multipliers (ADMM). GLasso and the efficient ADMM (eADMM) were applied to a real case study of subsurface modeling to demonstrate their performance in geotechnical practice.

Non-parametric construction of site-specific non-Gaussian multivariate joint probability distribution from sparse measurements

Construction of a joint probability distribution for correlated geotechnical properties is often needed in geotechnical reliability-based analysis and design. Geotechnical properties vary across sites and follow site-specific and non-Gaussian probability distribution, because of different geological processes that soils and rocks in different sites have undergone. In addition, site-specific measurements on geotechnical properties are usually sparse and correlated in geotechnical practice, leading to the difficulty in estimation of meaningful joint probability distribution when using conventional parametric statistical methods. To address this issue, this paper develops a non-parametric and data-driven approach for characterizing the site-specific non-Gaussian multivariate joint probability distribution without pre-selection of the marginal probability distribution type. Two key components for constructing a multivariate joint probability distribution (i.e., marginal probability distribution for each variable and correlation matrix for all variables) are estimated separately using Bayesian Gaussian mixture and Bayesian compressive sampling (BCS) and Karhunen-Loève (KL) expansion. The proposed method is illustrated using both simulated and real data in geotechnical site investigation. The results show that the proposed method performs well for both examples. The proposed method does not model spatial variability explicitly but is based on the assumption of independent measurement data along depth, and thus measurement records are required to be sufficiently spaced apart in depth (e.g., more than 1 scale of fluctuation) to satisfy this assumption.

Particle finite element method implementation for large deformation analysis using Abaqus

In this study, a simple PFEM approach for analyzing large deformation problems in geotechnical practice is implemented in the commercial FEM package Abaqus. The main feature of the proposed Abaqus-PFEM approach lies in its capability to absorb the advantages of the functionality available in Abaqus and integrate them into PFEM with a single Python script, which leads to a considerable reduction in coding work. By utilizing the built-in functions in Abaqus to fulfil the standard incremental FEM analysis, as well as the powerful mesh-to-mesh solution mapping technique, the proposed Abaqus-PFEM approach allows for the large deformation analysis automatically running with a single Python script and requires no intervention from the user. The accuracy of the proposed Abaqus-PFEM approach is firstly validated through a simple elastic cantilever beam bending problem. Then, the performance and robustness of the proposed Abaqus-PFEM approach are further examined by three illustrative numerical examples: penetration of rigid footing, penetration of T-bar and pipeline–soil interaction problem. The numerical results demonstrate that the proposed Abaqus-PFEM approach as a powerful and easily extensible numerical tool is capable of handling large deformation and soil–structure interaction problems in geotechnical engineering, and consequently, it offers an alternative way to tackle such problems.

A type of buried reinforced concrete structures in structurally unstable soils

The operational reliability of the constructed buildings and structures in the Arctic depends on the rationally adopted types of foundations. In cases of structurally unstable engineering and geological elements (EGE) in the base, stricter requirements shall be imposed on the design and construction of foundations. For bases composed of collapsing soils of natural occurrence, the coefficient of relative collapsing ɛsl and the initial collapse pressure Psl are the main deteriorating indicators. Disregard for their impact in most cases leads to the deterioration in the reliable operation of the erected structures. This paper addresses a case from geotechnical practice, when a timely discovered error of not taking collapsible characteristics into account made it possible to avoid an emergency.

Methods and technology of reinforcing a leaning slope

Geotechnical engineering is one of the most important components in the construction of the underground parts of facilities for various purposes. The vast potential of geotechnical technologies makes it possible to successfully complete foundation construction in any engineering and geological conditions and any area, including slopes, gullies, and embankments. The conditions of the Arctic regions are no exception. It is important to consider the specifics of each facility. It is common to see facilities erected on varying terrain with structurally unstable soils running across, loaded with slopes. In geotechnical practice, construction on such slopes is sometimes carried out without proper engineering support, i.e., without any engineering surveys or landslide protection measures. In most cases, disregard for generally accepted standards leads to undesirable consequences represented by the deformation of the constructed buildings. This paper reviews one of such cases.

Features of the Geotechnical Practice of Constructing a Four-Story Brick Building Near a Cultural Heritage Object

Features of the Geotechnical Practice of Constructing a Four-Story Brick Building Near a Cultural Heritage Object

Geotechnical practice of construction on permafrost soils near existing facilities

The construction of facilities in densely built-up areas is a complex geotechnical task that requires a special approach to ensure the trouble-free operation of the surrounding buildings. The problem becomes even more severe when works are carried out in permafrost and seasonally frozen soils. Such measures should be developed as flow charts or special schemes for the construction of buried structures, which would exclude damage to existing buildings and structures in the geotechnical influence area. It should be noted that the size of the geotechnical influence area under dynamic loads from driven prismatic piles requires clarification. In this paper, using the construction of a four-story public brick building next to a facility of regional significance as an example, we consider a solution to the issue of reducing the impact on surrounding buildings.

An Experience from the Geotechnical Practice of Reinforcing a Leaned Slope

An Experience from the Geotechnical Practice of Reinforcing a Leaned Slope

IMPROVEMENT OF GEOTECHNICAL MONITORING OF STRENGTHENING OF DEFORMED BUILDINGS ON PILE FOUNDATION

Object. Improve the geotechnical monitoring of the system “deformed building – driven prismatic piles in the composition of the strip grille – soil base with a weak underlying layer” before, during and after the supply of the existing grilles of the monolithic reinforced concrete slab. Method. Standard field and laboratory methods for determining the physical and mechanical properties of soils; normative methods of inspection of a technical condition of bearing building designs, their bases and the bases; methods of mathematical statistics for processing the results of experiments; long-term geodetic observations of deformations of a brick building on a pile foundation before and after its strengthening. Results.A system of geotechnical monitoring and scientific and technical support of the system "deformed building – driven prismatic piles as part of a belt grid – soil base with a weak underlying layer" was developed and tested on a typical natural object before and after supplying monolithic reinforced concrete slabs, in particular: the actual parameters of its foundations and foundations and their changes over time are determined; conducted geodetic observations of the deformations of the object before, during and after its strengthening to establish patterns of development and stabilization of these deformations over time, etc. Scientific novelty. The structural and technological solution of strengthening the foundations of driven prismatic piles in the belt grid by bringing under the existing grilles monolithic reinforced concrete slab and obtained new research data on the change of stress-strain state of the system “deformed building – driving prismatic piles in the belt grid – soil weak underlying layer” due to the supply under the existing grilles of the plate. The practical significance. Developed and implemented in geotechnical practice constructive-technological solution of reinforcement of foundations from driven prismatic piles as a part of a tape grid by bringing under existing grilles of a monolithic reinforced concrete plate and the corresponding technique of geomonitoring.

Relevant data-based approach upon reliable safety factor for pile axial capacity

Pile foundations are one of the significant marine substructure systems for a variety of offshore and onshore facilities. Thus, optimum and reliable design during their lifetime and under inherent uncertainties is noteworthy. Among various methods for predicting axial pile bearing capacity, cone penetration test (CPT)-based methods enhance geotechnical design to a more satisfying level due to continuous and reliable CPT records and their suitable performance in offshore environments. This article aims to reveal the importance of CPT and pile databases, especially in deltaic deposits. A new relevant CPT and pile data-based approach is introduced by assessing a few elaborated works on typical CPT and pile case studies. The proposed procedure assists in comparing the characteristics and conditions of a given pile with similar database cases through screening and, consequently, deciding on the design methods' priority. It is depicted that superior methods result in a more reliable design and higher resistance factors and efficiency ratios in load and resistance factor design (LRFD). Accordingly, it is engaged with lowered safety factors in the allowable stress design (ASD) approach. Eventually, upon various assessment criteria, the optimum site-specific methods are proposed leading to a performance-based design that can be realized in geotechnical practice.

Investigation on the undrained shear strength of loose sand with added materials at various mean diameter ratios

This study aims to investigate the undrained shear strength of sand with added materials at different mean diameter ratios D50/d50 (D50 and d50 respectively represent the mean diameter of host sand and added materials) in loose state by performing a series of undrained triaxial tests. For this purpose, a very low density index of sand matrix IDmat equaling to 0.00 was employed and the fines of C500 silt, Illite and Speswhite with distinct mean grain sizes were respectively added into the host HN31 sand at different contents Fc (5%, 10% and 15%). For comparison and further analysis, undrained triaxial tests were also carried out on Sand-Sand mixtures, created by adding the HN31 sand into the host HN31 sand at Fc of 5%, 10%, 14% and 18.7%. Results showed that, for low value D50/d50 (e.g., 1 for Sand-Sand), the undrained shear strength Su increased as Fc increased, which might be attributed to the increase of occlusal friction, and in that case the sliding of host sand became difficult. By contrast, in the case of higher value D50/d50 (e.g., 58.33 for Sand-C500, 159.09 for Sand-Illite and 500 for Sand-Speswhite), Su decreased as Fc increased. This was explained by the fact that, with increase of Fc, the quantity of added materials with small size increased, and in that case the sliding of host sand became easy. A critical value of D50/d50 (14.5) was thus deduced, which theoretically verified the negligible effect of Fc on Su. Furthermore, for sand mixed with fines (e.g., C500 silt, Illite and Speswhite clays), Fc has an insignificant effect on the peak value of Δu, while the increase of D50/d50 facilitated the generation of excess pore water pressure after reaching about Δumax. These findings provided useful information for analyzing the mechanical behaviour of sand with added materials in geotechnical practice.

Bayesian estimation of spatially varying soil parameters with spatiotemporal monitoring data

The characterization of in situ ground conditions is essential for geotechnical practice. The probabilistic estimation of soil parameters can be achieved via updating with monitoring data within the Bayesian framework. The estimation of spatially varying soil parameters is seldom undertaken with time-variant monitoring data. In this study, an efficient Bayesian method is presented for the estimation of spatially varied saturated hydraulic conductivity ks of unsaturated soil slope with spatiotemporal monitoring data. The computationally cheap surrogate model of the adaptive sparse polynomial chaos expansion method is adopted to approximate the transient numerical model. Markov chain Monte Carlo method is used for the probabilistic estimation of basic random variables. Based on the hypothetical cases, the effects of monitoring frequency and stage are studied. The errors and the uncertainties of the estimated ks fields are increased with the decreasing monitoring frequency. Bayesian estimation of spatial variability is more accurate when using the later stage of monitoring data. The estimated method is further verified with a real case study by the comparison of borehole data, dynamic probe test (DPT) data, and field monitoring data. The distribution of the soil types acquired from boreholes is reflected in the estimated ks. The estimated field of ks has a certain agreement with the borehole log and DPT measurements and can reproduce the spatial variability of the site to an acceptable degree.

Comparison of soil classification methods among domestic and oversea based on CPTU test

This article presents the comparison of two soil classification methods among domestic and oversea based on CPTU test in geotechnical practice of soft deposit subgrade. Although CPTU test exists earlier in the world, However, CPTU test has been not applied in geotechnical practice of road subgrade until in recent years in China. Two soil classification methods among domestic and oversea are applied to soil classification and differences of them are analyzed.

Laboratory-scale characterization of saturated soil samples through ultrasonic techniques

The propagation of poroelastic waves in a soil specimen is dependent on the physical and mechanical properties of the soil. In the geotechnical practice, such properties are obtained through in-situ geotechnical testings or element soil testings in the laboratory. These methods require almost advanced equipment and both testing and sample preparation may be expensive and time-consuming. This paper aims to present an algorithm for a laboratory-scale ultrasonic non-destructive testing to determine the physical and mechanical properties of saturated soil samples based on the distribution of stress waves. The ultrasonic setup, in comparison to most conventional soil lab testing equipment, is low-cost and non-invasive such that it reduces the soil disturbance. For this purpose, a poro-elastodynamic forward solver and differential evolution global optimization algorithm were applied to characterize the porosity, density, and other mechanical properties for a soil column. The forward solver was developed based on a semi-analytical solution which does not require intensive computational efforts encountered in standard numerical techniques such as the finite element method. It was concluded that the proposed high-frequency ultrasonic technique characterizes effectively the saturated soil samples based on the output stress wave measured by the receiver. This development makes geotechnical investigations time-efficient and cost-effective, and as such more suited to applications in remote areas.

Non-parametric machine learning methods for interpolation of spatially varying non-stationary and non-Gaussian geotechnical properties

Spatial interpolation has been frequently encountered in earth sciences and engineering. A reasonable appraisal of subsurface heterogeneity plays a significant role in planning, risk assessment and decision making for geotechnical practice. Geostatistics is commonly used to interpolate spatially varying properties at un-sampled locations from scatter measurements. However, successful application of classic geostatistical models requires prior characterization of spatial auto-correlation structures, which poses a great challenge for unexperienced engineers, particularly when only limited measurements are available. Data-driven machine learning methods, such as radial basis function network (RBFN), require minimal human intervention and provide effective alternatives for spatial interpolation of non-stationary and non-Gaussian data, particularly when measurements are sparse. Conventional RBFN, however, is direction independent (i.e. isotropic) and cannot quantify prediction uncertainty in spatial interpolation. In this study, an ensemble RBFN method is proposed that not only allows geotechnical anisotropy to be properly incorporated, but also quantifies uncertainty in spatial interpolation. The proposed method is illustrated using numerical examples of cone penetration test (CPT) data, which involve interpolation of a 2D CPT cross-section from limited continuous 1D CPT soundings in the vertical direction. In addition, a comparative study is performed to benchmark the proposed ensemble RBFN with two other non-parametric data-driven approaches, namely, Multiple Point Statistics (MPS) and Bayesian Compressive Sensing (BCS). The results reveal that the proposed ensemble RBFN provides a better estimation of spatial patterns and associated prediction uncertainty at un-sampled locations when a reasonable amount of data is available as input. Moreover, the prediction accuracy of all the three methods improves as the number of measurements increases, and vice versa. It is also found that BCS prediction is less sensitive to the number of measurement data and outperforms RBFN and MPS when only limited point observations are available.

Fractile-based method for selecting characteristic values for geotechnical design with LRFD

Load and resistance factor design (LRFD), also known as partial factor design, is becoming a design method of choice in geotechnical practice. The partial factors (i.e., resistance factor and load factor) to ensure safety are specified in the adopted code; however, engineers still need to select values for the uncertain soil parameters in a design. The selection of these parameter values, often called characteristic values, is quite challenging given soil variability and limited test data. This paper presents a fractile-based method for the selection of the characteristic values for the uncertain soil parameters in a design with LRFD. A framework that considers safety, cost, and robustness is established to determine an appropriate fractile for selecting the characteristic values. This framework is demonstrated with two examples, a drilled shaft in sand and a shallow spread foundation. The results show that robust designs can be achieved using LRFD with the characteristic values obtained through the proposed fractile-based method.

Structural geological methods in the geotechnical practice – rock mass rating. Advantages and problems of the rating methods

This paper presents a review of the most common geotechnical rock rating methods. The directional properties of the rock’s anisotropies are exemplified, by a case of resolution of stresses in folded and foliated metamorphic rocks. In such rocks, depending on the geometry of the folds, the ambient stress field can generate varying shear potential along the foliation planes in different parts of the excavation. The commonly used rating schemes, with accent on the geological feasibility of the classifications, are discussed – Protodiakonov’s rock scale, Terzaghi’s grading for construction of tunnels, then the rock quality designation of Deere, the Bieniawski’s rock mass rating (RMR), the Hoek, and Brown’s GSI and the Barton’s Q-system. It is emphasized that in spite of its broad use, the RQD is distorting the statistical weight of the joint groups as some steeply dipping joints may be completely neglected. It is recognized that the RMR is the simplest to use but underestimates the directional properties of the rock anisotropies, which require better definition and has no provision for lithologically varying rock packages, although it has the advantage of using the uniaxial compressive strength, which other systems do not employ. The Hoek and Brown’s criterion went too far with complex empirical relationships, which rely on extensive laboratory testing, so it is no more field criterion. Besides, its geological descriptive powers are rather poor and now, new form of GSI classification is offered for nearly every lithological type. Barton’s Q-system, being best suited to case studies of actual underground constructions, suffers from the fact that is centered nearly exclusively on joints, which may be justified in Norway, where mainly magmatic and high grade metamorphic rocks are present but should be applied cautiously in areas, where sedimentary, volcanic and strongly foliated rocks are exposed. In general, for all the discussed geomechanical classification systems (RMR, GSI, Q) the rule is valid, that they work better in an isotropic, strong but jointed rock masses and do not work well in week layered and foliated rocks.

Experimental Investigation of Geosynthetic‐Reinforced Pile‐Supported Composite Foundations under Cyclic Loading

A series of model tests were conducted in this study to investigate the deformation characteristics of geosynthetic‐reinforced pile‐supported (GRPS) composite foundations under cyclic loading. The effects of the applied load, the number of geogrid layers, and types of piles on the performance of the GRPS composite foundation were studied through 1g physical models of composite foundation with well‐planned instrumentation. Furthermore, a numerical fitting method was used to assess the relationship between the foundation settlement and the number of load cycles. The results show that with the increase in the magnitude of cyclic load and the number of load cycles, the settlement of GRPS composite foundations and the strain of the pile and geogrid increased accordingly. Adding rigid piles and increasing the number of geogrid layers both could reduce the settlement of GRPS composite foundations, while adding rigid piles was more effective. The relationship between the foundation settlement and the number of load cycles can be expressed by an exponential regression function. The pile strain varied from place to place that the strain of the upper part of the pile was greater than that of the lower part. The geogrid showed a significant impact on the load transfer mechanism of the composite foundation as the geogrid closer to piles endured larger strain. It is critical to consider the variation of the pile strain and the geogrid strain under cyclic loading in the geotechnical practice of composite foundation. The model test results also suggest that the use of GRPS system can effectively reduce the composite foundation settlement. This paper can provide useful references for developing the theoretical framework and design guides for GRPS composite foundations under cyclic loading.

Features of Piling and Their Interaction with Soil

In Belarussian geotechnical practice, there are often problems in the design, installation and testing of piles. These problems arise from incorrect knowledge of how piles interact with different soils. In this article, the authors propose solutions to such problems for improving the efficiency of pile foundations. The practical experience accumulated in the Republic of Belarus can also be useful for Iran and Iraq, where similar ground conditions occur during construction.