Geotechnical Practice Research Articles

Numerical study on stability of lignosulphonate-based stabilized surficial layer of unsaturated expansive soil slope considering hydro-mechanical effect

Numerous laboratory-based solutions have been proposed in the recent literature for the stabilization of unsaturated expansive soil by recycling lignosulphonate (LS). However, the practical assessments of these proposals for the treatment of the rainfall-induced surficial failure in unsaturated expansive soil slopes are required, considering the frequency of this failure and associated economic loss. Moreover, in conventional geotechnical practice, the slope stability is generally evaluated only with consideration of the hydraulic response of the soil, ignoring the hydro-mechanical coupling effect associated with the swelling behavior of soil. Since LS-based stabilizers mainly impart the reduction of the swelling potential of expansive soils, the assessment of the stability of the LS-treated surficial layer of unsaturated expansive soil slopes requires consideration of the hydro-mechanical effect. For this purpose, the uncoupled and hydro-mechanical coupled analyses were conducted for dealing with the hydraulic and hydro-mechanical responses of the surficial layer of soil slopes, respectively. Specialized experimentations and pertinent literature review were performed to acquire the required input data for these analyses. It is observed that the LS-based surficial layer treatment affects the pore water pressure (PWP) profiles as well as wetting front depth (WFD), which are the critical aspects for influencing the stability of unsaturated expansive soil slopes. Among all LS-based stabilizers, only the stabilizer named composite cementing admixture (CCA) reasonably ameliorated the PWP profiles and WFD of the slope considering disastrous environmental impacts (i.e., wetting–drying cycles). Moreover, the heave problem of expansive soil slopes was observed to be mitigated by LS-based treatment among which the CCA performed the most efficiently. Furthermore, the critical factor of safety (FS) required for slope stability was also affected by the LS-based treatment, whereas the CCA was observed to provide the safest critical FS for slope stability.

Exploration of Geotechnical Engineering Technology Innovation Method and Practice Based on Green Concept

Exploration of Geotechnical Engineering Technology Innovation Method and Practice Based on Green Concept

A multiple model machine learning approach for soil classification from cone penetration test data

The most popular methods for soil classification from cone penetration test (CPT) data are based on examining two-dimensional charts. In the last years, several authors have dedicated efforts on replicating and discussing these methods using machine learning techniques. Nonetheless, most of them apply few techniques, include only one dataset and do not explore more than three input features. This work circumvents these issues by: (i) comparing five different machine learning techniques, which are also combined in an ensemble; (ii) using three distinct CPT datasets, one composed of 111 soundings from different countries, one composed of 38 soundings with information of soil age and the third composed of 64 soundings taken from the city of São Paulo, Brazil; and (iii) testing combinations of five input features. Results show that, in most cases, the ensemble of multiple models achieves better predictive performance than any technique isolated. Accuracies close to the maximum were obtained in some cases without the need of pore pressure information, which is costly to measure in geotechnical practice.

Analysis method for consolidation of soil under vacuum preloading assisted by air booster

In this study, using pressurized air to split the soil between a booster tube and a plastic vertical drain (PVD), an air booster is employed to reduce clogging such that the vacuum preloading of the dredged soil is promoted. Under the framework of Hansbo's theory, an analysis method is conducted to understand the consolidation of dredged soil improved by vacuum preloading assisted by an air booster. Both increases in the consolidation stress and permeability of soil are introduced to consider the effect of the air booster on the consolidation of soil. The calculated results are compared with results of existing cases to verify the proposed method. A feasible range of increments for the consolidation stress and permeability of soil is derived from a back fit based on a coincided comparison between the calculated results and monitored data. The proposed method can be employed as a design tool to predict soil consolidation and settlement in geotechnical practice.

Earth Earth Anchor as a Deep Concrete Concrete Structure

Construction development of territories with complex engineering and geological conditions with the presence of unstable rugged relief is a complex geotechnical problem. Issues related to ensuring the safe production of installation work for the construction of any object in such territories relate to a multifactorial problem associated, first of all, with the development of special geotechnical technologies tied to real geotechnical conditions of the relief, loads from existing buildings and structures and, secondly, real their implementation at a specific construction site. Modern geotechnical construction has in its arsenal methods and technologies for solving these complex problems. The use of advanced computer programs such as GeoWall, GeoStab, Plaxis, etc. allows the development of geotechnical objects of any complexity. To identify the most appropriate geotechnical technology, it should be mandatory to use the interactive design method. This is “a developed project - an experimental site - a real project”. Moreover, this type of design should be multivariate using various geotechnical technologies and geotechnical structures. The feasibility study of all elements in interactive design is of no small importance. Any element in the design must be economically feasible and technically feasible. The considered case from the geotechnical practice of the construction of the object confirms the fact that thanks to the availability of modern design and production tools, it is possible to solve any complex problems.

The DINGO database of axial pile load tests for the UK: settlement prediction in fine-grained soils

ABSTRACT The availability of reliable field data is critical for the advancement of geotechnical engineering. This is particularly the case for piled foundations; due to the substantial geotechnical uncertainties. The settlement (performance) predictions from established analytical methods may deviate from field measurements by as much as an order of magnitude. This paper provides a statistical assessment of the uncertainty of predictions of pile performance under axial loading using an openly accessible geotechnical database of pile load tests from the United Kingdom. The collected database information was classified by pile type, location, test data quality and availability of geotechnical data. With reference to the data from fine-grained soils, two analytical models were employed to predict foundation settlement. The settlement prediction performance was then studied statistically and the model bias and error compared with reference to the aforementioned categories to identify the impact of different sources of uncertainty and evaluate the use of both models for future geotechnical practice. The two models investigated generally over-predict settlement, which is likely due to conservative selection of key model parameters, such as soil strength.

Coupled characterization of stratigraphic and geo-properties uncertainties – A conditional random field approach

Site characterization, which aims to characterize the subsurface stratigraphic configuration and the associated geo-properties, has long been a significant challenge in geological and geotechnical practice. Due to the complexity and inherent spatial variability of the geological bodies and the limited availability of borehole data, uncertainty is unavoidable in the characterized subsurface stratigraphic configuration and the associated geo-properties. In previous studies, the stratigraphic uncertainty and the geo-properties uncertainty were characterized separately. This paper proposes a conditional random field approach for a coupled characterization of stratigraphic and geo-properties uncertainties. The spatial correlation of the stratum existence between different subsurface elements and the spatial correlation of geo-properties are characterized by two autocorrelation functions, determined with the maximum likelihood principle. With the knowledge of the spatial correlation of the stratum existence, the stratigraphic configuration can be sampled using a modified random field approach. Then, the spatial correlation of the geo-properties is updated based on the sampled stratigraphic configuration. With the updated spatial correlation of the geo-properties, the spatial distribution of the geo-properties can readily be simulated with the conditional random field theory. The effectiveness of the proposed approach is demonstrated through a case study of probabilistic site characterization of an offshore wind farm site in Taiwan. To extend the applicability of the proposed approach, a probabilistic evaluation of liquefaction potential at this site under a given seismic shaking level is performed.

Machine learning method for CPTu based 3D stratification of New Zealand geotechnical database sites

Three-dimensional (3D) geotechnical site stratification is of vital importance in geotechnical practice. In this study, a set of methods for 3D site stratification based on CPTu measurements of New Zealand Geotechnical Database (NZGD) sites is proposed. One-dimensional (1D) soil stratification at discrete CPTu points is first conducted and then interpolated in 3D to achieve 3D site stratification. 1D soil stratification is achieved through a proposed soil classification model combined with a proposed soil layer boundary identification method, which achieves a correct soil profile length identification rate of 93%. The soil classification machine learning model classifies the soil within NZGD into three types, i.e. Gravel, Sand, and Silt, and is able to reflect the fines content for silty sand. The model innovatively incorporates local variation information of CPTu curves in the input for a random forest algorithm to significantly improve identification accuracy to over 90%. Accurately locating soil layer boundaries is achieved through proposing a modified WTMM boundary identification method. 3D site stratification is then realized through 3D interpolation of 1D stratification at discrete CPTu points using a generalized regression neural network (GRNN) method. The 3D site stratification method is validated for two independent geotechnical sites within NZGD, exhibiting the effectiveness of the proposed set of methods.

Monotonic and cyclic behaviour of sand in direct simple shear test conditions considering low stresses

Many geotechnical problems, such as buried pipeline–soil interaction and wave loading on sand seabeds, require the soil behaviour at relatively low effective stresses as compared to that in typical geotechnical practice. Monotonic and cyclic direct simple shear (DSS) tests were conducted on dry sand under constant normal stress, ranging from 12.5 kPa to 400 kPa, to investigate the effects of confining pressure on stress–strain behaviour. The tests were conducted using a combined advanced dynamic cyclic simple shear apparatus, which has a high-precision feedback system for controlling and measuring the forces and displacements while maintaining a high level of accuracy, which is essential, especially for tests at low normal stresses. The monotonic test results with this advanced system show an increased shear to normal stress ratio, thereby the mobilized friction angle, at the low-stress level compared to that of high normal stresses, as observed in some previous studies. The cyclic test results show that the load–displacement behaviour and cyclic compaction are governed by the normal stress. The sand becomes densified when the applied shear strain amplitude is greater than its threshold value. In constant strain amplitude cyclic loading, the lower normal stresses result in higher compaction; however, an opposite trend exists in constant stress amplitude cyclic tests.

Stability evaluation of cut slopes in highly weathered schists using limit equilibrium, kinematical and empirical methods

1. Extended abstractThe traditional limit equilibrium method and the kinematic analyses are the first choices in the geotechnical practice for the assessment of the slope stability of a particular rock slope. The reason is that very few empirical methods exist for this purpose.This paper presents results of the slope stability assessment with limit equilibrium, kinematical and empirical methods for over 50 deep cut slopes in highly weathered schists along the A2 motorway section Kicevo-Ohrid in RN Macedonia. The research area is mainly composed of phyllite, sericite schists, quartz-sericite schists and graphitic schists. These rocks are highly weathered, tectonically disturbed and often folded, which means they are prone to local deformations, especially in aspects of the long-term impact of atmospheric influences and the existence of unfavourable joint sets. Although most of the failures that occurred had local character, on several cut slopes global failure occurred. The slope stability assessment of the subject rock formations is a difficult challenge because the highly weathered phyllite and schists are difficult to be characterised, considering the uncertainties associated with the material anisotropy and the network of discontinuities.This study employs different failure mechanisms of cut slope stability in complex geological media. The rock masses were modelled according to the generalized Hoek-Brown criterion while the joints behaviour was modelled using the Barton-Bandis shear strength criterion. Rocscience software package was used for executing the limit equilibrium analyses and the stability analyses along discontinuities. The relatively new and intuitive empirical method Q-slope was applied for the stability assessment of the excavated rock slopes.According to the results and the findings, it can be emphasized that although the limit equilibrium analyses showed relatively stable slopes, significant failures on several cut slopes occurred on site. The stability conditions on site were confirmed with the kinematical analyses and the Q-slope method.The final decision of the slope geometry should be made after the inspection of the excavated surfaces because it is very difficult to register the discontinuity conditions before the construction phase starts. The best way to assess the stability condition is with a combination of different tools and methodologies, especially when we face highly weathered rock formations.The next step of this research will be to propose a methodology, where the long-term rock slope stability and the associated level of risk will be evaluated using graphical diagrams.

Application of in situ tests in unsaturated soils to analysis of spread footings

Spread footings are often supported in the upper zone of the soil profile, which is frequently unsaturated. It is common in geotechnical practice to use in situ testing to assess soil properties throughout the zone of influence for footings. These tests regularly include the Standard Penetration Test (SPT), and sometimes the Cone Penetration Test (CPT), and Pre-bored Pressuremeter Test (PMT). Yet degree of saturation is often not considered in the analysis of the test results. To investigate the importance of partial saturation, SPTs, CPTs, and PMTs were conducted at two test sites over two years covering dry and wet periods. Water content and suction profiles were established for each test date to assess their impact on the in situ tests. Results from this study revealed that changes in moisture content and suction had an important influence on the results of in situ tests and the soil parameters derived from these tests. Specifically, undrained shear strengths estimated from SPT penetration resistance and CPT tip resistance using empirical and semi-empirical equations, respectively, were significantly lower during wet periods compared to dry periods. Consequently, estimated bearing capacities for a shallow foundation varied considerably from dry to wet periods. Similarly, PMT limit pressures were significantly impacted by increases in moisture content. Associated reductions in limit pressures resulted in large reductions in predicted allowable bearing capacity. While PMT modulus did appear to decrease with increasing moisture, its impact on settlement was offset by the decrease in allowable bearing pressure under wet conditions.

Errors in Construction of Facilities in Restricted Conditions

The construction of facilities in cramped conditions requires a special approach to the need to develop and implement measures to ensure the safe operation of the buildings surrounding the building within the limits of geotechnical influence. Builders often neglect the impact of the new facility technology on the possible negative effects (cracks on facades due to uneven precipitation, heels, etc.) of the buildings in use. The term «minimum price» is still used when part of a building is erected below zero. This approach completely disregards the notion of «technical utility». At the same time the builders go to any tricks to reduce the cost. This «irrational» way of construction may eventually result in a substantial increase in the cost of constructing a zero part of a building and, as a general rule, in a longer construction period (agreement on a new project as a result of substitution of another geotechnical technology, passing of new construction expertise). This article examines one negative case from the geotechnical practice of constructing 16 storey dwellings next to an existing five-storey dwelling house.

Approaches to increase the load bearing capacity of bored injection piles

The issue of strengthening weak or overloaded bases is an important task for the development of underground space. This is especially true in the presence of alternating weak layers at the base. The paper considers a case from the geotechnical practice of strengthening the overloaded base of a reinforced concrete foundation plate of a 25-storey residential building under construction.Combined ground piles consisting of Get (type 1) ground concrete piles reinforced along the longitudinal axis with made drill-injection piles using electric discharge technology (EDT piles) are used as buried structures. This method of arrangement of a combined buried reinforced concrete structure is due to the need to increase the load-bearing capacity of the pile on the ground by two times or more

Common mistakes made under facility construction in cramped conditions

Construction of facilities in cramped conditions requires a special approach connected with the development and implementation of measures to ensure safe operation of the surrounding buildings within the geotechnical influence. Builders often neglect the impact of a new facility construction technology on possible negative effects resulted in the existing buildings (cracks on the facades due to uneven settlement, tilts, etc.). So far the concept of a minimum price has been used when erecting a building part below the zero mark. This approach completely ignores the notion of engineering viability. At the same time builders resort to every kind of trick to reduce the cost of construction. Such an irrational method may eventually result in a substantial increase in the cost of the zero building part construction. As a rule, it can increase the construction time (agreement on a new project when replacing it with another geotechnical technology, and undergoing new expert review). This paper examines a negative case from the geotechnical practice of constructing a 16-storey residential house next to the existing five-storey one.

Optimum Bored Pile Type Selection for Collapsible Soils

The operational reliability of the constructed buildings and structures depends on the rationally accepted type of foundation. In cases of presence of structurally unstable engineering-geological elements (EGE) in foundation, the increased requirements are imposed on design and construction of foundations. For foundation beds composed of collapsible soils of natural occurrence, the main deteriorating indicators are the relative collapsibility coefficient ɛse and the initial collapsible pressure Pse. The neglect of the influence of these indicators in most cases leads to deterioration in the reliable operation of the erected structures. The article presented here gives a case from geotechnical practice, when, a timely discovered error of not taking collapsible characteristics into account, made it possible to avoid an emergency situation at a structure under construction.

Utilization of Zeolite to Improve the Behavior of Cement-Stabilized Soil

In this paper, a series of unconfined compressive strength (UCS) tests were performed to study the effect of cement content, zeolite content, initial moisture content, number of freeze–thaw cycles, and curing time on the UCS of low-plasticity silty sand–clayey sand. The results indicate that zeolite can be used along with cement as a stabilizer to enhance mechanical behavior of the soils. The specimens containing cement and zeolite show better response with a higher UCS than the stabilized samples with cement or zeolite alone. The addition of zeolite has an important effect on the increase in both UCS value and failure strain of cement-stabilized specimen. However, the stress–strain curve of stabilized specimens is not influenced significantly by the increase of zeolite content from 3 to 9%. The UCS values of the stabilized specimens decreased as the number of freeze–thaw cycles increased. The cement-stabilized samples have freeze–thaw durability when zeolite content increases from 3 to 9%. The stabilized specimens with 6% cement and 9% zeolite have slightly higher freeze–thaw durability than other specimens. The UCS of the specimens compacted on the dry side is more than that of the compacted sample on the OMC or wet side of optimum for given additives contents. The specimens compacted on the dry side of optimum exhibited a lower failure strain. The implication of this work is significant in geotechnical practice; it provides a general knowledge of stabilization of soils using cement and zeolite and the quantities to use to achieve the desired geotechnical properties.

Study on anti-corrosion of PVA-treated wheat straw and its application in reinforcement of a silty soil

Silty soils are usually with poor mechanical performance and thus need reinforcement to meet the requirements in geotechnical practices. Wheat straw is low-cost, environment-friendly and wide spread, which has a great potential for use as reinforcement of the silty soils. In this study, the anti-corrosion effect of polyvinyl alcohol (PVA) treated wheat straw was investigated through the pore area ratio tests and the tensile tests. Test results indicated that the wheat straw was greatly improved in anti-corrosion, and tensile strength was considerably enhanced after the treatment. The optimum concentration of PVA solution and immersion duration were suggested. The PVA-treated wheat straw was then buried in the silty soil, and its corrosion resistance to the environment in the soil was validated under different moisture conditions. The treated wheat straw was then used as the reinforcing material for improvement of a silty soil. Triaxial compression were carried out on the samples reinforced with the material of various inclusion contents and lengths. Stress–strain curves and strength of the reinforced soil samples were analyzed, and the optimum inclusion content and length were discussed. The California bearing ratio (CBR) tests were then performed for the reinforced soil with the optimum inclusion content and length, and the test results showed that the reinforced silty soils met the requirements on CBR of the subgrade.

Entrapment of clay particles enhances durability of bacterial biofilm-associated bioclogging in sand

Utilization of bacterial biofilms and extracellular polymeric substances (EPS) for engineered bioclogging has recently garnered increasing attention in various geotechnical practices, such as leakage sealing in water-front structures, soil erosion protection, earthquake-induced liquefaction mitigation, and hydraulic barrier installation. However, the long-term durability is still questioned as to how long the biofilm-associated bioclogging would last as the biofilms readily degrade in nutrient-poor conditions. Therefore, we explore the feasibility of using fine clay particles to enhance the durability of biofilm-induced bioclogging. A series of column experiments were performed to compare the clogging durability of bentonite-associated biofilms against that of biofilms only. The results confirmed that a continuous feed of nutrients to the model bacteria, Bacillus subtilis, stimulated biofilm formation and caused a ~ 99% reduction in hydraulic conductivity of sands. However, nutrient-poor fluid flow caused instantaneous sloughing of biofilms and removal of bioclogging. By contrast, bioclogging associated with bentonite–biofilm aggregates demonstrated enhanced durability against shear detachment by fluid flows in a starved condition. EPS analysis and SEM imaging revealed that bentonite particles in the introduced suspension formed aggregates with biofilms by coating and being embedded within biofilms. This study suggests that the exploitation of bentonite–biofilm aggregations can remarkably enhance bioclogging durability in nutrient-poor conditions. This coupled clay–biofilm clogging approach is expected to provide benefits in developing a strategy for engineered bioclogging in geotechnical practices.

Shear wave velocity as a tool for characterising undrained shear strength of Nordic clays

There has been increasing recent use of shear wave velocity (Vs) measurements in geotechnical engineering practice. This has been driven by advances in cost effective and efficient methods of determination of Vs. Traditionally Vs measurements were used for seismic hazard assessment or dynamic analyses. However, they are being increasingly used for general site characterization studies, determination of strength and compressibility parameters by empirical correlation, assessment of sample disturbance effects and in the quality control of ground improvement schemes. This paper will briefly present the methods used to determine Vs and give some examples of Vs measurements in clays from Finland, Norway and Sweden. Despite similar depositional environments the range of Vs profiles for these three countries is significantly different. Differences in the profiles appear to be consistent with differences in basic clay properties, e.g. water content, density or plasticity. Nevertheless, the relationship between Vs and undrained shear strength (su) of clays appears to follow a similar trend for clays from Sweden, Finland and Norway. Correlations between Vs and su exist in the literature for Norwegian clays based on DSS tests. This paper studies the relationship between Vs and su from field vane test, which is commonly used in Finnish geotechnical practice. The proposed correlation is based on data from Sweden and Finland and is meant to be used for preliminary estimate of su from Vs in absence of test data or for validation of available test data.

A Laboratory Methodological Proposal for “Geotechnical Lime Stabilization of A-4 Soils”

This paper establish the beginning of a research process regarding the behavior of soils stabilized with lime. Generally, the geotechnical practice of soils stabilized with lime requires a first step conducted in the laboratory, to attest the features of “natural soils” in order to improve their behavior in term of geotechnical performance and, a second step, carried out onsite with experimental test fields, in order to verify the benefit obtained by the use of lime treatments. The topic of this research focuses on the first step above described. In order to provide geotechnical laboratory tests useful to our purpose, A-4 soils (according to HRB classification) and CL-ML (according to USCS soils classification) were tested. These soils show a large distribution in the Piedmont Po Plain (NW Italy): they outcrop in correspondence to terraced alluvial fans linked to alpine watercourses and are generally applied for stabilization with lime for foundation structures and pavements. Additionally, these soils are mainly inorganic with a marked tendency towards sandy silt soils with the presence of gravel. The presence of gravel results on a greater strain hardening in the behavior of shear strength of soils. Finally, in support of geotechnicians, who have to draw up specifications, a systematized laboratory methodology to follow for A-4 soils stabilization with lime is here reported and a detailed analyses of mechanical behavior obtained on “soil-lime-water mixtures” is described.