Developments in Sustainable Geomaterials and Environmental Geotechnics

This paper presents results of investigation of hydraulic conductivity of soil-bentonite backfill (referred as SB backfill) and sodium hexametaphosphate (SHMP)-amended soil-bentonite backfill (referred as SHMP-SB backfill) exposed to lead-impacted groundwater. Lead nitrate (Pb(NO₃)₂) solutions with various concentrations were tested as permeant liquids for the flexible wall permeameter hydraulic conductivity tests. Series of laboratory experiments were conducted to assess slump height of the backfills, free swell index of conventional bentonite with and without SHMP-amendment, and hydraulic conductivity of the backfills in tap water and Pb(NO₃)₂ solutions. The results showed that the moisture contents corresponding to the target slump were 38% and 32% for SB and SHMP-SB backfills, respectively. The free swelling index of conventional bentonite in the 50–60 mM Pb(NO₃)₂ solutions was enhanced with SHMP amendment. The hydraulic conductivity of SB and SHMP-SB backfills increased with increasing concentration of Pb(NO₃)₂ solutions as expected. The hydraulic conductivity of SHMP-SB backfill was below the commonly accepted value (10⁻⁹ m/s) regardless of the type of permeant liquid, whereas hydraulic conductivity of SB backfill was higher than 10⁻⁹ m/s in the Pb(NO₃)₂ solutions with concentrations of 50 and 500 mM.

In central part of India, an expansive soil commonly known as Black cotton (BC) soil is one of the most abundantly available geomaterial. It observed the presence of higher montmorillonite content. BC soil shows highly expansive and swelling characteristics, and exhibit elasto-visco-plastic behaviour. The soil undergoes continuous settlement under the application of constant load and swelling during unloading. It is regarded as an unsuitable filler material for construction projects. In this paper fly ash is used as a stabilizer and studied the relative swelling strain rate and creep behaviour of the blended mixture using the Elasto-Visco-Plastic model considers Swelling (EVPS) model. The experimental results along with major observation from the study are presented and discussed the effect of fly ash on the overall responses of BC-FA mixture in this paper.

Anthropogenic activity has created mine waste, particularly tailings, which are generated by many mining operations, and their storage provides an enormous challenge to designers and operators. The mechanical properties and characteristics of mine tailings can depend on many features such as the content of the desirable mineral in the ore, the efficiency of the mineral processing stage, and the duration of a specific operation. Furthermore, the microstructure of these deposits is influenced by the depositional technique used. Sphericity and roundness are physical characteristics that affect the mechanical behavior of mine tailings, and these parameters can often be ignored due to difficulty or subjectivity in obtaining them. In this paper, an image-based program has been used to assess the roundness and sphericity of tailing mine particles. To calibrate this procedure, digital images that contain geometrical objects were compared with results obtained with the procedure put forth here. Using a stereoscopic microscope equipped with an axial digital camera, digital images of different mine tailing grains at different scales were obtained to assess the sphericity and the roundness applying this approach.

Rock discontinuities are the basic component of the rock mass. Accurate investigation and collection of the spatial geometric information of rock discontinuities is an important basic work for rock mass stability analysis and evaluation. The three-dimensional laser scanning (3D-LS) technology has revolutionized the investigation manner of rock discontinuities, and has been used more and more widely in geological engineering investigation, especially the geological disaster emergency rescue project. Develop new 3D-LS methods with high accuracy and efficiency to identify rock discontinuities in an automatic or semi-automatic manner is a considerable challenge, as an alternative to the use of traditional manual methods. This work presents an optimal 3D-LS method that aims to achieve rapid registration and orientation of multi-site cloud and automatic/semi-automatic identify rock discontinuities. The method proposed herein starts multi-site cloud scanning based on RTK auxiliary orientation, and multi-site cloud scanning based on RTK auxiliary orientation. The development degree of rock discontinuities was then being estimated, and then proper method to extract the spatial orientation was determined: man-machine interactive extraction of orientations for the under-developed discontinuities or automatic extraction of multi-discontinuities using Discontinuity Set Extractor for the well-developed discontinuities. Through the single discontinuity scanning and orientation extraction tests and multi-discontinuities scanning and automatic orientation extraction tests of a rock specimen, the accuracy and efficiency of the methods proposed in this paper has been verified, and has high application promotion value. Besides that, a complete sensitivity analysis of the parameters has been performed for the automatic extraction of multi-discontinuities using Discontinuity Set Extractor, and the proper range of the parameters has been recommended.

Organoclays, often referred to as nanoclays (NCs), are organically modified phyllosilicates. They are derived from naturally occurring clay minerals and possess unique characteristics in improving the physical and mechanical properties of polymers and rubbers. Recently, NCs have drawn interest in the modification of asphalt binders as micro-scale fillers. A few recent studies have revealed that the addition of NCs in asphalt binders improved binders’ stiffness, aging characteristics, and fatigue resistance. This study aims to evaluate the changes in moisture resistance of different NC-modified asphalt binders through the surface free energy (SFE) technique. This technique estimates SFE properties of binders and aggregates from static contact angle (SCA) data measured from an optical contact angle analyzer (OCA). Further, this study examines the changes in chemical compositions (functional groups) of binders due to the addition of selected NCs by using the Fourier Transformation Infrared (FTIR) technique. To this end, a commonly used performance grade (PG) binder (PG 64-22) modified with four different types (shape and size) of NCs, namely, Cloisite® 15 (C-15), Cloisite® 20 (C-20), Cloisite® Na⁺ (C-Na), and Cloisite® Ca⁺⁺ (C-Ca) were evaluated in this study. The SFE data of five different types of aggregates from Oklahoma, namely, Davis Limestone (DL), Snyder Granite (SG), Dolese-Cooperton Limestone (DCL), Hanson-Davis Rhyolite (HDR), and Martin-Marietta-Mill-Creek Granite (MMMG), were used to perform their compatibility with the aforementioned NC-modified binders. The FTIR spectra revealed the presence of various alcohols, ethers, and esters in NC-modified asphalt binders. The moisture susceptibility analysis shows that the addition of NC results in an increase of SFE and cohesive energy of an asphalt binder, which are desired for improved moisture resistance. The addition of NC also shows improved compatibility in cases of all aggregates. Among the five aggregates, MMMCG showed the highest compatibility with all binders, followed by DCL, HDR, DL, and SG. In regard to NCs, the C-15 sample showed the highest compatibility followed by C-20, C-Na, and C-Ca.

Improvement of debilitated ground by strengthening it became the demand of construction industry and granular columns performs a satisfactory role in achieving the requirements. Granular columns have been used as the part of substructure for higher stiffness of ground, which influences overall compressibility of ground and causes lesser settlement of superstructure. Encasement of granular column further improves the efficiency of load transfer system, utilizes the bulging resistance to the nobler level together with intervening soil. In this paper an attempt is made to study the influence of multiple encasement layers on load carrying capacity offered by bulging of the granular column. In the laboratory model, various types of granular columns were installed in soft clay bed i.e. without encasement, with single layer encasement (SLE) (at the boundary of granular column) and with multiple layers of encasements (MLE). Load tests were conducted by loading the column area and unit cell area for each case. The behavior of bulging area and its impact on the stiffness is studied. The tests results indicate that the load carrying capacity of granular columns installed in soft clay bed with multiple encasement increases substantially in comparison with ordinary and single layer encasement.

Bogotá, the capital city of Colombia, is located on a large plain, known as the “SABANA”, 2600 m above sea level, on the eastern branch of the Andes mountains. The soils are of lacustrine and alluvial origin, mostly soft clays, several hundred meters thick. These were deposited during the last one million years (0.2 mm/year), over sedimentary rocks (from the cretaceous and early tertiary eras).

The upper 3 to 5 m are over consolidated due to desiccation and wetting; the water table fluctuates between 2- and 5-m below ground level. The clays below the topsoil suffer large volume changes due to water content changes. These movements, mostly consolidation but also sometimes expansion, result in a lot of damages to the infrastructure, and to light structures (houses and warehouses). Pavements suffer the most, with a lot of depressions that must be repaired (filled and repaved), with a large cost to the city; rarely do many roads last for the design period of asphalt pavement which is 10 years.

The paper explains the problem, how it works and some of the solutions implemented. It includes geotechnical characterization of the soils in the upper 5 m of the soil profile.

Modeling processes of a very different nature as a rule is concerned with the problem of approximation, inaccuracy and incompleteness of data on the simulated system, with its uncertainty. The concept of uncertainty is closely related to the concepts of heterogeneity and variability. In this study the measure of uncertainty is the correlation distance, which is defined as the length, within which the soil mass is assumed to be homogeneous. The study and analysis of uncertainty is reduced to two tasks: the construction of the uncertainty design model with a quantitative description of various aspects and the subsequent consideration of this model in stochastic calculations. To solve these problems a random limiting equilibrium method (RLEM) was used on the example of the dam stability assessment. An analysis of the results showed that under conditions of uncertainty of geotechnical system safety factor (Fs) is not a reliable parameter characterizing the dam slopes stability. With an increase in the heterogeneity of the soils composing the dam body Fs does not change, however, the probability of destruction increases. Also, the effect of heterogeneity on the slope stability is established in this work. With an increase in heterogeneity the Fs doesn’t change, but the reliability of the dam decreases.

The construction of hydropower engineering has many types of work, many equipments, three-dimensional intersection of working space, and fine division of labor in the construction market. Safety production management is facing huge challenges. In order to improve the safety production management level of hydropower engineering, the concept of mutual trust relationship in hydropower engineering safety management was put forward through the analysis of the characteristics of safety hazards in hydropower engineering and the mutual trust relationship between front-line production personnel and project managers. The following contents were included, such as the types, establish process and assessment methods of mutual trust relationship. Based on the ideas of bounded rationality and evolutionary game theory, the influence of factors such as rectification costs and rectification benefits of safety hazards on the mutual trust relationship of safety management was analyzed, and the development process and evolution results of the mutual trust relationship were revealed. Relevant suggestions were put forward such as increasing safety training, setting reward and punishment measures, and reducing the cost of rectification of safety hazards, and combined with a large hydropower engineering to verify the effectiveness of these suggestions, it provided reference for hydropower engineering safety management.