Geotechnical Index Research Articles

Experimental Study on the Water-Induced Weakening of Calcarenites

Carbonatic rocks, such as calcarenites, are very often subject to damage processes, causing a progressive degradation of their mechanical properties. In nature, in some cases, this phenomenon can cause the collapse of cliffs and underground cavities, with dangerous consequences for the anthropic environment. In this paper, the results of an experimental campaign, intended to both clarify and quantify the mechanical consequences of this process, are illustrated. To achieve such a goal, suitable physical and geotechnical indices are introduced and different time scales to describe the physical/chemical reactions induced by the water saturation of the material are taken into consideration. In particular, the authors have observed: (1) a short-term marked and instantaneous reduction in strength when water fills the pores of the rock; (2) a long-term dissolution; and (3) a progressive chemically induced reduction in the grain size. To describe the degradation processes induced by the material water saturation, owing to the complexity of the hydro-chemo-mechanical phenomena taking place within the material, suitably designed tests under controlled “weathering” conditions were also performed and discussed.

ALTERNATIF PONDASI TEROWONGAN LAYANG DALAM LAUT UNTUK PRASARANA TRANSPORTASI

A Submerged Floating Tunnel (SFT) is a tunnel that floats in water, supported by its buoyancy specifically by employing the hydrostatic thrust. In order to construct the foundation of the SFT, soil investigation has to be performed in advance. The soil investigation includes identification of subsurface soil profile, geotechnical index properties and parameters. Results of the soil investigation were used to he analyze and develop alternatives of the foundations for anchoring the prototype of the SFT. This paper discusses the alternatives of the foundations based on soil condition and applied tension leg. The research will be of interest to many practicing engineers and researchers regarding the subject matter.

Relationship between electrical resistivity and basic geotechnical parameters for marine clays

Recently, considerable efforts have been made in the attempt to map quick clay areas using electrical resistivity measurements. However there is a lack of understanding regarding which soil parameters control the measured resistivity values. To address this issue, inverted resistivity values from 15 marine clay sites in Norway have been compared with basic geotechnical index properties. It was found that the resistivity value is strongly controlled by the salt content of the pore fluid. Resistivity decreases rapidly with increasing salt content. There is also a relatively clear trend of decreasing resistivity with increasing clay content and plasticity index. Resistivity values become very low (≈5 Ω·m) for high clay content (>50%), medium- to high-plasticity (Ip ≈ 20%) materials with salt content values greater than about 8 g/L (or corresponding remoulded shear strength values greater than 4 kPa). For the range of values studied, there is poor correlation between resistivity and bulk density and between resistivity and water content. The data studied suggest that the range of resistivity values corresponding to quick clay is 10 to 100 Ω·m, which is consistent with other published limits. A comparison is made between two-dimensional electrical resistivity tomography (ERT) and resistivity cone penetration test (RCPTU) data for two of the sites and the two sets of data show similar trends and values irrespective of scale effect.

Inferring Hydrocarbon Migration and Sealing Potentials of Some Shales of the Anambra Basin (South-Eastern Nigeria) from Their Paragenesis and Geotechnical Index Properties

Shale samples from designated units of the Imo, Nsukka, Mamu, Enugu and Nkporo Formations of the Anambra Basin were subjected to X-ray diffraction and geotechnical index tests to determine the potential of the Formations to either create hydrocarbon migration pathways or to form seals for hydrocarbon entrapment. The X-ray diffraction results indicate that the shales are made up of silicate minerals with carbonates and sulphates. Results of the geotechnical index tests showed that the plasticity index (PI) for the Enugu shale ranges from 16 to 24 (average of 20) while the toughness index (TI) ranges from 0.4 to 0.8 (average of 0.7). The PI for the shales of Imo and Nsukka Formations ranges from 62 to 72 and 34–59 with averages of 67 and 46 respectively while their TIs range from 0.8 to 1.7 and 1.5–2.2 with averages of 1.3 and 1.9, respectively. These properties dispose the Enugu shale to easy amenability to loss of cohesion, deforming in a brittle manner, when subjected to shearing stress with the ability to create joints and faults that are pathways of hydrocarbon migration. Conversely, the properties of the shales of the Imo and Nsukka Formations give them the capacity to absorb high shearing stress without loss of cohesion thereby deforming in a ductile manner, which prevents the leakage of fluids in fluid migration. Hence, Enugu shale has the highest potential of creating hydrocarbon pathways while the shales of the Imo and Nsukka Formations are better seal rocks than others.

One-Dimensional Consolidation Parameters Of Cemented Paste Backfills / Parametry Jednowymiarowej Konsolidacji Podsadzki W Postaci Cementowej Pasty

Each year, mine and mill operations generate enormous amounts of two waste types - fine-grained tailings and coarse-grained waste rocks. Fine-grained tailings are either discharged in slurry form to surface tailings dams or delivered in cementitious form to underground mine stopes as backfilling, while coarse-grained rocks are typically stored by depositing as a dry material in large dumps. The engineering design of surface tailings dams or underground mine stopes is often controlled by the high compressibility and low shear strength characteristics of fine-grained tailings. Cemented paste backfill CPB indicating saturated, fine-grained backfills can undergo major consolidation settlement during early curing stages. Thus, a better understanding of the rate and magnitude of both differential and total settlement of CPB cured under stress is essential for a proper backfill geotechnical design. The consolidation parameters of CPB can be determined from an improved lab setup called CUAPS (curing under applied pressure system). This setup is capable of simulating the CPB placement and curing conditions, and measuring the consolidation parameters of CPB cured under effective stresses ranging between 0.5 and 400 kPa. In this study, a series of one-dimensional consolidation tests were conducted on CPB samples allowing for examination of the effects of binder type and rate as well as curing time on the compression properties (e.g., coefficient of consolidation cv, compression index Cc, and recompression index Cr) and the final geotechnical index properties (e.g., void ratio ef, water content wf, and degree of saturation Sf). Results showed that as the binder content increases, the initial resistance to consolidation increases. The cv value decreases over the course of time due to evolution of the CPB microstructure generated by the hydration process.

Laboratory-prepared iron oxide coatings on sands: Submicron-scale small-strain stiffness

Chemical weathering of iron-bearing rock minerals results in the formation of iron oxides, which can chemically adsorb onto soil surfaces, and/or absorb into their molecular structure. The objective of this paper is to use laboratory-prepared, iron oxide-coated sand to study the role of iron oxide coatings on the small-strain stiffness of coarse-grained soil. Ottawa sands were geochemically coated with iron oxides of goethite and hematite via a heterogeneous suspension reaction in the laboratory. Specimen preparation techniques were chosen to ensure that the soils were not cemented during preparation. SEM images, ICP analysis, and geotechnical index tests were used to characterize the submicron-scaled iron oxide coatings, and the bender element method was used to measure the shear wave velocities of uncoated and the two iron oxide coated sands. Contact mechanics and submicron scale mechanistic approaches were explored to interpret the experimental data, and results indicated that small-strain stiffness of iron oxide coated sands was higher than that of uncoated sands. Results also suggested that a small-strain stiffness behavioral hierarchy associated with iron oxide thermodynamic stability may exist. This study demonstrated that iron oxide coatings significantly influence sand grain-to-grain behavior, even in the absence of cementation or augmented contact area effects, due to an increase in the number of particle contacts present in the iron oxide coated sands.

Geotechnical characterization of marine sediments in the Ulleung Basin, East Sea

The geotechnical characteristics of Ulleung Basin sediments are explored using depressurized samples obtained at 2100 m water depth and 110 m below the sea floor. Geotechnical index tests, X-ray diffraction, and SEM images were obtained to identify the governing sediment parameters, chemical composition and mineralogy. We use an instrumented multi-sensor oedometer cell to determine the small-strain stiffness, zero-lateral strain compressibility and electromagnetic properties, and a triaxial device to measure shear strength. SEM images show a sediment structure dominated by microfossils, with some clay minerals that include kaolinite, illite, and chlorite. The preponderant presence of microfossils determines the high porosity of these sediments, defines their microstructure, and governs all macroscale properties. The shear wave velocity increases as the vertical effective stress increases; on the other hand, porosity, permittivity, electrical conductivity, and hydraulic conductivity decrease with increasing confinement. All these parameters exhibit a bi-linear response with effective vertical stress due to the crushable nature of microfossils. Well-established empirical correlations used to evaluate engineering parameters do not apply for these diatomaceous sediments which exhibit higher compressibility than anticipated based on correlations with index properties. Settlements will be particularly important if gas production is attempted using depressurization because this approach will cause both hydrate dissociation and increase in effective stress.

Method dependency of relationships between specific surface area and soil physicochemical properties

It is postulated that the behavior of fine-grained soils may be explained by the relationship between surface area and other geotechnical properties. To this end, there are several studies correlating geotechnical indexes with specific surface area (SSA). However, there is no universally accepted specific surface area determining method as several methods are available. Depending on the method employed, the measured specific surface area may show variations for a given soil. This is because the predictive power of each method depends on the type of minerals and organic matter that are present in the soil. Thus, different SSA determination methods yield widely different estimates of index properties and regression equations. To examine the role of method on SSA of soils, the SSAs of 32 soils with different mineralogies were determined using BET-N 2, EGME, MB-titration, and MB-spot test methods. The measured SSA of soils was correlated with their respective geotechnical index properties. Further, the data obtained in this study and those reported by previous researchers were compared. The results suggest that correlations between geotechnical index properties and SSA using different methods may not be comparable. Accurate prediction, however, is provided only if the relationship is calibrated using soils having similar physical and chemical characters.

Predicting soil swelling behaviour from specific surface area

Some geotechnical index properties, such as the liquid limit, plasticity index, clay content and cation exchange capacity, have been used to predict the swelling potential of soils. However, a literature review indicates that prediction of the swelling potential of soils using these index properties is not completely successful. At the same time, the methods used to determine swelling potential are time-consuming. Thus researchers have been investigating other methods that can predict the swelling potential of soils readily and accurately. To this end, in this study the BET (Brunauer, Emmett and Teller equation)-N2adsorption, ethylene glycol monoethyl ether (EGME) and methylene blue (MB) measured specific surface areas (SSA) are correlated with the swell index and modified free swell index of soils. The SSA and swell index of 16 remoulded and 15 undisturbed soils consisting of a wide range of mineralogy were determined. Results indicate that the correlation between the SSA and the swelling behaviour of the clayey soils examined is significant. A linear relationship is observed between the swell index, Cs, and the MB SSA: the swell index of the soils increases as the SSA increases. The correlation coefficient between the SSA and the modified free swell index (MFSI) is 0·93, indicating that the MB SSA does exert a significant influence on the swelling behaviour of clayey soils. Based on the test results obtained, a new swelling potential classification is proposed.

Bayesian Probabilistic Approach for the Correlations of Compression Index for Marine Clays

The compression index is an important soil property that is essential to many geotechnical designs. Over the decades, a number of empirical correlations have been proposed to relate the compressibility to other soil index properties, such as the liquid limit, plasticity index, in situ water content, void ratio, specific gravity, etc. The reliability and thus predictability of these correlations are always being questioned. Moreover, selection between simple and complicated models is a difficult task and often depends on subjective judgments. A more complicated model obviously provides better fit to the data but not necessarily offers an acceptable degree of robustness to measurement noise and modeling error. In the present study, the Bayesian probabilistic approach for model class selection is used to revisit the empirical multivariate linear regression formula of the compression index. The criterion in the formula structure selection is based on the plausibility of a class of formulas conditional on the measurement, instead of considering the likelihood only. The plausibility balances between the data fitting capability and sensitivity to measurement and modeling error, which is quantified by the Ockham factor. The Bayesian method is applied to analyze a data set of 795 records, including the compression index and other well-known geotechnical index properties of marine clay samples collected from various sites in South Korea. It turns out that the correlation formula linking the compression index to the initial void ratio and liquid limit possesses the highest plausibility among a total of 18 candidate classes of formulas. The physical significance of this most plausible correlation is addressed. It turns out to be consistent with previous studies and the Bayesian method provides the confirmation from another angle.

Engineering-geological properties of subsoil of Yenegoa in Niger Delta, Nigeria

The major aim of this research work is to determine the stratigraphy and engineering geological properties of foundation subsoils of Yenagoa, the fast growing capital city of Bayelsa state in the Niger Delta, which can be used as reference database for future infrastructure and environmental development of the area. A total of six (6) boreholes were drilled to depths of about 20m and soil samples were subjected to several geotechnical tests (including natural moisture content, particle size distribution, plasticity, bulk density, specific gravity, organic content, shear box test, consolidation, etc). The study revealed that the subsoil profile from 0 - 20m, essentially consists of an organic clayeysilt top layer, a middle sand stratum and a gravelly-sand at the bottom. There are great variations in the values of the geotechnical index properties of the soils hence the geotechnical data of one location cannot be used as a basis for design of foundation in other locations. The top organic silty clay horizon can only be considered as foundation substratum for very small/light civil engineering structures whilst the sand and gravelly- sand horizons constitute the best foundation substratum for medium and large civil engineering structures.

Evaluation of Linear Site-Response Methods for Estimating Higher-Frequency (> 2 Hz) Ground Motions in the Lower Wabash River Valley of the Central United States

The horizontal-to-vertical ratio of ambient noise ( H/V * N ) and the time-averaged S -wave velocity of the upper 30 m of soils and rock at a site ( V S 30 ) were evaluated for their suitability as techniques for estimating site effects in the lower Wabash River Valley area of southern Indiana and Illinois. We also calculated the horizontal-to-vertical ratio of the S wave ( H/V * S ) for the southwestern Indiana earthquake of 18 June 2002 and evaluated its effectiveness for estimating site effects. The database for the study consisted of new SH -wave seismic refraction/reflection profiles and ambient noise recordings at several blast monitor sites that recorded the M 4.5, 18 June 2002 earthquake, as well as the S -wave arrivals recorded by the blast monitors during the earthquake. Our results are limited to ground motions > 2 Hz because of the low-cut frequency of the velocity transducers used in the blast monitor systems. The shallow seismic refraction/reflection profiles allowed us to determine the S -wave velocities and soil-bedrock contact geometry, as well as the depth to bedrock, characteristic frequency, and V S 30 . These methods were compared with linear one-dimensional site amplification approximations. The results of the study are not encouraging. There is only a weak correlation between the linear 1-D amplification curves and the site effects predicted by the two horizontal-to-vertical ratios or the V S 30 classification of the site. Likewise, there is poor correlation between the two horizontal-to-vertical techniques or between V S 30 and the Modified Mercalli intensities reported for the 18 June 2002 earthquake. The results show that site effects in southern Indiana and southern Illinois are too complex for single-parameter characterization; consequently, a better evaluation likely requires a minimum of site-specific in situ seismic-velocity measurements, geotechnical index tests, and one-dimensional approximation.

Effect of curing under pressure on compressive strength development of cemented paste backfill

The mechanical performance of cemented paste backfill (CPB) placed in underground openings (e.g., mine stopes) often differs from laboratory-predicted performance, even under the same atmospheric curing conditions (ambient temperature and relative humidity). This is probably due to the specific self-weight consolidation, different drainage conditions and confinement pressures encountered in the paste backfilled stopes. A new test system named CUAPS (Curing Under Applied Pressure System) was designed at the Université du Québec en Abitibi-Témiscamingue (UQAT) to assess the hydro-mechanical performance of in situ CPB samples at laboratory scale. The CUAPS apparatus allows the effective curing of CPB samples subjected to an assortment of vertical pressure applications (curing under stresses) that can mimic in situ placement and consolidation conditions. The compressive strength development of CPB samples prepared from sulphide-rich mine tailings from Garpenberg polymetallic mine (Sweden) was investigated using CUAPS apparatus and conventional plastic moulds (unconsolidated undrained samples) in parallel. The effect of curing stress (i.e. simulating different consolidation conditions) on resultant geotechnical index parameters and hydromechanical properties of CPB samples was analyzed. The primary observation is the confirmation that the compressive strength development of the consolidated CPB samples is higher than that of unconsolidated undrained ones. It could be attributed to the removal of excess pore water mainly due to the applied pressure during the effective curing process, which seems to improve consolidation process of the CPB material. The results also account for the differences in the CPB strength observed between laboratory samples and in situ samples. Thus, CUAPS would be more suitable than conventional plastic moulds to collect data for preliminary and final design of CPB systems.

A Comparative Evaluation of the Geotechnical Index Properties of Clayey Sediments along the West Coast of India

Sediment core samples collected during geotechnical surveys along the West Coast of India in the near shore areas of Arabian Sea have generated data on the geotechnical index properties of clayey sediments up to nearly 5 m depth below seafloor. A comparative study of three sectors within themselves is attempted before carrying out a final evaluation between the sectors. Cohesive clayey sediments of Gujarat sector are comparable though widely variant in a few aspects; in the Maharashtra-Goa-Karnataka sector though, plasticity levels and clay type vary, and activity and consistency levels are quite similar. Though broadly comparable, the clayey sediments of Kerala-Tamilnadu sector have quite diverse characteristics that fail to conform to any particular pattern as each area has an exclusive set of geotechnical properties.

The Effects of Microstructure on Shear Properties of Shallow Marine Sediments

This study was undertaken to investigate the implication of geoacoustic behaviors in the shallow marine sediments associated with the changes in geotechnical index properties. Two piston cores (270 cm and 400 cm in core length) used in this study were recovered from stations 1 and 2, the western continental margin, the East Sea. Scanning electron microscopy (SEM) was employed to illustrate the effects of microstructure on shear properties. The direct SEM observation of sediment fabrics is inevitable to understand the correlation of the changes in geoacoustic properties to the sediment structure. The consolidation of sediments by overburden stress resulting in the clay fabric alteration appears to play an important role in changing shear properties. Water contents and porosity of sediments gradually decreases with increasing depth, whereas wet bulk density shows a reverse trend. It is interesting to note that shear wave velocities increase rapidly from 8 to 20 m/s while compressional wave velocities significantly fluctuate, ranging from 1450 to 1550 m/s with depth. The fabric changes in sediment with increasing depth for example, uniform grain size and well oriented clay fabrics may cause the shear strength increase from 1 to 12 kPa. Shear wave velocity is, therefore, shown to be very sensitive to the changes in undrained strength for unconsolidated marine sediments. This correlation allows an in-situ estimation of shear stress in the subsurface from shear wave velocity data.

Study on the swelling behaviour of blended clay–sand soils

Soils containing expansive clays undergo swelling that can be both detrimental and beneficial in various applications. In the Arabian Gulf coastal region, natural heterogeneous soils containing clay and sand (tills, shales, and clayey sands) support most of the civil infrastructure systems. Likewise, mixes of clay and sand are used for local earthwork construction such as roads and landfills. A clear understanding of the swelling behaviour of such soils is pivotal at the outset of all construction projects. The main objective of this paper was to understand the evolution of swelling with increasing clay content in local soils. A theoretical framework for clay–sand soils was developed using phase relationships. Laboratory investigations comprised of mineralogical composition and geotechnical index properties of the clay and sand and consistency limits, swelling potential, and morphology of clay–sand mixes. Results indicated that soil consistency of mixes of a local expansive clay and an engineered sand depends on the weighted average of the constituents. Mixes with 10% clay through 40% clay capture the transition from a sand-like behaviour to a clay-like behaviour. Influenced by the initial conditions and soil matrix, the swelling potential of the investigated mixes correlated well with soil plasticity (SP(%) = 0.16 (I p)1.188). The parameters sand void ratio and clay–water ratio were found to better explain the behaviour of blended clay–sand soils.

Environmental geological and geotechnical investigations related to the potential use of Ankara clay as a compacted landfill liner material, Turkey

Clay-bearing Upper Pliocene red clastics and Quaternary alluvial deposits occupy the Ankara basin. The clayey levels of the Upper Pliocene deposits, referred to as Ankara clay, is considered as a source for compacted clay liners due to their low coefficients of permeability and widespread distributions throughout Ankara. This study investigates the geological, geotechnical and mineralogical properties of the founding clayey soils at two sites of the Ankara region. The geotechnical index properties along with the hydraulic conductivities of the clayey soil samples collected from these sites were determined. A mathematical relation between the clay mineralogical content and hydraulic conductivity was established. The results of this investigation show that, from a geotechnical point of view, Ankara clay may be regarded as a highly suitable material for a compacted clay landfill liner given that its mineralogical compatibility with leachate is confirmed.

GEOLOGICAL CONTROLS ON INTACT ROCK STRENGTH. THE EFFECT OF ANISOTROPY

The factors that influence the strength and deformation of the intact rock are the mineral composition, the fabric, the grain size and the degree of alteration and weathering. Anisotropy is a characteristic of intact foliated metamorphic rocks (slates, gneisses, phyllites, schists). The current paper deals with the pronounced effect of the fabric of anisotropic rocks on the strength and deformation characteristics of intact rocks. It is part of ongoing research in the Department of Geotechnical Engineering, National Technical University of Athens. Testing was used to establish the anisotropic behaviour of selected metamorphic rocks. The effect of anisotropy on various mechanical properties (strength, deformation) and dynamic properties (wave velocity) was examined. The degree of strength anisotropy of these rocks can be indirectly estimated, by wave propagation through the rock, and thus they can be classified by means of geological and geotechnical indexes.

Influence of mineralogy on swelling and consolidation of soils in eastern Saudi Arabia

The mineral calcium sulphate transforms from anhydrite through bassanite to gypsum and then can convert back to bassanite and anhydrite. This transformation of calcium sulphate causes volume change that adds to the potential hazards with indigenous soils containing expansive clay minerals. Heave and settlement are the most important geotechnical problems associated with many argillaceous soils in eastern Saudi Arabia. Mineralogical evolution and engineering behaviour of such soils are governed by local geology and severe climatic and environmental conditions prevalent in the region. Based on laboratory investigations, this paper discusses the influence of mineralogy on swelling and consolidation of expansive clay, calcium sulphate forms, and their mixtures. Mineralogy is investigated using geotechnical index properties and thermal and X-ray diffraction analyses. Swelling and consolidation characteristics are directly determined and are studied in conjunction with microstructural assessment. Results indicate that under the hot and humid climate prevalent in eastern Saudi Arabia, form changes in calcium sulphate can take place in the time frame of engineering importance. The volume-change behaviour of local expansive clay depends on the form and amount of calcium sulphate present in the soil.Key words: calcium sulphate, expansive clay, swelling, consolidation.

The metastability of some gull-fill materials from Allington, Kent, UK

Samples of infill material from gulls in the Hythe Beds at Allington, Kent, England, were tested to determine their geotechnical index properties and their susceptibility to collapse when wetted under load in an oedometer. The soils accumulated during late Devensian, late Pleistocene, times within a periglacial environment. They probably represent, at least in part, an overlying layer of brickearth type material that gradually subsided into the gulls as the ice that occupied them melted with the onset of warmer conditions. The soils resemble, both in colour and their index properties, brickearth found elsewhere in Kent and in south Essex. All the gull-fill sample material had silt contents in excess of 75%, low dry densities (1.4–1.7 Mg m −3 ), medium to high porosities (35–47.5%) and carbonate contents below 0.5%. The results from the oedometer collapse tests showed that one of the samples was non-collapsible and that the others were conditionally collapsible. When these results were compared with several empirical collapse criteria, all derived from basic geotechnical soil properties, only some of the criteria showed reasonable agreement with the oedometerresults.