Geotechnical Laboratory Tests Research Articles

Fiber Bragg Grating-Based Performance Monitoring of Piles Fiber in a Geotechnical Centrifugal Model Test

In centrifugal tests, conventional sensors can hardly capture the performance of reinforcement in small-scale models. However, recent advances in fiber optic sensing technologies enable the accurate and reliable monitoring of strain and temperature in laboratory geotechnical tests. This paper outlines a centrifugal model test, performed using a 60 g ton geocentrifuge, to investigate the performance of pipe piles used to reinforce the loess foundation below a widened embankment. Prior to the test, quasidistributed fiber Bragg grating (FBG) strain sensors were attached to the surface of the pipe piles to measure the lateral friction resistance in real time. Via the centrifuge actuator, the driving of pipe piles was simulated. During testing, the variations of skin friction distribution along the pipe piles were measured automatically using an optical fiber interrogator. This paper represents the presentation and detailed analysis of monitoring results. Herein, we verify the reliability of the fiber optic sensors in monitoring the model piles without affecting the integrity of the centrifugal model. This paper, furthermore, shows that lateral friction resistance developed in stages with the pipe piles being pressed in and that this sometimes may become negative.

Stability, mobility and failure mechanism for landslides at the upper continental slope off Vesterålen, Norway

Abstract Several relatively small and spatially-isolated landslides with low mobility characterize the geomorphology of the upper continental slope off the Vesteralen islands. Here, we present results from a multidisciplinary study that integrates swath bathymetry data, high-resolution seismic reflection profiles and a multitude of geological and geotechnical laboratory tests from a 12 m long piston core in order to investigate the origin and hazard potential of these shallow landslides. Four of the landslides have their upper headwall around the 500 m isobath, whereas the main escarpments of another four landslides lie around 700 to 800 m. The slip planes of the translational landslides lie within laminated glacial marine clays, overlying a well-defined seismic horizon. These clays have a higher plasticity and water content compared to the surrounding soils (sandy clays), and they exhibit a modest strain-softening behaviour in triaxial tests. The interdisciplinary data set is used as input to various numerical analyses in order to assess the failure and triggering mechanisms for these landslides, as well as their hazard potential. Stability analyses, dynamic analyses and post-earthquake pore pressure dissipation modelling suggest that the margin is essentially stable and that it would require a large magnitude earthquake to trigger landslides. The resulting deformation and excess pore pressure generation occur primarily within the top 10 m of the soil, and they become more pronounced towards the surface. Finally, the run-out distance of these landslides is limited and strongly depends on the volume of displaced material and the slope angle. Mobility analyses reveal that the acceleration phase lasts about 1 min and that peak velocities may have reached up to 17 m/s. Hence, the consequences of such flows during a time of active seabed exploitation or the impact with seabed infrastructure could be devastating.

Micro-mechanical properties of crushable pumice sands

Pumice materials are problematic from engineering and construction viewpoints because of their lightweight, highly crushable and compressible nature. The mechanical properties of pumice sands at particle-size level were investigated to better understand their behaviour. X-ray computed tomography images showed internal and surface voids within the pumice particles. The surface characteristics of pumice were then compared with those of other hard-grained soils. Detailed investigation showed that pumice samples consist of different types of particles. Next, single-particle crushing tests were conducted and the results indicated that, under the same condition, the crushing strength of pumice increased with decreasing particle size, consistent with that observed in hard-grained soils; however, the crushing strength of pumice is one order of magnitude lower, highlighting its crushability. Finally, geotechnical laboratory tests such as cyclic undrained triaxial tests and bender element tests were performed on pumice sand specimens and the results were compared with those obtained from hard-grained silica sands. The results confirmed that the micro-level characteristics of the sand particles have a significant effect on their macro-level response.

Reclaimed Asphalt Pavement and Recycled Concrete Aggregate Blends in Pavement Subbases: Laboratory and Field Evaluation

In recent years, efforts have been made to incorporate reclaimed asphalt pavement (RAP) into pavement base or subbase applications by means of cement binder stabilization. This approach, however, may not be an environmentally friendly solution due to the high carbon footprint involved in the production of Portland cement. Recycled concrete aggregate (RCA), on the other hand, has been widely accepted in pavement applications. The sustainable solution of blending RAP with RCA was investigated in this research in an attempt to facilitate the usage of this blend as an alternative pavement subbase material. An extensive suite of geotechnical laboratory tests was undertaken on RAP with contents of 100, 50, 30 and 15% in blends with RCA. Results of the research study indicated that RAP/RCA blends with a low 15% RAP content meet the repeated load triaxial requirements for use in pavement subbase layers. Results of field performance of a pavement subbase constructed with untreated 100% RAP, at a private haul road field-demonstration site, confirmed that it had insufficient strength requirements to meet local road-authority pavement-subbase requirements. RAP and RAP/RCA blends, although found in this study to be not fully compliant with the local road-authorities requirements, could be potentially considered for lower traffic usage, such as haul roads and footpaths.

Modeling the pipe umbrella roof support system in a Western US underground coal mine

Weak roof conditions in underground coal mines are a common occurrence and cause significant problems in delaying production. This work presents innovative way of using directional drilling method for roof support in weak sandstone conditions other than conventional method such as bolting, trussing, and cribbing methods. This paper presents a conceptual model of pipe umbrella roof support methods intended for employment in the underground coal mining environment over a single entry of a development section.The design methodology was evaluated by examining a case study of a western U.S. coal mine, and its specific geologic conditions. This work used extensive literature reviews and laboratory test results of the mine. Geotechnical laboratory testing was performed for a weak sandstone channel material that occurs in large extents at the mine for input into numerical models. 2D and 3D models in FLAC were developed.These models utilize beam elements embedded in the continuum model. Results from the modeling showed that bending moments vary in the embedded beams based on the pipe spacing and the diameter of the pipes. A design criterion for a pipe umbrella system was based on the developed bending moment due to undermining and the commonly used flexure formula for bending stress. A safety factor approach was used in this paper for the design of a pipe umbrella system.

Assessment of structurally-controlled slope failure mechanisms and remedial design considerations at a feldspar open pit mine, Western Turkey

A variety of structural discontinuities crossing the slopes of Alipasa feldspar open pit mine, in western Turkey, caused different types of slope failures which led to interruptions in ore production. Thereupon, extensive geotechnical investigations, including geological characterization, in-situ and laboratory geotechnical testing, long-term movement monitoring, back-analyses and possible remedial measures, were conducted. Field observations and subsequent analyses suggested that the failures were limited to benches and the movement developed down-slope along discontinuities due to the following reasons: (i) unfavorable orientations of the foliation planes and joints, (ii) low shear strength along discontinuities and (iii) exceptionally heavy rains filling the tension cracks prior to failure. Comparisons between movement vectors and orientation of discontinuities showed a good agreement that indicates two types of instability, namely, planar and wedge failures. A back analysis procedure for the assessment of failures along the rough discontinuities, with non-linear failure envelopes, was successfully applied to the unstable slopes in the pit. The results of the 2-D limit equilibrium back-analyses and movement monitoring data suggested that the wedges and/or planar blocks formed at the uppermost benches tended to move down to fill the gap which resulted from the previous movement of the blocks in the benches. Remedial measures such as dewatering and reduction of height of the benches were suggested. Results of stability analyses conducted for possible remedial measures were presented and discussed.

Laboratory Evaluation of the Geotechnical Characteristics of Wastewater Biosolids in Road Embankments

An extensive suite of geotechnical laboratory tests were undertaken on wastewater biosolids to evaluate their sustainable usage as a fill material in road embankments. Geotechnical tests undertaken include particle size distribution, specific gravity, Atterberg limits, compaction, consolidation, hydraulic conductivity, California bearing ratio (CBR), field vane shear, direct shear, and triaxial shear. The geotechnical tests indicated that biosolids are equivalent to organic fine-grained soils of medium to high plasticity with high moisture content and liquid limit values. Consolidation tests indicate that biosolids have similar consolidation characteristics to that of organic soils. Shear strength tests on compacted biosolids samples indicated relatively high internal friction angles, comparable to that of inorganic silts. Compacted biosolids samples exhibit a modest cohesion comparable to organic clays. CBR tests results indicate high deformation potential of biosolids. Chemical and environmental assessment tests indicated that heavy metals, dichloro diphenyl trichloroethane (DDT) and organochlorine pesticides concentration along with pathogens (bacteria, viruses, or parasites) results were within acceptable limits for usage in geotechnical applications. With regards to contaminants containing nitrogen, phosphorus, and total organic carbon, the biosolids were found to require special protection in the event there is potential leaching/flow to adjoining water bodies. The geotechnical testing results indicate that untreated biosolids have insufficient bearing capacity to enable its usage as a fill material. The biosolids will have to be stabilized with an additive or blended with a high-quality material to enhance its geotechnical properties to enable it to be considered as an engineering fill material.

Dispersion Analysis in Geotechnical Laboratory Tests: Time-frequency and Time-scale Signal Transforms

Abstract Signal processing techniques are very important for the analysis of dispersion characteristics in geotechnical laboratory applications. The scope of this paper includes the study of advanced time-frequency and time-scale methods with regard to the development of an efficient method of group velocity determination based on the time-frequency behavior of propagating wave fields. The paper analyzes different time-frequency and time-scale transform methods for further use in group velocity determination as alternatives to conventional techniques. Besides the alternative itself, the presented scheme overcomes some existing problems of conventional methods in velocity determination. The advantages and disadvantages of the time-frequency and time-scale methods are presented and discussed. Finally, the applicability of given time-frequency and time-scale methods is validated by synthetic and experimental data.

APPLICATION OF MULTICHANNEL ANALYSIS OF SURFACE WAVES METHOD (MASW) IN AN AREA SUSCEPTIBLE TO LANDSLIDE AT UBATUBA CITY, BRAZIL

This paper presents results from the MASW method (multichannel analysis of surface waves) in a hill side area of unsaturated soils in the Ubatuba City,Brazil, a site where numerous mass movements have occurred. It discusses the influence of some acquisition parameters, such as, the natural frequency of geophones and minimum and maximum offsets in dispersion image results and does a comparative analysis of the results obtained in repeated tests carried out in the same place, under the same conditions, during the dry and rainy seasons. The comparative analysis for the inversion results in different periods showed that the values of S-wave velocity during the dry season were higher than those for the rainy season; these variations were attributed to the higher cohesion of the soil structure in the dry season. The final 1D velocity profile model with depth was consistent with the results of other geophysical and geotechnical investigations made. Although additional in situ and laboratory geotechnical tests, are necessary (to obtain soil parameters such as hydraulic conductivity, moisture content, soil suction, for example), for a complete characterization of the geotechnical properties of the investigated soil, the result shows that it is possible to use empirical correlations between the Vs profile, from the MASW method, and soil stiffness parameters in order to monitor areas susceptible to landslide.

Development of a new durability index for compacted shale

Many highway embankments in the East Central United States and around the world have been constructed using compacted shale. When weathered, shale tends to degrade into a fine-grained mass of soil with high compressibility and low shear strength. Unfortunately, there are no reliable methods to predict the long-term behavior of compacted shale subjected to deterioration resulting from the weathering process.This study presents the results of analyses for index and geotechnical laboratory tests on both weathered and unweathered shale samples, durability tests on unweathered samples, and compaction and triaxial shear tests on compacted weathered shale samples. The result of this effort is the development of a new durability index that better characterizes the durability behavior of shales than the standard slake durability index. This new index is simple to perform and is well correlated with index and geotechnical properties of unweathered and weathered shale. A secondary result of this study is the development of a simple and reliable means to evaluate the shear strength of compacted shale behavior and swelling of core samples as a function of durability.

Waste glass as additive to clayey material in subgrade and embankment of road pavement

In this paper the possibility of using waste glass in road construction is discussed. Samples of clay material with the addition of waste glass were subjected to a series of laboratory geotechnical tests performed at the Laboratory of Geotechnics at the Faculty of Civil Engineering and Architecture in Nis. The obtained results were compared with criteria defined in the document ?General technical requirements for road construction?. On this basis, the conclusions on the suitability of this mixture for the intended purpose are given.

Geotechnical Properties of Sandy Seafloors and the Consequences for Dynamic Penetrometer Interpretations: Quartz Sand Versus Carbonate Sand

The societal usage of coastal zones (including offshore wind energy plants, waterway deepening, beach conservation and restoration) is of emerging importance. Sediment dynamics in these areas result in sandy deposits due to strong tidal and wave action, which is difficult to simulate in laboratory geotechnical tests. Here, we present data from in situ penetrometer tests using the lightweight, free-fall Nimrod penetrometer and complementary laboratory experiments to characterize the key physical properties of sandy seafloors in areas dominated by quartzose (North Sea, Germany) and calcareous (Hawaii, USA) mineralogy. The carbonate sands have higher friction angles (carbonate: 31–37°; quartz: 31–32°) and higher void ratios (carbonate: 1.10–1.40; quartz: 0.81–0.93) than their siliceous counterparts, which have partly been attributed to the higher angularity of the coral-derived particles. During the in situ tests, we consistently found higher sediment strength (expressed in deceleration as well as in estimated quasi-static bearing capacity) in the carbonate sand (carbonate: 68–210 g; quartz: 25–85 g), which also showed a greater compressibility. Values were additionally affected by seafloor inclination (e.g., along a sub-aqueous dune or a channel), or layering in areas of sediment mobilization (by tides, shorebreak or currents). The study shows that the differences in in situ measured penetration profiles between carbonate sands and quartz sands are supported by the laboratory results and provide crucial information on mobile layers overlying sands of various physical properties.

Physical and Mechanical Properties of Serpentinized Ultrabasic Rocks in NW Turkey

Serpentinized ultrabasic rocks crop out at various places in the northwestern part of Turkey. They are the foundation rocks of some architecture and the ground under road bases in many areas. They are also frequently used for indoor work such as tables, shafts, pilasters, jambs for chimney pieces and ornaments of different kinds. Owing to their economic importance, in situ geophysical and geotechnical studies were conducted to determine their dynamic engineering parameters such as: P- and S-wave velocities, Poisson’s ratio, rigidity modulus, elasticity modulus, bulk modulus, natural period, safe bearing capacity, and bearing coefficient. Geophysical and geotechnical laboratory tests were performed on cylindrical specimens cored across and along the foliation planes: ultrasonic measurements of compressional pulse velocity (UPV), uniaxial compressive strength (UCS), point load index (Is(50)), and static elasticity modulus (Es); effective porosity (n), dry unit weight (DUW), and saturated unit weight (ϒs) sets of the rock specimens were determined. Finally, statistical correlations were performed by regression analysis to evaluate the relationships between UCS and Is(50), UPV, Es; UPV and Is(50), DUW, ϒs, n, and Es.

Recycled crushed glass in road work applications

A comprehensive suite of geotechnical laboratory tests was undertaken on samples of recycled crushed glass produced in Victoria, Australia. Three types of recycled glass sources were tested being coarse, medium and fine sized glass. Laboratory testing results indicated that medium and fine sized recycled glass sources exhibit geotechnical behavior similar to natural aggregates. Coarse recycled glass was however found to be unsuitable for geotechnical engineering applications. Shear strength tests indicate that the fine and medium glass encompass shear strength parameters similar to that of natural sand and gravel mixtures comprising of angular particles. Environmental assessment tests indicated that the material meets the requirements of environmental protection authorities for fill material. The results were used to discuss potential usages of recycled glass as a construction material in geotechnical engineering applications particularly road works.

Fine recycled glass: a sustainable alternative to natural aggregates

Fine recycled glass is the main by-product of the glass recycling industry in Victoria, Australia. Holding the maximum particle size of 4.75 mm, it mainly comprises of sand size particles with a small percentage of silt size particles. An extensive suite of geotechnical laboratory tests were carried out on representative samples of fine recycled glass. Test results were compared with other research works conducted on recycled glass sources around the world. Fine recycled glass is classified as well graded sand mixed with silt size particles, according to the Unified Soil Classification System. Laboratory experiments indicate that fine recycled glass exhibits geotechnical behavior similar to those of natural aggregate within the same soil classification. Hydraulic conductivity tests proved a better drainage capacity for fine recycled glass compared to natural aggregates. Results of a set of shear strength tests suggest that fine recycled glass shows shear strength behavior similar to that of natural sand with angular particles. An environmental assessment on organic content, debris level, total concentration and leachate concentration of fine recycled glass was undertaken to assess its environmental effects. Based on the tests results potential usages of fine recycled glass in geotechnical engineering applications are discussed.

Photogrammetry and Tomography Technique methods, its comparison with the conventional methods of geotechnical laboratory testing

This paper presents the investigation and testing of the foundation of the Cliff, whom has deteriorated due to the hydraulic and massive ice pressure and its freeze thaw cycles, a visual inspection and core samples were taken for the core reconnaissance of rock formation and elastic properties of the rock strata.Exploring these cavities by using the Crosshole Seismic Measurements and Tomography Technique methods [6] and comparing it with the conventional methods of geotechnical laboratory testing and its results, These Methods of the Crosshole Seismic and Tomography Techniques are used to determine the dynamic elastic properties of subsurface materials, to detect the fracture zones, and to delineate geological boundaries. Also to give other information which assists in the analysis of the Cliff stability or any foundation in order to have the correct and suitable methods and ways that helps in the reinforcement, renovation or reconstruction of any geotechnical foundation.

Geotechnical laboratory testing of biosolids

Biosolids is the end product of the wastewater treatment process. An innovative research project on biosolids is currently being undertaken in Melbourne, Australia to characterize its geotechnical characteristic which is essential to evaluate the performance of biosolids in various geotechnical applications. The geotechnical engineering characteristics of biosolids at Western Treatment Plant (WTP) in Melbourne, Australia was investigated and presented in this paper. The tests undertaken include consolidation, triaxial shear strength, hydraulic conductivity, compaction, California Bearing Ratio, Atterberg limits, particle density and particle size distribution.

Relationship between the residual shear strength and the methylene blue value in weathered clay soils

Abstract A new correlation is proposed between the residual shear strength and the methylene blue value (‘value of blue’; VB) for weathered clay soils on argillaceous bedrock and on alluvial soils in the Oltrepo Pavese area (Northern Italy), which can be considered as geologically representative of a large part of the Italian Apennines. Shallow landslides occur periodically in these soils as a result of high-intensity rainfall events. A number of soils were tested. Trench pits were used for sampling and for the soil profile description (lithology, structure, grade of weathering, thickness). Field surveys were integrated with some standard geotechnical laboratory tests. The methylene blue dye adsorption (VB) was determined in accordance with the French AFNOR standards. The residual strength friction angle was measured with direct shear tests; the procedure employed for the measure involved inserting the soil at the liquid limit in the direct shear ring, applying consolidation in stages and then shearing (Kanji method). The applicability of some existing correlations between the residual friction angle and index properties were tested. The correlations are characterized by a large amount of scatter in the data and tend to overestimate the residual friction angle. The VB test is easy and rapid to perform and appears to be a good indicator of the residual strength friction angle for the tested soils.

Geotechnical characterization and performance assessment of bentonite/sand mixtures for underground waste repository sealing

The objective of this study is to assess the performance of a bentonite/sand mixture for the sealing of underground waste repositories through performing geotechnical laboratory tests such as compaction and flow tests. Swelling, mechanical and shear strength tests along with analyses of seal/rock mechanical interactions of an axially loaded seal in rock have been conducted to recommend an optimum compacted bentonite/sand mixture and a suitable bentonite/sand seal length-to-radius ratio ( L/ a) as a function of water load. The bentonite used in this study was a natural sodium based non-treated bentonite possessing a high swelling potential and containing at least 90% montmorillonite. The results of the compaction permeameter tests led to a recommendation to select a mixture with a bentonite content of about 30% since it possessed the lowest hydraulic conductivity. Analysis of seal/rock mechanical interaction to reduce the possibility of seal slip was performed as a function of the axial load generated from a water column on the seal for seal length-to-radius ratios ( L/ a) ranging from 2.0 to 20.

Geotechnical Properties of JSC-1A Lunar Soil Simulant

For the success of planned missions to the moon in the near future, it is essential to have a thorough understanding of the geotechnical behavior of lunar soil. However, only a limited amount of information is available about geotechnical properties of lunar soils. In addition, the amount of lunar soils brought back to Earth is small. To help the development of new regolith moving machines and vehicles that will be used in future missions, a new lunar soil similant JSC-1A has been developed. A group of conventional geotechnical laboratory tests was conducted to characterize the geotechnical properties of the simulant, such as particle size distribution, maximum and minimum bulk densities, compaction characteristics, shear strength parameters, and compressibility.