Silt Mixtures Research Articles

Study of Activation Energy in Soil through Elastic Wave Velocity and Electrical Resistivity

Core Ideas The Arrhenius equation was applied to predict geophysical properties. Elastic and electromagnetic waves were selected. The activation energy exhibited a nonlinear curve. The elastic wave velocity and electrical resistivity of a medium are affected by changes in temperature, which can cause phase changes. The objective of this study was to predict the activation energy based on the Arrhenius equation using the elastic wave velocity and electrical resistivity. Sand with a degree of saturation of 40% was chosen as the medium; the characterization varied during freezing and thawing mechanisms. Silt was added to create a sand–silt mixture to observe the application of the Arrhenius equation under various soil conditions. The compressional wave velocity and shear wave velocity were measured using a piezo disk element and bender element. Four electrodes were used to measure the electrical resistivity of the soil. The temperatures were varied from 10 to −10°C. A thermocouple was installed in the specimen to accurately measure the temperature. The activation energy, which is a crucial parameter in the Arrhenius equation, was calculated using the relationship between the temperature and output values. The activation energies based on the elastic wave velocity and electrical resistivity exhibited different ranges due to the various factors causing chemical reactions in the final products. This study demonstrates that it is possible to predict the activation energy using elastic waves and electrical resistivity during temperature changes.

Dynamic Properties of Sand–Fines Mixtures

Dynamic properties namely shear modulus (G) and damping (h) are input parameters for predicting the ground response of natural soil deposits. The dynamic properties of sands and clays are dependent on many factors such as void ratio, confining pressure, strain amplitude, morphology, and plasticity characteristics. Considerable research has been reported in the recent past by Seed and Idriss (Soil moduli and damping factors for dynamic response analysis, 1970), Hardin and Drnevich (J Soil Mech Found Div ASCE 98(7):667–692, 1972); Seed and Idriss (Ground motions and soil liquefaction during earthquakes. Earthquake Engineering Research Institute, Berkeley 1982), Vucetic and Dobry (J Geotech Eng Div ASCE 117(1):89–107, 1991) and many others on dynamic properties of sands and clays. The factors affecting the dynamic properties of sands and clays are well documented, but soils generally, occur as mixtures of sand, silt and clay in various proportions. There is very little effort made in understanding the dynamic behavior of sand–fines mixtures and therefore there is a need to investigate the dynamic properties of sand–fines mixtures. In the present paper, the results of the behavior of sand–fines mixtures under cyclic loads are discussed. The experimental program consisted of a series of cyclic triaxial shear tests conducted as per ASTM D 3999 (Standard Test Methods for Determination of the Modulus and Damping properties of soils Using the cyclic Triaxial Apparatus. American Society for Testing and Materials 1991) to investigate the strain dependent shear modulus and damping of sand–fines mixtures of different plasticity. Sand was obtained from the Sabarmati river and three types of locally available fines i.e. low-plastic, medium- plastic and bentonite fines were used. Fines content was varied from 15 to 60%. The effect of fines content, plasticity, and relative density on shear modulus and damping is reported. Shear modulus at 0.005% strain level correlates well with the plasticity index for sand–fines mixtures of low to medium plasticity i.e. 0 < IP < 40.

Experimental characterization of the undrained instability and steady state of silty sand soils under monotonic loading conditions

This laboratory study aims to analyse the effects of gradation on the undrained instability using the undrained instability stress and steady-state ratios of silty sand soils. In this context, series of undrained compression triaxial tests were carried out on Fontainebleau (France) sand mixed with low plastic fines (Ip = 5%) range Fc = 0–30%. The samples were prepared at an initial relative density (Dr = 52%) and subjected to three different confining pressures ( = 100, 200 and 300 kPa). The test results indicate that the gradation has a significant influence on instability stress and steady-state ratios of sand–silt mixtures. Moreover, the obtained data confirm the existence of simple correlations between undrained instability stress, steady-state ratios, fines content, void ratios and grading characteristics (D10, D30, D50, D60 and Cu) of the materials under consideration. The introduced grading characteristics ratios (D10R, D50R and CUR) and the equivalent state parameter appear as pertinent parameters for the prediction of the undrained instability and steady-state of the sand–silt mixtures under study.

Suspended clays and silts: Are they independent or dependent fractions when it comes to settling in a turbulent suspension?

This research examines whether or not mixes of clay and silt in a turbulent suspension act and settle independent of each other. More specifically, we examine the following three questions: (1) does the presence of silt in suspension alter the size of mud flocs relative to those from a pure clay suspension of equivalent concentration? (2) can silt particles become bound inside clay flocs?; and (3) if silt is bound within flocs, how does this change the settling properties of the clay and silt mixture? These questions are explored through a series of laboratory experiments in which: (a) images of flocs and silt particles within the turbulent suspension are used to measure their size distribution as a function of time; and (b) the settling velocity of the individual aggregates from each of the suspensions are measured in a settling column. The experiments use pure clay, pure silt, and two different mixture ratios of silt and clay. The results show three primary conclusions. First, the presence of silt has no significant impact on floc size. Second, most of the silt in suspension became bound up within the floc aggregates. And third, the bound silt within the flocs increased the floc settling velocity by at least 50%. These results have potential implications for the modeling of suspended mud mixtures in rivers, estuaries, and turbidity currents.

Stability Analysis of River Dyke in Estuarine Environment

River dyke stability in estuarine environment is greatly influenced by the river stage fluctuations due to spring and neap tide variation in the zone of influence. The proposed river dyke will be located along the Nayachara island at the Rangafalla and Haldia end for protection of the proposed navigational channel across Nayachara, West Bengal, India. The navigational channel will connect the shipping route from Rangafalla to Haldia dock which the Kolkata Port Trust (KoPT) proposes as a long term solution for the shipping route to Haldia bypassing the existing troublesome route via Auckland and Jellingham, in order to reduce annual maintenance dredging burden to KoPT. The river dyke will be constructed artificially using sand as main core material. The soil profile of the site consists of mixture of river borne sand, silt and clay. The present site is located in a complex estuarine environment and the island has been formed due to siltation of very recent origin in geologic scale (about 70 years old). In this paper, stability analysis of proposed dyke for protection of the channel across Nayachara Island has been carried out using conventional limit equilibrium method and finite element method, considering the fluctuation of water level due to tidal effect. The factor of safety has been found out considering both drained and undrained conditions, simulating long term and short term stability of the dyke, respectively.

Three-Dimensional Stability Assessment of a Complex Landslide in the Rječina Valley, Croatia

The Grohovo landslide is located on the northeastern slope in the central Rjecina river valley, and the river mouth is located in the center of Rijeka city, Croatia. It is the largest active landslide along the Croatian coast of the Adriatic Sea. This complex retrogressive landslide was induced by earthquake occurred in the Rijeka City at the end of 18th century and was reactivated in December 1996. The Grohovo landslide poses a natural hazard to Rijeka city and it is necessary to perform 3D slope stability assessment. Slope deposits in the Grohovo landslide are mainly a mixture of clayey silt that was formed by the weathered Paleogene flysch rock and the fragments of limestone originating from the cliffs on the top of the slope. The basal failure surface is located at the contact between the slope deposits and the flysch bedrock. Based on borehole data, geological mapping, and the reconstruction of geological cross sections through the slope, this study interpolates the three dimensional shape and position of the sliding surface using a modified inverse distance weighted interpolation method. The entire Grohovo landslide and twelve separate sliding blocks, which have the same three-dimensional sliding surface, are analyzed using a modified 3D slope stability analysis based on a simplified force-equilibrium scheme.

Laboratory study on undrained shear behaviour of overconsolidated sand–silt mixtures: effect of the fines content and stress state

The post-liquefaction stability analysis of silty sand soil deposits that are prone to liquefaction becomes a major challenge in Geotechnical Earthquake Engineering. The objective of this laboratory investigation is to study the combined effect of the confining pressure and the low plastic fines (Ip = 5%) on the liquefaction resistance (undrained shear strength) of medium dense (Dr = 52%) overconsolidated sand–silt mixtures under monotonic loading conditions. In this context, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with fines content ranging from 0 to 40%. The different samples were prepared with dry funnel pluviation technique and subjected to different overconsolidation ratios (OCR = 1, 2 and 4). The results of this laboratory investigation indicate that the influence of low plastic fines on the undrained shear strength (liquefaction resistance) is clearly observed for the lower overconsolidation ratios (OCR = 1 and 2). This effect becomes insignificant for higher overconsolidation ratio (OCR = 4) for both confining pressures under consideration. The obtained data confirm the existence of a linear relationship between the undrained peak shear strength of overconsolidated Chlef sand samples (qpeak_OC) and undrained shear strength of normally consolidated Chlef sand (qpeak_NC) for the two selected confining pressures ( = 100 and 200 kPa) and initial relative density (Dr = 52%) under consideration.

Use of CPT and DCP based correlations in characterization of subgrade of a highway in Southern Ethiopia Region

Necessity of highway infrastructure development has been renowned all over the globe. Key success for highway projects mainly depends on the characterization of subgrade soil intended for thousands of kilometers. In practice, any one of the soil test data may not provide exact characterization of subgrade and at least minimum two tests can be used to develop design values of subgrade for a highway pavement. Also, there is a need to have relationship between two to three soil parameters so as to understand evidently about the soil characteristics and their behavior. Two test data such as CPT and DCP are utilized to develop statistical correlations for better site characterization. Ordinary least squares and the simple arithmetic mean methods are obtained for scatter plots of data pairs and different trends are fitted to the data. Correlation agreements between CPT and DCP for various combinations are plotted for 40 data sets. Liquid limit values ranged from 22 to 56 %, while plastic limits are ranging in between 16 and 43 %. Plasticity index values are varying from minimum 1 % to maximum of 29 %, indicating low to medium swelling potential. Based on the American Association of State Highways and Transportation Officials soil classification system, soil along the chosen highway alignment includes A–2–4, A–4, A–2–5, A–2–7, A–1(a), A–1(b), A–7–6 and A–6. Similarly, according to Unified Soil Classification System, the dominant soils along the highway stretched are placed into inorganic silts or organic clays (MH or OH), inorganic clays (CL), inorganic silts or organic silts (ML and OL), and combinations of the two (CL–ML). Deliberation of sleeve friction measurements resulted minor improvement in correlations and these may be considered trivial. According to Roberson’s chart, the distribution of CPT and DCP data obtained along the highway route encompasses four zones. Zone 4 (i.e., silt mixtures: clayey silt to silty clay), zone 5 (sand mixtures: silty sand to sandy silt), zone 6 (sands: clean sand to silty sand), and zone 8 (very stiff sand to clayey sand), with some scattered data points are located in zone 9 (very stiff, fine–grained). The correlations developed in this study indicates that, CPT (qc + fs) and DCP (qc) correlations are very much enhanced compared to other combinations studied in terms of higher coefficient of correlation and least transformation uncertainty. The CPT and DCP data obtained along the highway route is superimposed in Roberson’s chart to characterize the subgrade soil swiftly.

Reproductive properties of Zostera marina and effects of sediment type and burial depth on seed germination and seedling establishment

The dynamics of reproductive properties of Zostera marina in the Shandong Peninsula was recorded based on field investigations. Influences of sediment type and burial depth on seed germination and seedling establishment were studied in controlled laboratory conditions. In the field, the reproductive stage occurred from late March to late August. The reproductive properties showed obvious seasonal variation and had a significant impact on the cumulative seed production. Seed release began in early June, and the cumulative seed production was 10451±371.0seedsm−2, while the maximum production in a single week was 2907±258.1seedsm−2. The seed germination experiment showed significant effects of seed burial depth as well as the interaction between sediment type and burial depth on both seed germination and seedling establishment percentages (p<0.001). Seeds on the sediment surface or buried to 1cm could maintain high germination percentages (76±11.5% and 90±1.5%, respectively) regardless of sediment type. With increasing burial depth, germination percentages decreased gradually and were lower than 40% in all sediment types. Only seeds in sand:silt mixtures 2:1 could germinate when the burial depth increased to 5cm; the earliest germination appeared in the fifth week and the cumulative germination percentage was lower than 3%. Seedling establishment showed a similar trend to seed germination; seeds buried in shallow depths showed a higher seedling establishment percentage, and the maximum value was recorded in seeds that were buried to 1cm in sand:silt mixtures 2:1 (30.67%).

Undrained monotonic and cyclic response of sand–silt mixtures

Behavior of sand–silt mixture under cyclic loading and static loading has been studied. In cyclic triaxial test, specimens were prepared by moist-tamping method, and in static test both moist-tamping and air-pluviation methods were used to prepare the soil specimens. For the sand and the non-plastic silt, the Threshold Fines Content (Fth) and Limiting Fines Content (LFC) were found to be equal at 30% of this studied sand and silt. In moist-tamping method, it was observed that the Cyclic Resistance Ratio (CRR) and Static Shear Strength (SSS) decreased with increasing non-plastic silt content till LFC; later, it remained near about constant till the time when the specimen was pure silt at constant relative density. However, in air-pluviation method, there was a peak SSS at 5% silt content; later, the value decreased with increasing silt content till LFC, and thereafter it remained constant till the specimen was pure silt. All specimens prepared by air-pluviation method showed higher SSS than those prepared by moist-tamping method except clean sand. The concept of equivalent granular void ratio was found to be more appropriate to explain the behavior of sand–silt mixtures than that of relative density and global void ratio. In both moist-tamping and air-pluviation methods, the coefficient of permeability decreased with increasing non-plastic silt content till LFC; later, it remained near about constant till the specimen was pure silt.

Elastoplastic modeling of sand–silt mixtures

Experimental observations have shown that the mechanical behavior of sand–silt mixtures is highly dependent on the proportions of sand and silt. Our present paper proposes a simple elastoplastic model for the stress–strain behavior of sand–silt mixtures. The inter-grain contact index is firstly reviewed. A formulation which links the inter-grain contact index with the void ratio is then proposed and validated by measuring the index void ratios of various sand–silt mixtures. The formulation is applied to determine the position of the critical state line of sand–silt mixtures from sand to silt. Based on this formulation, a simple elastoplastic model is then developed. The model parameters can be easily determined from conventional triaxial tests and measurements of the index void ratios. The predictive capability of the model was examined by comparing the simulations and the experimental results of undrained triaxial tests on Foundry and Ottawa sand–silt mixtures from sand to silt.

Spotlight on Sediments: How is the Chesapeake Bay affected by storm flows from the Conowingo Reservoir?

Spotlight on Sediments: How is the Chesapeake Bay affected by storm flows from the Conowingo Reservoir?

Collapsibility, composition, and microstructure of loess in China

The collapse potential, mineralogy, microstructure, and particle morphology of a loess from the Loess Plateau, China, were characterized by double oedometer testing, X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and image analysis to elucidate the origin of its collapse behavior. Results show that the loess is highly collapsible with a maximum collapse index of 6.7% at a vertical stress of ∼200 kPa. The deposit contains both nonclay (i.e., quartz, albite, muscovite, and calcite) and clay (i.e., two chlorites) minerals. Microstructural, chemical, and image analyses indicate that interparticle calcite and clay cementation and silt particle morphology render the intact soil a metastable structure. Wetting-induced collapse is attributed to both primary and secondary microstructure features. The former is the abundance of weakly cemented, unsaturated, porous pure clay and clay–silt mixture aggregates whose slaking upon wetting initiates the overall structural collapse, while the latter consists of high porosity, unstable particle contacts, and clay coating on silt particles that act synergistically to augment the collapse. A conceptual microstructural model of a four-tiered hierarchy (i.e., primary clay and silt particles, clay aggregates and clay-coated silt particles, clay–silt mixture aggregates, and cemented aggregate matrix) is proposed to represent its structural characteristics and to account for its high collapsibility.

Piezocone-based prediction of secondary compression settlements of coastal defence structures on natural silt mixtures

This paper discusses the evaluation of long-term settlements of a predominantly silty seabed under a rubble mound breakwater using a simplified one-dimensional approach in conjunction with an empirical method for the estimate of one-dimensional creep characteristics of soils from cone penetration test data. In particular, the procedure is applied to the assessment of long-term settlements of two existing breakwaters built along the Venetian coastline as part of the coastal defence works included in the ambitious Mo.S.E. project for the temporary closure of the lagoon inlets. The effectiveness of two different CPTU-based empirical correlations for the estimate of the secondary compression index Cαε in sand and silt mixtures, recently calibrated on field data from a Test Site located in the Venetian Lagoon area, has been examined by comparing the computed settlements with actual vertical displacements obtained from Persistent Scatterer Interferometry (PSI). The paper aims at providing some practical guidance on the assessment of long-term settlements in soft soil deposits of different coastal areas, by illustrating a general and simple approach for the evaluation of secondary compression characteristics of a large variety of sediments, based on the use of a site investigation technique routinely employed in nearshore and offshore projects.

Undrained monotonic and cyclic response of sand–silt mixtures

Undrained monotonic and cyclic response of sand–silt mixtures

생물증강법을 이용한 오염해양준설토의 환경친화적 정화 및 재활용

Korea Maritime and Ocean University, Busan 49112, Republic of Korea(Received December 7, 2015; Accepted December 21, 2015)ABSTRACT: Occurrences of coastal dredged materials are ever increasing due to port construction, navigational course maintenance and dredging of polluted coastal sediments. Ocean dumping of the coastal dredged materials has become virtually prohibited as L ondon Treaty will be enacted as of the year 2012. It will be necessary to treat and recycle the dredged materials that may carry organic pollutants and heavy metals in a reasonable and effective process: collection of the dredged materials, liquid and solid separation, and treatment of organic compounds and heavy metals. In this study we have developed a continuous bioreactor system that can treat a mixture of silt and particulate organic matter using a microbial consortium (BM-S-1). The steady-state operation conditions were: pH (7.4–7.5), temperature (16°C), DO (7.5–7.9), and salt concentration (3.4–3.7%). The treatment efficiencies of SCOD, T-N and T-P of the mixture were 95–96%, 92–99%, and 79–97%. The system was also effective in removal of heavy metals such as Zn, Ni, and Cr . Levels of MLSS during three months operation period were 11,000 –19,000 mg/L. Interestingly, there was little sludge g enerated during this period of operation. The augmented microbial consortium seemed to be quite active in the removal of the organic component (30%) presen t in the dredged material in association with indigenous bacteria. The dominant phyla in the treatment processes were Proteobacteria and Bacteroidetes while dominant genii were Marinobacterium , Flaviramulus , Formosa, Alteromonadaceae_uc, Flavobacteriaceae_uc. These results will contribute to a development of a successful bioremediation technology for various coastal and river sediment s with a high content of organic matter, inorganic nutrients and heavy metals, leading to a successful reuse of the polluted dredged sediments.Key words: bioaugmentation, bioremediation, coastal dredged materials, reuse

Insight into the Effect of Granulometric Characteristics on the Static Liquefaction Susceptibility of Silty Sand Soils

Silty sands are the most common type of soil that is involved in monotonic or dynamic loading induced liquefaction. It is associated with a sudden drop of the shear strength of the soil leading to important damages to civil engineering and hydraulics structures. Therefore, it is of great importance to identify the influencing parameters on the liquefaction of soils for the purpose to develop design strategies and therefore mitigate earthquake damages due to liquefaction phenomena. Published literature indicates that particle shape and gradation are the most important parameters that would affect the liquefaction behavior of granular sandy soils. For this purpose, a series of undrained compression triaxial tests were carried out on reconstituted Chlef sand (Algeria) and Fontainebleau sand (France) samples with low plastic fines ranging from 0 to 40 % and initial relative density (Dr = 52 %) to study the liquefaction susceptibility of these soils. All the samples under study were subjected to an initial confining pressure of (\(\upsigma_{c}^{'}\) = 100 kPa). The evaluation of the obtained data indicates that the gradation and particle shape have a significant influence on the undrained shear strength (liquefaction resistance) of different silty sand soils under study. Moreover, test results confirm the existence of simple correlations between liquefaction resistance and different grading characteristics (D10, D30, D50, D60, and Cu) of the soils under consideration. New soil granulometric ratios (D10R = D10sand/D10mixture , D50R = D50sand/D50mixture, and CUR = Cusand/Cumixture) were introduced to discuss the sand–silt mixture liquefaction resistance susceptibility response. The used grading characteristics ratios (D10R, D50R and CUR) appear as pertinent parameters to predict the undrained shear strength response of the sand–silt mixtures for soil gradation under study.

OVERFLOWING TESTS AT THE POLISH DREDGDIKES RESEARCH DIKE – STABILITY OF THE DIKE SURFACE AGAINST EROSION

In the project DredgDikes the different research dike embankments were tested with respect to overflowing water induced erosion. Therefore, flumes were installed on the land side embankments in which the effect of overflowing water on the vegetated surface was investigated. On the Polish DredgDikes research dike near Gdansk, Poland, two parallel flumes were installed and the surface of the dike made of different mixtures of ash, silt and sand as well as clay was tested both in vegetated and unvegetated state. The results showed that the grass sods placed on the dike embankment had a comparably low erosion stability, particularly if placed directly on the hardened ash/silt dike cover with better results if placed on a clay cover, while the ash/silt mixture showed a high erosion resistance without vegetation. This results in the recommendation to use a thicker vegetation layer on top of the ash composite dike if the vegetation shall account for the erosion resistance or else, that even if the grass cover is washed away, a very solid cover made of the ash composite can withstand an overflowing event for considerable time.

Experiment inspired numerical modeling of sediment concentration over sand–silt mixtures

A series of flume experiments has been conducted to investigate sediment transport of sand–silt mixtures in both wave-only and wave-with-current conditions. Two types of sediments collected from a typical silty tidal flat were used: a silt-sized mixture with median grain size of 46μm, and a very fine sand-sized mixture with median grain size of 88μm. A high concentration layer (HCL) was observed near the bottom together with ripples under wave-only conditions. Sediment concentrations inside the HCL are quasi-stationary with the bulk Richardson number approaching a constant value. The thickness of the HCL can be scaled with approximately two times the damped wave boundary layer thickness. For the concentration profiles, we find that the vertical profile of the silt concentration appears different from the profile of the sand concentration, since the silt concentration decreases logarithmically within HCL, while homogeneously distributes outside the HCL. Finally, the reference concentration formulation of van Rijn (2007b) was recalibrated for the silt classes and applied in a multi-fraction model to predict the vertical concentration profile for silt and sand classes. The results show a promising agreement with the measurements, for both wave-only and wave-with-current conditions.

The effect of preloading on the liquefaction cyclic strength of mixtures of sand and silt

The paper studies the effect of preloading on the liquefaction cyclic strength of silty sands in the free field condition. This effect first is investigated by cyclic shear tests where horizontal shear stress oscillated about a zero mean value. Samples with varying fines content and at varying pre-stress ratios, densities and vertical stresses are tested. Test results show a marked increase of the liquefaction cyclic strength with the pre-stress ratio. The effect is more pronounced for tests with less liquefaction cyclic strength without pre-stress. Using critical state soil mechanics concepts, factors simulating the effect of preloading on the liquefaction cyclic strength are identified and based on the results of the laboratory program an empirical expression is proposed predicting the increase in the liquefaction cyclic strength induced by pre-stress. This expression is validated by numerical simulation of the relevant laboratory tests using an elastoplastic multi-mechanism model. In addition, based on the derived expression, a methodology is proposed predicting the increase in liquefaction cyclic strength as a result of preloading in the field in the case of the free field condition. This methodology is validated by the comparison with field measurements on liquefaction-susceptible soils before and after the field application of preloading. Last but not least, the increase in liquefaction cyclic strength which the proposed methodology predicts for typical soil profiles and embankment preloads is predicted and discussed.