A brief introduction to recent applications of several sediment-analysis techniques in palaeolimnological studies-dry bulk density and water content, mineral magnetism, carbonate content, and content of total organic carbon,nitrogen content and carbon/ni

Determination of dry bulk density and water content measurement of magnetic susceptibility (x) and saturation isothermal remanent magnetization (SIRM), determination of carbonate content, and determination of total organic carbon (TOC) content nitrogen content (N%) and carbon/nitrogen (C/N) ratio are some of the techniques which have been widely applied to lacustrine-sediment analyses. The techniques,complemented by others, are usually useful for revealing characteristics of lacustrine-sediments and thus for postulating hydrological regimes in the lake and environmental conditions and human activity around it in palaeolimnological studies. A very brief review is presented on recent applications of these techniques in palaeolimnological work with English literatures published mainly since 1985 and focus given on interpretations of results of these analyses related to palaeoenvironmental reconstructions. Low dry bulk density and high water content often imply relatively warm and wet conditions. High X and SIRM are usually resulted from reduced dilutions in the lake and intensified erosions on its catchment. both of which can be in turn attributed to environmental changes. While variations in patterns of X and SIRM may give further insight on mineral magnetism and thus implications on environmental conditions. Increased carbonate content seems likely to associate to warm and dry conditions.Increased TOC content is virtually used as one of indicators of warm and wet conditions and variations in C/N ratio may hint variations in relative contributions of different sources, aquatic and terrestrial, to the total organic matter in lake sediments and hence to lake-level fluctuations and climate changes.

Relative Dielectric Permittivity Variations during Compaction as a Mean of Compaction Quality Control: Case Study on Laterite Samples from Senegal

This study explores an alternative to the classical use of direct methods, as water content and dry density measurements, for compaction quality control. For this purpose, the dielectric properties of lateritic materials are determined by radar method and are compared with the permittivity determined from the Topp formula and from the CRIM model. This approach allowed to establish a relationship between the geotechnical properties determined during compaction such as dry density, water content or porosity with dielectric permittivity. The obtained results made it possible to determine an optimum dielectric permittivity corresponding to the optimum dry density and the optimum water content that could be used for non-destructive in situ compaction testing. Such an approach should improve the implementation and effectiveness of in situ compaction quality control of geotechnical infrastructures.

Stabilization of Clay Soil for the Durability of Structures: Case Study of the Soils of the Locality of Zalimé, Commune of Zogbodomey in the Republic of Benin

Structures erected on swelling clay soils are subjected to several stresses which are at the origin of the premature deterioration of the infrastructures. The soils being supports for the works, the improvement of their weak characteristics with cotton fibers will not only increase the bearing capacities of these soils and the resolution of the environmental problem, by eliminating the CO2 produced by the burning of the stems after harvest. The objective of this study is to contribute to the improvement of the characteristics by cotton stalk powder of the swelling clay soils used as the foundation of the infrastructures in order to guarantee their durability. Identification and mechanical parameterization tests were carried out on raw soil samples taken at 1.5 meters deep and on samples improved with cotton stalk powder at different levels (3%, 6% and 10%). The results from the physical tests reveal that the soil studied is very plastic silt. As for the mechanical tests, it appears that by adding 3% cotton stalk powder to dry density which goes from 1.435 t/m3 compared to the control sample with a dry density of 1.50 t/m3;which reflects an improvement in the compaction characteristics of the soil studied. The dry densities are 1.445 t/m3 and 1.29 t/m3 for the samples improved with 6% and 10% cotton stalk powder.

Physical and Mechanical Features of the Quaternary Basanites of the Cap-Vert Peninsula of Dakar (Senegal, West Africa)

This work presents the results of geotechnical tests carried out in the laboratory on specimens of Quaternary olivine basanites from the Cap-Vert peninsula of Dakar. The samples were taken following geotechnical investigations in the Fann-PE, Mermoz-Ouakam, Yoff and Ngor areas respectively. The results obtained show a dry density between 20.45 and 29.30 kN/m3 which corresponds to medium to high density basanites. The porosity varies between 0.33% and 4.20%. For microlitic basanites, the porosity remains low, on the other hand, for micrograined basanites;a slight increase in porosity is noticed. As for the methylene blue adsorption test value measured, it is between 0.25 and 1.10. The uniaxial compression strength (Rc) and Young’s modulus (E) vary respectively from 12.19 MPa to 41.748 MPa and from 1477.6 MPa to 7699.1 MPa. The low strength values are recorded in altered and vesicular basanites. Also, a correlation was made between uniaxial compression strength and porosity and showed a gradual decrease in strength with increasing porosity.

Effects of physical properties on electrical conductivity of compacted lateritic soil

Natural soils of various types have different electrical properties due to the composition,structure,water content,and temperature.In order to investigate the electrical properties of lateritic soil,electrical conductivity experiments have been conducted on a self-developed testing device.Test results show that the electrical conductivity of laterite increases with the increase of water content,degree of saturation and dry density.When the water content is below the optimum water content,the electrical conductivity of soils increases nonlinearly and the variation rate increases dramatically.However,when the water content,degree of saturation,or dry density increases to a certain value,the electrical conductivity tends to be a constant.In addition,soil electrical conductivity increases with the increase of temperature,and it is observed that the electrical conductivity decreases with the increase of the number of wetting–drying cycles.

On the hydro-mechanical behaviour of MX80 bentonite-based materials

Bentonite-based materials have been considered in many countries as engineered barrier/backfilling materials in deep geological disposal of high-level radioactive waste.During the long period of waste storage,these materials will play an essential role in ensuring the integrity of the storage system that consists of the waste canisters,the engineered barrier/backfill,the retaining structures as well as the geological barrier.Thus,it is essential to well understand the hydro-mechanical behaviours of these bentonite-based materials.This review paper presents the recent advances of knowledge on MX80 bentonite-based materials,in terms of water retention properties,hydraulic behaviour and mechanical behaviour.Emphasis is put on the effect of technological voids and the role of the dry density of bentonite.The swelling anisotropy is also discussed based on the results from swelling tests with measurements of both axial and radial swelling pressures on a sand-bentonite mixture compacted at different densities.Microstructure observation was used to help the interpretation of macroscopic hydromechanical behaviour.Also,the evolution of soil microstructure thus the soil density over time is discussed based on the results from mock-up tests.This evolution is essential for understanding the longterm hydro-mechanical behaviour of the engineered barrier/backfill.

Improvement of silty clay by vacuum preloading incorporated with electroosmotic method

A laboratory test was performed to assess the effectiveness of vacuum preloading incorporated with electroosmotic (EOM) treatment on silty clay (combined method) for reclamation projects like new disposal ponds, where the horizontal electrode configurations beneath the soil layer were possible and the drainage pipes and the prefabricated vertical drains (PVDs) system could be easily installed in advance before the sludge dragged from sea bed or river bed was filled into the site. Three groups of tests were conducted on the silty clay from Qinhuai River in Nanjing, China. The model is able to apply vacuum pressure at the bottom of the soil layer and a direct current electric field simultaneously. It is also possible to measure the pore pressures at different depths of soil column, and the changes in settlement and volume with the elapsed time. In this study, the vacuum preloading method, vacuum preloading applied at the bottom (VAB method), was applied and the cathodes were installed beneath the soil layer. The results obtained indicate substantial reduction in water content, and increases in dry density and undrained shear strength in comparison with those obtained by the vacuum preloading only, particularly at the positions close to the anode. The combined method utilizes the vertical drainage flow created by the electroosmosis integrating the horizontal drainage flow created mostly by the vacuum pressure. The total drainage flow can be calculated as a result of the vertical drainage flow by electroosmosis only and the horizontal drainage flow by the vacuum preloading only. The way of placement of the cathode and the anode in the combined method also overcomes the disadvantage of EOM method itself, i.e. the appearance of cracks between the anode and the surrounding soil. Moreover, it is observed that the vacuum preloading plays a primary role in earlier stage in deduction of free pore water; meanwhile, the electroosmotic method is more efficient in later stage for absorbing water in the diffused double layers of soil.

Performance evaluation of cement-stabilized pond ash-rice husk ashclay mixture as a highway construction material

This paper reports the results of an investigation carried out on clay soil stabilized with pond ash(PA),rice husk ash(RHA) and cement. Modified Proctor compaction tests were performed in order to investigate the compaction behavior of clay, and California bearing ratio(CBR) tests were performed to determine the strength characteristics of clay. For evaluation purpose, the specimens containing different amounts of admixtures were prepared. Clay was replaced with PA and RHA at a dosage of 30%e45% and5%e20%, respectively. The influence of stabilizer types and dosages on mechanical properties of clay was evaluated. In order to study the surface morphology and crystallization characteristics of the soil samples, scanning electron microscopy(SEM) and X-ray diffraction(XRD) analyses were carried out,respectively. The results obtained indicated a decrease in the maximum dry density(MDD) and a simultaneous increase in the optimum moisture content(OMC) with the addition of PA and RHA.Multiple linear regression analysis(MLRA) showed that the predicted values of CBR tests are in good agreement with the experimental values. Developed stabilized soil mixtures showed satisfactory strength and can be used for construction of embankments and stabilization of sub-grade soil. The use of locally available soils, PA, RHA, and cement in the production of stabilized soils for such applications can provide sustainability for the local construction industry.

The coupled hydro-mechanical behaviours of compacted crushed Callovo-Oxfordian argillite

Callovo-Oxfordian （COx） argillite obtained from the excavation of high-level radioactive waste geological disposal has been evaluated as an alternative sealing/backfill material in France. This paper presents an experimental investigation into the hydro-mechanical behaviour of compacted crushed COx argillite. A series of oedorneter compressive tests including various loading-unloading cycles were conducted on COx argillite powders at different initial water contents. After reaching the desired dry density （2.0 Mg/m^3）, the vertical stress was reduced to different levels （7.0 and 0.5 MPa） and the compacted sample was then flooded under constant volume conditions while measuring the changes in the vertical stress. It was found that the initial water content significantly affects the compressive behaviour. The measured saturated hydraulic conductivity is less than 1×10^-10m/s.

Experimental study on the dynamic modulus of compacted loess under bidirectional dynamic load

The dynamic characteristics of compacted loess are of great significance to the seismic construction of the Loess Plateau area in Northwest China,where earthquakes frequently occur.To study the change in the dynamic modulus of the foundation soil under the combined action of vertical and horizontal earthquakes,a hollow cy-lindrical torsion shear instrument capable of vibrating in four directions was used to perform two-way coupling of compression and torsion of Xi'an compacted loess under different dry density and deviator stress ratios.The results show that increasing the dry density can improve the initial dynamic compression modulus and initial dynamic shear modulus of compacted loess.With an increase in the deviator stress ratio,the initial dynamic compression modulus increases,to a certain extent,but the initial dynamic shear modulus decreases slightly.The dynamic modulus gradually decreases with the development of dynamic strain and tends to be stable,and the dynamic modulus that reaches the same strain increases with an increasing dry density.At the initial stage of dynamic loading,the attenuation of the dynamic shear modulus with the strain development is faster than that of the dynamic compression modulus.Compared with previous research results,it is determined that the dynamic modulus of loess under bidirectional dynamic loading is lower and the attenuation rate is faster than that under single-direction dynamic loading.The deviator stress ratio has a more obvious effect on the dynamic compression modulus.The increase in the deviator stress ratio can increase the dynamic compression modulus,to a certain extent.However,the deviator stress ratio has almost no effect on the dynamic shear modulus,and can therefore be ignored.

Effects of Soil-Cement Stabilization on the Index Properties of Subgrades of Three Selected Roads in the Niger Delta Region of Nigeria

In this study, the impact of soil-cement stabilization on the index properties of the subgrade of roads was investigated. Efforts were on the means of improving the bearing capacity of the subgrade of a flexible pavement structure. Three selected roads (Ogbia-Nembe, section of the East-West Road and section of Port Harcourt-Aba Road) in the Niger Delta Region of Nigeria were examined to determine the effect of sand-cement stabilization on the compaction index property of their undisturbed subgrade and the optimal ratio of soil-cement on the expansive soils at which the California Bearing Ratio (CBR) is optimized. Disturbed soil samples were collected from twenty trial pits on each of the three study roads using a hand ulger and tested for their respective compaction index properties. It was discovered that their California Bearing Ratio (CBR) was very low. Some of the collected specimen materials were stabilized with varying percentages of soil-cement contents ranging from 6% - 14% in order to ascertain its effects on the compaction index properties of the sample soils. Results of the various stabilization test procedures show that: Stabilization of the soil using Soil-Cement Stabilization affected the Compaction Index properties of the soil and further improved the California Bearing Ratio (CBR). On the Ogbia-Nembe Road;Soil-Cement stabilization improved the CBR and is optimized at a 10% sand-cement ratio with optimum moisture content ranging from 6.2% - 14%, maximum dry density ranges from 1700 - 1780 kg/m3, yielding an average CBR of 42.7% for soaked samples. On the section of East-West Road from Eleme Junction to Etteh Junction;Soil-Cement stabilization improved the CBR and is optimized at a 14% sand-cement ratio with optimum moisture content ranging from 6.2% - 14.2%, maximum dry density ranges from 1660 - 1800 kg/m3, yielding an average CBR of 43.9% for soaked samples. On the section of Port Harcourt-Aba Express Road from Eleme Junction to Osisioma Junction;Soil-Cement stabilization improved the CBR and is optimized at a 12% sand-cement ratio having an optimum moisture content ranging from 5.4% - 17.3%, maximum dry density ranges from 1610 - 1740 kg/m3, and an average California Bearing Ratio for soaked samples at 40%.

Size Variation of Palm Kernel Shells as Replacement of Coarse Aggregate for Lightweight Concrete Production

The utilization of palm kernel shells (PKS) as an alternative to conventional materials for construction is desirable to promote sustainable development. The purpose of this study is to investigate the properties of lightweight concrete produced with different sizes of PKS of 6, 8, 10, 12 mm and mix (consisting of 25% each of the four sizes). RPK sizes were used to replace coarse aggregate in the concrete and cured for 7, 14, 21 and 28 days. The tests performed on the concrete are dry density, compressive strength, flexural strength, EDS and SEM. It was revealed that the densities of the concrete specimens were all less than 2000 kg/m3, which implies that the PKS concrete satisfied the requirement of lightweight concrete for structural application. The compressive strength of the 12 mm PKS concrete specimens at 28-day of curing was 10.2 MPa which was 4% to 15.9% better than the other PKS sizes concrete. The flexural strength of the 12 mm PKS concrete specimens at 28-day of curing was 2.85 MPa which was also 3.2% to 57.07% better than the other PKS sizes concrete. It was also revealed by the SEM analysis that there was a good bond between the palm kernel shells and the mortar. A high calcium-silicate content was found in the concrete which resulted in a Ca/Si ratio of 1.26 and Al/Si ratio of 0.11. The study therefore concludes that size variations of PKS as replacement of coarse aggregate have an influence on the properties of the lightweight concrete and recommends 12 mm PKS for use by construction practitioners for lightweight concrete structural application.

Soil Improvement Using Waste Materials:A Review

With the industrialisation,industrial byproducts are produced in large quantities and create nuisance to natural habitats.The disposal of these wastes like fly ash,marble powder,construction and demolition(C&D)waste,brick powder,agricultural wastes etc.has become the potential threat to the ecosystem and need some real solutions.The direct disposal of such wastes into open land or water bodies causes circumambient pollution.One of the potential solutions is to utilise these wastes in the construction industry on large scale as subgrade rehab or additive to cement based materials.In the present study,the compaction and strength characteristics of stabilised soil have been studied by using various waste materials i.e.lime,cement,plastic waste,industrial waste,fibre,mushroom waste,wet olive pomace etc.and reviewed.The addition of additives improved the engineering properties of soil significantly.

Effects of moisture content and dry bulk density on the thermal conductivity of compacted backfill soil

Soil backfilling and compaction are often involved in urban construction projects like the burying of power cables.The thermal conductance of backfill soil is therefore of great interest.To investigate the thermal conductivity variation of compacted backfill soil,10 typical soils sampled in Zhejiang Province of China with moisture contents of 0%–25%were fully compacted according to the Proctor compaction test method and then subjected to thermal conductivity measurement using the thermal probe method at 20℃.The particle size distribution and the chemical composition of the soil samples were characterized to analyze their effects on thermal conductivity.The results showed that the maximum thermal conductivity of fully compacted soils generally exceeds 1.9 W/(m·K)and is 20%–50%higher than that of uncompacted soils.With increasing moisture content,soil thermal conductivity and dry bulk density first increase and then remain unchanged or decrease slowly;the critical moisture content is greater than 20%in most cases.Overall,the critical moisture content of soils with large particle size is lower than that of those with small particle size.Quartz has the highest thermal conductivity in the soil solid phase,and the mass percentage of quartz for most soils in this study is more than 50%,while that for yellow soil is less than 30%,which leads to the thermal conductivity of the former being nearly twice as great as that of the latter in most circumstances.Based on regression analysis,with moisture content and dry bulk density as the independent parameters,the prediction formulae for the thermal conductivity of two categories of compacted backfill soils are proposed for practical applications.

Phase Evolution Study and Optimization of the Heat Treatment Process for High Current Capacity Bi-2223 Tapes

Powder in tube process（PIT） was adopted for the fabrication of single filament Bi-2223 tapes, and a heat treatment process including the first heat treatment（HT1）, intermediate rolling（IR）, and second heat treatment（HT2） was performed. The phase evolution mechanism and microstructure changes during these heat treatment processes were systematically discussed. The influences of HT1 parameters on the phase evolution process of Bi-2223 tapes were discussed. With the optimized HT1 process, a proper Bi-2223 content of about 90% was achieved. HT2 process was also optimized by adding a post annealing process. An obvious increase of current capacity was obtained due to the enhancement of intergrain connections. Single filament Bi-2223 tapes with the critical current of Ic-90 A were fabricated with the optimized sintering process.

EXPERIMENTAL STUDY OF SCOUR RATE IN CONSOLIDATED COHESIVE SEDIMENT

The erosion process of a cohesive sediment after consolidation was studied experimentally in a closed conduit system. The test samples investigated in this study are mixtures of sand and clay with variable compositions and different consolidation times. The main concern of this study is the effects of the dry density of the consolidated sediment on scour rate. A scour rate formula is derived and further interpreted based on the experimental results.

Sediment rarefaction resuspension and contaminant release under tidal currents

Based on experiment in tidal flume, this paper analyzes the sediment rarefactive phenomenon and hydraulic characteristics of sediment resuspension with different physical properties under the effect of tidal current. According to this experiment, sediment resuspension is related to the hydraulic characteristics of overlying water and its own dry density, namely the moisture content of sediment and deposition time. Generally, river sediment can be classified into the upper layer of floating sludge and lower layer of deposit sediment. Incipient velocity goes higher as the sediment layer goes thicker. Based on the experiment, incipient velocity formula of sediment can be obtained. There is a cohesive force among natural fine sediment whose resuspension is almost irrelevant to their diameters. Therefore, the critical incipient velocity is determined by the cohesive force instead of particle diameter. The lower layer of deposit sediment is generally not so easy to start up. And it will be rarified and release into the overlying water when contacting with overlying water. However, this rarefaction release velocity is gentle and slow. Under the same flow condition, annual loss amount of lower layer deposited sediment is about one fifth of upper layer of floating sediment. Flow velocity of tidal river and variation of the water level are asymmetrical, both of which vary under different tidal cycles. During long tidal cycle, flow velocity and water level change in the same phase and amplitude with tide. During the whole ebb and flow, flow direction does not change as the water level goes under the influence of acceleration and deceleration. As the tide cycle increases, the incipient velocity of sediment goes higher. This means that the long period tide cycle plays buffer effect on the resuspension of sediment, which makes the sediment not so easy both to start up and to suspend.