Deep Mixing Research Articles

Study on Stress Distribution in Soft Ground Consolidated with Deep Cement Mixing Columns under Road Embankment

Soil consolidation using deep mixing method (DMM) is commonly used to protect soft ground in alluvial stratum in deltas such as Mekong Delta. In this study, the finite element method (FEM) using PLAXIS software is adopted to analyze the stress distribution on columns and ground base of the deep cement mixing (DCM) columns system combined with geotextiles in the consolidation of soft ground under road embankment in Tien Giang Province. With this method, the behavior of the DCM columns in soft ground treatment is examined by the distribution of stress and settlement of the DCM columns and soft soil layers. Simultaneously, the settlement of road base construction is monitored. The stress distribution on DCM columns and their settlement are also given from the analysis of FEM. The FEM models simulating the soft ground consolidated with DCM columns combined with geotextile under the road embankment in Tien Giang with the DCM columns of 0.6 m diameter, 11.2 m length and 1.0m center –to- center spacing show the largest settlement of 0.120 m and the stability coefficient of 1.679.

Unique surface density layers promote formation of harmful algal blooms in the Pengxi River, Three Gorges Reservoir

The Three Gorges Reservoir (TGR), China, is the largest man-made reservoir in the world. Harmful algal blooms (HABs) have become common since the reservoir’s impoundment in 2003. To investigate the mechanisms of HAB formation in the reservoir and to determine possible mitigation measures, we conducted surveys over a range of spatial scales and temporal resolutions over a 2-y period (March 2013–December 2014). The large-scale survey (the portion of the reservoir on the main stem of the Yangtze River and 22 tributaries) revealed that cyanobacteria blooms were restricted to the upper reaches of the tributaries. The medium-scale survey (1 tributary: Pengxi River) showed that cyanobacteria blooms were confined to the early-spring period with the initiation of thermal stratification in the deep-water column. The small-scale survey (a local, backwater lake in the Pengxi River), which was of higher-temporal resolution than the other 2 surveys, demonstrated that the bloom occurred at the same time as the formation of a surface-density layer unique to the geomorphology and water-control management of the reservoir. The vertical distributions of the bloom and surface-density layer appeared to be related, although the density layer persisted beyond the duration of the HABs. We hypothesized that limited nutrient diffusion into these density layers could result in nutrient limitation despite the hyper-eutrophic conditions that generally characterize the TGR basin. In the main stem of the Yangtze River and lower reaches of the tributaries in the TGR, algal blooms were not observed because of continuous, deep mixing throughout the year. We conclude that the hydrological stability and geomorphological characteristics of the TGR play critical roles in regulating the temporal and spatial patterns of algal blooms and that artificial mixing of the water column is currently the best option to limit HAB formation, especially in upper tributaries.

Evaluation of polyvinyl alcohol and high calcium fly ash based geopolymer for the improvement of soft Bangkok clay

Soft Bangkok clay (SC) is recognized as a problematic soil in Thailand. This research investigates the possibility of using polyvinyl alcohol (PVA) and high calcium fly ash (FA) geopolymers to improve the strength of SC in deep soil mixing applications. The liquid alkaline activator (L) was composed of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). The studied influence factors included FA content, water content, L content, Na2SiO3/NaOH ratio, PVA concentration, PVA content, and curing time. Strength development and microstructure in the PVA-FA geopolymer stabilized SC were evaluated via the unconfined compressive strength (UCS) test and scanning electron microscope (SEM) test. The optimum ingredient considering workability and cost of FA geopolymer stabilized SC was found to be at a mix design of 1.0LL, Na2SiO3/NaOH = 1, FA = 40% and L/FA = 0.6, whereby a 28-day UCS of 1026 kPa was attained. The optimum PVA content and PVA concentrations were found at 15% and 4%. The 7-day and 28-day UCS values were improved by PVA up to 40% and 42% compared to those of the specimen without PVA, respectively. The outcome of this research will promote the usage of PVA-FA geopolymer as an alternative green soil stabilizer alternative to Portland cement for a DM improved soft Bangkok clay.

Experimental evaluation of strength and durability characteristics of geopolymer stabilised soft soil for deep mixing applications

Vast deposits of high water content soft clays pose severe problems and are not suitable for construction of engineering projects due to their inadequate bearing capacity and inherent large swelling and shrinkage ability. Deep soil mixing (DSM) is one of the widely accepted methods for improving soft soil properties like increase in bearing capacity and reduction in settlement that are of utmost importance for the construction of any structure. In this study, ground granulated blast furnace slag (GGBS)-based geopolymer was used to investigate its efficiency as a sustainable replacement to cement for DSM applications, thereby reducing the carbon footprint. A total of 27 GGBS-geopolymer mixes and 9 cement-treated reference mixes were cast and tested for strength and durability characteristics. The variables of the study include binder content (10, 20, and 30%), activator/binder ratio (0.5, 0.75, and 1.0), and initial soil moisture content (0.75wL, wL, 1.25wL). Different tests were conducted to explore the properties of stabilised clays, such as unconfined compressive strength, flexural strength, and durability against wetting drying cycles. To meet the requirements of DSM application, binder dosage greater than 10% and A/B ratio greater than 0.5 were recommended. With an increase in initial soil moisture content, the strength of the treated specimens under unconfined compression and flexure reduced and thus increased binder dosage helps to meet the DSM requirements for high water content soils. From the present study, it can be concluded that using slag-geopolymer binder for stabilising soft soil is an effective and sustainable alternative to cement in DSM applications.

Nordic Seas Hydrography in the Context of Arctic and North Atlantic Ocean Dynamics

AbstractThe hydrography of the Nordic seas, a critical site for deep convective mixing, is controlled by various processes. On one hand, Arctic Ocean exports are thought to freshen the North Atlantic Ocean and the Nordic seas, as in the Great Salinity Anomalies (GSAs) of the 1970s–1990s. On the other hand, the salinity of the Nordic seas covaries with that of the Atlantic inflow across the Greenland–Scotland Ridge, leaving an uncertain role for Arctic Ocean exports. In this study, multidecadal time series (1950–2018) of the Nordic seas hydrography, Subarctic Front (SAF) in the North Atlantic Ocean [separating the water masses of the relatively cool, fresh Subpolar Gyre (SPG) from the warm, saline Subtropical Gyre (STG)], and atmospheric forcing are examined and suggest a unified view. The Nordic seas freshwater content is shown to covary on decadal time scales with the position of the SAF. When the SPG is strong, the SAF shifts eastward of its mean position, increasing the contribution of subpolar relative to subtropical source water to the Atlantic inflow, and vice versa. This suggests that Arctic Ocean fluxes primarily influence the hydrography of the Nordic seas via indirect means (i.e., by freshening the SPG). Case studies of two years with anomalous NAO conditions illustrate how North Atlantic Ocean dynamics relate to the position of the SAF (as indicated by hydrographic properties and stratification changes in the upper water column), and therefore to the properties of the Atlantic inflow and Nordic seas.

How zooplankton communities are shaped in a complex and dynamic coastal system with strong tidal influence

Temperate coastal marine environments are typified by strong seasonality and highly productive annual spring phytoplankton blooms. However, in areas of strong tidal activity, coastal waters may remain in a state of low productivity year-round due to light limitation induced by deep mixing. Such high-nutrient low-chlorophyll (HNLC) environments can be found in British Columbia, Alaska, Argentina, and the United Kingdom. This study aimed to examine how zooplankton communities are shaped by tidally mixed environments through direct comparison of adjacent stratified and mixed regions on the British Columbia coast. Stations located in five distinct regions of coastal BC were sampled during the most productive months (April to July) over two years. The most seasonally stratified station was characterized by a higher biomass of large zooplankton species, including calanoid copepods and euphausiids. In contrast, the mixed regions had a higher abundance of small (<2 mm) zooplankton species and a prevalence of meroplankton taxa. Zooplankton communities in tidally mixed regions had indicator species that reflected source waters in an adjacent stratified area. However, despite different source waters, tidally mixed regions showed a convergence of community structure pointing to a common community modification process. It may be the result of a combination of advective processes, zooplankton vertical migration behavior, enhanced predation due to close contact with bathymetry and daytime transport to the surface, and a large contribution of meroplankton. In areas with strong tidal exchange, zooplankton communities were more similar than expected based on the physical and chemical characteristics of the water column alone. The mosaic of primary productivity regimes on the BC coast therefore translates into similar spatial scale variation in zooplankton communities, resulting in a spatially heterogenous prey field for zooplankton consumers.

Seasonal variability and sources of in situ brGDGT production in a permanently stratified African crater lake

Abstract. Lake sediments are important archives of continental climate history, and their lipid biomarker content can be exploited to reconstruct paleoenvironmental conditions. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids widely used in paleoclimate studies to reconstruct past temperature. However, major gaps still exist in our understanding of the environmental controls on in situ (i.e. aquatic) production in lake systems. In Lake Chala, a permanently stratified tropical crater lake in East Africa, we determined the concentrations and fractional abundances of individual brGDGTs along depth profiles of suspended particulate matter collected monthly from September 2013 to January 2015 and in settling particles collected monthly at 35 m water depth from August 2010 to January 2015 and compared these brGDGT distributions with those in surficial lake bottom sediments and catchment soils. We find that brGDGTs are primarily produced within the water column and that their concentrations and distributions vary greatly with depth and over time. Comparison with concentration–depth profiles of the monthly distribution and abundance of bacterial taxa, based on 16S rRNA gene amplicon sequencing and quantification, indicates that Acidobacteria are likely not the main producers of brGDGTs in Lake Chala. Shallowing of the oxic–anoxic boundary during seasonal episodes of strong water column stratification promoted production of specific brGDGTs in the anoxic zone. BrGDGT distributions in the water column do not consistently relate with temperature, pH, or dissolved-oxygen concentration but do respond to transitions between episodes of strong stratification and deep (but partial) lake mixing, as does the aquatic bacterial community. Hence, the general link between brGDGT distributions and temperature in brGDGT-based paleothermometry is more likely driven by a change in bacterial community composition than by membrane adaptation of specific members of the bacterial community to changing environmental conditions. Although temperature is not the principal driver of distributional changes in aquatic brGDGTs in this system, at least not during the 17-month study period, abundance-weighted and time-integrated averages of brGDGT fractional abundance in the 53-month time series of settling particles reveal systematic variability over longer timescales that indirectly relates to temperature. Thus, although we do not as yet fully understand the drivers of modern-day brGDGT fluxes and distributions in Lake Chala, our data do support the application of brGDGT paleothermometry to time-integrated archives such as sediments. Highlights. BrGDGTs in the tropical African lake Chala are produced in situ. Acidobacteria are not the dominant source of aquatic brGDGTs. Stratification and mixing drive aquatic brGDGT production and their signature.

Mass stabilization as a modern method of substrate strengthening

The aim of the paper is to show one of the soil strengthening technologies - mass mixing. Two variations are to be distinguish – dry and wet type. In the first case the binding process take place with the use of ground water and the binder (cement, fly ash). In wet mass mixing the soil; is mixed with cement or cement-fly ash grout. The application of each type is dependent of the type of soil and its moisture content. The paper describes case studies of dry type: S5 road in the section Korzeńsko – Widawa, open pool complex in Oława, Szczecinek bypass. Wet type case study is described as well – part of the “Wiślanka” gallery in Żory and site in Warsaw. The analysis of mentioned case studies has shown that the technology can be used in all type of civil engineering objects. While it is one of the technologies which is based on mixing of the existing soil, it is especially important to do comprehensive soil investigation and trial mixes before the start of the jobsite. One of the advantages is that the quality control in case of wet mass mixing is made similarly to DSM (deep soil mixing).

Management of the dynamic properties of a base modified by deep soil mixing technology

Conversion of building properties is performed primarily to reduce the compressibility of the base and increase strength. However, in addition to changing the static properties of soils, it is necessary to take into account changes in dynamic properties, such as dynamic shear modulus, damping coefficient, velocity of elastic shear and longitudinal waves. Thus, it is possible to control the dynamic properties of the base by converting the construction properties of soils. In this paper, we consider the change in the velocity of shear waves in a base transformed by the technology of deep soil mixing (DSM). In the work, the influence of additional vertical stresses on the dynamic properties of the bases transformed using deep soil mixing technology was evaluated. As a parameter that allowed us to evaluate the dynamic properties, the propagation velocity of elastic shear waves was chosen. Shear wave velocity was estimated based on the results of triaxial tests using the method of low-amplitude torsional vibrations in a resonant column. The research results showed that at small values of axial strains, there is no significant increase in the velocity of shear waves, an increase in the speed of shear waves by two times with an increase in stress by 0.6 MPa.

Winter biogenic silica and diatom distributions in the Indian sector of the Southern Ocean

Spring and summer Southern Ocean phytoplankton communities have been well characterized, but winter communities are often overlooked. Diatoms are a major contributor to Southern Ocean particulate organic carbon (POC) production and export, and exert a strong control on Antarctic surface and Subantarctic thermocline nutrient concentrations, thus influencing the low-latitude nutrient supply. Understanding diatom distribution, seasonal community progression, and diatom-nutrient interactions is vital for improving biogeochemical models, particularly as climate change alters polar phytoplankton communities. We investigated the distribution of nanophytoplankton (≥3 μm) and their associated biogeochemical environments along 30°E across the Indian Southern Ocean (Subtropical Zone; STZ to Antarctic Zone; AZ) in July 2017. Phytoplankton productivity inferred from chlorophyll-a was low compared to previously-published summertime values. Mixed-layer nitrate (NO3−) and phosphate (PO43−) concentrations were similar to existing summer measurements, likely due to a combination of deep mixing and biological uptake, while silicic acid (Si(OH)4) was high relative to summer, particularly south of the Polar Front (PF). The PF emerged as an important biogeochemical boundary separating relatively high chlorophyll-a, flagellate-dominated northern waters from southern waters characterized by low chlorophyll-a and diatom-dominated communities. Mixed layer-integrated biogenic silica (bSi) decreased 12-fold from the southern AZ to the STZ, resulting in a strong south-north gradient in bSi-per-chl-a (from 3.6 to 0.1 mol/g) and bSi-per-POC (from 0.22 to 0.016 mol mol−1). We attribute this to a high abundance of heavily-silicified diatom species (e.g., Fragilariopsis spp., which dominated the AZ diatom community) and a limited contribution of other phytoplankton to chlorophyll-a and POC to the south – indeed, diatoms constituted 5–67% of the total POC south of the PF and only 3–7% to the north. While mixed-layer Si(OH)4 concentrations decreased more than NO3− across the PF, likely due to preferential Si(OH)4 consumption by iron-limited diatoms, our data imply a lower ratio of Si(OH)4 to NO3− uptake compared to summer. This suggests that iron limitation may be less severe in the AZ in winter, at least in the west Indian sector. We conclude that AZ diatoms impact the low-latitude nutrient supply and are potentially important for carbon export in winter, despite the lower productivity of the Southern Ocean during this season.

Contrasting surface warming of a marginal basin due to large-scale climatic patterns and local forcing

The Mediterranean Sea is one of the first regions where sea surface temperature (SST) increase was linked to greenhouse effects and global warming. Due to its sensitivity to climate variability and its high impact on local and remote climate conditions, much effort has been made to assess the SST variability in the Mediterranean as a whole. However, the Mediterranean is composed of several basins, each of which plays a different role in its conveyor belt’s function. This study focuses on the basin of the Tyrrhenian Sea which represents one of the crucial areas for deep mixing of the Mediterranean main water masses. Thirty-seven years (1982–2018) of satellite-derived data were used to investigate the SST variability in relation to large-scale and local forcing mechanisms. A significant warming trend of 0.034 ± 0.004 °C/year was found, which led to an average warming of 1.288 ± 0.129 °C over the considered period. The observed warming presents time-dependent spatial patterns as well as changes in the seasonal cycle. Our results highlight that the Tyrrhenian’s individual long-term surface variability has different characteristics than the Mediterranean as a whole and provide insight into the relative influence of large-scale teleconnection patterns and local air-sea interaction on this variability.

Rheological and strength performances of cold-bonded geopolymer made from limestone dust and bottom ash for grouting and deep mixing

This paper aims to research the potential use of cold-bonded geopolymer stabilizer made from limestone dust and bottom ash for grouting and deep soil (clay) mixing. For this purpose, the rheology and strength performances of the cement (PC)-based grouts with the stabilizers of limestone dust (LD), bottom ash (BA), geopolymerized cold-bonded limestone dust (GLD), and geopolymerized cold-bonded bottom ash (GBA) were investigated. The rheometer tests were conducted for the rheological performances at a wide range of stabilizer replacement (0–100%) and water/binder (w/b) ratio (0.75–1.5). Using proper replacements from the grout rheology, the unconfined compressive strength (UCS) tests (7 days, 28 days) were performed for the grouting (w/b = 1) and deep mixing (w/b = 1–1.25). The effect of stabilizer on the failure patterns was also examined from specimens of UCS tests. From the experimental work, the rheology of grout mixtures indicated (i) the adequacy of low amount of stabilizer replacements (< 50%); (ii) the dilatant behavior similar to PC; (iii) a decreasing trend of the shear stress, apparent viscosity, yield stress, and plastic viscosity with the increased w/b; (iv) slight to moderate responses of PC mostly; and (v) a potentially favorable rheology of cold-bonded stabilizers (GLD, GBA) for grout flow and workability regarding the yield stress and plastic viscosity. From the strength tests of grout mixtures (0–40%), the GBA additions yielded higher UCS performances for the grouting. For the deep mixing, both the additions of GLD and GBA were found more successful for the strength. The failure planes of UCS specimens were observed independent from the stabilizer types and dosage rates that dominantly failed in axially or near-axial splitting. From the study, the contributions of GLD and GBA from the potential of cold bonding are relatively promising for grouting and deep mixing.

INTEGRATION OF INFORMATION AND COMMUNICATION TECHNOLOGY (ICT) INTO CEMENT DEEP MIXING METHOD

In the deep mixing improvement method, soil-cement columns are installed in to an invisible ground, therefore it is impossible to visually confirm the circumstance of the constructions process. As the results, the inadequacy of construction data management and quality control of the constructed soil-cement columns may happen following re-construction of the columns, and structures failures/damages in some cases. By incorporating the Information and Communication Technology (ICT), authors have invented and developed a system to visualize the construction process of the deep mixing work in real-time, namely “3D Pile Viewer”. This system consists of two functions that are the positioning guidance and the visualization of the construction information. The former has been developed by using the combination of the Global Navigation Satellite System (GNSS) or the Total Station (TS), and the tilt sensor. The latter is to create three-dimensional model of all information during construction such as depth, electrical current value, amount of slurry, rotation speeds, etc., then sharing via internet. By introducing the newly developed system to various actual construction sites Japan and oversea, the practical performance of the system and its advantages have been confirmed.

Studies of the shear wave velocity in soil cement under the anisotropic stress state

Introduction. Deep soil mixing, that alters construction properties of foundations, allows to construct buildings and structures on the sites that have loose soils. As a rule, adverse geotechnical conditions are accompanied by dynamic forces that affect designed buildings and structures. The objective of these studies is to predict changes in mechanical properties of soils that follow the alteration of structural properties of a foundation. Soil cement is the focus of this study. Materials and methods. The findings of special laboratory tests of soil cement samples using the method of low amplitude torsional vibrations inside a resonant column in the anisotropic triaxial compression mode allowed to assess the effect of the supplementary vertical load on the velocity of shear elastic wave propagation. The co-authors present a description of the research method and provide an overview of the equipment used to conduct special laboratory tests. Tests were performed on undisturbed soil cement samples that had a natural water content. The anisotropic stress state of soil cement samples exposed to triaxial tests in the resonant column was caused by special behaviour features of the foundation. Results. In this study, laboratory tests had two stages. At the first stage, the effect of the vertical stress on the velocity of shear wave propagation was assessed. Correlation dependences between the shear wave velocity and the ratio of vertical and lateral stresses were obtained. At the second stage, shear wave propagation velocity values were identified at various combinations of lateral σ3 and vertical σ1 stresses. The results of the second stage are designated for the assessment of the effect of the anisotropic stress state and the projection of shear wave velocities at the stress levels anticipated on the site that will accommodate designed heavy structures. Conclusions. The findings allow to assess the effect of lateral and vertical stresses on changes of shear wave velocities in the triaxial compression mode. It was identified that at equal values of lateral stresses σ3, a 7-fold vertical stress σ1 increase leads to a 15 % increase in the shear wave velocity in soil cement Vs. At the same time, an increase in the ratio of vertical to lateral stresses σ1/σ3 by a factor of 15 causes an 11 % increase in the shear wave velocity. It is noted that the smaller the initial value of lateral stress σ3, the higher the rise in the shear wave velocity Vs in the course of testing. Correlation dependencies, presented in this study, can be used to assess the effect of the anisotropic state as the first approximation (for preliminary calculations) in the design of heavy structures on soil cement foundations.

Integrated Geoenvironmental and Geotechnical Risk Assessment of East Port Said Region, Egypt for Regional Development

The present paper discusses the use of integrated topographical, hydrogeological, and geotechnical data as a tool to assess the suitability of the East Port Said Region (EPR) for the establishment of new major projects. The method comprises geo-environmental and geotechnical characterization of the surficial soil layer and subsurface rock layers and identification of soil behavior along the proposed area. We analyze the digital elevation model to identify the topographic patterns across the project area. The geology of EPR comprises a normal to slightly consolidated fluvio-marine deltaic deposits of Pleistocene to Holocene age with more than 1000 m thick. We carry out a statistical analysis of geotechnical parameters to group the risky effective parameters for regional development. The study correlated the depth-averaged values of the design geotechnical parameters over the entire EPR. It also integrates the geotechnical properties with the topographical and hydrogeological parameters in the Geographic Information System (GIS) platform aiming to identify the spatial distribution and classes of the integrated risks across the EPR. For each geotechnical–environmental domain, it links the averaged values of geotechnical parameters to the groundwater levels and the topographic gradient that control groundwater flow. The methodological approach enters the hydrogeological model of EPR to the GIS environment and crossing with the results of the geotechnical analysis to identify zones of higher water saturation and possible geotechnical risk. The developed integrated geoenvironmental and geotechnical model assesses the prevailed hazards among the entire EPR. The integrated model uses to identify and delineate geotechnical hazards zones and to shape the spatial distribution of the geotechnical hazards classes, based on the dominant geotechnical and geo-environmental specifications. The achieved model shows that the risky zone spread widely along with the middle and southwestern sectors, while the marginal zones spread along with the southeastern and northwestern sectors. The study recommends applying the prefabricated vertical drains or deep mixing technique to stabilize the soft soil in the middle and northern risky zones of EPR. It also recommends the use of gravel drains and a well-compacted sub-base gravel layer for shallow foundations to enhance the properties of unstable clay formation at the southern risk and marginal zones of EPR.

Consolidation Behavior of Clay Supported by Soil-Cement Column

This paper presents the compression and consolidation behaviors of clay supported by soil-cement column. A series of consolidation tests was performed on kaolin samples supported by soil-cement column with the ratio between diameters of column and soil sample () ranging from 0 to 0.4. All samples with soil-cement column were cured for 28 days under the vertical pressure of 25 kPa. The sample preparation techniques simulating dry deep soil mixing method was developed. The test results showed the elastic region expanded with increasing value of . However, there was no effect of on deformation behavior in the elasto-plastic region. Moreover, the value of was considered constant over the range of testing stress level, for the value of of 0 and 0.2. For the value of of 0.3 and 0.4, the values of in the elastic region was greater than that in elasto-plastic region.

A Fukushima tracer perspective on four years of North Pacific mode water evolution

We present the results of a multi-platform investigation that utilizes tracer information provided by the 2011 release of radioisotopes from the Fukushima Dai-ichi Nuclear Power Plant to better understand the pathways, mixing and transport of mode waters formed in the North Pacific Ocean. The focus is on transition region mode waters and radiocesium (137Cs and 134Cs) observations obtained from the May–June 2015 GO-SHIP occupation of the 152°W line in the Northeast Pacific. Samples include profiles from the surface to 1000 m and surface/subsurface pairs that provide an average 1° of latitude spacing along 152°W. We find a clear Fukushima (134Cs) signal from the surface to 400 m. The core signal (134Cs ∼10 Bq m-3, 137Cs ∼12 Bq m-3) at 41°-43°N lies at 30–220 m where mode waters formed through deep winter mixing in 2011 outcropped in the western North Pacific. The strongest 2015 152°W Fukushima-source radiocesium signal is associated with Dense-Central Mode Waters consistent with the densest variety of these mode waters being formed off the coast of Japan 4 years earlier. The radionuclide signal transited the basin along subsurface mode water isopycnals mainly on the northern side of the subtropical gyre before outcropping at and to the east of the 152°W line. In 2015, the densest 152°W waters with 134Cs lie at ∼435 m in the bottom range of Dense-Central Mode Water at 40°N. There is a weak, but detectable, signal in the boundary current off both Kodiak and Sitka. The deepest detectable 137Cs (weapon's testing background) are found at and to the north of 45°N at 900–1000 m. With the exception of a single subsurface sample near Hawaii, as of spring 2015, the southernmost 134Cs was found above 200 m at 30°N. A total date-corrected 134Cs inventory of 11–16 PBq is estimated. Qualitative comparison to model output suggests good consistency in terms of general location, latitudinal breadth, and predicted depth of penetration, allowing discussion of the bigger picture. However, the model's 2015 152°W radiocesium signal is quantitatively weaker and the core is offset in latitude, potentially due to the lack of consideration of atmospheric deposition.

Intelligent modelling and design of soft soil improved with floating column-like elements as a road subgrade

The use of stone columns (SC) and deep cement mixing (DCM) columns to stabilize road subgrades are economical and reliable ground improvement techniques that have been extensively studied. The current study used an adaptive neural fuzzy inference system (ANFIS) hybridized with a particle swarm optimization (PSO) algorithm to develop models for estimating the ultimate bearing capacity (UBC) of soft soil improved with floating SC or DCM columns. A database of 86 physical modelling tests was used to create and train the ANFIS-PSO models. The input parameters used were the undrained shear strength of soft soil, area improvement ratio, and length-to-diameter ratio of the floating SC and DCM columns. The performance of the proposed ANFIS-PSO model has been validated using the testing data and a decision-making model for the design of the geotechnical properties of the floating SC and DCM columns has been proposed. The results show that the accuracy of the proposed ANFIS-PSO model in terms of the performance indices was satisfactory. The R2, VAF, and MSE values were obtained for the testing sets of the optimized ANFIS-PSO predictive model. This ANFIS-PSO model can be used by geotechnical engineers for the design of floating DCM and SC columns that increase the UBC of a road subgrade.

Point Foundation (PF) method: Principles and recent research findings

Conventionally, cement deep mixing (CDM) columns are designed to have constant diameters over the improved depth as this facilitates the construction procedures. However, this design pattern may be inefficient in cases of spread footings or shallow foundations. This paper first briefly introduces principles, construction procedures and quality control techniques of an innovative CDM method that can create head-enlarged column, named as Point Foundation (PF). The method is practically implemented with a specific binder that is environment-friendly and more effective in strength enhancing compared with the common binder as cement. Static load tests on three instrumented PF columns indicate that the variation trend of induced vertical stress profile along the columns in general is similar to that under the centre of shallow footings on elastic soil medium. However, the stress profile in the (semi-rigid) PF columns is larger than that in elastic soil but less than that in (rigid) PHC pile. This confirms the load transfer mechanism along semi-rigid columns like CDM/PF. Test results also indicate that at the depth of one to two times head diameters the induced stress remains just 20% the applied pressure. Findings on the trend of the induced vertical stress in the columns suggests that the settlement of common shallow footings on CDM/PF column-reinforced grounds should be evaluated using 3D condition taking into account the fact that the induced stress decreases with depth.&#x0D; Keywords:&#x0D; ground improvement; Point Foundation (PF); tapered cross section; load transfer mechanism; load-settlement behavior.

Marine Heatwaves in the Arctic Region: Variation in Different Ice Covers

AbstractThis study analyzes marine heatwaves (MHWs) in the Arctic for its variation in multiyear ice (MYI), first‐year ice (FYI), and open‐water areas. Results show that there is a significant annual growth in MHW frequency, duration, and intensity in the FYI region, especially for intensity. Since 2005, MHW in FYI increases remarkably in summer and the extent of the affected area continues to grow northward. Particularly, severe MHW events mainly occur in the area where sea ice concentration ranges between 0.1 and 0.5. Stratification in the FYI area impedes the deep mixing and downward transmission of energy from solar radiation, resulting in an anomalously high sea surface temperature in the FYI area. The implication is that MHW will keep growing as the extent of FYI in the Arctic increases.