Deep Mixing Research Articles

Deep-Current Intraseasonal Variability Interpreted as Topographic Rossby Waves and Deep Eddies in the Xisha Islands of the South China Sea

Abstract Strong subinertial variability near a seamount at the Xisha Islands in the South China Sea was revealed by mooring observations from January 2017 to January 2018. The intraseasonal deep flows presented two significant frequency bands, with periods of 9–20 and 30–120 days, corresponding to topographic Rossby waves (TRWs) and deep eddies, respectively. The TRW and deep eddy signals explained approximately 60% of the kinetic energy of the deep subinertial currents. The TRWs at the Ma, Mb, and Mc moorings had 297, 262, and 274 m vertical trapping lengths, and ∼43, 38, and 55 km wavelengths, respectively. Deep eddies were independent from the upper layer, with the largest temperature anomaly being >0.4°C. The generation of the TRWs was induced by mesoscale perturbations in the upper layer. The interaction between the cyclonic–anticyclonic eddy pair and the seamount topography contributed to the generation of deep eddies. Owing to the potential vorticity conservation, the westward-propagating tilted interface across the eddy pair squeezed the deep-water column, thereby giving rise to negative vorticity west of the seamount. The strong front between the eddy pair induced a northward deep flow, thereby generating a strong horizontal velocity shear because of lateral friction and enhanced negative vorticity. Approximately 4 years of observations further confirmed the high occurrence of TRWs and deep eddies. TRWs and deep eddies might be crucial for deep mixing near rough topographies by transferring mesoscale energy to small scales.

Optimization of Laboratory Molding Techniques for Nordic Dry Deep Mixing

Abstract The dry deep mixing method is a widely used stabilization method in the Nordic countries to improve the strength and deformation properties of soft clays. In engineering practice, laboratory tests normally precede in situ stabilization; however, previous studies have shown considerable differences between field and laboratory stabilization. The type of laboratory molding technique will determine how representative the specimen is compared with field conditions. A key property is the amount of entrapped air in the stabilized clay, which is shown to be very low in field stabilization. This paper presents a study of two different Norwegian molding techniques, including different optimizations to reduce the amount of entrapped air. The specimens are tested for density and strength, and it is shown that the strength increases with increasing density of the stabilized clay. Consequently, there is an inverse relationship between the amount of entrapped air and the strength, showing the importance of reducing the amount of entrapped air in laboratory specimens as much as possible. It is also shown that the wet mixing method does not necessarily give the same strength development as dry deep mixing given the same water to binder ratio.

Monitoring phosphorus in the tributaries of a deep lake from the perspective of the receiving water body

AbstractDeep lakes under climate change are experiencing reduced deep mixing, with a consequent increase in nutrients concentration and oxygen deficit in the hypolimnion. From this perspective, greater efforts should be made to reduce the phosphorus load delivered to these lakes by their tributaries. An essential precondition for this action is a reliable estimate of the loads, which is challenging due to the marked temporal variability of the hydrologically‐driven diffuse sources. In this article, we used a high‐resolution phosphorus time series measured at the mouth of the main tributary of Lake Iseo and a machine learning algorithm to show the dominant role played by the acute, storm‐dependent transport. The results emphasize the need to control loads strictly linked to precipitation and runoff in the drained watershed, representing 31% of the observed events but responsible for 64% of the overall load to the lake. We also proved evidence that the current obligations on nutrients monitoring miss the total phosphorus dynamics, leading to a systematic underestimation of the load conveyed by the inflows. Accordingly, we propose a sampling methodology where the timing and the methods for data interpolation are established according to the hydrological conditions in the drained watershed. Accounting for the economical and practical constraints imposed by the monitoring authorities, we propose to integrate, at the mouth of lake tributaries, a monthly manual sampling with an auto‐sampler programmed to fill 2 bottles in correspondence of each high flow event. Our simulations showed that in this case the load estimation error was reduced below 1%, implying, on average, 13 field surveys/year and 21 laboratory analyses/year only. It is reasonable to expect comparable performances in hydrologically similar watersheds.

Relationship of Area Ratio to Displacement on Subgrade Stabilized by Deep Soil Mixing

Expansive clay soil has high potential of swelling due to minerals content which bind water, therefore, soil improvement is required to stabilize the swelling behavior by add binder additive such as lime in deep soil mixing method (DSM). In this study, Finite Element model approach was performed with embankment provided on the top of expansive clay layer to provide bearing layer for road construction. As the deep soil mixing is applied on the subgrade (expansive clay layer), some model variation is performed such as diameter variation with 0.4m; 0.6m; 0.8m, depth variation with 5m; 6.5m; 8m and space variation 0.8 m;1.2m;1.6m; 2.4m. Area ratio parameter also used for ease understanding of deep soil mixing behavior with so many model variations provided. Analysis results shows that higher area ratio of deep soil mixing will provide lower displacement value either immediate displacement or consolidation displacement. Moreover, plot result of area ratio shows that area ratio of 0.4 provide effective value regarding consolidation displacement and duration.

Characteristics of Geotechnical Behavior of the Deep Cement Mixing Method According to the Placement Type

The improvement method for using the soft ground efficiently was applied in various manners depending on the site condition and development purpose. Recently, there has been an increasing interest in the deep cement mixing (DCM) method, in which the lower part of the ground is mixed with a solidifying agent to form an improved body of uniform strength. Although various studies are being conducted on this topic, studies on the behavioral characteristics of the improved ground according to the arrangement of the DCM improved body are insufficient. Therefore, in this study, an improved body was manufactured using a model soil with a similar ratio, and laboratory tests were conducted to understand the behavioral characteristics of the composite ground in pile-type and wall-type arrangements. The replacement rate of the composite ground was set at 46.2%. The improved body was manufactured at W/C = 40%. A shear test was performed after installing displacement gauges at 8 cm and 16 cm from the center of the load plate to clarify the ground behavior. The test results suggested that the wall type arrangement was advantageous in the force for the load acting vertically and the displacement for the lateral flow. Additionally, numerical analysis using the finite element method suggested that significant ground displacement occurred in the pile-type arrangement.

Stabilizers Effects Comprehensive Assessment on the Physical and Chemical Properties of Soft Clays

Deep soil mixing (DSM) is one of the practical methods of soil improvement in the world, which produces cement columns and modification by injecting stabilizing materials such as cement or lime using a mechanically hollow shaft drill in the soil. In this method, the soil characteristics are improved by mixing the soil with cementitious materials by deep mixers and creating cement soil columns. In addition, by overlapping the columns before full setting, continuous walls can be constructed below the ground. The aim of this study was to investigate the effect of the additive type on the strength of the samples. For soil samples stabilized with lime, the maximum value of uniaxial resistance was 247 kPa and for the mixture of 10% lime and 4% sodium silicate was obtained.

Application of cement-free media binder for the deep mixing method of CMD–SOIL

A cement-free eco-friendly porous media binder was developed as a cement replacement material (CRM) to be applied in the deep mixing method (DMM) for CMD–SOIL. We measured compression strengths for various mixtures and found that the compression strength of CMD–SOIL was 1.00–1.08 times higher than that of blast furnace slag cement (BFSC) and 1.410–1.945 times higher than the reference strength (2.0 MPa), depending on the moisture content, dosage, and water/binder ratio (W/B). The strength increment ratio (1.730) was slightly lower than that of BFSC (1.780), thereby proving its merit over BFSC as a binder for the DMM.

Globorotalia truncatulinoides in the Mediterranean Basin during the Middle–Late Holocene: Bio-Chronological and Oceanographic Indicator

The planktonic foraminiferal species Globorotalia truncatulinoides is widely used as a biostratigraphic proxy for the Quaternary in the Mediterranean region. High-resolution quantitative studies performed on sediment cores collected in the central and western Mediterranean Sea evidence a significant abundance of G. truncatulinoides during the Middle Holocene. The robust chronological frame allows us to date this bio-event to 4.8–4.4 ka Before Present (BP), very close to the base of the Meghalayan stage (4.2 ka BP). As a consequence, we propose that G. truncatulinoides can be considered a potential marker for the Middle–Late Holocene chronological subdivision. G. truncatulinoides is a deep-dwelling planktonic foraminifer and their distributional pattern in the central and western Mediterranean Sea provides a tool to monitor the onset of the regional deep vertical mixing of the water column. During the Holocene, the significant increase in the abundance of this species is in phase with the end of African Humid Period, which marks the transition from a more humid climate to the present-day semi-arid climate.

Two Sources of Deep Decadal Variability in the Central Labrador Sea Open‐Ocean Convection Region

AbstractThe ventilation of the central Labrador Sea is important for the uptake of ocean tracers and carbon. Using historical ocean observations, we construct a simple multiple linear regression model that successfully reconstructs the decadal variability of the upper ∼2,000 m of the central Labrador Sea water properties based on observed indices that represent two different open‐ocean ventilation mechanisms. The first mechanism is the modification of deep ocean properties through local decadal variability of the Labrador Sea deep convective mixing. The second, more novel, mechanism is the climatological convective vertical redistribution of upper central Labrador Sea temperature and salinity anomalies associated with the nonlocal large‐scale subpolar Atlantic Multidecadal Variability and the Atlantic Meridional Overturning Circulation. The ventilated decadal central Labrador Sea signal subsequently spreads into the western subpolar North Atlantic. The results have important implications for predicting decadal ventilated signals in the Labrador Sea that are associated with the large‐scale climate variability.

Development of Design Guideline for Deep Soil Mixing (DSM) to Stabilize Expansive Soils using Fly Ash as the Stabilizer

"ENGINEER", established in 1973 by The Institution of Engineers, is a Journal for dissemination of Engineering knowledge, published quarterly.If you are interested in contributing an Original Technical Paper based on research by the author(s) (intended for Section I) or an Original Article of Professional or Technical interest related to Engineering. (Section II) to this journal please go through the publication checklist which can be downloaded from here.Cover DescriptionCover images show views of the Giant tank and the Tekkama anicut.

Numerical Study of Soft Clay Reinforced with Deep Cement Mixing Technique

Numerical Study of Soft Clay Reinforced with Deep Cement Mixing Technique

Subtropical Contribution to Sub‐Antarctic Mode Waters

AbstractSub‐Antarctic Mode Waters (SAMW) form to the north of the Antarctic Circumpolar Current (ACC) through deep winter mixing. SAMW connect the atmosphere with the oceanic pycnocline, transferring heat and carbon into the ocean interior and supplying nutrients to the northern ocean basins. The processes controlling SAMW ventilation and properties remain poorly understood. Here, we investigate the significance and origin of a ubiquitous feature of SAMW formation regions: The seasonal build‐up of a subsurface salinity maximum. With biogeochemical Argo floats, we show that this feature influences SAMW mixed‐layer dynamics, and that its formation is associated with a decline in preformed nutrients comparable to biological drawdown in surface waters (∼0.15 mol m−2 y−1). Our analysis reveals that these features are driven by advection of warm, salty, nutrient‐poor waters of subtropical origin along the ACC. This influx represents a leading‐order term in the SAMW physical and biogeochemical budgets, and can impact large‐scale nutrient distributions.

LABORATORY MODEL DESIGN FOR DEEP SOIL MIXING METHOD

One of the most critical problems in the construction sector is the inadequate bearing capacities of subsoils. To solve this problem, various soil improvement methods are employed. Soil improvement is defined as the improvement in soil properties to the desired level by using various methods when the soil is not suitable for superstructure loads. Various types of soil improvement methods exist, and their application depends on the construction site, soil properties, earthquake zone, application time, and cost. One of the most widely used methods recently is the deep soil mixing method. In this study, a laboratory-scale deep soil mixing device is first developed; subsequently, the effects of injection pressure, mixing time, and dosing parameters on application are investigated. Deep soil mixing columns are prepared using different injection pressures, mixing times, and dosages and then subjected to the unconfined compression test. Results show that the effects of injection pressure, cement dosage, and mixing time on the unconfined compressive strength of deep soil mixing samples vary based on the initial soil properties.

Increasing of strength-rigidity parameters of bases of metallic silos

To date, effective codes of Ukraine limit settlement of foundations of metallic silos to 15 cm. To provide normative settlement of foundation with diameter up to 40 m and more is not always possible without additional essential measures for strengthening or changing base soils. Taking into account high levels of loads, soils of bases in natural condition can not carry stress under the base of foundation and require strengthening. Execution of works on change of soils of bases or installation of soil cushions is not always possible taking into account underflooding of territory, building development that exist near at hand, or other complicating factors. Soil cement after Deep Soil Mixing (DSM) technology, Jet Grouting, injection and micropiles were considered for different types of strengthening taking into account application in great volumes. From analysis of the obtained results, it was determined that soil cement after Deep Soil Mixing technology is the most economically justified method. Application of Jet Grouting is justified during strengthening of soil thicknesses locally separated by depth. Injection and micropiles are used appropriately only in conditions of reconstruction under absence of direct access to the base.

Effect of grid-form deep soil mixing on the liquefaction-induced foundation settlement, using numerical approach

Effect of grid-form deep soil mixing on the liquefaction-induced foundation settlement, using numerical approach

Bottom‐Reached Near‐Inertial Waves Induced by the Tropical Cyclones, Conson and Mindulle, in the South China Sea

AbstractMoored current observations in the northwestern South China Sea (SCS) captured two events of near‐inertial waves (NIWs) induced by the tropical cyclones Conson and Mindulle, which propagated to the seafloor from the base of the mixed layer. The time taken by the Conson‐induced near‐inertial kinetic energy (NIKE) to reach the bottom of the ocean was approximately 12 days. This NIKE was twice as fast as the Mindulle‐induced NIKE to reach the bottom of the ocean, which was mainly dependent on the properties of the NIWs deeply affected by the background vorticity. The NIWs in the upper layer induced by Conson/Mindulle showed a significant blue/red shift (1.07/0.85 ) as the observation site was located outside/within an exceptional anticyclonic eddy. The bottom NIWs showed an obvious blue shift, aligning with the result of ray tracing, which revealed that the bottom wave packets originated from higher latitudes. We estimated an NIW vertical energy flux of up to 0.22 m W m−2 in the abyssal ocean, which represents about 29% of the upper layer NIKE. The reached seabed NIWs had high vertical shear and might dissipate locally and play an important role in the maintenance of deep mixing of the SCS.

실내모형시험을 통한 지반혼합 및 주입공법의 노후저수지 차수 보강성능 비교 연구

Of the 17,106 domestic reservoirs(as of December 2020), 14,611 are older than 50 years, and these old reservoirs will gradually increase over time. The injection grouting method is most applied to the reinforcement method of the aging reservoir. However, the injection grouting method is not accurate in uniformity and reinforced area. An laboratory model test was conducted to evaluate the applicability of the deep mixing method, which compensated for these shortcomings, as a reservoir reinforcement method. As a result of calculating the hydraulic conductiveity for each method through the model test results, the injection grouting method was calculated as a hydraulic conductiveity value that was about 7.5 times larger than that of the deep mixing method. As a result of measuring the water level change in the laboratory model test, it was found that the water level change decreased in the injection method and deep mixing method compared to the non-reinforcement method. In addition, deep mixing method showed a water level change of about 15% based on 40 hours compared to the injection method, indicating that the water-reducing effect was superior to that of the injection method.

Microbial community day-to-day dynamics during a spring algal bloom event in a tributary of Three Gorges Reservoir

The microbial food-loop is critical to energy flow in aquatic food webs. We tested the hypothesis that species composition and relative abundance in a microbial community would be modified by the development of toxic algal blooms either by enhanced carbon production or toxicity. This study tracked the response of the microbial community with respect to composition and relative abundance during a 7-day algal bloom event in the Three Gorges Reservoir in May 2018. Chlorophyll a biomass, microscopic identification and cell counting of algae and algal abundance (ind. L−1) and carbon, nutrient concentrations (total phosphorus and nitrogen, dissolved total phosphorus and nitrogen), and DNA high throughput sequencing were measured daily. Algal density (1.2 × 109 ind. L−1) and Chlorophyll a (219 μg L−1) peaked on May 20th–21st, when the phytoplankton community was dominated by Chlorella spp. and Microcystis spp. The concentrations of both dissolved total nitrogen and phosphorus declined during the bloom period. Based on DNA high throughput sequencing data, the relative abundance of eukaryotic phytoplankton, microzooplankton (20–200 μm), mesozooplankton (>200 μm), and fungal communities varied day by day while the prokaryotic community revealed a more consistent structure. Enhanced carbon production during the bloom was closely associated with increased heterotrophic microbial composition in both the prokaryotic and eukaryotic communities. A storm event, however, that caused surface cooling and deep mixing of the water column greatly modified the composition and relative abundance of species in the microbial loop. The high temporal variability and dynamics observed in this study suggest that many factors, and not just algal blooms, were interacting to determine the composition and relative abundance of species of the microbial loop.

Lime-cement stabilisation of Trondheim clays and its impact on carbon dioxide emissions

Dry deep mixing is used throughout Norway to improve soft and sensitive clays. Traditionally, binders such as lime and cement have been used in combination with relatively high binder contents. The production of lime and cement causes large emissions of carbon dioxide, and it is therefore desirable to reduce the binder contents in engineering practice. This paper presents results from a comprehensive study of various lime-based binders, with the aim to improve the understanding of the engineering properties of such stabilised clays when using reduced binder contents. Results from analyses on pH, plasticity and mineralogy are presented, and it is concluded that fine-grained quartz particles exhibit relatively high pozzolanic properties giving a considerable strength development over time, also with low binder contents. A novel correction of the binder content has been used, based on the active CaO of the binders. This correction gives remarkably consistent results between the water-binder ratio and the strength development. These results have also enabled estimations of carbon dioxide emissions as a function of binder type and strength development. It is concluded that the type of lime-based binder has little influence on the carbon dioxide emissions per unit strength for binder contents higher than 30–40 kg/m3. For lower binder contents, there is a tendency that binders with low active CaO-content give lower carbon dioxide emissions per unit strength, however, these low binder contents are difficult to obtain in field applications.

Geomechanical Behaviour of Clay Stabilised with Fly-Ash-Based Geopolymer for Deep Mixing

Geopolymer has recently become an attractive alternative to traditional binders (e.g., cement and lime) used for chemical soil improvement, with several environmental benefits including lower toxic emissions and energy consumption. This paper presents an evaluation of the geomechanical behaviour of soft clay treated with fly-ash-based geopolymer incorporating slag for deep soil mixing (DSM) applications. The geomechanical properties of stabilised clay were evaluated using unconfined compressive strength (UCS) tests and durability against wetting–drying. Thermal conductivity and pH tests along with microstructural analysis using scanning electron microscopy (SEM) were also performed to provide insights into the effect of geopolymer on treated clay. The results indicate that the inclusion of geopolymer with the increase in curing time and activator content considerably improves the geomechanical performance of geopolymer-treated soft clay in terms of stress–strain response and attainable peak compressive strength. Although it was found that a small percentage of geopolymer can enhance the initial compressive response, a larger dosage of geopolymer up to 30% was necessary to maintain stable durability performance over successive wetting–drying cycles. Such improved durability performance is related to the enhanced soil structure due to the cementation development and overall reduction in thermal conductivity. The reduction in thermal conductivity of treated clay was found to be activator-dependent and was suppressed steadily with the increase in activator concentration. Overall, geopolymer-treated clay showed promising potential for DSM applications due to its enhanced strength and durability responses.