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• Ca-based, non-Ca-based additives and recycled solid wastes reduce PI and enhance TD. • These active ingredients improve soil texture via cation exchange and flocculation. • Transition metal oxides catalyze TD of nonchlorinated POPs via two mechanisms. • We also reviewed alkali, solid wastes and nano metals as catalysts to enhance TD. • Additives in photo- and photo-thermal-catalysis and their mechanisms are reviewed. High temperatures and providing sufficient time for the thermal desorption of persistent organic pollutants (POPs) from contaminated clay soils can lead to intensive energy consumption. Therefore, this article provides a critical review of the potential additives which can improve soil texture and increase the volatility of POPs, and then discusses their enhanced mechanisms for contributing to a green economy. Ca-based additives have been used to reduce plasticity of bentonite clay, absorb water and replenish system heat. In contrast, non-Ca-based additives have been used to decrease the plasticity of kaolin clay. The soil structure and soil plasticity can be changed through cation exchange and flocculation processes. The transition metal oxides and alkali metal oxides can be applied to catalyze and oxidize polycyclic aromatic hydrocarbons, petroleum and emerging contaminants. In this system, reactive oxygen species (•O 2 − and •OH) are generated from thermal excitation without strong chemical oxidants. Moreover, multiple active ingredients in recycled solid wastes can be controlled to reduce soil plasticity and enhance thermal catalysis. Alternatively, the alkali, nano zero-valent iron and nano-TiN can catalyze hydrodechlorination of POPs under reductive conditions. Especially, photo and photo-thermal catalysis are discussed to accelerate replacement of fossil fuels by renewable energy in thermal remediation. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of crop rotation on soil-borne diseases is a representative case of plant–soil feedback in the sense that plant disease resistance is influenced by soils with different cultivation histories. This study examined the microbial mechanisms inducing the differences in the clubroot (caused by Plasmodiophora brassicae pathogen) damage of Chinese cabbage (Brassica rapa subsp. pekinensis) after the cultivation of different preceding crops. It addresses two key questions in crop rotation: changes in the soil bacterial community induced by the cultivation of different plants and the microbial mechanisms responsible for the disease-suppressive capacity of Chinese cabbage. Twenty preceding crops from different plant families showed significant differences in the disease damage, pathogen density, and bacterial community composition of the host plant. Structural equation modelling revealed that the relative abundance of four key bacterial orders in Chinese cabbage roots can explain 85% and 70% of the total variation in pathogen density and disease damage, respectively. Notably, the relative dominance of Bacillales and Rhizobiales, which have a trade-off relationship, exhibited predominant effects on pathogen density and disease damage. The disease-suppressive soil legacy effects of preceding crops are reflected in compositional changes in key bacterial orders, which are intensified by the bacterial community network. [ABSTRACT FROM AUTHOR]

To comprehensively analyze the muck cake risk of shield tunneling and plastic flow characteristics of muck, a series of tests on rotational shear, triaxial, and slump are conducted to explore the adhesion characteristics and shear strength parameters of moderately-weathered mudstone in Changchun, China. Based on muck strength, reasonable improvements for the slump of the mudstone are proposed, and their rationality is validated in actual engineering. The main conclusions drawn include the following: (1) With the increase in the water content, the (interfacial adhesion) cohesion of the moderately-weathered mudstone increases first and then decreases, and the (interfacial) friction angle gradually decreases. At the water content of 22.58% -27.36%, soil and metal exhibit a greater interfacial adhesion than cohesion. Moreover, when the water content is 15.99% -24%, the interfacial friction angle is greater than the internal friction angle. (2) The slump value is closely related to muck strength. With the increase in the slump value, the adhesion and shear strengths of the muck exhibit a rapid decrease. When the slump value is greater than 4 cm, adhesion and shear strengths show relatively small changes. In addition, at the slump value between 0.5 and 1 cm, the muck attains a greater adhesion strength than shear strength. Therefore, the slump value of moderately-weathered mudstone during shield tunneling should not be less than 1 cm, and that of muck should be as large as possible that is, more than 4 cm, to reduce the muck's strength and increase its fluidity sufficiently. [ABSTRACT FROM AUTHOR]

The high permeability of gravel sand increases the risk of water spewing from the screw conveyor during earth pressure balance (EPB) shield tunnelling. The effectiveness of soil conditioning is a key factor affecting EPB shield tunnelling and construction safety. In this paper, using polymer, a foaming agent, and bentonite slurry as conditioning additives, the permeability coefficient tests of conditioned gravel sand are carried out under different injection conditions based on the factorial experiment design. The interactions between different concentrations of conditioning additives are analyzed. A prediction model for soil conditioning during shield tunneling based on particle swarm optimization (PSO) and relevance vector machine (RVM) algorithms is proposed to accurately and efficiently obtain the soil conditioning parameters in the water-rich gravel sand layer. The experimental results indicate that the improvement effect of the foaming agent on the permeability of the conditioned gravel sand gradually diminishes with the growing concentration of bentonite slurry. Under conditions of high polymer concentration, further increasing the concentration of bentonite slurry and foaming agent has a weak impact on the permeability coefficient when the concentration of bentonite slurry exceeds 10%. The significance of main effects, first-order interactions, and second-order interaction on the permeability of conditioned gravel sand are as follows: polymer concentration (A) > foaming agent concentration (B) > bentonite slurry concentration (C) > first-order interactions (A × B, A × C, B × C) > second-order interaction (A × B × C). The first-order interaction mainly manifests as a synergistic effect, while the second-order interaction primarily exhibits an antagonistic effect. Case studies show that the maximum relative error between predicted and experimental values is less than 3%. A field application of shield tunneling demonstrates the good performance of real-time optimization of soil conditioning parameters based on the PSO–RVM algorithm. This research provides a new method for evaluating the effectiveness of soil conditioning in the water-rich gravel sand layer. [ABSTRACT FROM AUTHOR]

Soil conditioning is essential for addressing the stratum applicability problem of earth pressure balance (EPB) shields. Under high water pressures, EPB shields spew water and soil when excavating coarse-grained strata. Typically, foam combined with polymers and slurry is used to solve spewing. However, in current techniques, slurry, foam, and the other agents are mixed with soil separately, their synergistic effect is seldom realized. In this study, an anionic surfactant was used to foam in bentonite slurry to form bubble–slurry to maximize the synergy between bubbles and slurry. The slump, volume stability, and permeability test of bubble–slurry-conditioned sand was conducted to examine the conditioning effect, and the stratum applicability of bubble–slurry was determined from the perspective of permeability. It was found that the conditioning effect of bubble–slurry in coarse gravel soil was excellent and could expand the applicability of EPB shields. The main stabilization mechanism of bubble–slurry is that bentonite particles provide a space barrier for bubbles. And three seepage modes of bubble–slurry-conditioned sand were innovatively defined, and the occurrence conditions of the three seepage modes were analyzed according to the permeability coefficient of sand, initial dynamic shear force of bubble–slurry, and hydraulic gradient. [ABSTRACT FROM AUTHOR]

Parameters of foam penetration in earth pressure balance (EPB) shield tunnelling, such as permeability coefficients and penetration distances, significantly impact tunnel face stability. However, existing studies have faced inaccuracies in analysing these parameters due to imitations in experimental methods. This study addresses this issue by employing enhanced methods for a more precise analysis of foam penetration. Experiments involving three distinct sand types (coarse, medium, and fine) and three foam expansion ratios (FER) (10, 15, and 20) are conducted using a modified model test setup. Benefiting from a novel computer vision-based method, the model test outcomes unveil two distinct foam penetration paths: liquid migration (Lw) and bubble migration (Lf). Three penetration phases — namely, injection, blockage & drainage, and breakage — are identified based on Lw and Lf variations. The initial “injection” phase conforms to Darcy's law and is amenable to mathematical description. The foam with FER of 15 has the maximum viscosity and, hence the Lf and permeability in the penetration tests with FER of 15 are the lowest in the same sand. The bubble size distribution of foam with different FER shows minor differences. Nevertheless, the characteristics of foam penetration vary due to the distinct particle size distribution (PSD) of different sands. Foam penetration creates low-permeability layers in both medium and fine sands due to the larger bubble size of the foam compared to the estimated pore sizes of medium and fine sands. While the coarse sand results in a different situation due to its large pore size. The distinctive characteristics of foam penetration in different sand strata are notably shaped by FER, PSD, and pore size distributions. These insights shed light on the complex interactions during foam penetration at the tunnel face, contributing valuable knowledge to EPB shield tunnelling practices.

Previous research has demonstrated the ability of isolate Pseudomonas thivervalensis SC5 to express the enzyme 1-aminocyclopropane-1-carboxylate deaminase (ACC), which regulates ethylene levels, one of the most important phytohormones in the regulation of plant growth and development. Thus, the present study evaluated the agronomic efficiency of a biological conditioner based on P. thivervalensis SC5 in the growth and productivity increases of corn in Brazil. It was found that corn was highly responsive to the inoculation of P. thivervalensis SC5, with increments ranging from 10.1 to 40.6% in the production of dry shoot biomass (DSB) compared to the control, while for grain yield the increments ranged from 9.0 to 27.8%. The increments are related to the levels and accumulations of N and P in the shoots of the plants. This suggested the participation of P. thivervalensis SC5 in mechanisms of soil modulation and nutrient acquisition. The inoculation of P. thivervalensis SC5 provided average increments in FDA hydrolysis ranging from 16.7 to 47.4% compared to the control, confirming the ability of this strain to increase the supply of nutrients to plants. Therefore, it is concluded that Pseudomonas thivervalensis SC5 participates in key mechanisms in the soil-plant system, with a consequent improvement in soil quality and other plant-related parameters. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Nonferrous Metals (Mineral Processing Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Both foam and bentonite slurry are commonly employed in soil conditioning to prevent water spewing during earth pressure balance (EPB) shield tunnelling. A novel calculation model to estimate the permeability coefficient of soils conditioned with foam and bentonite slurry is developed. In this model, bentonite particles are assumed to adhere to the foam film in a monolayer of bridging particles, and the permeation channels within the conditioned soil are updated using the Kozeny-Carman equation. A series of permeability tests on conditioned soil, varying conditioning parameters and water heads, validate the accuracy of the model. The measured results that the value of permeability coefficient can be well captured by the calculation results, which indicates that the model can accurately predict the permeability of soil conditioning by foam and bentonite slurry. While there is a slight reduction in accuracy for conditioning states with high foam and bentonite slurry injection ratios, the model remains conservative for tunnelling engineering safety due to calculated values consistently exceeding measured ones. Furthermore, the model performs well in cases of foam-conditioned soil from previous studies. Additionally, the model underscores the significant influence of bentonite slurry on the permeability coefficient by altering soil grain gradation. [ABSTRACT FROM AUTHOR]

The effect of crop rotation on soil-borne diseases is a representative case of plant–soil feedback in the sense that plant disease resistance is influenced by soils with different cultivation histories. This study examined the microbial mechanisms inducing the differences in the clubroot (caused by Plasmodiophora brassicae pathogen) damage of Chinese cabbage (Brassica rapa subsp. pekinensis) after the cultivation of different preceding crops. It addresses two key questions in crop rotation: changes in the soil bacterial community induced by the cultivation of different plants and the microbial mechanisms responsible for the disease-suppressive capacity of Chinese cabbage. Twenty preceding crops from different plant families showed significant differences in the disease damage, pathogen density, and bacterial community composition of the host plant. Structural equation modelling revealed that the relative abundance of four key bacterial orders in Chinese cabbage roots can explain 85% and 70% of the total variation in pathogen density and disease damage, respectively. Notably, the relative dominance of Bacillales and Rhizobiales, which have a trade-off relationship, exhibited predominant effects on pathogen density and disease damage. The disease-suppressive soil legacy effects of preceding crops are reflected in compositional changes in key bacterial orders, which are intensified by the bacterial community network.

The high permeability of gravel sand increases the risk of water spewing from the screw conveyor during earth pressure balance (EPB) shield tunnelling. The effectiveness of soil conditioning is a key factor affecting EPB shield tunnelling and construction safety. In this paper, using polymer, a foaming agent, and bentonite slurry as conditioning additives, the permeability coefficient tests of conditioned gravel sand are carried out under different injection conditions based on the factorial experiment design. The interactions between different concentrations of conditioning additives are analyzed. A prediction model for soil conditioning during shield tunneling based on particle swarm optimization (PSO) and relevance vector machine (RVM) algorithms is proposed to accurately and efficiently obtain the soil conditioning parameters in the water-rich gravel sand layer. The experimental results indicate that the improvement effect of the foaming agent on the permeability of the conditioned gravel sand gradually diminishes with the growing concentration of bentonite slurry. Under conditions of high polymer concentration, further increasing the concentration of bentonite slurry and foaming agent has a weak impact on the permeability coefficient when the concentration of bentonite slurry exceeds 10%. The significance of main effects, first-order interactions, and second-order interaction on the permeability of conditioned gravel sand are as follows: polymer concentration (A) > foaming agent concentration (B) > bentonite slurry concentration (C) > first-order interactions (A × B, A × C, B × C) > second-order interaction (A × B × C). The first-order interaction mainly manifests as a synergistic effect, while the second-order interaction primarily exhibits an antagonistic effect. Case studies show that the maximum relative error between predicted and experimental values is less than 3%. A field application of shield tunneling demonstrates the good performance of real-time optimization of soil conditioning parameters based on the PSO–RVM algorithm. This research provides a new method for evaluating the effectiveness of soil conditioning in the water-rich gravel sand layer.

Earth pressure balance (EPB) shield tunneling in coastal silty clay strata often faces the problems of clogging on the screw conveyor or the belt conveyor due to lumps of clay soils formed because of the large cohesion of clay particles. Soil conditioning using common foaming agents is not enough to alleviate the problem. Therefore, the novel dispersed foaming agent was studied in this work using performance and orthogonal compound tests. The foam microstructure was observed using an electron microscope to analyze the evolution mechanism of bubbles for different additives. Both laboratory and in situ tests were carried out to assess the effectiveness of the novel dispersed foaming agents. The testing results showed that 50 vol.% is an optimum foaming injection ratio to improve rheological properties and undrained shear strength of silty clay to avoid the unnecessary waste of conditioning materials. The half-life time (T1/2) and foam expansion ratio (FER) of novel foaming agents using the formation ionic solution as the solvent increased due to existing hydrophilic polar groups based on undisturbed soil samples taken from a Xiamen Metro construction site. It was shown that acids, alkalis, and salt ions had little effect on the FER and T1/2 of foaming agents (Foams A and B) using the macromolecular dispersant. The variations in the plasticity index were similar to those of the liquid limit for the muck conditioned using dispersed foaming agents with sodium citrate, sodium bicarbonate, and sodium chloride at a concentration of 0.1 wt%. Sodium bicarbonate had the most significant impact on the foaming agents' anticlay effect. Compared with commercial and house-made foaming agents of the Fuzhou Metro project, the muck was effectively conditioned by Foams A and B based on the slump and temperature values. In addition, the average cutter-head torque was reduced by about 250 kN·m. The amount of foaming agents used was reduced by about 18.6% and 12.9% on average in the two testing sites, respectively. [ABSTRACT FROM AUTHOR]

As weathered granite soils are extensively distributed in the Korean Peninsula, determining the optimal foam conditioning parameters for weathered granite soils can provide a high workability, low permeability, and high compressibility of weathered granite soils for successful operation of an earth pressure balance (EPB) shield tunnel boring machine (TBM). In this study, a laboratory-scale excavation apparatus was developed to conduct various laboratory excavation simulations for measuring the excavation-induced torque and the abrasivity of cutter bits. In addition, slump values, compressibility, and permeability were measured to evaluate the workability of foam-conditioned weathered granite soils. From the experimental results, the optimal foaming conditions for the weathered granite soil was obtained at foam injection ratios (F/Rs) of 60–70%, foam expansion ratios (FERs) of 15–18, and foaming agent concentrations (Cf) of 3–4%. The experimental results presented in this study can provide the rheological, mechanical, and hydraulic behavior of foam-conditioned weathered granite soils for successful EPB TBM operation. [ABSTRACT FROM AUTHOR]

In coarse-grained soils, the reduction of soil permeability via conditioning can effectively prevent groundwater from entering the chamber, thus providing better tunnel face control and ultimately preventing excessive settlements of the surface. In this study, several mixtures of coarse-grained and soil-foam mixtures were utilized in experiments. In which, effects of the foam expansion ratio, foam injection ratio, soil water content, pressure, and grain size distribution on the soil permeability were investigated. In these experiments, two soil types of poorly graded sand (SP) and poorly graded sand with silt and gravel (SP-SM), with different grain sizes were utilized. Based on the experimental results, it has been observed that the soil permeability increases with increasing foam expansion ratio, water pressure, and the coarse-grained portion of the soil. Meanwhile, soil permeability decreases with increasing foam injection ratio and soil water content. Based on the observations, it can be inferred that optimal soil permeability for soil moisture of 15 %, the pressure of 1 bar with a certain grain size occurs at a foam expansion ratio of 7.5 and a foam injection ratio of 52 %.

Soil plays a vital role in agriculture by providing essential nutrients, water, and support for crop growth. Therefore, the maintenance of healthy soil is imperative for the sustainability of agriculture and the assurance of food security. However, soil quality has been undermined by a range of factors, encompassing adverse environmental conditions, the impact of climate change, and inappropriate human activities. To address these issues, soil conditioners have been used to remedy soil quality. Alginate, a polysaccharide derived from brown algae, emerges as a promising soil conditioner due to its attributes of being biodegradable, non-toxic, cost-effective, easy to handle, and capable of forming gels with ease. When employed as soil conditioners, both alginate and its derivatives have demonstrated the capacity to enhance water retention in soil, augment nutrient availability, improve soil structure, and offer effective mulch films. This review aims to provide a comprehensive discussion on the utilization of alginate as a soil conditioner, covering alginate's properties, mechanisms of action, and diverse applications to enhancing soil quality and agricultural productivity. [ABSTRACT FROM AUTHOR]

Copyright of Fly Ash Comprehensive Utilization is the property of Hebei Fly Ash Comprehensive Utilization Magazine Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Earth pressure balance (EPB) shield excavation in cohesive strata frequently encounters cutterhead clogging, consuming time and economic costs. Engineering practice shows that cutterhead aperture ratio, soil chamber pressure and soil conditioning have important influences on the clogging behavior of EPB shields. In order to study these factors, a series of laboratory tests were conducted using a setup that can closely simulate the shield tunnelling process. The indicators analyzed were excavation speed, torque, specific energy and soil distribution on the cutterhead. The results indicate that cutterhead aperture and cutter arrangement are important factors in clogging potential. Clogging creates a significant reduction in excavation speed. Torque is not a sensitive parameter reflecting clogging because of the effect of the consolidated soil on the cutters. The presence of soil chamber pressure makes it difficult to remove the clogging through the shearing action of the excavation surface. The injection of a sufficient amount of foam can reduce the risk of shield clogging, but it may lead to an increase of soil adhesion on the cutterhead. The amount of soil that adheres to the cutterhead cannot be used as a classification criterion for clogging potential. Based on experimental phenomena and established studies, a mechanical model called 'beam-bridge' was proposed to study the behavior of the soil through the cutterhead opening and damage form of clogging. The results will help to the excavation control of EPB shields. [ABSTRACT FROM AUTHOR]

Soil conditioning is essential for addressing the stratum applicability problem of earth pressure balance (EPB) shields. Under high water pressures, EPB shields spew water and soil when excavating coarse-grained strata. Typically, foam combined with polymers and slurry is used to solve spewing. However, in current techniques, slurry, foam, and the other agents are mixed with soil separately, their synergistic effect is seldom realized. In this study, an anionic surfactant was used to foam in bentonite slurry to form bubble–slurry to maximize the synergy between bubbles and slurry. The slump, volume stability, and permeability test of bubble–slurry-conditioned sand was conducted to examine the conditioning effect, and the stratum applicability of bubble–slurry was determined from the perspective of permeability. It was found that the conditioning effect of bubble–slurry in coarse gravel soil was excellent and could expand the applicability of EPB shields. The main stabilization mechanism of bubble–slurry is that bentonite particles provide a space barrier for bubbles. And three seepage modes of bubble–slurry-conditioned sand were innovatively defined, and the occurrence conditions of the three seepage modes were analyzed according to the permeability coefficient of sand, initial dynamic shear force of bubble–slurry, and hydraulic gradient. [ABSTRACT FROM AUTHOR]

Seashore saline soil is a kind of soil formed after the sediments flowing into the sea with surface runoff or shallow sea sediments lifted up by wind and waves, flocculated and deposited in the intertidal zone under the action of tides and ocean currents, and finally exposed to the sea surface as the result of continuously silting up. The seashore saline soil in Guangdong Province is rich in resources, mainly distributed in Zhanjiang, Zhuhai, Jiangmen, Shantou and other places, and has an extremely important strategic position in the coastal economic development. Seashore saline soil is one of the main types of low and medium yielding fields, and the soils are characterized by high salt content and salinization. Due to the high nutrient content, rich soil organic matter and high potential fertility, they can become good fields through appropriate improvement measures. The management strategies of seashore saline soil utilization include isolating seawater from invading farmland again through engineering measures; improving drainage and irrigation conditions, applying rainwater dewatering and desalination technology, using artificial dewatering and desalination technology, planting combined wtih dewatering and desalination technology and other measures to drain and reduce salt. The sustainable utilization of seashore saline soil can be realized through soil improvement, scientific fertilization, root strengthening cultivation, selection of rice varieties resistant to salt or aquatic crop rotation and other technical measures. The seashore saline soil is an important reserve resource for the future development of arable land in Guangdong Province, and the full development and utilization of seashore saline soil is of great significance in increasing the sown area of grain, expanding arable land resources and ensuring food security. Based on the current situation of seashore saline soils in Guangdong, it is proposed to attach great imporntance to the special investigation of eashore saline soil resources, strengthen financial investment, promote scientific research, and establish long-term positioning observation stations for comprehensive management.

In order to solve the current situation that a large amount of waste silty clay is generated during the excavation of earth pressure balance shield and station pit, a new plan of using waste silty clay to make slurry to modify the shield soil was proposed. Taking the silt clay in Shenyang area as the research object, the silt clay slurry was modified by adding different admixtures to study the effects of changes in soil-water ratio, admixture type and admixture amount on the funnel viscosity, acidity and alkalinity, filtration loss and colloid rate of the modified slurry. The microscopic modification mechanism of silty clay slurry was studied by scanning electron microscopy (SEM). The results show that pure silty clay slurry has poor stability and high water secretion, which cannot effectively improve the soil. Sodium carbonate and sodium pyrophosphate have a good effect on the modification of silty slurry, with a reasonable admixture of 1% ~ 3% . The modified silty clay slurry can effectively improve the plastic flow properties of the soil in the gravel sand stratum, reasonable soil-water ratio of silty clay slurry is 9∶ 11, sodium pyrophosphate dosing is 3%, and the injection ratio is 24% ~ 28% . The study verifies the feasibility of using silty clay slurry as a shield soil conditioner and provides a new idea for the reuse of waste silty clay. [ABSTRACT FROM AUTHOR]

Background and aims: Host-specific Epichloë spp. are endophytic fungal symbionts of pooid grasses that produce herbivore-deterring alkaloids and alter the host's metabolite and protein profiles. Early observations suggested that Epichloë may have negative allelopathic effects on neighbouring plant species, particularly Trifolium spp. clovers, but subsequent allelopathy experiments produced variable results. We examined two hypotheses: (1) Epichloë strains differ in allelopathic effect, and (2) Epichloë allelopathy negatively affects other plant species. Methods: We performed a greenhouse experiment using root exudates from Lolium perenne L. hosting different E. festucae var. lolii (Latch, M.J. Chr. & Samuels) C.W. Bacon & Schardl strains to compare their allelopathic effects on native legumes and forbs. We then used meta-analysis to examine the evidence to date for allelopathic effects of Epichloë endophytes. Results: We found little difference in effect among E. festucae var. lolii strains and very little evidence for negative allelopathic effects of Epichloë in cool-season grasses across a range of methodologies, target plant species, and response measures. Negative allelopathic effects were detected only for root hair measures, which were from a single study. Positive effects on biomass were found for some experimental subgroups, including legumes. However, the majority of response variables showed no evidence for Epichloë allelopathy. Conclusions: Although there is currently little evidence for negative Epichloë allelopathic effects, our meta-analysis identified several research gaps. Experiments testing the functional belowground effects of Epichloë presence may help to determine its effects on non-host plant performance via plant-soil feedbacks. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

During EPB (earth pressure balance) shield tunnelling in cohesive soils, the excavated soil may stick to the cutters, causing clogging. Clogging could reduce the efficiency of tunnelling as the cutters may be covered with excavated soil, the opening ratio of the cutterhead may be reduced by the sticked soil, and increased torque may be required. This paper studies clogging by testing adhesion strength and tangential adhesion strength with modified pullout tests and direct shear tests, respectively. Strong weathered granite and 11 artificial soil samples are tested to check the feasibility of the modified pullout tests and direct shear tests in the clogging study. The repeatability and accuracy of the modified pullout test are improved by building a new soil container and using a new loading method. Soil conditioning by injecting chemical additives such as foam and dispersant into the excavated soil can be used to reduce the clogging potential during shield tunnelling. The influences of foam and dispersant on Atterberg limits, adhesion and tangential adhesion in strong weathered granite are also studied. Test results show that the Atterberg limits decreased in conditioned soil, and soil conditioning has a greater influence on tangential adhesion than on adhesion. A new clogging potential assessment method for conditioned soil is proposed based on the pullout and direct shear test results. Validations using strong weathered granite show that this method is more suitable for conditioned soils than the traditional methods. [ABSTRACT FROM AUTHOR]

Interactions between plants and the soil are an important ecological process in terrestrial ecosystems as they affect plant community structure: when and where we find different plant species. Those interactions are typically thought of as one‐directional: local soil conditions filter through dispersing species to produce a community of locally adapted plants. However, plants can modify local physicochemical soil conditions via their roots and associations with soil microbes. These may in turn affect the local fitness of other plants, making plant–soil interactions bidirectional. In order to understand how they differ from other ecological processes that structure plant communities, we need a theory connecting these individual‐level plant–soil feedbacks to community‐level patterns. Here, we build this theory with a mathematical model of plant community dynamics in which soil conditioning is explicitly modeled over time and depends on the density of the plants. We analyze this model to describe the long‐term composition and spatial distribution of the plant community. Our main result is that positive plant–soil feedbacks will create clustering of species with similar soil preferences. The composition of these clusters is further influenced by niche width and conditioning strength. In contrast with competitive dynamics driven by niche overlap, only species belonging to the same cluster can maintain high relative abundance in the community. Spatial heterogeneity in the form of an environmental gradient generates patches, each representing a single cluster. However, such patchiness is disfavored when species differ in dispersal ability. We show that stronger dispersers cannot take over the habitat as long as an exogenous driver favors soil conditions that benefit the other species. If exogenous drivers supersede soil conditioning by plants, we retrieve classic habitat filtering, where species are selected based on their suitability to the local environment. Overall, we provide a novel mathematical model for positive plant–soil feedback that we use to describe the spatial patterns of plant abundance and traits related to soil preference and conditioning ability. [ABSTRACT FROM AUTHOR]

This paper presents new methods to evaluate the conditioned soil clogging potential taking into account the slump value and consistency index of the conditioned soil with pure water. In this regard, the results of some field tests performed in two metro tunnels constructed by EPB TBMs are discussed. Major geotechnical data and soil conditioning parameters discussed in this paper include Atterberg limits, natural soil consistency index, water content, liquid injection ratio (LIR), and excavated soil workability (e.g., slump test values). In this regard, using statistical analysis, two practical formulas are developed for the evaluation of the consistency index of the conditioned soil and the slump value with the coefficients of determination of 81 and 71%, respectively. A discussion is also conducted on the clogging potential evaluation, and an improved clogging potential evaluation chart is presented with slump value iso-lines. With this, it is possible to define the required water injection and slump value for the consistency index of 0.4–0.5, which refers to low clogging potential. Based on the results, the sole information of slump is not sufficient to judge the consistency index. The new charts provided in this paper help to fine-tune the slump values corresponding to the proper range of application of EPB TBMs in various plasticity index values. [ABSTRACT FROM AUTHOR]

Plant inoculation with arbuscular mycorrhizal fungi (AMF) can be a useful tool to overcome challenges in dry forest restoration. However, advances are still needed to guide choices regarding soil origin and inoculum production methods, since outcomes can vary due to plant–soil feedbacks (PSF). We evaluate how soil origin and host plant used for inoculum production affect AMF community and therefore the plant biomass accumulation and functional traits.In the conditioning phase, we investigated whether soils originating from a recovered area (Quarry) and a vegetation fragment (Caatinga) would have their AMF communities modified due to the growth of Sorghum bicolor (used for inoculum production) and Senna uniflora (used in Brazilian semiarid restoration). In the feedback phase, we compared the performance of four plants species growing on a degraded soil and inoculated or not by a mixture of AMF isolates in comparison to soil inoculum prepared from the conditioning phase.The inoculum from Caatinga presented seven times more AMF species compared to that from the Quarry, which presented ruderal and stress tolerant species. The soil inoculum conditioned by S. uniflora, regardless of origin, presented greater evenness compared to the soil inoculum produced with S. bicolor and promoted 33% more plant biomass compared to the control without inoculation. Root colonization by AMF increased PSF and decreased plant investment in functional traits such as specific root length (SRL) and specific leaf area (SLA).Our results demonstrate the importance of adopting strategies that preserve local adaptation of inoculants produced. The use of native plant for propagation of native AMF in the conditioning phase provided more positive responses for Mesosphaerum suaveolens and Rhaphiodon echinus than inoculated with introduced AMF isolates. This is probably due to the interaction of inoculated plants with responsive AMF present in the soil.Synthesis and applications. Our study shows that conditioning field‐collected soil with Senna uniflora and using it for inoculation can be a simple technique to promote biomass accumulation for other native herbaceous species. This preserves the compatibility between the soil inoculum produced with native AMF and native plants, representing an important tool for restoration programs. [ABSTRACT FROM AUTHOR]

Tunnelling with earth pressure balance – tunnel boring machine (EPB-TBM) in clayey soil requires a careful conditioning to reduce the effect of clogging and stickiness. In the last decade, many researches have been carried out to understand how to reduce these negative behaviors using conditioning agents, and different laboratory test procedures have been proposed using both powdered clay and clay chips to quantify and assess the effect of conditioning in terms of reduction of clogging and stickiness. In this paper a review of the various proposed tests is presented. Unfortunately, it can be seen that no unified assessment method on the soil conditioning is available and therefore the designers do not have consistent data on which their choices are based. The present research proposes a laboratory test methodology to study clay conditioning taking both the behavior of chips and powdered clay into account. The proposed procedure has been applied on two different clays, and the test results are presented and discussed to show how the proposed methodology could be applied.

Most shield tunnels in urban soft clay or mudstone strata are constructed by Earth Pressure Balance shield (EPB shield). When tunneling in similar strata, the clay soils may clog easily in the cutter head, soil chamber or screw conveyor. In mudstone stratum, assessing a reasonable conditioning state of clay soil is key to ensuring improved shield tunnelling efficiency. The fluidity and adhesion of clay soil are important evaluation indexes of the soil conditioning effect of clay soil. In order to explore the factors affecting the conveying properties of screw conveyor under certain pressure difference in medium-weathered mudstone strata, the changes of clay soil fluidity and adhesion under foam improvement were studied through slump and mixing tests. A screw conveyor model device was developed, and its torque, bearing capacity and discharging efficiency under different soil chamber pressure conditions are comprehensively analyzed combined with the fluidity and adhesion of the soil to help optimize a reasonable slump value of clay soil according to the change of soil chamber pressure in practical engineering. In-situ data from the Ziyang Line of the Chengdu Metro show that the recommended slump value of mudstone stratum can effectively improve soil discharging efficiency and ensure construction safety. [ABSTRACT FROM AUTHOR]

• The active learning approach accelerates foaming agent design, creating new applications and saving time and money. • The new foam agent formulation has a 945s half-life and 500ml foaming volume for EPB soil conditioning. • ETR predicts volume with great accuracy and CB estimates half-life duration with good accuracy. • Shear strength of NF foam conditioned soil decreases with increasing FIR, while slump values decline and then rebound. Injecting soil conditioner into the soil during EPB shield construction is crucial for soil enhancement. Foam agent consumption is common but developing their composition and qualities is time-consuming. Hence, there is an urgent need for a novel approach to material design. This study presents the development of an active learning-based model for foam agents to enhance soil conditioning in gravel strata during EPB shield operations. Foaming volume and half-lift time were forecasted using six machine learning algorithms. The Extra Tree Regression (ETR) model was the most effective for volume prediction, while CatBoost Integration (CB) model performed best for time prediction. The new foam has a half-life of 945 s and the Foam Expansion Ratio (FER) of 21, suitable for EPB shield soil conditioning. The results of slump value and shear strength experiments show a positive correlation between soil slump value, shear strength, and an increase in Foam Inject Ratio (FIR). [ABSTRACT FROM AUTHOR]

Soil conditioning with foam agents can reduce the permeability of virgin soils and mitigate the risk of uncontrollable mud gushing during the excavation of Earth Pressure Balanced (EPB) shield machines. This study employs a combined Computational Fluid Dynamics (CFD) − Discrete Element Method model (DEM) method to simulate the seepage process in foam-conditioned excavated soil. Through discovering migration patterns of foam particles and their effects on macroscopic permeability under various hydraulic gradients, this study unveils the micro-mechanisms governing the permeability of foam-modified soil. Results indicate the feasibility of using hydraulic gradient amplification to examine foam particle migration channels and permeability changes. Furthermore, the findings show that the initial stabilization period in the seepage experiment arises from a dynamic equilibrium between the inflow and outflow of foam in the lower layers. In the upper and middle soil layers, foam migration paths show resilience to water pressure during the initial stage of seepage, but become increasingly responsive to the pressure when migration is hindered. The migration paths of the foam particles in the lower layers remain consistent across different water pressures. The migration speed of individual foam particles is determined by both water pressure and pore structure, while the overall migration speed of the foam increases as water pressure rises. [ABSTRACT FROM AUTHOR]

It is widely recognized that the improvement effects of the foam on the soil properties during earth pressure balance shield (EPBS) tunnelling can be well characterized by some conditioning evaluation indices such as shear strength, flowability, and compressibility. The number of EPBS has increased significantly worldwide in the past few decades. Consequently, recycling the EPBS muck wastes for other applications becomes important, and in this context, estimating the recycling potential of foam-conditioned soils is of great practical significance. Although numerous studies have proved dewaterability to be one of the most important indices to assess the reusability of clay muck wastes, the dewatering behaviors of foam-conditioned clay soils and their quantitative interrelations with common conditioning evaluation indices are still not properly understood. To understand the comprehensive effects of foams on high-saturation clay soil that is comparable to natural clays of real tunnels, a series of laboratory experiments were carried out, including undrained shear tests, flowability tests, and vacuum filtration tests. The concept of specific resistance was introduced to characterize the dewaterability, taking the effects of filtration time and pressure into consideration. The moisture migration mechanisms at both the conditioning and dewatering stages were analyzed using low-field nuclear magnetic resonance tests. It was found that increasing the degree of saturation and the foam injection ratio could lead to a significant enhancement in the flowability (vertical and horizontal slumps), compressibility, and dewaterability, but a reduction in the undrained shear strength. The injected foams caused the moisture to migrate from micropores to mesopores during conditioning, but from mesopores to micropores and macropores during dewatering. Accordingly, quantitative expressions were established to determine the interrelations between conditioning and dewatering indices. The specific resistance was also demonstrated to be an effective alternative variable to characterize the conditioning performance of foams for high-saturation clay soils. Finally, a new application diagram of different evaluation indices, which can assist engineers in effectively assessing the foam's effects on clay soils, was provided to contribute valuable knowledge to EPBS tunnelling practices. [ABSTRACT FROM AUTHOR]

The present study aimed to evaluate the effect of the combination between nitrogen rates and the management of straw mulches for the cultivation of peppers. The treatments comprised three managements of straw on the ground (no straw, Urochloa ruziziensis, and millet) and five nitrogen rates (0, 50, 100, 150, and 200% of the recommended dose of 120 kg ha-1). Mulch presence results in better physiological activity in the plants, while the rates of N positively affect the physiological and biometric characteristics of the plants up to 127.50% and 181.21%, respectively. Rates up to 145.62% increased fruit length in the treatment composed of U. ruziziensis straw, while rates relative to 154.65%, 127.98%, and 138.55% for the control, U. ruziziensis and millet treatments provided productive gains of 202.52%, 267.44%, and 473.18%. We concluded that straw mulching improves the physiological condition of sweet pepper plants and the application of nitrogen fertilizer; using straw from millet plants, combined with the dose of 138.55% N, results in greater yield gains.

Copyright of Guangdong Agricultural Sciences is the property of South China Agricultural University, Guangdong Academy of Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The slurry–earth pressure balance dual-mode shield has an earth pressure balance (EPB) and slurry shield functions. Based on a shield tunnel project of Guangzhou Metro Line 12 in China, this study investigates the clogging prevention of a slurry–earth pressure balance dual-mode shield in a composed stratum with medium–coarse sand and argillaceous siltstone. The results show that the slurry mode was not applicable to the composed stratum with medium–coarse sand and argillaceous siltstone. The excavated soil accumulated easily in the slurry chamber, causing shield clogging. The total thrust force of the shield increased significantly, the tunneling speed gradually decreased to 0, and the torque of the cutterhead increased slightly after the slurry shield was clogged. The fluctuation in the total thrust force, the cutterhead torque, and the tunneling speed also increased significantly. The EPB mode is recommended for composed strata with medium–coarse sand and argillaceous siltstone. The dispersible foam agent and water needed to be used for soil conditioning. The injection amount of foam and water was determined according to the status of the mud discharged by the screw conveyor. Water absorption can be used to characterize the water absorption capacity of particles larger than 0.15 mm. The ideal soil state was that the consistency index of the particles smaller than 0.15 mm was less than 0.5 to prevent the EPB shield from clogging. The water absorption of soil with a particle larger than 0.15 mm should be removed when calculating the consistency index. [ABSTRACT FROM AUTHOR]

The cutterhead of an earth pressure balance (EPB) shield usually relies on a large torque when tunneling through a water-rich and high-permeability sand layer. Sandy soils may lead to severe wear of the cutter tools and make the screw conveyor vulnerable to spewing. In this study, we investigate the characteristics of the soil conditioned by means of foam, bentonite slurry, and carboxymethyl cellulose solution. The mechanical and friction properties of the conditioned soil were tested by the triaxial shear, Laboratoires Central des Ponts et Chaussees (LCPC), and sliding tests, under considering the influence of soil consolidation time. The test results showed that the conditioned sand presents dilatancy, and its cohesion enhances but its internal friction angle decreases. The changing trend of these properties is more prominent with the increase of consolidation time but they stabilize after 12 h. The starting torque of the shield machine in 3-h shutdown reaches 60% of the rated torque, while the starting torque in 6-h shutdown exceeds 80% of the rated torque. To avoid a large starting torque, we suggest that the cutterhead is idled for a short time within 12 h after the shield machine is shutdown. Finally, the theoretical calculation method of torque on cutterhead was developed, and the prediction by such method is in good agreement with the in situ measured data in the cutterhead. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The management of dredged sediments is a challenging issue since it involves the interconnection of complex economic, social, technical and environmental aspects. The EU LIFE SURE project aimed to apply a more sustainable dredging technique to Malmfjärden Bay in Kalmar/Sweden (a shallow urban water body with a high content of nutrients) and, additionally, it involved beneficial uses for the dredged material, in line with the circular economy concept. To achieve this, a life cycle assessment (LCA) study was carried out to assess the potential environmental impacts associated with two scenarios: sediment landfilling (S1) and soil conditioning (S2). This LCA study also aimed to evaluate and compare the costs related to each scenario. S1 contemplated the construction and operation of the landfill for 100 years, including the collection and discharge of leachate and biogas. S2 included the use of sediments in soils and the avoidance of producing and using fertilisers. Results showed that (S2) soil conditioning (total impact: −6.4 PE) was the scenario with fewer environmental impacts and the best economic evaluation. The S2 scenario was mainly related to the positive environmental savings produced by reducing fertiliser consumption (which also avoided purchase costs). However, S2 was also linked to potential negative effects associated with eutrophication and toxicity categories of impacts due to the possible spread of nutrients and pollutants in terrestrial and aquatic environments. In order to mitigate this problem, the sediments could be pre-treated to reduce their risk of pollution. Moreover, the main impact of the landfilling scenario (S1, total impact: 1.6 PE) was the emission of global warming-contributing gases during the operation of the facility. Implementing the soil conditioning scenario was therefore recommended, in line with the aim of the LIFE SURE project. Finally, it was recommended that LCA studies should be applied more often in the future when selecting beneficial uses for dredged sediments. The decision-making process is facilitated when the positive and negative impacts produced by each handling option are considered. [ABSTRACT FROM AUTHOR]

When excavating tunnels in the clay stratum by using earth pressure balance (EPB) shields, the cutterhead is prone to clogging and may lose its ability to excavate. To investigate the clogging mechanism, a cutterhead device equipped with a driving system was developed to emulate the cutterhead behavior of the EPB shield in conditioned soils. The influences of water content, consolidation time, and soil conditioning factors on clay adhesion were evaluated and compared based on general laboratory and cutterhead model tests. The mixing test results showed that the water content influenced considerably clay adhesion. A water content interval near the liquid limit caused a decrease in the adhesion coefficient, and the change in water content was more effective than that in clay conditioning. Direct shear tests revealed that soil conditioning could reduce clay strength, and the effect was evident when the consolidation time was less than 6 h. A peeling point was observed in the adhesion curve of the clay and steel blocks. The peeling point for unconditioned clay was greater than the corresponding shear failure strength, which indicated that the clay had failed before it was detached from the steel block surface. However, contrasting results were obtained for conditioned clay. The cutterhead model test also showed that the water content had the greatest influence on clay adhesion according to the torque and thrust. [ABSTRACT FROM AUTHOR]