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Purpose: The combined contamination of As, Pb, and Cd in soil has caused serious environmental problems. In order to find a more suitable remediation method, this study used the combination of amendment materials and microorganisms to synchronously stabilize As, Pb, and Cd in compound contaminated soil. Materials and methods: The metallogenic characteristics of Lysinibacillus fusiformis were verified by SEM, XRD, FTIR, and other characterization methods; four kinds of amendment materials and microbial agent were used to carry out the comparative experiments of unitary and binary remediation respectively to stabilization soil potentially toxic element(s) (PTEs). By changing the addition amount of materials, the effects on soil physical and chemical properties, speciation transformation, and content of As, Pb, and Cd were discussed. Results: The results of comparative experiments show that the stabilization effects of loess combined with microbial agent on As and Pb are significantly improved, reaching 43.86% and 83.52%, respectively. The combination of compost sludge and microbial agent can effectively improve the stabilization effect of As, reaching 44.53%. Compost sludge can effectively reduce the content of exchangeable fraction of Pb whether used alone or combined with microorganisms. In the experiments of different addition amounts, there was no significant relationship between the addition amount and the stabilization efficiency of three PTEs when loess was added alone, but after combined with microbial agent, the stabilization efficiency of As, Pb, and Cd increased with the increase of the addition amount of loess. Conclusions: The combination of loess and MICP may be an effective method to synchronously stabilize As, Pb, and Cd in soil. Loess, attapulgite clay 1, and attapulgite clay 2 are suitable for As stabilization. Compost sludge and attapulgite clay 1 are more favorable for Pb stabilization. Loess, compost sludge, and attapulgite clay 1 promote Cd stabilization effect. Loess and compost sludge are more suitable for combination with microorganisms. [ABSTRACT FROM AUTHOR]

Press-in open caisson method, which sinks into soil with the aid of mechanical pressure without excavation, is becoming an important method of construction in extremely soft foundations. However, many engineering problems are prone to occur in the construction of caissons, such as sinking and large deformation. In this study, the stratigraphic response model, such as soil migration during the press-in process of open caisson, is focused on. Through model tests of soil and caissons, the migration patterns of each part of the soil were carried out, and the mechanism underlying the stratigraphic response pattern was investigated. The three primary conclusions are as follows: 1) The bottom edge foot of caisson produces lateral extrusion on surrounding soil in the range of 10 cm (20%H) below, resulting in lateral movement of soil. 2) two kinds of plug, i.e., "wedged" and "unwedged" plugs exist, and the driven forces for the soil migration can be divided into three stages, i.e., caused by soil plug with active arch, by soil plug with passive arch and caused by soil squeezing effect. 3) there is a significant linear correlation between the soil plug changes, the horizontal movement of the deep soil body, and the displacement of the surface uplift. The soil plugging effect and squeezing effect are interacted and enhanced with each other. This study provides a new understanding of the stratigraphic response in the construction of press-in open caissons, and guides safety control of open caissons construction. [ABSTRACT FROM AUTHOR]

Purpose: The combined pollution of soil heavy metals has always been a difficult problem for remediation. The combined pollution in soil also has great potential risks to crop safety and groundwater safety, and more research needs to be carried out on the remediation of soil heavy metal combined pollution. In addition, there is a large gap in the application of biological manganese oxide in soil. Materials and methods: In this study, the treatment effects of As, Pb, and Cd in water and soil systems were studied by combining biochar with manganese-oxidizing bacteria repair agent. The orthogonal experiment was used to study the effect of different proportions of addition on the remediation effect of three heavy metals, and the contribution of each component added in the remediation was discussed by the control experiment. The effects of soil physicochemical properties including pH, EC, and DOM (dissolved organic matter) on the transformation and migration of heavy metals were also analyzed in detail. Results and discussion: The combined remediation showed a high removal rate of Pb (97.71%) in water and increased the removal rate of Cd alone to 96.5%. Compared with the microbial remediation, the removal rate of As decreased (25.5%), which may be related to the adsorption of Fe2+ and Mn2+ by biochar. The combined application of biochar and manganese-oxidizing bacteria in soil could significantly improve the passivation of Pb, reduce the passivation rate of As, and increase the concentration of exchangeable Cd. Treatment of heavy metal combined pollution by combined remediation can achieve the best benefits, and the most suitable ratio is 2% (w/w) of biochar and 60% (v/w) of manganese oxide bacteria remediation agent. The migration of cadmium in soil induced by biochar and manganese-oxidizing bacteria may be due to the increase of DOM. Conclusions: Compared with the single application, the combined remediation of biochar and manganese-oxidizing bacteria has better effect on composite pollution. Combined remediation is more suitable for soil contaminated by Pb and As, and it is difficult to efficiently solve the simultaneous Cd pollution. At the same time, combined remediation has greater development potential for Pb and Cd pollution in water. [ABSTRACT FROM AUTHOR]

Pipe-roof Pre-construction Method (PPM) is a pre-reinforcement method widely adopted in shallow large section tunnelling in the urban area. As one of the key indexes needed to be controlled, ground surface settlement and axis deviations induced by pipe-roof tunnelling attract increasing attention, but the interaction between socketed pipes (ISP), including shielding and constraint effects, has been lack of consideration in practice. By incorporating deformation coefficient and deviation coefficients, this paper proposed a new analytical method to account for the effect of ISP on the ground movement. Then, a numerical model to consider ISP and sequential jacking process was established and a series of simulations were carried out for a large pipe-roof tunnelling project. By comparing with the analytical results, the deviation coefficients were determined for the proposed model and the effect of ISP on the surface settlement was further revealed. Finally, the rationality and effectiveness of the proposed method were confirmed by contrasts with traditional methods and numerical calculations. The results show that an approximately 37% error rate could be reduced by the new method. This research is helpful for a better understanding of the effect of ISP, and therefore benefits the effective prediction and control of the surface settlement induced by pipe-roof tunnelling. [ABSTRACT FROM AUTHOR]

There are many studies on the treatment of heavy metals by manganese-oxidizing bacteria and the reaction is good; the problem of compound pollution of heavy metals in soil has been difficult to solve. In this study, the application of manganese-oxidizing bacteria in soil was studied. The tolerance of manganese-oxidizing strains (Pseudomonas taiwanensis) to environmental conditions and the treatment effect of heavy metals As, Pb, and Cd in aqueous solution were investigated, and the effect of iron-manganese ratio on the treatment effect was discussed. The results showed that the suitable pH conditions for the growth of P. taiwanensis were 5–9, and the salt tolerance was 6% (by sodium chloride). The tolerant concentrations for heavy metals As(V) and Mn(II) were 500 mg L−1 and 120 mg L−1, respectively. The strains were enriched by nutrient broth medium. After the logarithmic phase, the bacterial suspension was mixed with ATCC#279 medium at a ratio of 1:10, and a certain amount (10 mg L−1) of Mn(II) was added. The results of As, Pb, and Cd removal in the composite polluted water phase were 22.09%, 30.75%, and 35.33%, respectively. The molar ratio of manganese and iron affected the removal efficiency of single arsenic, the highest efficiency is 68%, and the ratio of iron to manganese is 1:5. However, when the soil was treated by the same method, the results showed that not all metals were passivated, such as Cu. At the same time, for As, Pb, and Cd, the treatment effects in soil were worse than those in water, perhaps more consideration should be given to environmental conditions, such as soil moisture and temperature, when manganese-oxidizing bacteria are used to treat soil. [ABSTRACT FROM AUTHOR]

Purpose: In situ remediation techniques are currently limited for agricultural soil contaminated by heavy metal(loid)s, particularly for alkaline soil. In this study, we applied the amendments (Chinese loess, attapulgites, and composted sludge) to a contaminated alkaline agricultural soil to compare their effectiveness in immobilizing heavy metal(loid)s. Materials and methods: Soil was collected from the uppermost 20 cm of a heavily contaminated cornfield in Baiyin, China. The amendments were added to the soil at the ratios of 1%, 5%, 10%, and 15%. Controls without amendment were also included. The effectiveness of amendments was evaluated using single extractions and Tessier sequential extraction procedure. The extractants in the single-step extraction were H2O, calcium chloride (CaCl2), diethylenetriaminepentaacetic acid (DTPA), and hydrochloric acid (HCl). Seed germination was performed with the soil after immobilization for 180 days. Results: Chinese loess effectively reduced the toxicity of heavy metal(loid)s and improve seed germination rates compared with attapulgites (ATPs) and composted sludge. Composted sludge effectively transformed heavy metal(loid)s, particularly Cu, from the carbonate fraction into the organic matter or the residual fraction. The concentrations of heavy metal(loid)s extracted with DTPA were positively correlated with the summation of the exchangeable and carbonate fractions (P < 0.05). A high seed germination rate could be obtained when the four amendments were added at the ratios between 5 and 10%. Conclusions: Chinese loess was effective and safe to immobilize heavy metal(loid)s in contaminated alkaline agricultural soil. DTPA performed the best in predicting the availabilities of As, Cd, Pb, Cu, and Zn in the soil. [ABSTRACT FROM AUTHOR]

The objective of this study is to propose a new method to evaluate the performance of different evacuation modes, and to find a rational evacuation mode for long underwater vehicle tunnels. In this study, a combined evacuation model (TPES) incorporating both a traffic flow module and a crowd evacuation module is proposed to simulate the integrated crowd evacuation with the effects of traffic flow, and the model is partially validated by a field evacuation test and a verified model Simulex. A vehicle tunnel was modeled to simulate fire-related traffic congestion and passenger evacuation, and then the evacuation performance index Im of three evacuation modes in different fire situations were calculated. The results revealed that the hybrid evacuation mode performs best among the three modes, with Im superior to other two modes by up to 26%. The transversal evacuation passage mode performs better than the longitudinal mode under the same conditions. However, the transversal and longitudinal modes can be equivalent when the passage spacing difference is within a range of 150–200 m. The critical spacing of the evacuation passage in a simple evacuation process lies in between 100 m and 350 m at confidence level of 90% for the transversal evacuation mode. [ABSTRACT FROM AUTHOR]