The physical and mechanical properties of rocks can be reduced significantly by an acidic environment, resulting in engineering weaknesses, such as building foundation instability, landslides, etc. In order to investigate the mechanical properties of rocks after hydrochemical erosion, a chemical damage constitutive model was established and used to analyze chemical damage variables and energy transformation. It is assumed that the strength of the rock elements obeyed Weibull distribution, considering the nonuniformity of rock. The chemical damage variable was proposed according to the load-bearing volume changes in the rock under water–rock chemical interactions. The chemical damage constitutive model was derived from coupling the mechanical damage under the external load and the chemical damage under hydrochemical erosion. In order to verify the accuracy of the model, semi-immersion experiments and uniaxial compression experiments of black sandy dolomite were carried out with different iron ion concentrations. Compared with the experimental data, the chemical damage constitutive model proposed could predict the stress–strain relationship reasonably well after water–rock interaction. The effects of water–rock interaction on the rock were a decrease in peak stress and an increase in peak strain. The peak strain increased by 4.96–29.58%, and the deterioration rate of peak strength was 0.19–4.18%. The energy transformation of the deterioration process was analyzed, and the results showed that the decrease in releasable elastic energy, U_e, is converted into dissipated energy, U_d, after hydrochemical erosion.

Foundation pit excavation is common in urban construction, while safety evaluation is always significant in every specified project. The soil material properties, groundwater level, excavation method, supporting structure, monitoring points’ arrangement, and so on distinguish from one site from another. Thus, many studies have looked into the safety and reliability of designated projects. This paper was based on the co-construction underground tunnel project of a deep foundation pit excavation in Suzhou, China. This paper aimed to perform a safety evaluation on this foundation pit by means of numerical simulation for parameter influence analysis, as well as scientific comparison with in-site monitoring data. To minimize the energy consumption and contribute to the carbon neutrality, a brief energy consumption analysis was also conducted. The results indicated that the maximum deformation of the foundation pit bottom is 4.5 cm and the deformation of the foundation pit is within the allowable range. The maximum horizontal displacement of each excavation is approximately at 10 m to 12 m of the diaphragm wall and the largest deformation is 28 mm. The maximum ground settlement is less than 16 mm, which confirmed the safety during excavation. It is ideal that the above deformation law will provide a reference for similar projects. Furthermore, this research simulated and monitored the whole cycle of foundation pit excavation, and contributes to savings in energy consumption and limiting of carbon emissions.

Carbon emission is one of the main causes of global climate change, thus it is necessary to choose a low-carbon method in the contaminated soil remediation. This paper studies the adsorption ability of ZVI on Pb(II) contaminated soils under different working conditions. The removal efficiency of Pb(II) was 98% because of the suitable ZVI dosage, log reaction time and low initial solution concentration. The whole balancing process was much fast according to the pseudo-second-order kinetic and Freundlich isothermal model. Moreover, sequential extraction procedure (SEP) showed Pb(II) was transformed from Fe/Mn oxides-bound form to residual form in Pb(II) contaminated soils. From scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET) and X-ray diffraction (XRD) results, it was confirmed that zero-valent iron (ZVI) stabilizes Pb(II) pollutants mostly through the combination of chemical adsorption and physical adsorption. The economic and carbon emission assessments were used to compare the cost and carbon emissions of different methods. The results show that ZVI adsorption has excellent economic benefits and low carbon emission.

Greenhouse gas emission has been a serious problem for decades. Due to the high energy consumption of traditional construction and building materials, recycled aggregate and other environmentally-friendly materials or recycled materials have been researched and applied. The treatment and reuse of construction and demolition waste (CDW) is a good way to reasonably distribute the renewable resources in the urban city. The recycled aggregate can be used in road engineering, geotechnical engineering and structural engineering. The combined use of natural aggregate and recycled aggregate may possess better performance in real constructions. This paper investigates the mechanical performance, micro-mechanism and CO₂ footprint assessment of NAM (natural aggregate mortar) and RAM (recycled aggregate mortar). Compressive strength test, flexural strength test, XRD and SEM, and CO₂ emission evaluation were conducted and analyzed. The results indicate that NAM depicts better compressive strength performance and RAM has higher flexural strength. The XRD and SEM patterns illustrate that the ettringite and C-S-H are the most important role in shrinkage-compensating mechanism, which is more obvious in RAM specimens. The proportion of CaO and MgO hydrated into Ca(OH)₂ and Mg(OH)₂ is also a key point of the volume expansion through the curing period. Finally, the CO₂ emission of NA is higher than RA per unit. This indicates that utilizing recycled aggregate over other conventional resources will reduce the energy consumption, and hit the mark to be environmental-friendly.

The restoration and reconstruction of ecosystems is the basis of the landscape reconstruction of construction and demolition waste (CDW) landfills, in which landscape plants play a prominent role. To screen appropriate landscape plants that could survive and grow in a mixture of CDW and soils, the Fenghuangshan CDW landfill in Suzhou, China, was taken as an example to study restoration technology by plants. The growth and physiological parameters of ten herbaceous species with high ornamental values, healthy growth and easy maintenance in the green space of Suzhou were measured under a mixture of CDW and soils. A comprehensive evaluation was conducted with the membership function method. The results showed that Hemerocallis fulva, Panicum virgatum, Heliopsis helianthoides, Sedum aizoon and Carex oshimensis ‘Evergold’ were well adapted to the mixed environment of CDW and soil in Suzhou. Among them, Hemerocallis fulva ranked first with a comprehensive evaluation index of 0.87. It could be the best herbaceous species for landscape reconstruction of CDW landfills. The study is instructive for vegetation restoration in surrounding areas and provides a method for plant selection and evaluation for vegetation restoration of CDW landfills.

Rural domestic sewage has become very serious, while only 17.4% of it is treated centrally or partially, which results in environmental pollution and waste of water resources. To solve this problem, a wastewater treatment system by modular coupling is proposed, and the processing module includes two or three of multi-stage ecological pond, multi-stage drop aeration ecological ditch and multi-stage drop dam. The analysis of three examples shows that the system has a good treatment effect on chemical oxygen demand (COD), total nitrogen (TN), ammonium nitrogen (NH4 +-N) and total phosphorus (TP), and the removal ratios are 90.22%, 82.07%, 91.60%, 81.48%, respectively, when the flow rate is 3 m3/h. After 28 days of continuous operation, the treatment capacity decreases by about 10%, indicating that the system has good long-term treatment performance. The removal ratio decreases slightly under different flow rates, which shows its great adaptability in different hydraulic conditions. In practical application, the system can select different coupling systems according to rural terrain and wastewater quality, and it is suitable for the treatment of rural domestic sewage and agricultural non-point source sewage and the repairment of urban sewage and lake eutrophic water body.