In order to study the effect of cadmium ions on the mechanical properties and micro-structure characteristics of the red clay in Guilin, we have conducted triaxial test and the scanning electron microscope tests to analyze the effects of cadmium ion concentration and the number of dry and wet cycles on the mechanical properties and micro-structure changes of the red clay. The results showed the effects of cadmium ions and dry-wet cycles destroy the structure of red clay. The cohesive force of red clay decreases with the increase of cadmium ion concentration, and the internal friction angle first increases and then decreases. With the rise in the number of dry and wet cycles, the cohesive force of cadmium-contaminated red clay first increases and then decreases, and the angle of internal friction rises gradually. Under the action of different cadmium ion concentrations, the stress-strain curve is strain hardening. With the concentration of cadmium ions increases, the strain hardening becomes more apparent; the peak value reached faster. and the axial strain corresponding to the peak value of the line decreases. With the increase in the number of wet and dry cycles, the volume of cadmium-contaminated red clay shrinks and its compactness increases; it gets the peak shear strength faster during the shearing process, and its peak value becomes larger and larger. The main reason for the phenomenon is that cadmium ions destroy the cementation between the particles. The soil particles are mainly in point contact which loosens the structure of the soil; on the other hand, the thickness of the surface diffusion layer of the clay particles increases through chemical action, The exchange of cations increases the porosity of the soil and weakens its strength. The dry-wet cycle shrinks the volume of the red clay, and the soil particles are mainly in surface contact; as the number of dry-wet cycles increases, the soil particles connection is closer, the soil porosity decreases and the strength increases.

This paper reviews two important sources of innovation linked to the maritime environment and more importantly to ports: the potential coupling of sediment management and (bio)remediation. The detrimental effects of dredging are briefly considered, but the focus here is on a sustainable alternative method of managing the problem of siltation. This technique consists of fluidizing the sediment in situ, lowering the shear strength to maintain a navigable under-keel draught. Preliminary investigations show that through this mixing, aeration occurs, which results in a positive remediation effect as well. An overview of port contamination, remediation, and the recent research on aerobic (bio)degradation of port contaminants is made in order to show the potential for such innovative sediment management to reduce dredging need and remediate contaminated mud in ports. This review also highlights the lack of full-scale field applications for such potential remediation techniques, that remain largely confined to the laboratory scale.

The use of granular steelmaking slag as a substitute for natural sand in the construction of tidal flats was investigated. Using an intertidal flat simulator, we evaluated dephosphorization slag mixed with 8% by dry weight of dredged sediment (DPS+DS) as a basal medium for the growth of benthic macro- and microalgae in comparison with silica sand mixed with 8% dredged sediment (SS+DS). Species compositions of macro- and microalgae were distinctly different between DPS+DS and SS+DS. The mean dry weight of macroalgae on DPS+DS was three orders of magnitude higher than that on SS+DS. Sediment shear strength and pH were higher in DPS+DS than in SS+DS or in the sediment of natural tidal flats. These results suggest that DPS contributes to changing the sediment environment, thereby changing the algal composition compared to the composition on natural tidal flats.

The reinforcement strength characteristics of mechanically biologically treated (MBT) waste were studied by conducting consolidated undrained triaxial tests with MBT waste collected from the Hangzhou Tianziling landfill pilot project. In the tests, the effects of the reinforcement material used (geomembrane, geotextile, and geogrid) and the number of reinforcement layers used (one, two, and three layers) were assessed. The results showed the following: (1) even through the axial strain increases up to 25%, the deviator stress of MBT waste could not reach a well-defined peak; (2) the reinforcement effect is related to the type of reinforcement material, with geogrid exhibiting the best reinforcement effect and geomembrane the worst; (3) the strength ratio of reinforced MBT waste is related to the confining pressure and the number of reinforcement layers, with a greater strength ratio in the MBT waste attained with a lower confining pressure in a logarithmic relationship and a greater strength ratio in the MBT waste attained with a greater number of reinforcement layers in a linear relationship; (4) the reinforced MBT waste shear strength parameter variation ranges for the cohesion (c), internal friction angle (φ), effective cohesion (c′), and effective internal friction angle (φ′) are 3.92–13.69 kPa, 19°–29°, 10.10–27.94 kPa, and 24°–45°, respectively; and (5) the deviations in the test values from the apparent cohesion method and the semi-empirical formula method are less than 15%, indicating that these two theories of reinforced sand can also be applied to MBT waste. The results of this study are useful as a baseline reference for the stability assessment of MBT waste landfills.

Mechanically and biologically treated (MBT) waste has significant characteristics such as high stability and low moisture content, which can reduce water, soil, and gas pollution in subsequent treatments. This pre-treatment method is environmentally friendly and sustainable and has become a popular research topic in the field of environmental geotechnical engineering. Using a direct shear test apparatus and five shearing rates (0.25, 1, 5, 10, and 20 mm/min), the shear strength characteristics of MBT waste at the Hangzhou Tianziling Landfill were studied. The results indicate the following: (1) With the increase in horizontal shear displacement, the shear stress of MBT waste gradually increases without a peak stress phenomenon, which is a displacement hardening curve; (2) the shear strength increases with an increase in the shearing displacement rate, and the sensitivity coefficient is 0.64–2.66; (3) a shear strength, shearing rate, and normal stress correlation model is established, and the model has a high degree of fit with the overall experimental data; (4) cohesion (c), internal friction angle (φ), and the logarithm of the shearing rate are linear; (5) the range of c of MBT waste is 22.32–39.51 kPa, and φ is 64.24–68.52°. Meanwhile, the test data are compared with the test data in the literature. The ranges of c and φ of municipal solid waste determined via the shear test are found to be wider than those of MBT waste. The results of this study can provide a reference for the stability calculation of MBT landfills.

The main problem in the reduction of river bottom sediments is to solve the dewatering of the sludge. The commonly used natural air drying method requires a large amount of time and economic cost. In this paper, different treatments were developed for the needs of the project, and related tests were carried out on the reduction of the sludge. Firstly, two or more flocculants were compounded according to the nature of the sludge. The 6 different treatments were determined according to the sedimentation and the turbidity value of the supernatant. Secondly, the dewatering test was carried out on river sediments after flocculation-vacuum preloading. The dewatering effect of different flocculants, water quality, dissipation of pore water pressure, vane shear strength, compression coefficient, and coefficient of consolidation have been analyzed after flocculation-vacuum preloading. The polysilicate aluminium ferric (PSAF) can greatly increase the dewatering efficiency of the filter press membrane, and the final dewatering amount could reach 310 g. The effect of purifying water quality was PSAF>PAM (polyacrylamide, PAM-1(18 million): PAM-2(23 million) = 3:7)>PAC (polyaluminium chloride). The PSAF and PAC could increase the pH of the water during the vacuum preloading test. The PAM has the best the vane shear strength. Lime could improve the vacuum preloading and the vane shear strength when it was added to other flocculants. The incorporation of PSAF could accelerate the dissipation and increase the final dissipation value of pores water pressure. Compared with PAM+PAC+lime, PAM+lime, PAM+PSAF+lime, PAM+PSAF, and PAM+PAC, the overall effect and price of the PAM is optimal.

An in situ erosion flume was used to measure the stability of sediment deposits in Hamilton Harbour, Ontario, Canada. The flume consists of a rectangular duct with an opening at the bottom. A submerged pump attached to the downstream end of the flume circulates the ambient water through the flume, thereby generating turbulent shear flows inside the flume. When the flume rests on a sediment deposit, the exposed part of the sediment deposit is subjected to the flow shear stress. By applying a continually increasing flow shear stress on the sediment deposit and by measuring the amount of sediment erosion, it is possible to assess the erosional stability of the sediment deposits. An under water video camera was mounted on the flume to get visual images of the sediment erosion process. The flume was used at two sites in the Harbour. The erosional resistances measured by the flume for the two sites were different. Measurement of dry density of the sediment deposits using an ultrasonic device was carried out to explain the differences in the stability of sediment deposits from the two sites.

Understanding the effect of acid rain to landslides is crucial for a better landslide risk assessment. This work aims to reveal the unsuspected but key role of acid rain in Panzhihua airport landslide, China. Firstly, we propose a hypothesis that acid rain may aggravate the slaking behavior of mudstone at weak interlayer and make it more fragmented, eventually further reducing its shear strength and predisposing the Panzhihua airport landslide. Subsequently, mudstone samples are subjected to slaking durability test, respectively, using water with a pH of 7 and two dilute hydrochloric acid solution with pH of 5 and 3. Slaking durability index (Idₙ) is adopted aiming to quantitatively evaluate the impact of acid rain on the slaking. Moreover, the mechanisms of acid rain affecting the slaking behavior of mudstone are revealed by (1) analyzing cation compositions changes in different pH slaking fluid and (2) observing micro-structure change of mudstone-chip before and after acid rain treatment. Finally, three works are conducted as evidences to prove that acid rain indeed plays a key role in the occurrence of Panzhihua airport landslide, including (1) analysis of the link between the slaking behavior of mudstone and its shear strength, (2) comparison of cations between spring water at the edge of the toe of landslide and acid rain, and (3) comparison of mineral contents of mudstone samples collected from different locations. These findings have implications for comprehensively analyzing the formation mechanism of landslide in acid rain area (such as Europe, North America, and China).

The properties of municipal solid waste (MSW) in landfills vary considerably, depending on the waste’s composition, time, and density. This variability in MSW properties leads to many uncertainties in the analysis of landfill performance. Therefore, this study aimed to evaluate landfilled waste’s physical, chemical, and mechanical properties for 8 days. Throughout this study, it was possible to investigate the gravimetric composition, density of solid particles, moisture content, volatile solids, pH, total alkalinity, chemical oxygen demand (COD), ammoniacal nitrogen (N-NH₃), grain size distribution, compaction properties, and shear strength of the landfilled waste. It was found that 71% of the waste corresponds to the denominated “others” category, the content of fine materials is 65%, the optimum water content is 34%, the moisture content is 41%, and the volatile solids is 67%. The chemical parameters indicated that the MSW was in the initial phase of biodegradation (acidogenesis), as the pH, total alkalinity, COD, and N-NH₃ showed to be 5, 1575 mgCaCO3.L⁻¹, 13698.6 mgO2.L⁻¹, and 56 mgN-NH3.L⁻¹, respectively. On the mechanical aspect, the waste presented a cohesion of 17 kPa and an internal friction angle of 16°. In general, the results showed that the waste’s physical, chemical, and mechanical properties altered during the landfilling process.

For safe disposal of wastes in landfills, compacted bentonite is recommended as bottom liners due to their significant cation exchange (CEC) and swelling capacity, low permeability and large specific surface area (SSA). The present investigation carried out various experimental studies determining the compressibility behaviour and unconfined compressive strength (UCS) of two different compacted bentonites in the presence of municipal solid waste (MSW) and synthetic MSW leachates. Various examinations were conducted determining alterations in consolidation parameters like the coefficient of consolidation (cᵥ), time taken for 90% consolidation (t₉₀) and compression index (Cc) with both leachates. The outcomes reveal that Cc and t₉₀ values of both bentonites declined; however, cᵥ value rose. Results also indicated that under any given consolidation pressure, a lesser void ratio was achieved for leachates. UCS of both bentonites reduced with leachates’ interaction yet, lying within the recommended a value higher than 200 kPa. A comparative assessment of the two bentonites displayed that bentonite having higher CEC and swelling capacity, and SSA unveiled more excellent Cc and t₉₀ values and a reduction in the UCS. A higher variation in behaviour of bentonites was perceived in the existence of MSW leachate in comparison to synthetic MSW leachate.