Abstract Deep cement mixing piles are a key technology for treating settlement distress of soft soil subgrade. However, it is very challenging to accurately evaluate the quality of pile construction due to the limitations of pile material, large number of piles and small pile spacing. Here, we propose the idea of transforming defect detection of piles into quality evaluation of ground improvement. Geological models of pile group reinforced subgrade are constructed and their ground-penetrating radar response characteristics are revealed. We have also developed ground-penetrating radar attribute analysis technology and established ground-penetrating radar technical system for evaluating the quality of ground improvement. We further prove that the ground-penetrating radar results integrating single-channel waveform, multi-channel section and attributes can effectively detect the defects and stratum structure after ground improvement. Our research results provide a rapid, efficient and economic technical solution for the quality evaluation of ground improvement in soft soil subgrade reinforcement engineering. 

Quality evaluation of ground improvement by deep cement mixing piles via ground-penetrating radar

Effects of pyrolysis conditions and heteroatom modification on the polycyclic aromatic hydrocarbons profile of biochar prepared from sorghum distillery residues.

Fe(III) (oxyhydr)oxides are ubiquitous in paddy soils and play a key role in Cd retention. Recent studies report that pyrogenic carbon (PC) may largely affect the microbial transformation processes of Fe(III) (oxyhydr)oxides, yet the impact of PC on the fate of Fe(III) (oxyhydr)oxide-associated Cd during redox fluctuations remains unclear. Here, we investigated the effects of PC on Cd retention during microbial (Shewanella oneidensis MR-1) transformation of Cd(II)-bearing ferrihydrite under varying redox conditions. The results showed that in the absence of PC, microbial reduction of ferrihydrite resulted in Cd release under anoxic conditions and Fe(II) oxidation by oxygen resulted in Cd retention under subsequent oxic conditions. The presence of PC facilitated microbial ferrihydrite reductive dissolution under anoxic conditions, promoted Fe(II) oxidative precipitation under oxic conditions, and inhibited Cd release under both anoxic and oxic conditions. The presence of PC and frequent shifts in redox conditions (i.e., redox cycling) inhibited the transformation of ferrihydrite to highly crystalline goethite and magnetite that exhibited less Cd adsorption. As a result, PC enhanced Cd retention by 41-59% and 55-77% after the redox shift and redox cycling, respectively, while in the absence of PC, Cd retention decreased by 5% after the redox shift and increased by 11% after redox cycling. Sequential extraction analysis revealed that 63-78% of Cd was associated with Fe minerals, while 3-12% of Cd was bound to PC, indicating that PC promoted Cd retention mainly through inhibiting ferrihydrite transformation. Our results demonstrate the great impacts of PC on improving Cd retention under dynamic redox conditions, which is essential for applying PC in remediating Cd-contaminated paddy soils.

Pyrogenic Carbon Improves Cd Retention during Microbial Transformation of Ferrihydrite under Varying Redox Conditions.

Impacts of Biochar Aging on its Interactions with As(Iii) and the Combined Cytotoxicity

In situ aging can change biochar properties, influencing their ecosystem benefits or risks over time. However, there is a lack of field verification of laboratory methods that attempt simulation of long-term natural aging of biochar. We exploited a decade-scale natural charcoal (a proxy for biochar) aging event to determine which lab-aging methods best mimicked field aging. We oxidized charcoal by ultraviolet A radiation (UVA), H2O2, or monochloramine (NH2Cl), and compared it to 10-year field-aged charcoal. We considered seven selected charcoal properties related to surface chemistry and organic matter release, and found that oxidation with 30% H2O2 most representatively simulated 10-year field aging for six out of seven properties. UVA aging failed to approximate oxidation levels while showing a distinctive dissolved organic carbon (DOC) release pattern. NH2Cl-aged charcoal was the most different, showing an increased persistent free radical (PFR) concentration and lower hydrophilicity. All lab oxidation techniques overpredicted polycyclic aromatic hydrocarbon release. The O/C ratio was well-correlated with DOC release, PFR concentration, surface charge, and charcoal pH, indicating the possibility to accurately predict biochar aging with a reduced suite of physicochemical properties. Overall, our rapid and verified lab-aging methods facilitate research toward derisking and enhancing long-term benefits of biochar application.

Rapid Simulation of Decade-Scale Charcoal Aging in Soil: Changes in Physicochemical Properties and Their Environmental Implications.

The low-strain integrity testing of large-diameter piles has attracted more and more attention because of its wide application in offshore engineering, such as for wind turbines, etc. Body and Rayleigh waves generate on the top surface of large-diameter piles after the excitation load. The multi-reflections of these waves from the pile side result in the obvious three-dimensional effect at the pile top. Therefore, one-dimensional wave theory is no longer suitable for interpreting the wave propagation in the pile body under vertical excitation. In this paper, based on the “pile in pile” conception, both the pile and soil were simulated using a three-dimensional continuum model, considering the vertical displacement, to investigate the influence of the three-dimensional effect of the pile-soil system on the vertical dynamic response of large-diameter piles in low-strain integrity testing. The axisymmetric solution to the three-dimensional pile-soil system was obtained, and the rationality of the proposed solution was verified by comparing it with the results of the finite element method and the results of other existing solutions. Arithmetic examples were used to describe the influence of the three-dimensional effect of the pile-soil system on the vertical dynamic response of large-diameter piles.

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Influence of the Three-Dimensional Effect of Pile-Soil System on the Vertical Dynamic Response of Large-Diameter Piles in Low-Strain Integrity Testing

The discontinuity’s surface topography is often assumed as smooth and straight. To overcome non-considering roughness of discontinuity, direct shear numerical experiment is proposed to research influences of discontinuous roughness on its strength. Firstly, based on researched mechanical properties of discontinuity, the laws how asperity inclination angles and asperity heights of discontinuity and the mechanical behavior of discontinuity are studied. The results show that the failure of discontinuity considering roughness is not instantaneous. It is a complex process which goes through energy accumulation. The cohesive force increases with asperity inclination angle and asperity height increasing. The inner friction angle also goes through the same changes. However, when the normal stress reaches 500kPa for asperity inclination angle and 700kPa for asperity height, the shear strength experiences a decreasing process.

Numerical Experimental Research on Shear Strength of Rock Mass Discontinuity Concerning Roughness

Whether the inhomogeneity of mudstone foundation leads to abnormal bearing capacity of the driven pile remains controversial. This study introduces the standard penetration test hammering number and needle penetration strength for quantitative analysis by macroscopic observation of the engineering field on the mudstone stratum self-structure and microscopic observation by simple and feasible electronic magnification. The analysis of typical engineering examples demonstrated that the abnormal bearing capacity of piles in the mudstone stratum was related to mudstone inhomogeneity. This study also proposes a method of evaluating mudstone uniformity using the heterogeneous index η, in which η > 2 suggests the need for engineering measures. These findings assist in determining a reasonable solution to the problem of abnormal bearing capacity at driven piles in mudstone foundations.

https://www.frontiersin.org/articles/10.3389/feart.2022.1101955/pdf

Xiao Bing Gao

Papers

Rapid Simulation of Decade-Scale Charcoal Aging in Soil: Changes in Physicochemical Properties and Their Environmental Implications.

Influence of the Three-Dimensional Effect of Pile-Soil System on the Vertical Dynamic Response of Large-Diameter Piles in Low-Strain Integrity Testing

Numerical Experimental Research on Shear Strength of Rock Mass Discontinuity Concerning Roughness

Bearing capacity of driven pile and determination of inhomogeneous mudstone around the pile