Search Results (8)

This study focuses on the use of alkali-activated materials and geopolymer grouts in deep soilmixing. Three types of grouts, incorporating metakaolin and/or slag and activated with sodium silicate solution, were characterized at different scales to understand the development of their local structure and macroscopic properties. The performance of the soilmix was assessed by using combinations of the grouts and model soils with different clay contents. Feret’s approach was used to understand the development of compressive strength at different water-to-solid ratios ranging from 0.65 to 1. The results suggested that incorporating calcium reduced the water sensitivity of the materials, which is crucial in soilmixing. Adding soils to grouts resulted in improved mechanical properties, due to the influence of the granular skeleton. Based on strength results, binary soilmix mixtures containing 75% of metakaolin and 25% of slag, with H₂O/Na₂O ratios ranging from 28 to 42 demonstrated potential use for soilmixing due to the synergistic reactivity of metakaolin and slag. The optimization of compositions is necessary for achieving the desired properties of soil mixtures with higher H₂O/Na₂O ratios. Full article

Recent decades have witnessed the increasing usage of deep cement mixing (DCM) mixers in the field of marine infrastructure construction. The mixing performance, including the torque history, can be helpful for structural safety evaluation, design, and the optimization of agitators, which is of engineering significance. However, to the best of the authors’ knowledge, there are no related publications that have reported the mixing behaviors of deep cement mixing agitators. In light of this, the present work conducts experimental and numerical investigations of the mixing behaviors of a DCM ship mixing agitator. To achieve this end, a model test device is established, and mixing experiments using two- and three-blade mixers are respectively conducted. Silt and clay soils are considered in the experiments with a three-blade mixer, while clay soils are used for those with a two-blade mixer. In addition, this work designs a torque transducer placed inside the rotating rod to accurately measure the torque history of the agitator during model test experiments. The experimental results show that, when mixing clay using agitators with different blades, the average torque value required for a two-blade agitator is slightly larger than that for a three-blade one. This study also presents a computational framework based on the arbitrary Lagrangian–Eulerian (ALE) method for an efficient and accurate modeling of the soil-mixing behaviors of the agitator. The numerical results are found to be in good agreement with the experimental data from model tests in terms of torque history, which demonstrates the effectiveness and capacity of our presented computational framework. The numerical results show that the average torque value is smaller at a higher rotational speed during the mixing of clay using a two-bladed agitator, but the effect of rotational speed on the torque history is small. The experimental and numerical methods introduced in the present work can act as a useful tool for investigations of mixing behaviors of DCM agitators. Full article

Based on a foundation pit project in Fuzhou, China, the influence of foundation pit excavation on the supporting structure and surrounding environment in a soft-soil area is studied. This study was based on actual monitoring data and investigated the variations in the supporting structure, surrounding constructions, and groundwater levels during excavation. The analysis of the monitoring data demonstrates the presence of pronounced ‘spatial effects’ and ‘temporal effects’ on the deformation of the support structure and surrounding structures. The deformation of the support structure and surrounding structures exhibits distinct spatial distribution characteristics at different locations along the excavation pit wall. Typically, more significant deformations are observed in the middle section of the pit wall, while deformations decrease as the distance from the pit corner decreases. The support structure’s and surrounding structures’ deformation characteristics vary during different construction stages. During the excavation phase, the rate of deformation increase in the support structure and surrounding structures is notably higher. In contrast, during the construction of the underground basement floor and the backfilling phase of the excavation pit, the rate of deformation increase in the support structure and surrounding structures is relatively lower. Throughout the entire construction period of the excavation pit, the groundwater level in the vicinity of the pit exhibits a fluctuating trend. Apart from the influence of rainfall, the overall variation in groundwater level is minimal, indicating the effective water-sealing performance of the combined Soil-Mixing Wall (SMW) support structure within the circular enclosure. Full article

Deep soil mixing has been widely used to construct subsurface barriers (cut-off walls) in contaminated sites for contamination containment. Non-invasive geophysical methods are promising for the characterization and assessment of such barriers. The aim of this study was to assess and compare the characterization performance of four geophysical methods (i.e., electrical resistivity tomography, ground-penetrating radar, seismic imaging, and the transient Rayleigh surface wave method) for a subsurface barrier built using soil-mixing technology. The electrical resistivity tomography results show that the overall resistivity of the stratum on the barrier wall increased markedly, and local defects such as pockets of clay appeared as low-resistance anomalies on the resistivity profile. In contrast, the ground radar method failed to make a reasonable evaluation of the quality of the barrier wall because the surrounding environment caused great noise interference. The seismic mapping method had a better performance when the lateral geological conditions were studied. It is also suggested that to improve the signal-to-noise ratio of the surface wave signal, a vibrator with stronger energy should be used, and if conditions permit, the surrounding vibration sources should be shut down during geophysical tests. It is therefore recommended that decision makers and engineers consider using a combination of geophysical methods to evaluate the quality of barrier walls. They should also pay close attention to the specific geological conditions of a survey area, such as the presence of saltwater layers and interference from nearby structures, in order to choose the most appropriate method. Full article

The major focus of this study was determining the effectiveness of new construction specifications regarding the method of cement grout injection for the jet grouting system (high-pressure injection stirring method), with the objective of developing a sustainable ground improvement method. The recent innovative jet grouting techniques allow for improvement at middle pressure, but the mud discharge amount is drastically increased. This produces a serious environmental and financial burden during the disposal of mud discharge. This study attempts to develop a sustainable jet grouting method. The simulation model was prepared by the 3D AutoCAD software, and the analysis was conducted using the moving particle semi-implicit method (MPS method). The study focused on the changes that occurred in the mixing ratio of cement slurry and soil due to the changes made in cement milk spraying during the construction phase and compared it with the traditional method of cement milk spraying. All other construction parameters were kept the same for both cases, and the comparison result shows that the modified construction specification provides a denser and larger improved soil body than the traditional method. Furthermore, the density of the number of particles was determined at the upper, middle, and lower portions of the improved body for comparison. Full article

The soil in some areas of northern China is heavy owing to the presence of clay and stones, which significantly affects the normal operation of a planter as well as the growth of rice. In this regard, this study proposes a seedbed clearing and shaping device for dry direct-seeded rice, which can be used to remove stones in the seeding area, break soil blocks, for soil leveling, and groove forming. The overall structure and roller of the proposed device was developed based on theoretical calculations, discrete element modeling (DEM) simulations, and field tests. The soil-mixing tooth was distributed on the roller based on the double-helix rule, and the two sides of the helix were configured according to the right-hand and left-hand. Subsequently, DEM was used to develop a 3³ box-bench design. According to the agronomic requirements and operating speed ratio, the forward speed was set to 0.5 m/s. Furthermore, the optimization parameters combination of the device obtained by simulation experiments was: forward speed 0.5 m/s, soil depth 61 mm, and rotation speed 110 r/min, which obtained a stone removal rate of 85.65%, stone removal efficiency of 35.47 pieces/m, operating resistance of 719.23 N, and torque of 174.89 Nm. The field verification test results indicated that the stone removal rate was 77.23% under the optimization parameters combination, and the mean relative error of the simulated experiments value was 8.42%, which showed that the performance of the proposed device functioned stably and reliably, thereby providing a high-quality seedbed for sowing and rice growth. The developed device represents a useful solution for the seedbed clearing and shaping. Full article

We aimed to compare psychophysiological responses in adults according to cognitive demand levels for horticultural activities to confirm the feasibility of horticultural activity for improving attention and emotional states. A total of 60 adults in their 20s were included in this crossover design study. Participants performed soil-mixing activities with 2 cognitive demand levels for 2 min each. Electroencephalography (EEG) and electrocardiography (ECG) were performed during these activities. After each activity, the semantic differential method (SDM) was used to evaluate the emotional states of the participants. EEG results revealed that relative fast alpha and low beta power spectrums in the frontal lobes were high during the activity with high cognitive demand compared to those during the low demand activity, which indicates activation in the prefrontal cortex. ECG results showed that during the high cognitive demand activity, the standard deviation of the RR intervals of male adults was high, indicating a high-stress resistance ability of the autonomic nervous system. However, as a result of the SDM, there were no significant differences in emotional states according to the level of activity difficulty. Therefore, this study confirmed the possibility that the intervention of horticultural activities of an appropriate difficulty did not negatively affect subjective emotional changes and could have a positive effect on the improvement of attention levels and emotional stability in adults. Full article

The use of biochar is an important tool to improve soil fertility, reduce the negative environmental impacts of agriculture, and build up terrestrial carbon sinks. However, crop yield increases by biochar amendment were not shown consistently for fertile soils under temperate climate. Recent studies show that biochar is more likely to increase crop yields when applied in combination with nutrients to prepare biochar-based fertilizers. Here, we focused on the root-zone amendment of biochar combined with mineral fertilizers in a greenhouse trial with white cabbage (Brassica oleracea convar. Capitata var. Alba) cultivated in a nutrient-rich silt loam soil originating from the temperate climate zone (Bavaria, Germany). Biochar was applied at a low dosage (1.3 t ha⁻¹). The biochar was placed either as a concentrated hotspot below the seedling or it was mixed into the soil in the root zone representing a mixture of biochar and soil in the planting basin. The nitrogen fertilizer (ammonium nitrate or urea) was either applied on the soil surface or loaded onto the biochar representing a nitrogen-enhanced biochar. On average, a 12% yield increase in dry cabbage heads was achieved with biochar plus fertilizer compared to the fertilized control without biochar. Most consistent positive yield responses were observed with a hotspot root-zone application of nitrogen-enhanced biochar, showing a maximum 21% dry cabbage-head yield increase. Belowground biomass and root-architecture suggested a decrease in the fine root content in these treatments compared to treatments without biochar and with soil-mixed biochar. We conclude that the hotspot amendment of a nitrogen-enhanced biochar in the root zone can optimize the growth of white cabbage by providing a nutrient depot in close proximity to the plant, enabling efficient nutrient supply. The amendment of low doses in the root zone of annual crops could become an economically interesting application option for biochar in the temperate climate zone. Full article