Search Results (8)

Conventional ureolytic microbial soil stabilization can generate ammonium-containing by-products and may show reduced treatment uniformity in deep soils where mass transport is limited. This study investigated the feasibility of using facultatively anaerobic yeast to stabilize loess under aerobic and anaerobic curing conditions. Specimens were prepared using a single-mixing method and cured for 3, 7, 14, and 28 days. Unconfined compression tests, unconsolidated–undrained triaxial tests, scanning electron microscopy, X-ray diffraction, and acid-washing analysis were conducted. Yeast treatment increased the unconfined compressive strength of loess to 99.8–109.9 kPa under aerobic curing and 89.1–95.7 kPa under anaerobic curing, compared with 81.3 kPa for untreated loess. Cohesion increased from 25.30 kPa to 27.24–33.14 kPa, whereas the internal friction angle remained within 37–39°. Microstructural observations revealed fibrous and film-like bonding materials between soil particles, while no obvious newly formed crystalline calcium carbonate was detected. The acid-washing results also indicated no evident net increase in calcium carbonate content. The strengthening effect was therefore attributed mainly to particle bonding associated with polymeric or extracellular-polymeric-substance-like products, rather than extensive calcium carbonate precipitation. These results demonstrate the potential of yeast as an environmentally friendly biological agent for loess stabilization. Full article

Silts are generally unsuitable for direct use as subgrade fill material due to their low shear strength and deformation resistance. In this study, a novel technique for strengthening silt using enzyme-induced calcium carbonate precipitation (EICP) with the addition of non-fat milk powder is proposed to improve the mechanical properties of silt for use as subgrade fill material. The effect of EICP on the mechanical properties of silt, in terms of internal friction angle and shear strength, was examined through consolidated undrained (CU) triaxial shear tests. The results showed that, with the EICP technique involving non-fat milk powder, the mechanical behaviors of silts were significantly enhanced due to the improved bonding ability of the silt particles. Furthermore, an optimum content of non-fat milk powder of 6 g/L is proposed to increase the mechanical properties. Compared with EICP treatment alone, under the optimum condition of 6 g/L non-fat milk powder and 14 days of curing, the shear strength, cohesion, and internal friction angle increased by 44.1%, 51.86%, and 31.4%, respectively. Finally, microstructural analyses were conducted using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) to provide insight into the mechanisms underlying the improvement of silt. The findings of this study can provide guidance for the application of silt improvement through the EICP technique involving non-fat milk powder. Full article

To address the engineering challenges associated with Guilin red clay, such as its potentially low strength and unfavorable mechanical behavior, this study investigated the effectiveness of lignin and lime as modifiers. Consolidation undrained triaxial tests and scanning electron microscopy (SEM) were employed to evaluate the strength characteristics and microstructural changes in modified clay specimens with varying dosages. The results demonstrate distinct strengthening mechanisms: Lignin exhibits an optimal dosage (6%), significantly increasing cohesion and internal friction angle through physical reinforcement (“soil fiber” formation), but higher dosages (8%) lead to particle separation and strength reduction. In contrast, lime provides continuous and substantial strength enhancement with increasing dosage (up to 8%), primarily through chemical reactions producing cementitious compounds (e.g., C-S-H, C-A-H) that densify the structure. Consequently, lime-modified clay shows significantly higher cohesion and internal friction angle compared to lignin-modified clay at equivalent or higher dosages, with corresponding stress–strain curves shifting from enhanced (strain-hardening) to softening behavior. These findings provide practical insights into red clay improvement in geotechnical engineering applications. Full article

To investigate the slope instability caused by differential frost heaving mechanisms from the slope crest to the toe during frost heave processes, this study takes a typical silty clay slope in Xinjiang, China, as the research object. Through indoor triaxial consolidated undrained shear tests, eight sets of natural and frost-heaved specimens were prepared under confining pressure conditions ranging from 100 to 400 kPa. The geotechnical parameters of the soil in both natural and frost-heaved states were obtained, and a spatiotemporal thermo-hydro-mechanical coupled numerical model was established to reveal the dynamic evolution law of anchor rod axial forces and the frost heave response mechanism between the frame and slope soil. The analytical results indicate that (1) the frost heave process is influenced by slope boundaries, resulting in distinct spatial variations in the temperature field response across the slope surface—namely pronounced responses at the crest and toe but a weaker response in the mid-slope. (2) Under the coupled drive of the water potential gradient and gravitational potential gradient, the ice content in the toe area increases significantly, and the horizontal frost heave force exhibits exponential growth, reaching its peak value of 92 kPa at the toe in February. (3) During soil freezing, the reverse stress field generated by soil arching shows consistent temporal variation trends with the temperature field. Along the height of the soil arch, the intensity of the reverse frost heave force field displays a nonlinear distribution characteristic of initial strengthening followed by attenuation. (4) By analyzing the changes in anchor rod axial forces during frost heaving, it was found that axial forces during the frost heave period are approximately 1.3 times those under natural conditions, confirming the frost heave period as the most critical condition for frame anchor design. Furthermore, through comparative analysis with 12 months of on-site anchor rod axial force monitoring data, the reliability and accuracy of the numerical simulation model were validated. These research outcomes provide a theoretical basis for the design of frame anchor support systems in seasonally frozen regions. Full article

Given that the existing drainage strengthening methods for underwater damaged piers are expensive, inefficient, and cause shipping traffic disruptions, an urgent need exists to explore undrained strengthening methods, such as the precast concrete segment assembly method (PCSAM). However, the PCSAM has certain limitations, including a considerable strength loss of filled concrete, poor accuracy, poor connection performance of the segment sleeves, etc. Hence, this study developed an improved PCSAM (IPCSAM) by adopting self-stressed anti-washout concrete (SSAWC) as the filling material and developing a lining concrete segment sleeve (LCSS) based on the design principle of shield tunnel lining segments. Subsequently, the seismic performance of the strengthened piers was investigated. First, nine 1/5-scale pier column specimens were designed by considering different influencing factors: the self-stress of the SSAWC, LCSS reinforcement ratio, and initial damage and length–diameter ratio of the pier column. These specimens were tested under low reversed cyclic loading. Second, an extended parameter analysis was performed based on the established numerical models consistent with the quasi-static test’s parameter settings. Finally, a restoring force model of the strengthened piers, including the trilinear skeleton curve model and hysteresis curve model, was established based on the results of the quasi-static test and parameter analysis. The results indicated that the bearing capacity, ductility, and initial stiffness of the specimens strengthened using the IPCSAM increased by approximately 83.5–106.4%, 16.3–50.2%, and 83.9–177.3%, respectively, with the energy dissipation capacity also significantly improved. The self-stress of the SSAWC should not exceed 2.2 MPa, and the recommended ratio of the LCSS thickness to pier column diameter is 1/10. Additionally, the proposed restoring force model is highly accurate and applicable, able to provide a reference for the practical seismic strengthening design of piers. Full article

Compared with the conventional drainage strengthening techniques, the precast concrete segment assembly strengthening method (PCSAM) is regarded as a fast, more economical, and traffic-friendly underwater strengthening method for damaged bridge piers and piles, as the drainage procedure can be omitted. However, this method still has some disadvantages, such as strength loss of the filling material, debonding of the interface due to shrinkage of the filling material, poor connection effects, and poor durability of the segment sleeves. To solve these problems, the PCSAM is improved in this study by using self-stressed anti-washout concrete (SSAWC) as the filling material and by developing a lining concrete segment sleeve (LCSS) by referring to the design theory for shield lining segments. Six specimens are designed and prepared with consideration of the influential factors, such as the self-stress, thickness of the filled concrete, and concrete strength of the LCSS, then the monotonic axial compression test is carried out to investigate the improvements in the axial compression properties of the specimens. Accordingly, extended parametric analyses are performed based on the established numerical models. Finally, the calculation formula for the bearing capacity is proposed based on the analysis results. The results indicate that the SSAWC can provide initial confining compressive stress in the core region of the piers, in addition to increasing the bearing capacity and ductility of the specimens. The improved LCSS segment connection is more reliable and increases the strengthening efficiency. The influence of self-stress on the bearing capacity of the specimens is cubic and the influence of the filled concrete strength on the bearing capacity of the specimens is nonlinear. The calculation formula for predicting the bearing capacity of axially compressed columns possesses good applicability and can be used as a reference for practical engineering. Full article

This paper presents a new macro-element modelling framework for plate anchors which enables the effect of pore water pressure changes and the related evolution of soil strength during the process of cyclic loading and consolidation to be captured. The proposed modelling framework combines an advanced macro-element model for plate anchors, expanded to capture the cyclic loading behaviour, with a simple one-dimensional model of undrained shearing and consolidation for a soil element representative of the whole soil mass around the anchor. The representative soil element tracks the effects of changes in effective stress on the soil strength, which in turn governs the anchor capacity in the macro-element model. The two modelling components are linked through a mobilised capacity compatibility condition. It will be firstly shown that such modelling framework is able to capture the expected changes in an anchor’s capacity related to cyclic pore pressure generation and consolidation under one-dimensional cyclic loading of the anchor. Then, the model will be used to explore the plate anchor’s behaviour and failure mechanisms under loading conditions which mobilise its full three-dimensional cyclic loading capacity. The macro-element model will identify some conflicting mechanisms (i.e., the anchor’s kinematic/rotation and soil weakening/strengthening) governing the three-dimensional capacity of the anchor. Full article

Offshore wind turbine foundations are commonly subjected to large horizontal, vertical, and bending moment loads. Marine soils have high moisture content, high compressibility, high sensitivity, and low strength, resulting in insufficient foundation bearing capacity. In order to improve the bearing capacity of wind turbine foundations and reduce foundation settlement, an internal vacuum preloading method combined with electroosmosis reinforcement is used to reinforce the soil within bucket foundations. The pore water pressure, vertical settlement, pumping quality of the soil during the reinforcement process, soil moisture content before and after the reinforcement, and undrained shear strength were analyzed. Horizontal and vertical bearing capacity model tests were carried out on the reinforced and nonreinforced soil inside the bucket foundation. Results show that vacuum preloading combined with electroosmosis reinforcement reduces soil moisture content inside the bucket foundation by approximately 20%, and the undrained shear strength of the internal soil increases by approximately 20 times. Soil reinforcement has high spatial uniformity. Results of the bucket foundation bearing capacity model show that when the soil inside the bucket foundation is strengthened, horizontal bearing capacity increased by 2.9 times and vertical bearing capacity increased by 2.1 times. Vacuum preloading combined with electroosmosis reinforcement can effectively improve the shear strength of soft soil and enhance the bearing capacity and stability of bucket foundations. Full article