Guoliang Yu

Bio: Guoliang Yu is an academic researcher from Shanghai Jiao Tong University. The author has contributed to research in topics: Drag coefficient & Acceleration. The author has an hindex of 6, co-authored 9 publications receiving 111 citations.

Vacuum preloading method for land reclamation using hydraulic filled slurry from the sea: A case study in coastal China

Abstract: This study observed an engineering project, in which the vacuum preloading method incorporated with the vertical drain system was applied to the improvement of the dredged marine clay slurry as the fill as well as the in-situ soft ground for land reclamation. The site conditions, field instrumentation, construction process and partial requirements of the vacuum preloading project are described in this paper. Field monitoring data is presented and analyzed. After the vacuum preloading, the average degree of consolidation achieved was more than 88%, and the bearing capacity of the dredged marine clay slurry was improved from less than 4 kPa to be higher than 50 kPa. Specifications of construction techniques were detailed which would be useful and referenceable to engineers. Three empirical prediction methods for estimating the ultimate settling and consolidation degree are reviewed. Several key parameters and their optimal values in the formulae are discussed and suggested, respectively. Prediction results show that the Asaoka's method is the most preferable for predicting the settling of dredged marine clay slurries with high initial water content improved by vacuum preloading.

On the estimation of the falling velocity and drag coefficient of torpedo anchor during acceleration

Abstract: Torpedo anchor installation is a new kind of anchoring system which is much more economical than other conventional anchoring methods. However, there are few studies on the falling velocity and drag coefficient of the torpedo anchors. In this study, seven torpedo anchors with different densities, aspect ratios, scale ratios and fin sizes were utilized to investigate their influence on the falling velocity of the anchor during acceleration. Anchors were released in a water tank and the falling process was recorded using a fast speed video camera. Accordingly, the corresponding drag coefficients against the Reynolds numbers during acceleration were calculated. The Reynolds numbers varied between 4.8×105 and 2.16×106 and the drag coefficients varied between 0.2 and 1.2. The differences between the falling velocities and the drag coefficient for anchors with different shapes, sizes, densities and directional stability were illustrated and the reasons for the differences were explained. The final drag coefficients versus the Reynolds numbers were compared with other representative models found in the literature. The influence of acceleration on the drag coefficient or falling velocity was emphasized. Finally, an Extrapolation Mathematical Model for the motion of the anchor in the fluid was proposed and the results were compared to the experimental data.

Erodibility of fluidized cohesive sediments in unidirectional open flows

Abstract: In this study, the erodibility of fluidized cohesive sediments from the seabed of Hangzhou Bay, China, was experimentally investigated in unidirectional open flows. The results indicated that the yield stress is a major factor influencing the erodibility of cohesive sediments. As the yield stress increases, the critical Shields parameter, critical velocity, and critical shear stress increase, but the scour rate decreases. However, a lower yield stress of sediment indicates higher potential of being eroded. Furthermore, the equation for the critical condition of sediment motion, as well as the equation for the scour rate, without considering the degree of fluidization of sediments, may have limited application ranges. Hence, the bed shear stress, critical shear stress, and yield stress should be considered to predict the scour rate. Finally, a modified empirical equation based on the Partheniades (1962) equation is proposed by introducing the yield stress, which is a rheological parameter, in order to calculate the scour rate of cohesive sediments.

Penetration depth of torpedo anchor in cohesive soil by free fall

Abstract: Developing deep sea technologies, many marine novel facilities have been introduced; and mooring systems, however, have become more expensive, complex, and hard cooperative in deep-water marine industry. The torpedo anchor is regarded as a modern technology benefits from easy installation, cost efficiency, and high level of anchor force. In this study, the penetration depth of a free falling torpedo anchor into cohesive soil has been laboratory investigated. 128 Sets of tests have been conducted with nine different torpedo anchors not only in shape, but also in size. Three anchor aspect ratios and three different types of muds were tested while mud rheological properties such as the yield stress and flow curves were also measured. Finally, a formula calculating the penetration depth of the anchor, regardless of soil separation has been proposed based on energy conservation principle and experimental measurements. Results indicate that the predicted penetration depth has a good conformity with the measured penetration depths in laboratory and field tests. Static undrained shear strength values should be reduced in formula when the impact velocity exceeds a critical value. Soil separation occurs depending on the anchor nose angle and surface roughness, and also soil properties. Nevertheless, the critical impact velocity resulting into soil separation and its degree require further study in the future.

Permeability of muddy clay and settlement simulation

Abstract: In this study, the permeability characteristics of hydraulic-filled mud from Yueqing port and natural clays from the Minghang River, China, were investigated in a laboratory. The obtained experimental results, when combined with other researchers׳ experimental data, indicate that the void ratio and clay content are two major factors influencing the permeability of muddy clays. The variation of the permeability with the void ratio is best represented by a linear e vs. lg k relationship. Furthermore, the permeability decreases as the clay content increases. Then, a new empirical formula of the form lg k=A(P)e+B(P) is proposed to calculate the permeability of fine-grained muddy clays with the clay content P as a parameter. By using this formula and Gibson׳s equation, the complete settling process of a reclamation foundation that has been newly filled with dredged mud is simulated. The simulation results show that the variation of the void ratio and temporal settlement amount are in line with the measured field data.

Mechanistic insights into red mud, blast furnace slag, or metakaolin-assisted stabilization/solidification of arsenic-contaminated sediment.

Abstract: Elevated level of arsenic (As) in marine sediment via deposition and accumulation presents long-term ecological risks. This study proposed a sustainable stabilization/solidification (S/S) of As-contaminated sediment via novel valorization of red mud waste, blast furnace slag and calcined clay mineral, which were selected to mitigate the increased leaching of As under alkaline environment of S/S treatment. Quantitative X-ray diffraction and thermogravimetric analyses illustrated that stable Ca-As complexes (e.g., Ca5(AsO4)3OH) could be formed at the expense of Ca(OH)2 consumption, which inevitably hindered the hydration process and S/S efficiency. The 29Si nuclear magnetic resonance analysis revealed that incorporation of metakaolin for As immobilization resulted in a low degree of hydration and polymerization, whereas addition of red mud promoted Fe-As complexation and demonstrated excellent compatibility with As. Transmission electron microscopy and elemental mapping further confirmed the precipitation of crystalline Ca-As and amorphous Fe-As compounds. Therefore, red mud-incorporated S/S binder achieved the highest efficiency of As immobilization (99.9%), which proved to be applicable for both in-situ and ex-situ S/S of As-contaminated sediment. These results advance our mechanistic understanding for the design of green and sustainable remediation approach for effective As immobilization.

Effect of strain rate and strain softening on embedment depth of a torpedo anchor in clay

Abstract: Torpedo anchors (of diameter ~1 m) are released from a height of 50–100 m from the seabed, achieving velocities up to 35 m/s at impacting the sediment. The strain rates induced in the surrounding soil by this dynamic installation is therefore significantly higher than those associated with installation of other offshore foundations and anchoring systems. The high strain rates enhance the mobilised undrained shear strength compared to that measured by in-situ penetrometer or laboratory tests. This paper reports the results from dynamic installation of a torpedo anchor in strain softening, rate dependent soft clays, quantifying the effects relative to results for ideal Tresca material. The three-dimensional dynamic large deformation finite element (LDFE) analyses were carried out using the coupled Eulerian–Lagrangian approach. The simple elastic-perfectly plastic Tresca soil model was modified to allow strain softening and strain rate dependency of the shear strength. Parametric analyses were undertaken varying the strain rate parameter, the sensitivity and ductility of the soil, and the soil undrained shear strength. Overall, embedment depth for rate dependent, strain softening clays lay below that for ideal Tresca material. Increased strain rate dependency of the soil led to marked reduction in embedment depth, only partly compensated by brittleness. Key results have been presented in the form of design charts, fitted by simple expressions to estimate the embedment depth of a torpedo anchor.

An investigation into the relationship between saturated permeability and microstructure of remolded loess: A case study from Chinese Loess Plateau

Abstract: Understanding the permeability law of remolded loess is important for engineering construction in the loess area. To gain insights into the changes of saturated permeability and microstructural evolution of remolded loess for different dry densities, the loess from the Chinese Loess Plateau was used as a test material and was remolded as samples with different dry densities at the optimum water content state. The saturated seepage test and scanning electron microscopy (SEM) imaging were conducted on the remolded loess samples. The microscopic properties of the loess pores in the SEM images were identified using Image-Pro Plus software. The relationship between the micro-parameters of the pores and permeability were explored using multivariate statistical analysis. Results from this study highlight that the dry density of samples can be classified into three categories: Group I (1.30 and 1.35 g·cm−3) shows permeability decreasing with seepage time, Group II (1.40 g·cm−3) shows permeability initially increasing and then decreasing with seepage time, and Group III (1.45–1.65 g·cm−3) shows permeability increasing with seepage time. Correspondingly, the dry densities of these groups were found to be unsuitable, doubtful, and suitable, respectively, for laboratory study on the saturated permeability of remolded loess. In addition, the evolution mode of remolded loess structure is basically overhead-interlocking-matrix with increasing compactness. In this process, the macropores transform into mesopores and then to small pores, while the change in micropore content is weak. Also, the directional distribution of the pores weakens, while the pore morphology changes little. Furthermore, the contents of macropores and mesopores, as well as the pore diameters, play a positive role in permeability, while the contents of small pores and micropores, and directional probability entropy have a negative impact on permeability.

Numerical investigation on the penetration of gravity installed anchors by a coupled Eulerian–Lagrangian approach

Abstract: Gravity installed anchors (GIAs) are released from a height of 30–150 m above the seabed, achieving velocities up to 19–35 m/s at the seabed, and embed to depths of 1.0–2.4 times the anchor length. Challenges associated with GIAs include the prediction of anchor initial embedment depth, which determines the holding capacity of the anchor. Based on the coupled Eulerian–Lagrangian approach, a numerical framework is proposed in this paper to predict the embedment depth of GIAs, considering the effects of soil strain rate, soil strain-softening and hydrodynamic drag (modeled using a concentrated force), with the anchor-soil friction described appropriately. GIAs are influenced by the hydrodynamic drag before penetrating into the soil completely, hence the anchor accelerates less than the previous investigations in shallow penetration, even decelerates directly at the terminal impact velocity. The hydrodynamic drag has more influence on OMNI-Max anchors (with an error of ∼4.5%) than torpedo anchors, and the effect becomes more significant with increasing impact velocity. An extensive parametric study is carried out by varying the impact velocity, strain rate and strain-softening parameters, frictional coefficient, and soil undrained shear strength. It is concluded that the dominant factor affecting the penetration is the soil undrained shear strength, then are the impact velocity, strain rate dependency and frictional coefficient, and the minimal is the strain-softening of soil. In addition, although the strain rate dependency is partly compensated by the softening, the anchor embedment depth accounting for the effects of strain rate and strain-softening is lower than that for ideal Tresca soil. Strain rate dependency dominates the combined effects of strain rate and strain-softening in the dynamic installation of GIAs, on which should pay more attention, especially for the calibration of the related parameters and the measured solutions. In the end, the theoretical model based on the bearing resistance method is extended by accounting for the hydrodynamic drag effect.