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Rapid advances in deep-sea mining engineering have created an urgent need for the accurate evaluation of the undrained strength of marine soils, especially surface soils. Significant achievements have been made using full-flow penetration penetrometers to evaluate marine soil strength in the deep penetration; however, a method considering the effec...
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... probe below the mudline, m 3 ; q sat the saturation density of marine soil, kg/m 3 ; a the acceleration due to centrifugal effect (in normal environment, a = g), m/s 2 ; and q w the density of water, kg/m 3 . Fig. 8 shows that the function V depends on h. A geometrical analysis yields calculation formulas for V of different probes, as given by Eqs. ...
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... This discrepancy is attributed to the precision limitations of the CPT test. Actually, in centrifuge tests, CPT results are more reliable when the penetration depth exceeds ten times the diameter of the CPT tip cone [58]. Given the 12 mm diameter of the CPT used in the model's measurements, accuracy is achieved for a prototype depth higher than 6 m (10 times the diameter, under 50 g, converting mm to m by dividing by 1000). ...
The paper focuses on the identification of the 3D failure envelope of a shallow foundation on soft soil reinforced by rigid inclusions. A nonlinear 3D finite element model is first validated against literature results and novel centrifuge experimental data. The failure envelope, defined in the vertical force (V), bending moment (M) and horizontal force (H) space, is then constructed using numerical swipe tests. Analytical formulas are introduced to describe the 3D failure envelope shape and inclination, considering the influence of the coverage area, the thickness, and the friction angle of the load transfer platform. Finally, the efficiency of a rigid inclusion foundation is highlighted by comparing its failure envelope to that of the same foundation without rigid inclusions. The proposed analytical failure envelope can be used by engineers to quantify the bearing capacity of rigid inclusion foundations and by researchers to develop novel macroelements submitted to complex coupled loads.
... For some natural saturated soft clay, numerous studies (e.g., Davis and Booker, 1973;Houlsby and Wroth, 1983;Bransby and Randolph, 1998;Zou et al., 2018;Guo et al., 2022) have shown a linear increase in undrained shear strength with depth, as illustrated in Fig. 1(a). This can be expressed as ...
Marine-sensitive soils exhibit significant strength heterogeneity and nonlinear strain softening, which are vital characteristics in geotechnical engineering. This study introduces a novel soil strength formulation that effectively captures both of these key characteristics. This formulation is incorporated into the Mohr-Coulomb matched Drucker-Prager yield criterion. To address the mesh-dependence challenges typically encountered in classical finite element (FE) analysis for strain localization, this paper establishes a robust constitutive integration algorithm within the framework of Cosserat continuum theory. The numerical implementation is accomplished through the UEL function in the ABAQUS FE software. Following validation, the methodology is applied to conduct thorough FE analyses on the bearing capacity and progressive failure process of strip footings. Additionally, through parametric investigations, we explore the influence of nonlinear strain softening parameters and the heterogeneity parameter on the bearing capacity coefficient (Nc) and the underlying foundation failure mechanisms. By simulating the complete progressive failure process of the foundation, this numerical method exhibits its remarkable capability to accurately replicate the entire progressive instability process. Derived from parametric analyses, a remarkably accurate formula (Nc (λ = 0)) is obtained, accounting solely for nonlinear strain softening. Furthermore, a comprehensive formula (Nc) is introduced, capturing both strength heterogeneity and nonlinear strain softening.
... The movement and evolution of submarine slides occur in distinct stages, and each stage exhibits relatively independent physical and mechanical characteristics [22,31]; this phenomenon also constitutes a typical chain disaster, as shown in Fig. 2. The entire process of the formation and evolution of a typical submarine slide includes seafloor instability, block sliding, debris/mud flow, turbidity current, and heavy water flow [14,20,22]. According to a large number of marine geology investigations, deep-sea shallow-layer sediments mainly comprise viscous sediments [32][33][34]. The movement and mechanical states of such deep-sea viscous sediment slides can be summarized into three stages: (1) the block sliding stage, in which the slide exhibits elastic-plastic deformation behavior, indicating a solid state [35,36]; (2) the debris/mud flow stage, in which the slide exhibits both solid and fluid properties, and non-Newtonian fluid rheological models are commonly used for quantification [37][38][39][40][41]; and (3) the turbidity and heavy water stage, in which the slide behaves as a fluid, and the shear behavior of the slide is commonly quantified using the viscosity of Newtonian fluids [40,42]. ...
Deep-sea pipelines play a pivotal role in seabed mineral resource development, global energy and resource supply provision, network communication, and environmental protection. However, the placement of these pipelines on the seabed surface exposes them to potential risks arising from the complex deep-sea hydrodynamic and geological environment, particularly submarine slides. Historical incidents have highlighted the substantial damage to pipelines due to slides. Specifically, deep-sea fluidized slides (in a debris/mud flow or turbidity current physical state), characterized by high speed, pose a significant threat. Accurately assessing the impact forces exerted on pipelines by fluidized submarine slides is crucial for ensuring pipeline safety. This study aimed to provide a comprehensive overview of recent advancements in understanding pipeline impact forces caused by fluidized deep-sea slides, thereby identifying key factors and corresponding mechanisms that influence pipeline impact forces. These factors include the velocity, density, and shear behavior of deep-sea fluidized slides, as well as the geometry, stiffness, self-weight, and mechanical model of pipelines. Additionally, the interface contact conditions and spatial relations were examined within the context of deep-sea slides and their interactions with pipelines. Building upon a thorough review of these achievements, future directions were proposed for assessing and characterizing the key factors affecting slide impact loading on pipelines. A comprehensive understanding of these results is essential for the sustainable development of deep-sea pipeline projects associated with seabed resource development and the implementation of disaster prevention measures.
... Nature gas hydrate (NGH) is a solid ice-like substance formed by water and methane in a low-temperature and high-pressure environment (Jiang et al., 2022a) and is regarded as a promising clean fuel source with high energy density (Guo et al., 2022). To exploit the NGH stored in the deep-sea sediments, different exploitation strategies are proposed (Zhu et al., 2021) and divided into the following four steps, namely drilling a deep well into the NGH reservoirs, increasing the reservoir permeability by hydraulic fracturing, hydrolyzing the NGH into gas and water, and pumping the decomposed natural gas. ...
The low permeability of the methane hydrate-bearing sediment limits the methane gas extraction. To enhance methane hydrate extraction, hydraulic fracturing can be a promising approach to improve the hydrate reservoir permeability by creating a fracture network in the reservoir. In this study, a coupled thermo-hydro-mechanical-chemical mathematical model and its numerical implementation based on finite element technology are introduced to analyze the methane hydrate extraction through fractured methane hydrate-bearing sediment considering methane hydrates dissociation, gas-water two-phase flow, heat transfer, dynamic changes of the sediment permeability, and deformation of both sediment matrix and fractures as well as capturing the interplay between them. The coupled thermo-hydro-mechanical-chemical numerical model is verified by reproducing a methane hydrates dissociation laboratory test. Finally, we conduct a series of simulations for the methane gas depressurization extraction through the sediments with the DFNs assigned as diverse geometrical characteristics. The influence of hydraulic fracture network geometrical and hydraulic characteristics on methane hydrate extraction are discussed. The results can offer a reference for enhancing the methane hydrate extraction efficiency.
... This method is characterized by its simple equipment and convenient applicability. However, it can only measure the undrained shear strength at a specific depth during each instance and is greatly influenced by the torsional shear rate [7]. Another widely used method is the static cone penetration test, which offers the capability to assess the continuous variation of undrained strength in cohesive soil with increasing depth. ...
... According to the fitting equation, as the penetration velocity decreases, the sediment tends to reach a steady state, and the penetration resistance coefficient stabilizes at around 10. This stable value is consistent with the penetration resistance coefficient suit for the static cone penetration test conducted at a constant penetration speed of 0.02 m/s [7]. This trend is similar to some numerical simulations, but they do not provide specific formulas [52]. ...
... To ensure optimal permeability, a 2.5 cm thick geotextile was installed. Additionally, considering the latest research findings [34] that suggest high strength at the bottom of the deep-sea seabed, we incorporated a 5 cm thick layer of sand and a 5 cm thick layer of gravel at the bottom. The in-situ sediment characteristics were measured at the seafloor sampling location for comparison with the experimental seabed. ...
... It is assumed that a high-density submarine turbidity current occurs on the northern continental slope of the South China Sea (Guo et al., 2022d), and the physical and mechanical properties (Guo et al., 2021b) of the turbidity current are selected for numerical analysis as follows: the density is 1312 kg/m 3 , and the dynamic viscosity is 0.118 Pa s (approximately 133 times the dynamic viscosity of water). We collected gravity core samples in the submarine landslide-prone area during marine geological surveys, mixed them with seawater to prepare samples, and measured their mechanical parameters using a rheometer (Guo et al., 2021b). ...
Pipelines in the deep sea are at risk of damage due to submarine landslides, which can result in the loss of costly infrastructure and pollution stemming from hydrocarbon leaks. Submarine landslides can exhibit a wide range of flow characteristics, which in turn can affect how they interact with pipelines. Researchers have previously focused on pipelines impacted by submarine debris and/or mud flows described by non-Newtonian fluid rheological models and the laminar model. However, the impact of larger-scale and higher-speed submarine turbidity currents described by turbulence models on pipelines has been overlooked. In this study, we address this gap by utilizing a more accurate turbulence simulation method, namely, the large eddy simulation (LES) method, to analyze the effect of submarine turbidity currents on fixed spanning pipelines, and we validate the effectiveness of the proposed method via typical circular cylinder flow experiments and numerical simulations. We find that the lift force on the pipeline impacted by submarine turbidity currents under high-Reynolds number (Re) conditions is particularly significant relative to debris and/or mud flows under low-Re conditions. In parallel, the vortex shedding frequency increases with increasing Re, and the Strouhal number basically remains unchanged and ranges from 0.2–0.25 at 1,112 ≤ Re ≤ 333,559. Furthermore, the vortex structure and its arrangement behind the spanning pipeline become irregular with increasing Re, forming a turbulent vortex street, which reveals the mechanism of pipeline vibration. Finally, a methodology for predicting characteristic drag force and lift force coefficients is established for submarine pipeline design.
... In general, deep-sea surface sediments characterized by low strength, high compressibility, and significant fluidity (Nian et al., 2019;Zhang et al., 2021a;Sabetamal et al., 2021) present the shear behavior of a non-Newtonian fluid with shear thinning characteristics (Boukpeti et al., 2009(Boukpeti et al., , 2012Randolph et al., 2010;Hermidas et al., 2019), i.e., the viscosity of the fluid decreases as the shear rate increases (Guo et al., 2020Lu et al., 2022a). Considering the challenges associated with sampling these surface sediments, the in situ full-flow penetration test technique offers great promise for assessing the strength of marine surface sediments (DeJong et al., 2010;Morton et al., 2015;Zhou et al., 2016;Guo et al., 2022b). In practical engineering applications, a full-flow penetrometer needs to be equipped with a seabed base (Fig. 1). ...
The undrained shear strength of marine surface sediments is critically important for both the development of marine resources and environmental protection. In situ full-flow penetration tests offer significant advantages for evaluating these surface sediments, particularly those with low strength. Accurately analyzing the strength of surface sediments during in situ full-flow penetration tests relies on correctly identifying the sediment-water interface, also known as the mudline. Unfortunately, there is currently no established method for solving this problem. This study utilizes computational fluid dynamics to conduct a numerical analysis of full-flow penetrometer probes (specifically of ball and T-bar probes) as they penetrate marine surface sediments of varying strengths and densities from different heights. By examining the variation in the dimensionless drag force coefficient of the probes in relation to the dimensionless penetration depth, the impact of the mudline on the drag force trend is systematically analyzed. Additionally, a methodology for determining the mudline location using a mudline distinguishing factor is proposed. This mudline distinguishing factor was tested during a field trial of the in situ ball full-flow penetration device in the Philippine Sea, The proposed methodology for identifying the mudline and analyzing the strength of marine surface sediments has significant value for the field.
... The relationship between the compressive strength of different rocks under dry and saturated state and strain rate is shown in Fig. 12. [53].Generally, the compressive strength of dried and saturated rock increases with strain rates, owing to the rate dependent effect. The compressive strength of the saturated rock is always lower than that of the dry rock under quasi-static loading, regardless of rock types [54]. In the dynamic loading tests with a strain rate range of 15-250 s À1 , the compressive strength of the saturated rock is usually lower than that of the dry rock. ...
... For polymetallic nodules, the subsea mining vehicle (SMV) generally works at the seabed with an average depth of 6000 m and a water pressure of 60 MPa. Under the tough deep-sea environment of high pressure, high permeation pressure and complex submarine topography [54], the capability of SMV is not only to collect mineral efficiently on the thin and soft seabed with obstacles following the predetermined route, but also to work in a stable and controllable way. The traveling mechanism should have the ability of strong traction force, large bearing capacity, small disturbance on the seabed, less sediment carrying, low energy consumption and high collection efficiency, etc., and also works well with automatic obstacle avoidance, scheduled trajectory tracking and subsidence prevention. ...
... However, the full-flow penetration test, constrained by the aforementioned full-flow failure mechanism, is primarily used to analyze the strength of seabed sediments through deep ball penetration, i.e., the tested seabed sediment can reach the full failure mode. When the ball is used in a natural seafloor environment, it penetrates the seabed surface sediment from the mudline, and the seabed sediment flowing through the ball surface cannot achieve full reflux due to the influence of the overlying ambient water (Guo et al., 2022b(Guo et al., , 2022c, as shown in Fig. 2. Past some studies on the deep penetration resistance coefficient and the surface penetration resistance coefficient obtained without considering ambient water conditions cannot be used to evaluate the strength of surface sediments. The failure state of the seabed surface sediment penetrated by the ball continually changes under the influence of the overlying ambient water, and thus, the corresponding surface penetration resistance coefficient is also changes accordingly. ...
... The failure state of the seabed surface sediment penetrated by the ball continually changes under the influence of the overlying ambient water, and thus, the corresponding surface penetration resistance coefficient is also changes accordingly. Guo et al., 2022bGuo et al., , 2022c introduced centrifugal testing and CFD numerical methods to identify the critical depth at which seabed surface sediment reaches a stable failure state. They used a simplified and homogeneous strength model and a mini ball with a diameter of 15.8 mm and evaluated the accuracy and applicability of the developed CFD method, which is currently limited to laboratory-scale application scenarios. ...
... The CFD model is validated by numerical simulations (Guo et al., 2021b(Guo et al., , 2022b, centrifugal tests (Guo et al., 2022c), and analytical solutions (Randolph and Houlsby, 1984;Martin and Randolph, 2006). First, the slow impact of the seabed sediment (5 kPa) with a velocity of 50 mm/s on the pipe with a diameter of 25 mm under ideal conditions (i. e., the CFD model is not affected by surrounding boundary conditions) is further simulated. ...
Sampling fluidized seabed surface sediments with viscous fluid characteristics is highly challenging, making in situ penetration tests essential to evaluate their strength. Unfortunately, an in situ full-flow spherical penetrometer (i.e., ball) is typically used to assess the strength via deep penetration, and research on surface penetration, extensive viscous fluid shear behavior of fluidized surface sediments, and ball-ambient water-surface sediment interaction is lacking. To address this gap, this study utilizes a computational fluid dynamics (CFD) model validated through centrifugal tests to examine the penetration of balls with free and no-slip in fluidized seabed surface sediments with the shear rate effect. This study analyzes the stress characteristics on a ball under complex conditions and proposes three phases of the penetration resistance coefficient of the ball in fluidized surface sediments. Additionally, this study quantifies the effects of various factors, such as initial undrained shear strength, rate effect, ambient water above the ball, and contact relationship between the ball and fluidized seabed surface sediment, on sediment strength evaluation. Finally, this study establishes a three-phase method to evaluate the undrained shear strength of fluidized seabed surface sediments by full-scale spherical penetrometer tests. This method calculates the surface penetration resistance coefficients as functions of the dimensionless penetration depth, providing a vital basis for acquiring the strength of fluidized seabed surface sediments.
