ORCID Profile
0000-0002-8666-9383
Current Organisation
Dalian University of Technology
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Publisher: Canadian Science Publishing
Date: 14-04-2023
Abstract: Tracked vehicles are widely deployed for heavy lifting and transportation on inaccessible terrains such as sw s, bogs, and peatlands. The stability of a tracked vehicle is traditionally assessed only under uniaxial loading conditions and the impact of combined loading from different directions is ignored. This makes the conventional design framework somewhat unreliable. The failure envelope approach has been widely employed to assess the load-carrying capacity of shallow foundations. However, the failure envelopes available in public domain mainly focused on single isolated foundations, ignoring the interference effect between the tracks due to the rigid connection of the vehicle. This paper aims to develop an integrated framework to assess the stability of a tracked vehicle on a soft soil under fully three-dimensional loading conditions. The finite element method is adopted to simulate the soil-vehicle interactions, with the tracks idealised as two shallow foundations in parallel. The stability of the foundation system is described in terms of failure envelopes considering various track configurations and load combinations. Failure envelopes are represented by expressions and ultimately integrated into a multiple-nested function to determine the overall stability factor. The framework is demonstrated by a case study of designing a tracked vehicle under combined loading conditions.
Publisher: Elsevier BV
Date: 11-2019
Publisher: Elsevier BV
Date: 03-2016
Publisher: Thomas Telford Ltd.
Date: 15-11-2022
Abstract: Large seabed trenches have recently been found adjacent to suction caissons with taut and semi-taut moorings. Seabed trenching leads to loss of soil support and additional caisson rotation, and can therefore significantly decrease geotechnical capacity. In this paper, upper-bound solutions are presented that enable calculation of the reduction in ultimate load-carrying capacity of a suction caisson in a trenched seabed compared to optimal capacity in an intact seabed. Failure mechanisms for caissons embedded in an intact seabed are augmented to incorporate a kinematically admissible mechanism for a trench extending from the mudline. The rate of work dissipation is calculated to determine the optimised solution of the inclined capacity of suction caissons. Comparisons of the results of the upper-bound solutions with finite-element analyses show that the failure mechanisms and the calculated load-carrying capacities derived from the two methods agree well. Therefore, the analytical upper-bound method presented in this paper can be employed for efficient routine calculations of suction caisson capacity under inclined load considering seabed trenches, which are increasingly encountered in engineering practice.
Publisher: Thomas Telford Ltd.
Date: 04-2017
Abstract: Rectangular mudmat foundations are frequently used for supporting subsea structures for offshore oil and gas developments. The self-weight of the subsea structure and mudmat often mobilise a relatively small proportion of the vertical bearing capacity and horizontal–torsional sliding generally represents the governing load case. However, the effect of torsion on mudmat capacity is not explicitly considered in current guidelines for geotechnical design of offshore foundations. In this paper, upper-bound plastic limit analysis is used to develop explicit expressions for the combined horizontal and torsional capacity of skirted mudmats. The results of the limit analyses are compared with results from finite-element analysis, and with other published solutions. A method is proposed for estimating the translational sliding resistance from the interaction diagram for biaxial horizontal loading and a unique expression is proposed to define the normalised H–T failure envelope. The effects of foundation aspect ratio, foundation embedment ratio, skirt–soil interface roughness, direction of horizontal loading and degree of soil strength heterogeneity are investigated systematically.
Publisher: Elsevier BV
Date: 2022
Publisher: Thomas Telford Ltd.
Date: 2014
Abstract: Mudmats are used in the offshore oil and gas industry to support subsea infrastructure for pipeline terminations and well manifolds. Expansion and contraction of connected pipelines and jumpers due to changing thermal and pressure conditions impose fully three-dimensional loading on the foundations, dominated by horizontal, moment and torsional loading rather than high vertical loads. The mudmat foundations are rectangular, and include shallow skirts in order to increase capacity, particularly for sliding. Offshore design guidelines for shallow foundations tend to excessive conservatism optimisation of mudmat capacity under general loading has thus become critical in order to keep foundation footprints within the limits of current installation vessels. The paper presents an alternative design method, based on failure envelopes derived from an extensive programme of three-dimensional finite-element analyses, focusing on the sliding and rotational capacity of the foundation. Starting from expressions that quantify the uniaxial capacity under each of the six degrees of freedom, failure envelope shapes for different biaxial combinations are developed. Ultimately, the allowable capacity under the six-degree-of-freedom loading is expressed in terms of a two-dimensional failure envelope for the resultant horizontal and moment loading, after due allowance for the vertical and torsional components of load.
Publisher: American Society of Mechanical Engineers
Date: 17-06-2018
Abstract: The embedded portion of a mooring line plays an important role for efficient and economic design of an overall mooring system. This paper presents a methodology for numerical simulation of the behaviour of an embedded anchor chain as it cuts through the soil, focusing on the tensioning of a catenary mooring. The Coupled Eulerian–Lagrangian (CEL) approach within ABAQUS is used to capture the interaction between the embedded chain (Lagrangian structure) and the soil (Eulerian material). The anchor chain is simulated by a series of rigid cylindrical segments connected together by LINK connectors. Before analysing the global behaviour of an embedded chain, a calibration exercise is undertaken where a straight multi-link portion of the chain is displaced normally and axially in soil. The resulting normal and frictional resistances (per unit length) are compared with those adopted in general practice, in order to calibrate the relationship between the diameter of the cylindrical segments and the bar diameter of the chain. After that, the tensioning process of an anchor chain is simulated, starting from an initial configuration with a 9 m length embedded vertically (attached to a fixed padeye), with the remaining length lying on the seabed. Horizontal tensioning of the chain causes it to cut through the soil until it forms an inverse catenary with an angle of just under 35 degrees to the horizontal at the padeye (and zero degrees at the mudline). The loading curve, and also the inverse catenary profile of the chain for different angles at the padeye, are shown to agree well with the Neubecker-Randolph closed-form analytical solution. However, the ratio of the tensions at the padeye and the mudline from the CEL results differs significantly from the analytical solution. Insights from the CEL results indicate that this is because the frictional soil resistance is not fully mobilised, particularly for the portion of the chain in the stronger soil at depth, near the padeye, where the axial displacements are small. This result has significant implications for the geotechnical design of anchoring systems that involve a (nominally) fixed padeye. The simulation methodology also has considerable potential for exploring the creation of an open trench adjacent to a fixed anchor due to monotonic and cyclic perturbations of the anchor chain.
Publisher: Springer Science and Business Media LLC
Date: 06-2013
Publisher: Elsevier BV
Date: 02-2020
Publisher: Thomas Telford Ltd.
Date: 06-2016
Abstract: Subsea infrastructure for deep-water oil and gas developments is often supported by mudmat foundations. Traditionally, subsea mudmats are designed to resist the loads imposed by pipeline thermal expansion and contraction while remaining stationary. As subsea facilities have grown, the required size and weight of the mudmats challenge the handling capacity of installation vessels and raise costs. Tolerable mobility of a subsea mudmat can significantly relieve the applied loads, leading to reduced mudmat size and weight. In this paper, the cyclic shearing and reconsolidation response of fine-grained soil around a tolerably mobile mudmat is investigated through results of finite-element analysis using a critical state soil model. The mudmat was subjected to a simulated lifetime of operation, with many cycles of undrained sliding with intervening consolidation between cycles. The sliding resistance was shown to rise exponentially with cycles and reach the drained limit, accompanied by significant strength gain in the subsoil because of the intervening consolidation between movements. The degree of reconsolidation between slides affects the number of cycles required to mobilise the drained limit. The hardening response for periodic shearing with intervening consolidation is shown to scale from the hardening response for continuous undrained shearing by an amount depending on the degree of intervening consolidation during pipeline operation. Expressions for the rate of hardening of sliding resistance of a tolerably mobile mudmat foundation are proposed in this paper to assist design practice.
Publisher: Elsevier BV
Date: 10-2014
Publisher: Thomas Telford Ltd.
Date: 07-2015
Abstract: Submarine sediments in many deep-water regions exhibit a thin crust overlying geologically normally consolidated clay. Load-carrying capacity of mudmat foundations for supporting subsea infrastructure installed on seabeds with a surficial crust is of great interest to foundation designers. Finite-element analyses have been performed to investigate the undrained response of mudmats under combined six degree-of-freedom loading in terms of the effect of crust thickness, foundation embedment and relative shear strengths of the underlying soft clay and crust. Results are presented as failure envelopes and expressions are presented to enable calculation of the uniaxial and combined load capacities under fully three-dimensional loading.
Publisher: American Society of Mechanical Engineers
Date: 08-06-2014
Abstract: Rectangular mudmat foundations are extensively deployed in deep waters to support subsea infrastructure leading to renewed interest in optimizing the design of offshore shallow foundations. Offshore industry guidelines (e.g. API RP2GEO and ISO 19901-4) are based on classical bearing capacity theory of a plane strain strip foundation resting on the surface of a uniform Tresca material. More realistic conditions are accounted for through a range of superposed empirical modification factors and the effective width principle. In practice, subsea foundations experience complex loading in six degrees-of-freedom (vertical load, biaxial horizontal load, biaxial moment and torsion), due to expansion and contraction of connected pipelines and jumpers they may be able to mobilize transient tensile capacity and they are typically three-dimensional in plan, shallowly embedded and founded on soft, normally consolidated, soils with linearly increasing strength with depth. Accurate determination of the ultimate limit state of subsea mudmats is best achieved by considering the relevant foundation, soil and loading boundary conditions explicitly. In this paper, a simplified approach for predicting the ultimate limit state of mudmat foundations under six degrees-of-freedom, based on failure envelopes, obtained from extensive finite element analyses, is compared with the traditional bearing capacity methods as recommended in industry guidelines.
Publisher: American Society of Civil Engineers (ASCE)
Date: 10-2020
Publisher: Elsevier BV
Date: 08-2022
Publisher: Thomas Telford Ltd.
Date: 07-2015
Abstract: A generalised framework is presented for predicting the consolidated undrained capacity of rectangular mat foundations on normally consolidated soft clay under combined loading in six degrees of freedom as a function of relative preload and degree of consolidation. Consolidated undrained response is investigated by coupled small-strain finite-element analysis using the modified Cam Clay plasticity constitutive model. Increases in the load-carrying capacity of a foundation under combined loading in six degrees of freedom following vertical preload with subsequent consolidation are demonstrated and quantified. The results are presented as failure envelopes in multi-directional load space and are shown to expand proportionally as a function of degree of consolidation for a given relative preload. A methodology and a set of expressions are provided to predict the shape and size of failure envelopes for rectangular mat foundations for any degree of preloading and consolidation.
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2019
Publisher: Thomas Telford Ltd.
Date: 04-2017
Abstract: The effect of soil–foundation interface condition on the undrained capacity of rectangular mudmat foundations under loading in six degrees of freedom is investigated. Undrained failure envelopes for mudmats with zero-tension interface have been derived from finite-element analyses, and compared with the solutions from traditional methods and established for an unlimited-tension interface condition. The zero-tension interface has minimal effect on failure envelopes in the absence of moment, but significantly reduces the load-carrying capacity of mudmats under all other load paths that include moment. The traditional method for predicting the capacity of shallow foundations under multi-directional loading generally predicts lower capacity under any combined loading condition in comparison with the finite-element results for mudmats with zero-tension interface. Algebraic expressions are proposed to describe failure envelopes for mudmats with zero-tension interface. The proposed expressions can be implemented in an automated calculation tool to enable essentially instantaneous generation of failure envelopes and optimisation of a foundation design as a function of foundation dimension or material factor.
Publisher: Thomas Telford Ltd.
Date: 16-01-2023
Abstract: Tolerably mobile subsea foundations may be used to replace conventional fixed mudmat foundations for pipeline infrastructure and are designed to slide on the seabed along with the connected pipeline, in order to accommodate thermally induced horizontal forces. This allows the size of the foundation and the resulting fabrication and installation costs to be substantially reduced. The performance of mobile foundations is explored in this paper through four centrifuge model tests on a normally consolidated or lightly over-consolidated reconstituted calcareous silt obtained from the Northwest Shelf of Western Australia. The results are compared to three existing tests performed on a kaolin clay. The results show that under typical periodic surface sliding and intervening rests, sliding resistance evolves within a cycle with resistance peaks evident at either end of the sliding footprint due to the formation of berms, and the residual resistance increasing with sliding cycles towards a drained state. Shear and consolidation-induced settlements accumulate with sliding cycles although at a reducing rate. The tests in the calcareous silt show higher normalised initial peak sliding resistance, a more dramatic loss and slower recovery of sliding resistance with cycles, and slower rate of decrease of incremental settlement compared with the response in kaolin clay.
Publisher: Elsevier BV
Date: 2019
Publisher: Thomas Telford Ltd.
Date: 10-2017
Abstract: Pilot tests on the usage of vacuum preloading combined with short prefabricated vertical drains (PVDs) to form a working platform for future soil improvement work were conducted at a land reclamation site in Tianjin, China. The short PVDs were connected using three methods – the conventional vacuum preloading method, fish-bone connectors and embedded horizontal pipes. To investigate the influence of PVD spacing, short PVDs were installed in square grids with spacings of 0·4 m and 0·6 m. The ground surface settlement, pore water pressures, water content and undrained shear strength of the soil were measured during the specific period of vacuum preloading. The pilot tests indicated that short PVDs connected using embedded vacuum pipes installed at 0·4 m spacing were the most suitable method to form a working platform on the surface of the dredged marine clay. This method yields a substantial saving on construction cost and time while exhibiting similar efficiency to the conventional vacuum preloading method. The undrained shear strength and degree of consolidation of the soil after 60 d of vacuum preloading were 23·6 kPa and 85·1%, respectively, which met the requirements for the working platform.
Publisher: American Society of Mechanical Engineers
Date: 09-06-2013
Abstract: Embedment of offshore shallow foundations is typically achieved by ‘skirts’, i.e. thin vertical plates that protrude from the underside of a foundation top plate and penetrate the seabed confining a soil plug. Skirted shallow foundations are often idealized as a solid, rigid element for geotechnical analysis of the foundation, on the assumption that sufficient skirts, or ‘shear keys’ will be provided to ensure that the deformable soil plug displaces as a rigid body. Should too few shear keys be provided, failure mechanisms involving deformation within the soil plug may occur, leading to a reduction in load-carrying capacity. There is currently no formal guidance regarding the optimal spacing of shear keys to ensure rigid body displacement of the soil plug. The absence of guidance may lead to unconservative designs if the number of shear keys is under estimated to save on fabrication or to conservative designs if additional shear keys are provided to minimize the risk associated with the uncertainty. Either case is undesirable and clear benefit is to be gained from a better understanding of shear key spacing. This paper presents guidance on the minimum number of shear keys required to achieve optimal capacity of square and rectangular skirted foundations (i.e. equivalent to that of a solid rigid foundation) under undrained generalized six degree-of-freedom loading in soft soils with linearly increasing shear strength with depth.
Publisher: Elsevier BV
Date: 05-2017
Publisher: Elsevier BV
Date: 09-2023
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