Stability of Submarine Foundation Pits Under Wave Loads

2012 ◽  
Author(s):  
Julian Bubel ◽  
Jürgen Grabe
Keyword(s):  
Ground Surface ◽  
Friction Angle ◽  
Shallow Foundation ◽  
Cohesionless Soil ◽  
Wave Loads ◽  
In Situ Tests ◽  
Sea Floor ◽  
The North ◽  
The Stability ◽  
Wave Induced

Shallow foundation structures offer ecological benefits compared to pile foundations as less noise is emitted at sea floor level during construction process. On the other hand, shallow offshore foundations can rarely be placed on top of the sea floor. Weak soils usually need to be excavated to place the foundation structure on more stable ground and thus, anthropogenic submarine pits result. Steep but stable slopes of the pit meet both economic and ecologic aims as they minimise material movement and sediment disturbance. According to Terzaghi [1] the angle β between slope and the horizontal of the ground surface of cohesionless soil is at most equal to the critical state friction angle φc. However, it can be observed that natural submarine slopes of sandy soils are always much more shallow. Artificial (temporary) slopes do not appear and behave as natural submarine slopes, since the latter are already shaped by perpetual loads of waves, tide and mass movements. Physical simulations of different scales were presented at the OMAE 2011 [2] to analyse the stability of artificial submarine slopes of sandy soil in the North Sea. The laboratory tests focused on gravitational forces and impacts from the excavation processes. This paper presents additional numerical simulations of wave-induced bottom pressure on the suggested submarine foundation pits. Furthermore, in-situ tests will be performed in 2012 and 2013. Both dredging process and resulted foundation pits will be considerably surveyed.

Stability of Artificial Subaqueous Slopes in Sandy Soils Under Wave Loads

2015 ◽  
Author(s):  
Julian Bubel ◽  
Marc-André Pick ◽  
Jürgen Grabe
Keyword(s):  
Surface Waves ◽  
Wave Length ◽  
Ground Surface ◽  
Sandy Soils ◽  
Wave Theory ◽  
Friction Angle ◽  
Shallow Foundation ◽  
Cohesionless Soil ◽  
Linear Wave ◽  
Wave Loads

Shallow foundation structures in marine environments can rarely be placed on top of the sea floor. Weak soils usually need to be excavated to place the structure on more stable ground. Steep but stable slopes of the resulting pit meet both economic and ecologic aims as they minimise material movement and sediment disturbance. This paper focuses changes of geometry of submarine slopes in non-cohesive soils (erosion, sedimentation, breach failure, liquefaction failure) due to surface waves. After Terzaghi the angle between slope and the horizontal of the ground surface of cohesionless soil is at most equal to the critical state friction angle, as obviously true for dry soil. However, it can be observed that natural submarine slopes of sandy soils are always mildly sloped. During the construction of artificial submarine pits under offshore conditions it should be considered that the long-term slope-inclination is less than onshore due to hydrodynamic actions (e. g. flow, waves, earthquakes). Large surface waves cause excess pore water pressures within the soil body, leading to a reduction of effective stresses and in case of submarine slopes to changes of the slope geometry depending on wave length L, wave height H, water depth h and soil properties (permeability k, relative density Dr). During our preliminary work we investigated such processes based on the coupling of linear wave theory and linear quasistatic consolidation theory (e.g. [1]). With the help of numerical modelling we solved corresponding equations considering also materially nonlinear consolidation. However, deformations were always limited by used Lagrangian-FEM. Recent developments at our Institute enable the use of an Eulerian-FEM approach with an u-p-Formulation for fully saturated soil [2]. This allows larger deformations of the subaqueous slope to be numerically investigated.

Stability of Temporary Submarine Slopes

2011 ◽  
Author(s):  
Julian Bubel ◽  
Christina Rudolph ◽  
Ju¨rgen Grabe
Keyword(s):  
North Sea ◽  
Critical State ◽  
Slope Angle ◽  
Friction Angle ◽  
Shallow Foundation ◽  
Offshore Wind ◽  
Coarse Grained ◽  
Sea Floor ◽  
The North ◽  
The North Sea

Shallow foundation structures for offshore wind turbines offer ecological benefits compared to pile foundations as less noise is emitted at sea floor level during construction process. On the other hand, shallow offshore foundations can rarely be placed on top of the sea floor. Weak soils usually need to be excavated to place the foundation structure on more stable ground and thus, anthropogenic submarine slopes result. Steep but stable slopes meet both economic and ecologic aims as they minimise material movement and sediment disturbance. After Terzaghi [1] the angle β between slope and the horizontal of the ground surface of coarse-grained soil is at most equal to the critical state friction angle φc. However, it can be observed that natural submarine slopes of sandy soils are always much more shallow. Particularly fine-grained, cohesionless or almost cohesionless soils failed in the past, although the slope angle was much smaller than the critical state friction angle φc. Artificial (temporary) slopes do not appear and behave as natural submarine slopes, since the latter are already shaped by perpetual loads of waves, tide and mass movements. Physical simulations of different scales are used to analyse the stability of artificial submarine slopes with sandy soil of the North Sea. The study focuses on gravitational forces and impacts from the excavation processes. The simulations and theoretical considerations result in suggested slope angles for future shallow offshore foundations of wind farms in the North Sea.

Fatigue Damage Assessment of Container Ships Concerning Wave-Induced Torsion

2010 ◽  
Author(s):  
Zhiyuan Li ◽  
Jonas W. Ringsberg ◽  
Wengang Mao
Keyword(s):  
Fatigue Damage ◽  
North Atlantic Ocean ◽  
Direct Calculation ◽  
Wave Loads ◽  
The North ◽  
Torsion Rigidity ◽  
Fatigue Damage Accumulation ◽  
Stress Components ◽  
Hydrodynamic Code ◽  
Wave Induced

The traditional method to assess fatigue damage of ship structures assumes moderate wave amplitudes and linear responses. This method can be questioned when applied on container ships that are characterized by large deck openings, because the low torsion rigidity of this type of ship makes it sensitive to oblique waves. In this paper, the 3D hydrodynamic code WASIM is used to simulate a 4400 TEU container ship operating in the North Atlantic Ocean. Nonlinear wave loads are utilized for direct calculation of the stress histories under severe sea states. The warping stress from wave-induced torsion is separated from the stress components from vertical and horizontal bending. The contribution to fatigue damage accumulation from warping stresses is evaluated. For comparison, the results from the numerical simulations and fatigue calculations are verified with full-scale measurements made on a similar type of container vessel.

scholarly journals Assessment of the Stability of an Unlined Rectangular Tunnel with an Overload on the Ground Surface

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Jian Zhang ◽  
Zhibin Hang ◽  
Tugen Feng ◽  
Feng Yang
Keyword(s):  
Upper Bound ◽  
Failure Modes ◽  
Ground Surface ◽  
Friction Angle ◽  
Unit Weight ◽  
Rigid Block ◽  
Tunnel Stability ◽  
Failure Patterns ◽  
The Stability ◽  
Rectangular Tunnel

City tunnels are often constructed at shallow depths, and tunnel failure may be initiated by overloads resulting from surrounding buildings, structures, heavy-haul trailers, and other installations. Although several works have been reported on tunnel stability, stability numbers have mainly been obtained for cases with fully cohesive soils. Moreover, little information has been presented about the influence of overloads on the failure patterns for unlined rectangular tunnels. This paper uses upper-bound finite element methods to assess the stability of an unlined rectangular tunnel in cohesive-frictional soils with an overload acting on the ground surface. A complete set of dimensionless parameters covering the tunnel size and shallow tunnel depth and Mohr-Coulomb material parameters are determined to obtain the dimensionless overload. In addition, failure modes that are similar to slip line fields are acquired. A failure mechanism that may cause base heave is proposed in this paper to improve the accuracy of the results. These failure patterns are more complex for cases with larger dimensionless depth, larger internal friction angle, and smaller dimensionless unit weight. Compared with the rigid-block mechanisms from the upper-bound rigid-block analysis method, these computed failure mechanisms are better suited for rectangular tunnel stability analysis.

scholarly journals Field Experimental Study on the Broken Rock Zone of Surrounding Rock and the Rock Borehole Shear Tests of the Large Deformation Tunnel

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Guansheng Han ◽  
Bo Meng ◽  
Hongwen Jing ◽  
Jiangyu Wu
Keyword(s):  
Large Deformation ◽  
Field Experiments ◽  
Friction Angle ◽  
Surrounding Rock ◽  
Test Results ◽  
In Situ Tests ◽  
Tunnel Support ◽  
The Status ◽  
The Stability

A large deformation tunnel in LIXIANG railway, named Zhongyi tunnel is located in Southwest of China, was taken for the engineering background. The field experiments of the broken rock zone and the borehole shear test were conducted. The results show that the range of the broken rock zone of the test sections is 4.20∼4.45 meters. The cohesive force and the internal friction angle of the test sections are 221.4∼224 kPa and 14.25∼15.14°, respectively. The test results are in good agreement with the status of the surrounding rock. The surrounding rock is mainly composed of shale, which is badly broken, and the integrity and the stability are poor. In this study, the reasons for the deformation and instability of the tunnel are analyzed combined with the in situ tests and the site condition, and the suggestions for the tunnel support are put forward. This study is of great significance to ensure the safety of the constructors and can improve the service years of the tunnel. In addition, it can provide reference for the same type of the tunnel construction.

scholarly journals A Bio-Inspired Compliance Planning and Implementation Method for Hydraulically Actuated Quadruped Robots with Consideration of Ground Stiffness

Sensors ◽  
2021 ◽  
Vol 21 (8) ◽  
pp. 2838
Author(s):  
Xiaoxing Zhang ◽  
Haoyuan Yi ◽  
Junjun Liu ◽  
Qi Li ◽  
Xin Luo
Keyword(s):  
Harmonic Oscillation ◽  
Ground Surface ◽  
Legged Locomotion ◽  
Soft Ground ◽  
Quadruped Robots ◽  
In Series ◽  
Reaction Forces ◽  
Implementation Method ◽  
The Stability ◽  
Natural Dynamics

There has been a rising interest in compliant legged locomotion to improve the adaptability and energy efficiency of robots. However, few approaches can be generalized to soft ground due to the lack of consideration of the ground surface. When a robot locomotes on soft ground, the elastic robot legs and compressible ground surface are connected in series. The combined compliance of the leg and surface determines the natural dynamics of the whole system and affects the stability and efficiency of the robot. This paper proposes a bio-inspired leg compliance planning and implementation method with consideration of the ground surface. The ground stiffness is estimated based on analysis of ground reaction forces in the frequency domain, and the leg compliance is actively regulated during locomotion, adapting them to achieve harmonic oscillation. The leg compliance is planned on the condition of resonant movement which agrees with natural dynamics and facilitates rhythmicity and efficiency. The proposed method has been implemented on a hydraulic quadruped robot. The simulations and experimental results verified the effectiveness of our method.

scholarly journals Tunnel Back Analysis Based on Differential Evolution Using Stress and Displacement

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Joon-Sang An ◽  
Kyung-Nam Kang ◽  
Ju-Young Choi ◽  
Won-Suh Sung ◽  
Vathna Suy ◽  
...  
Keyword(s):  
Differential Evolution ◽  
Differential Evolution Algorithm ◽  
Back Analysis ◽  
Friction Angle ◽  
Internal Displacement ◽  
Average Error ◽  
Analysis Algorithm ◽  
Evolution Algorithm ◽  
Displacement Based ◽  
The Stability

The stability of tunnels has mainly been evaluated based on displacement. Because displacement due to the excavation process is significant, back analysis of the structure and ground can be performed easily. Recently, the length of a segment-lined tunnel driven by the mechanized tunneling method is increasing. Because the internal displacement of a segment-lined tunnel is trivial, it is difficult to analyze the stability of segment-lined tunnels using the conventional method. This paper proposes a back analysis method using stress and displacement information for a segment-lined tunnel. A differential evolution algorithm was adopted for tunnel back analysis. Back analysis based on the differential evolution algorithm using stress and displacement was established and performed using the finite difference code, FLAC3D, and built-in FISH language. Detailed flowcharts of back analysis based on DEA using both monitored displacement stresses were also suggested. As a preliminary study, the target variables of the back analysis adopted in this study were the elastic modulus, cohesion, and friction angle of the ground. The back analysis based on the monitored displacement is useful when the displacement is significant due to excavation. However, the conventional displacement-based back analysis is unsuitable for a segment-lined tunnel after construction because of its trivial internal displacement since the average error is greater than 32% and the evolutionary calculation is finalized due to the maximum iteration criteria. The average error obtained from the proposed back analysis algorithm using both stress and displacement ranged within approximately 6–8%. This also confirms that the proposed back analysis algorithm is suitable for a segment-lined tunnel.

Episodes of sea-floor spreading recorded by the North Atlantic basement

1971 ◽  
Vol 12 (3) ◽  
pp. 211-234 ◽  
Author(s):  
P.R. Vogt ◽  
G.L. Johnson ◽  
T.L. Holcombe ◽  
J.G. Gilg ◽  
O.E. Avery
Keyword(s):  
North Atlantic ◽  
Sea Floor ◽  
The North ◽  
The North Atlantic ◽  
Sea Floor Spreading

Contrôle de la stabilité des remblais par la mesure des déplacements horizontaux

1974 ◽  
Vol 11 (1) ◽  
pp. 182-201 ◽  
Author(s):  
René Marche ◽  
Robert Chapuis
Keyword(s):  
Factor Of Safety ◽  
Soft Clay ◽  
Ground Surface ◽  
Soft Layer ◽  
The Stability ◽  
Horizontal Displacements

The horizontal displacements measured at the toe of eight embankments are analyzed as a function of the factor of safety. The embankments are built on layers of soft clay. Only the undrained stage is studied.When the factor of safety of the embankments is higher than about 1.4, the horizontal displacements on the ground surface, at the toe of the embankment seem to follow an elastic law which is highly dependent on the ratio of the thickness of the soft layer to the width of the embankment. When the factor of safety is lower than about 1.4, the horizontal displacements do not follow an elastic law, they increase considerably. Consequently, it is suggested that the horizontal displacements be precisely measured at the toe of embankments during construction. These measurements are simple and sensitive to the approach of failure, they can be efficiently used to control the stability of embankments. This study also gives some information concerning the variation of horizontal displacements versus depth.

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