Effect of a Strong Middle Layer on Spudcan Penetration

2014 ◽  
Author(s):  
Wen Gao ◽  
Tom Harrup ◽  
Yuxia Hu ◽  
David White
Keyword(s):  
Bearing Capacity ◽  
Layer Thickness ◽  
Soft Clay ◽  
Soil Layer ◽  
Strength Ratio ◽  
Top Soil ◽  
Flow Mechanisms ◽  
Soil Flow ◽  
Jack Up ◽  
Peak Resistance

The rapid penetration of one or more of the foundations of a mobile jack-up rig into the seabed is an ongoing major problem in the offshore industry, with the potential to cause major damage to the structure and endangering any personnel on board. A recent example is the jack-up drilling rig Perro Negro 6 incident happened near the mouth of the Congo river in July 2013 with one of the rig’s crew of 103 reported missing and six others injured. This uncontrollable displacement is due to a form of failure known as punch through failure and commonly occurs on stratified seabed profiles. It has been reported that unexpected punch-through accidents have resulted in both rig damage and lost drilling time at a rate of 1 incident per annum with consequential costs estimated at between US$1 and US$10 million [1]. This paper presents the bearing capacity profiles and associated soil flow mechanisms of a common spudcan foundation penetrating into a three layer soft-stiff-soft clay soil through the use of large deformation finite element (LDFE) analysis. The Remeshing and Interpolation with Small Strain (RITSS) [2, 3] technique was implemented in the software package AFENA [4] to conduct the LDFE analysis. Both soil layer thickness and soil layer strength ratios were varied to study their effect on the spudcan penetration responses. The LDFE results of spudcan penetration into the soft-stiff-soft clay soils were calibrated by existing centrifuge test data. A parametric study was then conducted to study the bearing capacity responses and soil flow mechanisms during spudcan large penetrations by varying the soil layer strength ratio and relative layer thickness to the diameter of spudcan. It was found that there were three types of bearing responses during continuous penetration of spudcan: (a) when the top soft layer is relatively thin, the spudcan bearing response was similar to that of two layer soils with stiff over soft clays; (b) when the top soil layer thickness is medium, a peak resistance is observed when spudcan penetrates into the middle stiff layer followed by reduction; (c) when the soil layer is thick, the peak resistance occurs when spudcan gets into the bottom soft soil layer. The critical thickness of top soil layer is a function of soil strength ratio and middle stiff soil layer thickness. The bearing response types were also corresponding to the soil cavity formations during spudcan initial penetration.

Predicting the overall horizontal bearing capacity of jack-up rigs using deck–foundation–soil-coupled model

2020 ◽  
pp. 147509022092590
Author(s):  
Qilin Yin ◽  
Jinjin Zhai ◽  
Sheng Dong
Keyword(s):  
Bearing Capacity ◽  
Failure Mode ◽  
Double Layer ◽  
Soft Clay ◽  
Coupled Model ◽  
Single Layer ◽  
Horizontal Load ◽  
Foundation Soil ◽  
Failure Envelopes ◽  
Jack Up

The overall bearing capacity of a jack-up rig under horizontal load is conducted using finite element models that consider the deck–foundation–soil interaction. In these models, the simplified horizontal load acts on the deck and increases until the platform loses its stability. The effects of the self-weight of the platform W and load direction α on the ultimate horizontal bearing capacity Hult are investigated, and W- Hult failure envelopes under different α conditions are obtained. Two typical seabed types, including the double-layer seabed of sand overlying soft clay and the single-layer seabed of sand, are considered. The results show that a critical self-weight Wcritical exists in the double-layer seabed. Based on Wcritical, the failure of the platform presents two different modes. When W <  Wcritical, the windward leg is pulled up, and Hult increases with the increase in W. When W >  Wcritical, the failure mode is the leeward leg or legs puncturing the bearing sand layer, and Hult decreases with the increase in W. In the single-layer seabed, the failure mode is the windward leg being pulled up, and Hult increases with the increase in W throughout the whole range. The W- Hult envelopes in these two types of seabeds are basically the same when W <  Wcritical.

Bearing Behaviour of Spudcan Foundation on Uniform Clay During Deep Penetration

2004 ◽  
Author(s):  
M. S. Hossain ◽  
Y. Hu ◽  
M. F. Randolph
Keyword(s):  
Bearing Capacity ◽  
Failure Mechanisms ◽  
Model Tests ◽  
Deep Penetration ◽  
Centrifuge Tests ◽  
Soil Failure ◽  
Flow Mechanisms ◽  
Soil Flow ◽  
Piv Analysis ◽  
Penetration Depths

In order to design a safe spudcan foundation, it is important to predict its bearing behaviour accurately based on the corresponding soil failure mechanisms. Thus, the performance of spudcan foundation, during deep penetration into uniform soil, is investigated physically and numerically. In physical testing, a series of centrifuge tests are carried out in a drum centrifuge. The half-spudcan model tests with subsequent Particle Image Velocimetry (PIV) analysis are conducted to reveal soil failure mechanisms during spudcan penetration. And the full spudcan model tests are conducted to investigate the bearing capacity of spudcan. In numerical simulation, FE analyses are performed considering smooth and rough soilspudcan interface. From the physical tests and numerical analyses, it is observed that the cavity is formed above the spudcan as it is penetrating into uniform clay. At certain penetration depths, the soil underneath the spudcan starts to flow back on top of the spudcan, which leads the spudcan to be embedded with further penetration. Soil flow mechanisms, at various penetration depths, play a key role in footing bearing response. And the ultimate undrained bearing capacity factor of Nc = 10.5 (smooth) and 12 (rough) are obtained at deep penetration.

Bearing Capacity Characteristics of Lacustrine Soft Clay Hard Shell Layer Foundation

2013 ◽  
Vol 347-350 ◽  
pp. 1203-1206
Author(s):  
Jia Jia Zheng ◽  
Li Jian Wu ◽  
Run Hua Guo
Keyword(s):  
Bearing Capacity ◽  
Failure Mode ◽  
Shear Failure ◽  
Soft Soil ◽  
Soft Clay ◽  
Soil Layer ◽  
Shell Layer ◽  
Soft Foundation ◽  
Hard Shell ◽  
Punching Failure

In order to provide a theoretical basis for the use of lacustrine soft clay hard shell layer, the first thing to do is understanding its bearing capacity characteristics. Based on the project of Nan-Mao section in Hunan provincial highway S204, combining with bearing capacity test, the bearing capacity characteristics and failure mode of hard shell foundation was comprehensively analyzed. From the field bearing capacity test, it is found that the PS curve of hard shell layer has obvious changes from elastic to plastic, while the PS curve of soft soil layer under hard shell layer just has elastoplastic stage from the beginning, and the failure mode of foundation mainly are punching failure and general shear failure. So for the quality control of lacustrine hard shell soft foundation mainly includes two aspects: the deformation and overall stability.

Spudcan Penetration in Loose Sand Over Uniform Clay

2009 ◽  
Author(s):  
Long Yu ◽  
Yuxia Hu ◽  
Jun Liu
Keyword(s):  
Finite Element ◽  
Clay Soil ◽  
Clay Soils ◽  
Loose Sand ◽  
Finite Element Analyses ◽  
Flow Mechanisms ◽  
Soil Flow ◽  
Jack Up ◽  
Penetration Depths ◽  
Sand Plug

Punch through failures of spudcan foundations of mobile jack-up rigs have been reported every year. The potential of punch through failure of spudcan foundations on loose sand over uniform clay soils was studied numerically in the present paper. Large deformation finite element analyses were carried out to simulate the load-penetration responses of a 14m diameter spudcan during continuous penetration into this sand over clay soil. The numerical results were compared with existing centrifuge data. The critical penetration depths were derived from the load-penetration responses. The soil flow mechanisms, the shape of sand plug and the distribution of plastic points were also reported.

Large Deformation FE Analyses of Cone Penetration in Single Layer Non-Homogeneous and Three-Layer Soft-Stiff-Soft Clays

2014 ◽  
Author(s):  
Hongliang Ma ◽  
Mi Zhou ◽  
Yuxia Hu ◽  
Muhammad Shazzad Hossain
Keyword(s):  
Bearing Capacity ◽  
Large Deformation ◽  
Single Layer ◽  
Offshore Structures ◽  
Capacity Factor ◽  
Cone Penetration ◽  
Soft Clays ◽  
Flow Mechanisms ◽  
Soil Flow ◽  
Bearing Capacity Factor

Continuous profiles from in-situ penetrometer tests are now identified as essential for site specific soil investigation as part of designing offshore structures in deep and ultradeep waters and in highly layered seabed conditions. This paper describes the results from large deformation FE (LDFE) analysis undertaken to provide insight into the behavior of cone penetrometer penetrating through single layer non-homogeneous clays and three-layer uniform soft-stiff-soft clays. For the smooth cone penetration in non-homogeneous clays, the soil strength non-homogeneity factor was shown to have insignificant effect on the cone bearing capacity factor. However, for the rough cone, the bearing capacity factor in non-homogeneous clay was about 10∼12% lower than that in uniform clay. Bearing capacity factors for smooth and rough cones were also similar for non-homogeneous clay. For cone penetration in stratified soft-stiff-soft clays, a minimum layer thickness of 20 diameters was required to mobilise the full resistance of the stiff layer. The corresponding soil flow mechanisms are also discussed linking directly to the profile of penetration resistance.

Microbial and biochemical changes induced by rotation and tillage in a soil under barley production

1993 ◽  
Vol 73 (1) ◽  
pp. 39-50 ◽  
Author(s):  
D. A. Angers ◽  
N. Bissonnette ◽  
A. Légère ◽  
N. Samson
Keyword(s):  
Alkaline Phosphatase ◽  
Organic Matter ◽  
Microbial Biomass ◽  
Phosphatase Activity ◽  
Alkaline Phosphatase Activity ◽  
Soil Layer ◽  
Red Clover ◽  
Organic C ◽  
Top Soil ◽  
Total Organic C

Crop rotations and tillage practices can modify not only the total amount of organic matter (OM) in soils but also its composition. The objective of this study was to determine the changes in total organic C, microbial biomass C (MBC), carbohydrates and alkaline phosphatase activity induced by 4 yr of different rotation and tillage combinations on a Kamouraska clay in La Pocatière, Quebec. Two rotations (continuous barley (Hordeum vulgare L.) versus a 2-yr barley–red clover (Trifolium pratense L.) rotation) and three tillage treatments (moldboard plowing (MP), chisel plowing (CP) and no-tillage (NT)) were compared in a split-plot design. Total organic C was affected by the tillage treatments but not by the rotations. In the top soil layer (0–7.5 cm), NT and CP treatments had C contents 20% higher than the MP treatment. In the same soil layer, MBC averaged 300 mg C kg−1 in the MP treatment and up to 600 mg C kg−1 in the NT soil. Hot-water-extractable and acid-hydrolyzable carbohydrates were on average 40% greater under reduced tillage than under MP. Both carbohydrate fractions were also slightly larger in the rotation than in the soil under continuous barley. The ratios of MBC and carbohydrate C to total organic C suggested that there was a significant enrichment of the OM in labile forms as tillage intensity was reduced. Alkaline phosphatase activity was 50% higher under NT and 20% higher under CP treatments than under MP treatment and, on average, 15% larger in the rotation than in the continuous barley treatment. Overall, the management-induced differences were slightly greater in the top layer (0–7.5 cm) than in the lower layer of the Ap horizon (7.5–15 cm). All the properties measured were highly correlated with one another. They also showed significant temporal variations that were, in most cases, independent of the treatments. Four years of conservation tillage and, to a lesser extent, rotation with red clover resulted in greater OM in the top soil layer compared with the more intensive systems. This organic matter was enriched in labile forms. Key words: Soil management, soil quality, organic matter, carbohydrates, microbial biomass, phosphatase

The bearing capacity of footings on a sand layer overlying soft clay

Géotechnique ◽  
1997 ◽  
Vol 47 (2) ◽  
pp. 339-345 ◽  
Author(s):  
M. J. Kenny ◽  
K. Z. Andrawes
Keyword(s):  
Bearing Capacity ◽  
Soft Clay ◽  
Sand Layer

Study on Reinforce Saturated Soft Clay Foundation with Dynamic Consolidation by Drainage

2013 ◽  
Vol 438-439 ◽  
pp. 1171-1175
Author(s):  
Zhi Li Sui ◽  
Zhao Guang Li ◽  
Xu Peng Wang ◽  
Wen Li Li ◽  
Tie Jun Xu
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Clay ◽  
Soil Layer ◽  
Good Effect ◽  
Loading Test ◽  
Test Plate ◽  
Dynamic Consolidation ◽  
Saturated Soft Clay

Dynamic consolidation method has been widely used in improving soft land, but always inefficient to saturated soft clay land, which is hard to improve, and even leads to rubber soil. Dynamic and drain consolidation method will deal with it well, with drainage system, pore-water can be expelled instantly from saturated soft clay as impacting. The pore-water pressure and earth pressure test in construction, the standard penetration test, plate loading test, geotechnical test after construction, which are all effective methods for effect testing. There is a comprehensive detection through different depth of soil layer with different detecting means on construction site. The results show that improving saturated soft clay land with dynamic and drain consolidation method has obtained good effect, and the fruit can be guidance for such construction in the future.

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