Pipe Clamping Mattresses to Mitigate Flowline Walking; Physical Modelling Trials on Three Offshore Soils

2021 ◽  
Author(s):  
Colm O’Beirne ◽  
Phil Watson ◽  
Conleth O’Loughlin ◽  
David White ◽  
Alexander Hodson ◽  
...  
Keyword(s):  
Soil Type ◽  
Physical Modelling ◽  
Silty Sand ◽  
Clay Soils ◽  
Unit Weight ◽  
Excess Pore Pressure ◽  
Operating Life ◽  
Conventional Concrete ◽  
Centrifuge Tests ◽  
Axial Resistance

Abstract Pipe clamping mattresses (PCMs) are a relatively new system for providing anchoring force to pipelines, to mitigate offshore flowline ‘walking’. They represent a cost-effective and highly efficient alternative to anchor piles, rock dump and conventional concrete mattresses. The system comprises a hinged concrete structure that clamps onto a section of laid pipeline, with concrete ballast logs securing the clamping action – with the benefit that 100% of the submerged weight of the PCM contributes to axial friction. PCMs have been applied successfully to one deepwater project, but performance data showing the influence of soil type, and allowing a general design framework to be established, has not yet been available. This paper addresses this gap by investigating the performance of PCMs through three series of centrifuge tests, supported by three Operators. Each series comprises tests on a different reconstituted deepwater soil as follows: (a) West African clay; (b) Gulf of Mexico clay; and (c) carbonate silty sand. In each test, a scaled pipeline is installed in-flight and cycled axially to represent its prior operating life. Scaled PCM models and ballast units are then installed onto the pipe in-flight, mimicking the use of PCMs to mitigate pipeline walking during operation. After installation of the PCMs, further axial cycles are applied, with the system settlement and changes in axial resistance and excess pore pressure measured. The paper shows the performance and applicability of PCMs for a range of soil types, highlighting variations in axial resistance and settlement. The suite of results will help to calibrate design tools for industry, removing unnecessary conservatism and enabling an optimised pipeline anchoring solution to be designed. Key results are equivalent friction factors for the combined pipe-PCM system and PCM settlement, which both show behaviour dependent on soil type. In the clay soils, friction increases significantly over time due to ‘consolidation hardening’. This provides validation of an important effect that has only recently been recognised in pipeline design. In contrast, hardening behavior is not evident in silty sand – although the study suggests there is potential for increasing resistance associated with settlement, which appears to mobilize additional (wedging) stress around the pipeline. Upon PCM installation, the pipelines embed further due to the added weight. Additional settlement occurs during cycling of the system, due to immediate soil deformation and consolidation-related compression. The magnitude of embedment is greater for the clay soils, but in all cases does not cause the clamping action to release. Overall, the efficiency of the PCM system in providing a high level of anchoring force per unit weight placed on the seabed is confirmed. Long term anchoring forces in the range 50-100% of the submerged weight of the PCM are demonstrated. This is several times more efficient than the commonly used alternative of a rock berm.

Excess Pore Pressures Around Underground Structures Following Earthquake Induced Liquefaction

2012 ◽  
Vol 3 (2) ◽  
pp. 25-41 ◽  
Author(s):  
Siau Chen Chian ◽  
Santana Phani Gopal Madabhushi
Keyword(s):  
Pore Pressure ◽  
Underground Structure ◽  
Unit Weight ◽  
Excess Pore Pressure ◽  
Earthquake Loading ◽  
Underground Structures ◽  
Floating Structure ◽  
Centrifuge Tests ◽  
Liquefiable Soil ◽  
Excess Pore

Underground structures located in liquefiable soil deposits are susceptible to floatation following an earthquake event due to their lower unit weight relative to the surrounding saturated soil. This inherent buoyancy may cause lightweight structures to float when the soil liquefies. Centrifuge tests have been carried out to study the excess pore pressure generation and dissipation in liquefiable soils. In these tests, near full liquefaction conditions were attained within a few cycles of the earthquake loading. In the case of high hydraulic conductivity sands, significant dissipation could take place even during the earthquake loading which inhibits full liquefaction from occurring. In the case of excess pore pressure generation and dissipation around a floating structure, the cyclic response of the structure may lead to the reduction in excess pore pressure near the face of the structure as compared to the far field. This reduction in excess pore pressure is due to shear-induced dilation and suction pressures arising from extensile stresses at the soil-structure interface. Given the lower excess pore pressure around the structure; the soil around the structure retains a portion of this shear strength which in turn can discourage significant uplift of the underground structure.

scholarly journals Sustainable Measures for Protection of Structures Against Earthquake Induced Liquefaction

2021 ◽  
Author(s):  
Gopal S. P. Madabhushi ◽  
Samy Garcia-Torres
Keyword(s):  
Soil Liquefaction ◽  
Excess Pore Pressure ◽  
Economic Losses ◽  
Element Analysis ◽  
Centrifuge Testing ◽  
Centrifuge Tests ◽  
Liquefiable Soil ◽  
Recent Earthquakes ◽  
Excess Pore Pressures ◽  
Excess Pore

AbstractSoil liquefaction can cause excessive damage to structures as witnessed in many recent earthquakes. The damage to small/medium-sized buildings can lead to excessive death toll and economic losses due to the sheer number of such buildings. Economic and sustainable methods to mitigate liquefaction damage to such buildings are therefore required. In this paper, the use of rubble brick as a material to construct earthquake drains is proposed. The efficacy of these drains to mitigate liquefaction effects was investigated, for the first time to include the effects of the foundations of a structure by using dynamic centrifuge testing. It will be shown that performance of the foundation in terms of its settlement was improved by the rubble brick drains by directly comparing them to the foundation on unimproved, liquefiable ground. The dynamic response in terms of horizontal accelerations and rotations will be compared. The dynamic centrifuge tests also yielded valuable information with regard to the excess pore pressure variation below the foundations both spatially and temporally. Differences of excess pore pressures between the improved and unimproved ground will be compared. Finally, a simplified 3D finite element analysis will be introduced that will be shown to satisfactorily capture the settlement characteristics of the foundation located on liquefiable soil with earthquake drains.

scholarly journals Suitability Assessment of Selected Lateritic Soils For Highway Construction In Anambra State, Nigeria

2020 ◽  
Vol 5 (2) ◽  
Author(s):  
Charles M.O. Nwaiwu ◽  
Ibeawuchi S Chidera ◽  
Franklin C Uzodinma
Keyword(s):  
Highway Construction ◽  
Soil Samples ◽  
Silty Sand ◽  
Coarse Grained ◽  
Unit Weight ◽  
Index Properties ◽  
Clayey Sand ◽  
British Standard ◽  
Lateritic Soils ◽  
Anambra State

Fifteen samples of coarse-grained lateritic soils obtained from different parts of Anambra State were assessed for their suitability as materials for highway construction. The soil samples were subjected to laboratory tests to obtain their index properties, compaction and California bearing ratio (CBR) characteristics. Three compactive efforts namely, British Standard Light (BSL) compaction, West African Standard (WAS) and British Standard Heavy (BSH) compaction were employed in the compaction tests. Samples were soaked for 48hrs prior to CBR testing. The index properties of the soils were used to classify the soils as   silty sand (SM) or silty sand/clayey sand (SM-SC) based on the Unified Soil Classification System (USCS) classification as well as silty soils (A – 4) or silty/clayey gravel and Sand (A – 2 -4) based on American Association of State Highway and Transportation Officials (AASHTO) classification. All the fifteen soils fell under “grading F” based on AASHTO standard specification designations for particle size distribution. The maximum dry unit weight (MDUW) of the soil samples ranged from 16.203 kN/m3 to 19.424 kN/m3,17.385 kN/m3 to 19.996 kN/m3 and from 18.126 kN/m3 to 21.473 kN/m3 with  corresponding optimum moisture content of 11.4% to 21.4%, 12.45% to 12.5%  and 8.5% to 11.75% for BSL, WAS and BSH respectively. The CBR values ranged between 7.92% and 18.87%. Most of the soil (more than 50%) did not meet the lower values of MDUW while only 20% of the soils had CBR values above 10% which is specified for subgrade soils by the AASHTO standard and the Nigerian Highway Design Manual, Federal Ministry of works and Housing.Keywords: coarse-grained, lateritic soils, highway pavement materials, USCS, AASHTO

VARIATION IN MINERAL CONTENT OF SASKATCHEWAN FEED GRAINS

1977 ◽  
Vol 57 (4) ◽  
pp. 679-687 ◽  
Author(s):  
B. D. OWEN ◽  
M. J. FARMER ◽  
F. SOSULSKI ◽  
K. K. WU
Keyword(s):  
Soil Type ◽  
Mineral Content ◽  
Clay Soils ◽  
Seasonal Effects ◽  
Soil Types ◽  
Soil Zone ◽  
Coefficients Of Variation ◽  
Oat Cultivars ◽  
Low Levels ◽  
Gray Soil

The concentration of Ca, P, Mg, K, Zn, Cu, Mn, Fe and Se were determined in wheat, barley and oat cultivars grown in four soil zones incorporating two soil types during a 5-yr period. Ca and K in Saskatchewan grains were much lower than published values, while Zn and Fe values were much higher. Se contents in each grain averaged 0.25 ppm and were substantially below values reported in the literature. Se and Cu levels were extremely variable (CV = 31–81%), but coefficients of variation (CV) for other minerals ranged from 9 to 35%. The effects of season, soil zone, soil type and cultivar on composition of Ca, P, Mg and K were significant in most grains. Seasonal effects on Zn, Cu, Mn and Fe were quite marked, but soil type had little effect and there were few significant differences between cultivars. Grain samples from Gray soil locations were characteristically high in Zn and low in Mn. Average Se content in grain from the Brown soil zone (0.39–0.55 ppm) was highest. There was a progressive decrease through the Dark Brown and Black soils to very low levels in samples from the Gray soil zone (0.06–0.07 ppm). In each type of grain, clay soils were associated with higher Se levels than loam soils.

Scaling law of static liquefaction mechanism in geocentrifuge and corresponding hydromechanical characterization of an unsaturated silty sand having a viscous pore fluid

2015 ◽  
Vol 52 (6) ◽  
pp. 708-720 ◽  
Author(s):  
Amin Askarinejad ◽  
Alexander Beck ◽  
Sarah M. Springman
Keyword(s):  
Pore Pressure ◽  
Scaling Laws ◽  
Scaling Law ◽  
Pore Fluid ◽  
Silty Sand ◽  
Excess Pore Pressure ◽  
Geotechnical Centrifuge ◽  
Time Scaling ◽  
Static Liquefaction ◽  
Viscous Solution

Fast landslides induced by rainfall impose considerable damage on infrastructure and cause major casualties worldwide. Static liquefaction is one of the triggering mechanisms mentioned frequently in the literature as a cause of this type of landslide. The scaling laws required to model this mechanism in the geotechnical centrifuge are developed, and it is shown that either a reduction in the soil pore size or use of a viscous pore fluid is needed to unify the time scaling factors of contractive volume change of the saturated voids and dissipation of the excess pore pressure generated. The latter option was used in this research; therefore, the influences of the viscous pore fluid on the hydromechanical characteristics of a silty sand were investigated. Subsequently, geocentrifuge tests were conducted to compare the behaviour of a slope having a viscous solution as the pore fluid with that of a model with water as the pore fluid. Both slopes were subjected to rainfall, and the evolution of the pore pressure and surface movements were monitored.

scholarly journals Influence of Energy on Compaction Characteristics of High Expansive Soils

2020 ◽  
Vol 9 (5) ◽  
pp. 1344-1348
Keyword(s):  
Moisture Content ◽  
Soil Type ◽  
Expansive Soils ◽  
Unit Weight ◽  
Dry Density ◽  
Maximum Dry Density ◽  
Compaction Characteristics ◽  
Dry Unit Weight ◽  
Comparison Results ◽  
Compaction Energy

Each soil type has different behavior with regard to determination of maximum dry density and optimum moisture content and therefore any soil type has its own compaction requirements for experimental purposes and for control the compaction in the field. The general purpose of this study is to a better understanding of the compaction characteristics of high expansive soils, with emphasis on the relationships of moisture content and dry density of high expansive soils at a range of compaction energy levels. To achieve this purpose, high expansive soils samples were subjected to Atterberg limit and a set of laboratory compaction tests to find compaction characteristics namely; maximum dry unit weight and optimum water content of high expansive soils at different compaction energy (compaction effort) for different number of hammer blows per each layer range from 10 to 50, which varied the energy per unit volume from 356 KN/m3 to 1188 KN/m3.Rather than single peak compaction curves, the most achieved compaction curves are an irregular one and half peak compaction curves. According to the comparison results of different compaction energy, it was concluded that the maximum dry unit weight of high expansive soil was not highly affected by gradually increase of applied energy. The results showed that, the maximum dry density of tested expansive soils sample increased from 1.48g/cm3 to 1.6g/cm3 with increase of compaction energy from 356 KN/m3 to 1188 KN/m3.

scholarly journals Evaluation of mechanical properties of concrete produced with binary and ternary mixtures of aggregate

2021 ◽  
Vol 10 (1) ◽  
pp. e43410111948
Author(s):  
Fernanda Cavalcanti Ferreira ◽  
Yane Coutinho ◽  
Arnaldo Manoel Pereira Carneiro
Keyword(s):  
Grain Size ◽  
Compressive Strength ◽  
Size Composition ◽  
Ternary Mixtures ◽  
Metropolitan Region ◽  
Unit Weight ◽  
Lower Amount ◽  
Mechanical Resistance ◽  
Conventional Concrete ◽  
Grain Size Composition

Cement is the costlier component of concrete, and its productive process causes considerable environmental impact. Thus, alternatives are studied to reduce the amount of cement used. An option is the use of optimized grain size curves of aggregates, aiming to achieve a higher compactness of concrete. An ideal grain size distribution results in a higher mechanical resistance of concrete, providing a reduction in cost and consumption of materials, and, consequently, in environmental impacts. Therefore, the present study aims to improve the properties of conventional concrete through optimized grain size distributions. In this research, concrete was produced with binary mixtures with rolled pebbles from Belém region, in Pará state, and ternary mixtures of granitic crushed stone from the metropolitan region of Recife, in Pernambuco state, and concrete properties in the hardened state were studied. The mix design IPT/EPUSP method was used and grain size composition, unit weight, water absorption by capillarity, and compressive strength tests were performed. It was observed an increase in compressive strength with for higher fine contents. Furthermore, for both aggregates studied, there was no loss in strength with the lower amount of cement used, due to the increased compactness of the concrete, indicated by the unit weight of the aggregate mixture. Therefore, the optimization of the grain size composition of the coarse aggregate provided a reduction in the cement consumption for the same required strength and for both analysed aggregates.

Developing Porous Concrete Interlocking Pavement Blocks Utilizing Recycled Concrete Aggregate for Rainfall Harvesting Use

2021 ◽  
Vol 28 (3) ◽  
pp. 48-60
Author(s):  
Mahdi Mahdi ◽  
Raad Irzooki ◽  
Mazin Abdulrahman
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Coarse Aggregate ◽  
Concrete Pavement ◽  
Recycled Concrete ◽  
Recycled Aggregate ◽  
Unit Weight ◽  
Conventional Concrete ◽  
Porous Concrete ◽  
Porous Pavement

Rainwater harvesting and flood prevention in cities are significant urban hydrological concerns. The use of porous pavement is one of the most effective solutions to handle this matter. Thus, this study aims to develop Porous Interlocking Concrete Pavement (PICP) using recycled aggregate from concrete waste. This porous pavement, then later, can be utilized in low traffic areas and parking lots to harvest water by infiltration and reduce surface runoff. First, the physical properties of the porous concrete blocks, such as density (unit weight), absorption, coefficient of permeability, and porosity, were studied. Also, the mechanical properties of concrete mixtures like compressive strength and flexural strength were tested. This study used two types of PICP, the first one with ordinary coarse aggregate (P1) and the second with recycled crushed concrete coarse aggregate (P2), and then compared their performance to the conventional concrete pavement blocks used the two types of coarse aggregate (R1 and R2). The results show that the unit weight (density) of porous types was reduced by 25% and 26%, and the total porosity increases by around 2.4 times and 18 times respectively, as compared to conventional concrete pavement types. However, the compressive strength and flexural strength of porous concrete types decreased by (55% and 71%), respectively, compared to conventional types. Overall, the infiltration test results showed that the infiltrated water through porous concrete increased by about 83% in comparison to conventional concrete. From the results, utilizing porous concrete pavement can be considered a promising material in terms of water harvesting and decreasing rainwater flooding. Additionally, using recycled concrete can bring economical and environmental benefits.

THE INFLUENCE OF FREEZE–THAW CYCLES ON UNCONFINED COMPRESSIVE STRENGTH OF CLAY SOILS TREATED WITH LIME

2015 ◽  
Vol 76 (1) ◽  
Author(s):  
Ali Akbar Firoozi ◽  
Mohd Raihan Taha ◽  
Ali Asghar Firoozi ◽  
Tanveer Ahmed Khan
Keyword(s):  
Compressive Strength ◽  
Unconfined Compressive Strength ◽  
Conventional Technique ◽  
Silica Sand ◽  
Clay Soils ◽  
Unit Weight ◽  
Freeze Thaw ◽  
Long Term Stability ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle

There are several questions that are not well understood with respect to the long-term stability characteristics of lime-treated clay soils in spite of being used as a conventional technique to improve the properties of clay soils. This paper investigates the influence of freeze-thaw cycles on the unconfined compressive strength of kaolinite and illite mixed with silica sand. The results of this study show that an increase in the number of freeze-thaw cycles decreases the unconfined compressive strength. The role of lime increasing the soil strength is more significant in the case of samples exposed to freeze-thaw cycles compared to those not exposed to freeze-thaw cycles. The effect of freeze-thaw cycles on the dry unit weight and moisture content is insignificant compared to unexposed samples. The maximum volumetric changes occurred in the first freeze-thaw cycle, and afterward, the rate of volume change decreased with an increase in freeze—thaw cycles.

scholarly journals Centrifuge Testing of Model Levees atop Peat: Experimental Data

2016 ◽  
Vol 32 (3) ◽  
pp. 1903-1924 ◽  
Author(s):  
Anne Lemnitzer ◽  
Riccardo Cappa ◽  
Samuel Yniesta ◽  
Scott Brandenberg
Keyword(s):  
Pore Pressure ◽  
Large Scale ◽  
Ground Motions ◽  
Pressure Sensors ◽  
Cyclic Behavior ◽  
Excess Pore Pressure ◽  
Data Repository ◽  
Centrifuge Testing ◽  
Centrifuge Tests ◽  
Seismic Deformation

Four large-scale centrifuge tests were performed at the NEES@UCDavis equipment site to study the cyclic behavior of levee structures resting atop soft organic peat. The model configurations using a non-liquefiable levee focused on the seismic deformation potential of peat during primary consolidation and secondary compression. The tests performed with a sandy levee studied the liquefaction potential of saturated loose sand fill overlying soft peat as well as the levee-peat-interaction under different loading conditions. The models were subjected to scaled ground motions representative of the Sacramento/San Joaquin Delta. System instrumentation consisted of linear potentiometers, pore pressure sensors and accelerometers. Slow data recorded at 1 Hz document the settlements during spin up, application of ground motions, and spin down. Fast data sampled at 4,167 Hz measured the dynamic response of the system, the excess pore pressure increase and immediate settlements. The project is archived at the NEES data repository under nees.org/warehouse/project/1161 .

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