scholarly journals MODEL TESTING OF THE "PILE-SOIL" INTERACTION UNDER AXIAL FORCE

2021 ◽  
pp. 102-111
Author(s):  
M.P. Doubrovsky ◽  
◽  
V.O. Dubravina ◽  
Keyword(s):  
Bearing Capacity ◽  
Early Stage ◽  
Large Diameter ◽  
Fine Sand ◽  
Offshore Platforms ◽  
Structural Element ◽  
Soil Plug ◽  
Pile Shaft ◽  
Plug Formation ◽  
Soil Level

Modern marine structures (berths, breakwaters, offshore platforms, etc.) often include steel tubular piles of essential length (80-100 m and more) that should provide high bearing capacity in case of external axial loads application. Interaction between elements of the system “piled structure – soil media” is not studied sufficiently yet. It relates also to the bearing capacity of the long steel tubular piles of large diameter. One of the interesting peculiarities of long tubular piles behavior is the formation of soil plug at the piles tip. There are a lot of suggestion and methods aimed to increase piles bearing capacity under static pressing load. One of them relates to use of the additional structural element, i.e., the internal diaphragm welded to the internal surface of the pile shaft. Such approach has been applied in some practical cases of marine construction and demonstrated its effectiveness. At the moment there are no researches focused on study of the peculiarities of internal diaphragm application. So proposed research aimed to study two connected processes during steel tubular pile driving: soil plug formation at the tip of the open-end pile and soil behavior under the internal diaphragm fixed inside the tubular pile shaft. To study mentioned processes we provided several series of laboratory experiments fulfilled at the Geotechnical laboratory of the Department “Sea, River Ports and Waterways” in Odessa National Maritime University. In these experiments the model of steel tubular pile has been driven (pressed) into fine sand by mechanical jack. The first series was devoted to determination of the conditions related to the soil plug formation at the pile tip. The next series were aimed to study the influence of the flat rigid diaphragm inside the pile shaft. Obtained experimental results allow to conclude that (a) in the fine sand the plug is formatted at the comparatively early stage of pile installation (in case of our modeling – at the penetration depth of some 4-5 pile diameter); (b) our empirical assessment of the conditions of soil plug formation corresponds to the approaches based on PLR and IFR characteristics; (c) formation of soil plug at the pile tip is followed by decreasing of soil level in the pile shaft relatively its initial value (on completing the plug formation the soil level in the shaft become stable); (d) regarding above mentioned, we may note that in case of use of internal diaphragm on the recommended depth (5-7 pile diameters) there may be no contact between diaphragm and the soil inside the pile (e) application of the diaphragm may lead to increasing of the pile’s bearing capacity. It was proposed (and checked by our tests) the technological improvement based on sand filling into space under the internal diaphragm to provide constant diaphragm-soil contact and related soil resistance.

scholarly journals Physical modeling of steel tubular piles installation into sandy soil

2020 ◽  
pp. 14-21
Author(s):  
Michael Doubrovsky ◽  
Vladyslava Dubravina
Keyword(s):  
Bearing Capacity ◽  
Early Stage ◽  
Large Diameter ◽  
Soil Surface ◽  
Fine Sand ◽  
Initial Value ◽  
Soil Plug ◽  
Surface Level ◽  
Plug Formation ◽  
Soil Level

Modern marine structures (berths, breakwaters, offshore platforms, etc.) often include steel tubular piles of essential length (80-100 m and more) that should provide high bearing capacity in case of external axial loads application. Interaction between elements of the system “piled structure – soil media” is not yet studied sufficiently. It relates also to the bearing capacity of the long steel tubular piles of large diameter. One of the interesting peculiarities of long tubular piles’ behavior is the formation of soil plug at the piles’ tip. There are a lot of suggestion and methods aimed to increase piles bearing capacity under static pressing load. One of them relates to use of the additional structural element, i.e., the internal diaphragm welded to the internal surface of the pile’s shaft. Such approach has been applied in some practical cases of marine construction and demonstrated its effectiveness. At the moment there are no researches focused on study of the peculiarities of internal diaphragm application. So proposed research aimed to study two connected processes during steel tubular pile driving: soil plug formation at the tip of the open-end pile and soil behavior under the internal diaphragm fixed inside the tubular pile’s shaft. To study mentioned processes we provided several series of laboratory experiments fulfilled at the Geotechnical laboratory of the Department “Sea, River Ports and Waterways” in Odessa National Maritime University. In these experiments the model of steel tubular pile has been driven (pressed) into fine sand by mechanical jack. The first series was devoted to determination of the conditions related to the soil plug formation at the pile’s tip (results are presented in this paper). The next series were aimed to study the influence of the rigid diaphragm inside the pile’s shaft (to be presented in the further publications). Obtained experimental results allow to conclude that (a) in the fine sand the plug is formatted at the comparatively early stage of pile installation (in case of our modeling - at the penetration depth of some 4-5 pile’s diameter); (b) our empirical assessment of the conditions of soil plug formation corresponds to the approaches based on PLR and IFR characteristics; (c) formation of soil plug at the pile’s tip is followed by decreasing of soil level in the pile’s shaft relatively its initial value (on completing the plug formation the soil level in the shaft become stable); (d) regarding above mentioned, we may note that in case of use of internal diaphragm on the recommended depth (5-7 pile’s diameters) there may be no contact between diaphragm and the soil inside the pile and the diaphragm does not come up with the soil. So, for the next series of our experiments, it should be foreseen assured contact of the diaphragm’s surface with soil underneath. As proved by previous studies, one of the interesting features of the behavior of long tubular piles is the formation of a soil plug at the lower end of the pile. From this point of view, it is important to study the effect of soil plug not only on the bearing capacity at the lower end of the pile, but also on the behavior of the soil inside the pile. It is shown that in fine-sandy soils a plug is formed at a relatively early stage of pile immersion (in this case - at a depth of immersion of about 4-5 pile diameters). The process of forming a soil plug at the lower end of the tubular pile during its immersion is accompanied by a decrease in soil surface level in the pile trunk relative to its initial value (upon completion of plug formation the soil surface level in the pile trunk stabilizes).  

Stress Development Inside Large Diameter Pipe Piles Using a Soil Plug Forcing System

2012 ◽  
Author(s):  
Jan Fischer ◽  
Sascha Henke ◽  
Sebastian Höhmann
Keyword(s):  
Bearing Capacity ◽  
Large Diameter ◽  
Significant Rise ◽  
Full Scale ◽  
Analysis Program ◽  
Soil Plug ◽  
Stress Development ◽  
Large Diameter Pipe ◽  
Diameter Pipe ◽  
Steel Piles

It is well known that soil plugging inside tubular steel piles will only appear in rather small diameter piles during impact driving. Therefore, large open ended steel piles, which are often used for the fixation of offshore buildings, such as wind farms, are highly unlikely to develop an internal soil plug. To take advantage of a soil plug, where a significant rise in the piles’ bearing capacity generally appears, a large diameter pipe-pile with an inner steel ring was designed by the third author. The location of the steel ring was determined by the soil formation in situ. To avoid increasing pile driving energy, the internal ring should dip into dense soil conditions only for the last few decimeters of driving. In October 2010, a full scale test was performed in the harbor of Hamburg, using two tubular piles with an outer diameter of 1220 mm. One pile was equipped with an inner steel ring as described above. The second pile was a typical tubular pile without any attached systems. To better compare the results, both piles were driven next to each other. Both piles were equipped with internal total stress and pore water pressure sensors at the pile tip to investigate the radial stress development during and after installation. Acceleration and strain at the pile head were measured to predict the bearing capacity. Using the numerical analysis program CAPWAP (Case Pile Wave Analysis Program) [15], the distribution of shaft and toe friction can be determined additionally. Furthermore, the internal soil movement was surveyed during driving. The results of the measurements showed, that when using an inner steel ring, a significant rise in internal radial stresses and the piles’ bearing capacity occurs. To better understand the stress development inside and outside the two investigated piles during driving, a numerical back-calculation of the recorded measurements was performed. The results of the full scale and numerical simulations, with a particular focus on the use of an internal steel ring to force the soil to plug behavior in large diameter pipe piles, is presented in the following paper.

scholarly journals Numerical and Experimental Study on Soil Plug Resistance of Open-Ended Pipe Pile with a Restriction Plate

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yuan Guo ◽  
Shaoyang Dong ◽  
Jiale Li ◽  
Xiong (Bill) Yu
Keyword(s):  
Numerical Model ◽  
Bearing Capacity ◽  
Large Diameter ◽  
Force Transmission ◽  
Cohesionless Soils ◽  
Soil Plug ◽  
Geotechnical Centrifuge ◽  
Arching Effect ◽  
End Bearing Capacity ◽  
Circular Holes

The end bearing capacity of open-ended pipe piles is highly dependent upon the soil plugging behavior inside the pipe wall. For large-diameter open-ended pipe piles, the arching effect due to inner soil-pile friction may be insufficient to generate a fully plugged condition, which compromises the end bearing capacity after the pile installation. Here, we propose two innovatively designed restriction plates installed inside the pipe to facilitate the soil plugging process, that is, a restriction plate with one circular hole and a restriction plate with four semisized circular holes. By use of the discrete element method, the mechanical behaviors of soil plugs in cohesionless soils with different restriction plates are analyzed. The numerical model has been validated by comparing the simulations to the results of a series of laboratory-scale experiments over different pile diameters, plug length-diameter ratios, and different types of restriction plates. It is shown that the numerical model can accurately predict the soil plug resistance and the particle-scale force transmission. Both numerical simulations and experiments validate that the arching effect is significantly enhanced by the restriction plate, especially with the four-hole restriction plate. Furthermore, the geotechnical centrifuge principle is adopted into the DEM model to study the mechanical behavior of large-diameter soil plugs. It is found that the effectiveness of restriction plate decreases as the pile diameter increases. However, even for the 2 m in diameter soil plugs, the plug resistance is increased by 252% with one-hole restriction plate and 281% with four-hole restriction plate compared to that of traditional pipe piles.

Numerical Simulation Analysis of Bearing Performance of Extra-Long and Large-Diameter Single Pile

2014 ◽  
Vol 1065-1069 ◽  
pp. 943-948
Author(s):  
Zhi Meng Zhao ◽  
Jin Yi Chai ◽  
Cai Xia Fan
Keyword(s):  
Numerical Simulation ◽  
Elastic Modulus ◽  
Bearing Capacity ◽  
Simulation Analysis ◽  
Large Diameter ◽  
Ultimate Bearing Capacity ◽  
Single Pile ◽  
Pile Shaft ◽  
Settlement Ratio ◽  
Pile Length

The effects of pile diameter, the property of pile end bearing stratum, the material parameters of pile shaft and the changes of pile length on the bearing performance of extra-long and large-diameter single pile were examined with the finite element software ABAQUS to make the numerical simulation analysis, by establishing the overall axial symmetry model, which was based on the data of static load test of single pile at the Yellow River Bridge site. The results show that the ultimate bearing capacity of single pile, the stiffness and the end resistance ratio would increase gradually, whereas the compression settlement ratio decreases slowly; the pile end grouting can significantly increase the ultimate loads, and therefore, improve the bearing performance of piles, but it has little effect on the stiffness of pile when loading was smaller; the elastic modulus of pile shaft has no effect on the ultimate bearing capacity of friction piles, little on the end resistance ratio, while the pile compression settlement ratio would gradually decrease and the stiffness would increased with the increase of the elastic modulus of pile shaft, and this increase of stiffness would slow down with the increase of elastic modulus of pile shaft; it is unreasonable to improve the ultimate bearing capacity of extra-long single pile only by means of increasing the pile length.

Centrifuge Model Tests on Effects of Spudcan Penetration on Adjacent Loaded Piles

2020 ◽  
Author(s):  
Jianhua Wang ◽  
Yifei Fan
Keyword(s):  
Model Test ◽  
Frictional Resistance ◽  
Fine Sand ◽  
Model Tests ◽  
Offshore Platforms ◽  
Pile Head ◽  
Centrifuge Model ◽  
Pile Shaft ◽  
Axial Forces ◽  
Centrifuge Model Tests

Abstract It is very important for designers of offshore platforms to understand affecting mechanism of mobile jack-up spudcan penetration and extraction on adjacent loaded piles. Existing centrifuge model tests are on effects of spudcan penetration on adjacent unloaded piles. In engineering, offshore platform piles are subjected to lateral and vertical pile head loads before spudcan penetration. In order to understand affecting mechanism of spudcan penetration on adjacent loaded piles, centrifuge model tests were conducted under 50g condition. Model test strata are the saturated soft clay and the fine sand and the model pile head constraint is free. Spudcan penetration resistances, lateral earth pressures along pile shaft, lateral pile deflection, vertical pile displacement, bending moments and axial forces along pile shaft are measured during spudcan penetration and after extraction. Effects of spudcan penetration on the pile-soil interaction p-y relationship and the bearing capacity of piles are analyzed based on model test results. Results show that the lateral soil resistance affected by spudcan penetration decreases due to soil movement. The lateral deflection of loaded pile obviously increases, the side frictional resistance decreases and the end resistance increases during spudcan penetration. The spudcan penetration-induced incremental pile response does not disappear after spudcan extraction. These results are helpful for understanding the effect mechanism of spudcan penetration and extraction on adjacent loaded piles.

scholarly journals Laboratory Plate Loading Test on Calcareous Sands from a Hydraulic fill Reef Island

2021 ◽  
Author(s):  
Xing Wang ◽  
YANG WU ◽  
Jie Cui ◽  
Chang-qi Zhu ◽  
Xin-zhi Wang
Keyword(s):  
Bearing Capacity ◽  
Deformation Modulus ◽  
Fine Sand ◽  
Medium Sand ◽  
Calcareous Sand ◽  
Loading Test ◽  
Moisture Condition ◽  
Hydraulic Fill ◽  
Deformation Properties ◽  
Plate Loading

Abstract The landforms and vertical strata distribution characteristics of Yongxing Island show that the reclaimed reef island is characterized by soft upper strata (calcareous sand) and hard lower strata (reef limestone). In this study, a series of plate loading tests was conducted to examine the influences of particle gradation, compactness, and moisture condition on the bearing mechanism and deformation properties of the calcareous sand foundation. When the foundation is shallowly buried, the relative density range corresponding to a calcareous sand foundation exhibiting local shear failure is narrower than that of a terrigenous sand foundation. For the same compactness, dry calcareous medium sand has a much larger bearing capacity and deformation modulus than dry calcareous fine sand. The effect of water on the bearing capacity of the calcareous medium sand is greater than the effect on calcareous fine sand. Its weak cementation and low permeability make the initial deformation of saturated calcareous fine sand slightly smaller than that under dry conditions. The stress dispersion angle of the calcareous medium sand foundation is 52°, which is larger than that of terrigenous sand. A larger stress dispersion angle leads to a higher bearing capacity and deformation modulus than those of terrigenous sand.

Advantages of Using a Time-Domain Approach for Dynamic Positioning (DP) Pipelay Studies

2014 ◽  
Author(s):  
Evren Armaoğlu ◽  
Paolo Monti
Keyword(s):  
Time Domain ◽  
Early Stage ◽  
Large Diameter ◽  
Weather Forecast ◽  
Dynamic Simulations ◽  
Power Generators ◽  
Fully Integrated ◽  
Critical Areas ◽  
Deep Waters ◽  
Slow Drift

Normally, the DP capability of a vessel is calculated through the use of static force equilibrium programs in which the dynamic effects are either not taken into account or taken into account by empirical load amplification factors. However, competitive and safe S-laying of large diameter pipelines in deep waters lead to large and long pipe lay vessels for which DP requirements are demanding. The power/propulsion requirement of the vessel needs to be considered from an early stage especially when accounting for the pipe laying equipment demands. This imposes a need for detailed dynamic analysis of the lay vessel. This analysis needs to include the slow drift oscillations counteracted by DP and the analysis in entirety needs to ensure the pipe string integrity is maintained. To this purpose Saipem developed in-house a time-domain simulator (FIPLA – Fully Integrated Pipe LAying) that employs all environmental forces (i.e. wind, wave, current) as well as the pipe tension on the vessel. It is used to assess the DP performances and laying capabilities of pipe lay vessels in harsh dynamic environments as well as critical areas for operations. The software can also be used to assess the performance of the vessel in case of failure of thrusters, power generators or bus bars, study DP Control System improvements, and assess the interaction between vessel, tensioner and pipe in deep and shallow waters. This paper focuses on the advantages of using dynamic simulations as an enhancement to the static DP capability charts, to produce detailed information for the DP Operator (DPO) in terms of setting of the DP parameters and to analyze critical laying events. This information can be used together with the weather forecast and can help getting the best performance out of the DP system in harsh environments, reducing downtime, improving operability and ensuring a safe operation.

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