Effects of Relative Roughness and Particle Size on the Interface Behavior of Concrete Suction Caisson Foundation for Offshore Wind Turbines

The interface behavior between a caisson and the surrounding soil plays an important role in the installation of suction caissons as foundations for offshore wind turbines. A series of shear tests were carried out using a modified direct shear apparatus to study the interface shear behavior between sand and concrete. Sand samples with three particle size ranges (0.63–1.25 mm, 1.25–2.5 mm, 2.5–5.0 mm) and concrete plates with different relative roughness were used to explore the influence of the relative roughness parameter (Rn) and mean particle size (D50) on shear behavior. The responses from the pure sand shear test are also discussed for comparison. Test results show that the higher the relative roughness (Rn), the greater the maximum shear stress (τmax) appeared. The interface shear stress was weaker than that of the pure sand test. Furthermore, the interface friction angle (φ) of sand–concrete was closely related to the relative roughness of the concrete surface. Under the same conditions, the interface friction angle (φ) increased with relative roughness due to the effect of sand particles breakage and redistribution. By contrast, the effect of the mean particle size (D50) on the interface friction angle (φ) was less significant. However, for the pure sand shear test, the friction angle (φ′) obtained from the traditional shear test apparently increased with D50, indicating that the friction angle was more affected by D50 in the pure sand test than in the interface shear test.

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Effects of Groove Feature on Shear Behavior of Steel-Sand Interface

Advances in Civil Engineering ◽

10.1155/2020/9593187 ◽

2020 ◽

Vol 2020 ◽

pp. 1-15 ◽

Cited By ~ 1

Author(s):

Jukun Guo ◽

Xiaowei Wang ◽

Shengyou Lei ◽

Rui Wang ◽

Hailei Kou ◽

...

Keyword(s):

Shear Stress ◽

Normal Stress ◽

Friction Angle ◽

Groove Width ◽

Hyperbolic Model ◽

Shear Direction ◽

Intersection Angle ◽

Interface Shear ◽

Interface Friction ◽

Peak Shear Stress

Surface groove morphology of structure and particle distribution of soil had a significant effect on the surface friction of structure. In order to investigate the interface shear stress-shear displacement curves, interface model and interface shear strength index when normal stress, groove width, and groove angle change, the interface shear tests of standard sand with steel plates are performed using an improved direct shear apparatus. Test results indicate that the peak shear stress increases with normal stress and the intersection angle between groove direction and shear direction. When the angle increases by 45°, the peak shear stress increases range from 4% to 13%. The peak shear stress increases with groove width, for every 1 mm increase in groove width, and the increasing extent of peak shear stress ranges from 4% to 22%, 3% to 13%, and 1% to 6%, respectively. When the groove angle is 45° and 90°, the increasing extent of peak shear stress decreases with groove width, but when the groove angle is 0°, the decrease regularity of peak shear stress increasing extent is not obvious. The hyperbolic model and Gompertz-C model are used to study the shear stress-shear displacement curves of sand-steel interface. The ratio of the interface peak shear stress of the hyperbolic model and Gompertz-C model to that of the shear test ranges from 0.90 to 1.03 and 0.88 to 0.98, respectively. The interface friction angle at the sand-steel interface ranges from 22° to 29°, and the friction angle of the rough interface is larger than that of the smooth interface. The interface friction angle increases with the intersection angle between the groove direction and the shear direction, the largest at 90°, the second at 45°, and the smallest at 0°. Under the same groove angle, the interface friction angle increases with the groove width, for every 1 mm increase in groove width, and the increasing extent of interface friction angle ranges from 4% to 15%, 4% to 7%, and 2% to 3%, respectively. The increasing extent of interface friction angle decreases with groove width, and this change rule is more obvious at the groove angle of 45° and 90° than at 0°.

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Characterization of Shear Strength and Interface Friction of Organic Soil

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.857.203 ◽

2020 ◽

Vol 857 ◽

pp. 203-211

Author(s):

Majid Hamed ◽

Waleed S. Sidik ◽

Hanifi Canakci ◽

Fatih Celik ◽

Romel N. Georgees

Keyword(s):

Shear Stress ◽

Shear Strength ◽

Internal Friction ◽

Moisture Content ◽

Water Content ◽

Friction Angle ◽

Structural Materials ◽

Organic Soil ◽

Internal Friction Angle ◽

Interface Friction

This study was undertaken to investigate some specific problems that limit a safe design and construction of structures on problematic soils. An experimental study was carried out to examine the influence of loading rate and moisture content on shear strength of organic soil. Influece of moisture content on interface friction between organic soil and structural materials was also attempted. A commonly used soil in Iraq was prepared at varying moisture contents of 39%, 57% and 75%. The experimental results showed that the increase in water content will decrease the shear stress and the internal friction angle. An increase of the shearing rate was found to decrease the shear stress and internal friction angle for all percetanges of water contents. Further, direct shear tests were carried out to detect the interface shear stress behavior between organic soil and structural materials. The results revealed that the increase in water content was shown to have significant negetavie effects on the interface internal friction and angle shear strength.

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Influence of Structural Plane Microscopic Parameters on Direct Shear Strength

Advances in Civil Engineering ◽

10.1155/2018/9178140 ◽

2018 ◽

Vol 2018 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

Yanhui Cheng ◽

Weijun Yang ◽

Dongliang He

Keyword(s):

Particle Size ◽

Shear Strength ◽

Internal Friction ◽

Direct Shear Test ◽

Shear Test ◽

Friction Angle ◽

Internal Friction Angle ◽

Direct Shear ◽

Stiffness Ratio ◽

Structural Plane

Structural plane is a key factor in controlling the stability of rock mass engineering. To study the influence of structural plane microscopic parameters on direct shear strength, this paper established the direct shear mechanical model of the structural plane by using the discrete element code PFC2D. From the mesoscopic perspective, the research on the direct shear test for structural plane has been conducted. The bonding strength and friction coefficient of the structural plane are investigated, and the effect of mesoscopic parameters on the shear mechanical behavior of the structural plane has been analyzed. The results show that the internal friction angle φ of the structural plane decreases with the increase of particle contact stiffness ratio. However, the change range of cohesion is small. The internal friction angle decreases first and then increases with the increase of parallel bond stiffness ratio. The influence of particle contact modulus EC on cohesion c is relatively small. The internal friction angle obtained by the direct shear test is larger than that obtained by the triaxial compression test. Parallel bond elastic modulus has a stronger impact on friction angle φ than that on cohesion c. Under the same normal stress conditions, the shear strength of the specimens increases with particle size. The shear strength of the specimen gradually decreases with the increase of the particle size ratio.

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Experimental study on mechanical properties of steel - sand interface

E3S Web of Conferences ◽

10.1051/e3sconf/202014301030 ◽

2020 ◽

Vol 143 ◽

pp. 01030

Author(s):

Zhaoxiao Fang ◽

Weijiang Wang ◽

Zhaoli Fang

Keyword(s):

Mechanical Properties ◽

Particle Size ◽

Friction Coefficient ◽

Average Particle Size ◽

Average Particle ◽

Shear Tests ◽

Axial Pressure ◽

Interface Shear ◽

Interface Friction ◽

Sand Particles

The interface between steel and sand can be regard as a steel-sand system, and its mechanical properties have an important role in many geotechnical applications. The mechanical properties of various steel-sand interfaces classified by sand mean particle size D50 were investigated through interface shear tests. The results show that for a given steel-sand interface, the peak strength of the interface increase with increasing axial pressure. As the D50 value increases, the cohesions for steel-sand interfaces decrease, while the friction angles of the interfaces first increase and then decrease. In the process of shearing, the shrinkage of steel-sand interface occurs, mainly due to the broken of sand particles. The decrease in interface friction coefficients due to an increase in axial pressure was observed. Particle size distribution has a significant effect on the interface friction coefficient of steel-sand interface. When the average particle size D50 changes from 0.1 mm to 0.47 mm, the friction coefficient of steel-sand interface increases by 134%-161%.

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Study on Shear Properties of the Soil-rock Mixture

E3S Web of Conferences ◽

10.1051/e3sconf/202016504079 ◽

2020 ◽

Vol 165 ◽

pp. 04079

Author(s):

B Li

Keyword(s):

Particle Size ◽

Moisture Content ◽

Large Scale ◽

Direct Shear Test ◽

Shear Test ◽

Friction Angle ◽

Direct Shear ◽

Shear Properties ◽

Maximum Particle Size ◽

Maximum Particle

In order to study the shear properties of the soil-rock mixture, a large-scale indoor direct shear test is used to test the shear strength (τ) of SRM under different positive pressures, and calculates the internal friction angle (φ) and cohesive force (c) according to the molar theory. The effects of soil-rock ratio, gradation, maximum particle size, moisture content, and compaction on the shear properties of the soil-rock mixtures are studied. The results show that as the soil-rock ratio decreases, the τ and φ of the SRM increase, while the c increases first and then decreases, and reaches the maximum peak when the soil-rack ratio is 40:60. As the maximum particle size increases, the τ and φ of the SRM increase, while the c decreases. With the increase of the moisture content, the τ, φ and c of the SRM all increase first and then decrease, and reach the maximum peaks when the moisture content is 10.5%, 10%, and 12%, respectively. With the increase of compaction, the τ, φ and c of SRM all increase. The effect of gradation on τ, φ and c is small.

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Determination of the Effect of Soil Particle Size Distribution on the Shear Behavior of Sand

Journal of Advanced Engineering and Computation ◽

10.25073/jaec.202152.331 ◽

2021 ◽

Vol 5 (2) ◽

pp. 125

Author(s):

Mohammad Afrazi ◽

Mahmoud Yazdani

Keyword(s):

Particle Size ◽

Shear Strength ◽

Direct Shear Test ◽

Shear Test ◽

Friction Angle ◽

Particle Sizes ◽

Direct Shear ◽

Shear Tests ◽

Direct Shear Tests

Many geotechnical problems require the determination of soil engineering properties such as shear strength. Therefore, the determination of the reliable values for this parameter is essential. For this purpose, the direct shear test, as one of the oldest tests to examine the shear strength of soils, is the most common way in laboratories to determine the shear parameters of soil. There are far too many variables that influence the results of a direct shear test. In this paper, a series of 10 × 10 cm direct shear tests were carried out on four different poorly graded sands with different particle size distributions to determine their shear behaviors. Four different poorly graded sands with a different median diameter or medium value of particle size distribution (D50) (0.2, 0.53, 1.3, and 2.3 mm) has been selected, and about 40 direct shear tests were conducted. It was concluded that a soil’s friction angle is affected by coarse-grained material. Accordingly, sandy soils with bigger particle sizes record a higher friction angle than soils containing small particles. The investigations also showed that sand with bigger particle sizes has a higher dilation angle. In addition, a non-linear regression analysis was performed to establish the exact relationship between the friction angle of the soil and the characteristics of the soil particles. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

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Effect of Particle-Size Gradation on Coarse Sand-Geotextile Interface Response in Cyclic and Postcyclic Direct Shear Test

Advances in Civil Engineering ◽

10.1155/2020/1323296 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Jun Wang ◽

Meng-Jie Ying ◽

Fei-Yu Liu ◽

Hong-Tao Fu ◽

Jun-Feng Ni ◽

...

Keyword(s):

Particle Size ◽

Shear Stress ◽

Shear Strength ◽

Shear Behaviour ◽

Direct Shear ◽

Interface Shear ◽

Cycle Number ◽

Cyclic Shear ◽

Stress Degradation ◽

Particle Size Gradation

In order to investigate the influence of sand particle-size gradation on cyclic and postcyclic shear strength behaviour on sand-geotextile interfaces, a series of monotonic direct shear (MDS), cyclic direct shear (CDS), and postcyclic direct shear (PCDS) tests were performed using a large-scale direct shear apparatus. The influence of cyclic shear history on the direct shear behaviour of the interface was studied. The results indicated that cyclic shear stress degradation occurred at the sand-geotextile interface. Shear volumetric contraction induced by the cyclic direct shear increased with the increase in cycle number. The lowest final contraction value was observed in discontinuously graded sand. In the MDS tests, there were great differences in interface shear strength due to the different particle-size gradations, whereas the differences between shear volumes were negligible. In the PCDS tests, the shear stress-displacement curves exhibited postpeak stress hardening behaviour for different particle-size gradations, and differences in shear volumes were detected. The well-graded sand-geotextile interface had a higher value of shear stiffness and a higher damping ratio relative to the other interfaces. Postcyclic shear stress degradation was observed for the discontinuously graded sand-geotextile interface.

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Concept Research of a Countermeasure Device for Preventing Scour around the Monopile Foundations of Offshore Wind Turbines

Energies ◽

10.3390/en11102593 ◽

2018 ◽

Vol 11 (10) ◽

pp. 2593 ◽

Cited By ~ 3

Author(s):

Wenxian Yang ◽

Wenye Tian

Keyword(s):

Shear Stress ◽

Wind Turbines ◽

Surface Profile ◽

Offshore Wind ◽

Optimal Size ◽

Offshore Wind Turbines ◽

Service Period ◽

Horseshoe Vortices ◽

Calculation Results ◽

The Impact

Scouring has long been considered to be a major issue affecting the reliability of the monopile foundations of offshore wind turbines (OWTs) on sandy seabeds. To reduce the impact of scouring, several tons of rock/stone are usually placed around the foundations shortly after the installation of them. Such a measure is costly. Moreover, rock and stone may spread widely on the seabed during the long-term service period of OWTs. It has no doubt that recycling these rock and stone on the seabed is quite difficult in future decommission. For this reason, a new scour-countermeasure device (SEMCD) is proposed and studied in this paper. Considering that the major driver of scouring is horseshoe vortices around the monopile foundation, a hollow horn-like SEMCD with an arc surface profile is designed for weakening the horseshoe vortices. The SEMCD is made of either cement or other kinds of corrosion resistant materials. It is light in weight, and easy to install and decommission. In the paper, the working mechanism of the SEMCD is first explained. Then, its scouring mitigation effect (SME), i.e., its contribution to the reduction of horseshoe vortices and the mitigation of seabed erosion around the foundation, is studied through investigating its influences on down/up-flow and seabed shear stress. Finally, the optimal size of the SEMCD is discussed through investigating the impact of its size on the speeds of up and down flows and the shear stress on seabed surface. The calculation results have shown that the proposed SEMCD has great potential to prevent scouring and seabed erosion, so that it is of significance to improve the reliability of the monopile foundations of OWTs.

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