Model testing of tripod caisson foundations in silty clay subjected to eccentric lateral loads

Abstract

In this study, model tests were conducted to investigate the bearing capacities of tripod caisson foundations subjected to eccentric lateral loads in silty clay. Lateral load–rotation curves of five eccentric-shaped tripod suction foundations were plotted to analyze the bearing capacities at different loading angles. It was observed that the loading angle significantly influenced the bearing capacity of the foundations, particularly for eccentric tripod caisson foundations. Compared with eccentric tripod caisson foundations, the traditional tripod foundation has a relatively high ultimate lateral capacity at the omnidirectional loading angle. By analyzing the displacement of the caissons, a formula for the rotational center of the tripod caisson foundation subjected to an eccentric lateral load was derived. The depth of the rotation center was 0.68–0.92 times the height of the caisson when the bearing capacity reached the limit. Under the undrained condition, suction was generated under the lid of the “up-lift” caisson, which helps resist lateral forces from the wind and waves.

Graphical abstract

Keywords

tripod caisson foundation / silty clay / eccentric lateral capacity / model tests

1 Introduction

Offshore wind power is utilized as a clean, renewable, and promising choice to decrease the use of fuel sources in response to global energy shortages [1]. Currently, the 35 GW power used in China is generated in offshore areas, which has been recognized as a potential area of development for wind power. The foundation may account for up to 35% of the installation cost of a wind turbine [2]. Suction caissons, a type of foundation for offshore platforms, have recently been developed and used in recent research and development projects because of their competitive technical and economic advantages and repetitive usability over other foundation types [3,4].

Suction caissons are large cylindrical thin-walled steel or upturned concrete buckets [5]. The primary challenge in designing an offshore wind turbine foundation is the significant overturning moments generated by lateral loads from the wind and waves under comparatively low vertical loading [6]. Several studies on the lateral behavior of suction caissons have been conducted [2,7–10]. Ibsen et al. [11] evaluated the behavior of suction caissons using the macromodel approach by conducting a series of small-scale tests. The lateral bearing capacity of suction caissons was investigated using tests and the finite element method in the sand, and Liu et al. [8] found that the center of rotation changes with the height–diameter ratio. However, a few studies have described laboratory tests on suction caissons subjected to lateral loads in silty clay. Taiebat and Carter [12] presented numerical analysis results and observed that the lateral capacity of a caisson depends on the location of the padeye along the caisson skirt. An optimized failure envelope was proposed by Wang et al. [13] to reduce the degree of coupling between the horizontal and moment loads by moving the load reference point to the rotation center of the suction caisson.

2 Tripod caisson foundations

Tripod caisson foundations can provide more stability and stiffness than single-suction caissons during hurricanes and typhoons [14]. Because they are cost-effective, tripod foundations consisting of three suction caissons represent a promising solution compared to large-diameter monopiles [15]. A tripod caisson foundation with a diameter of 13 m and height of 11 m was first utilized as a support structure for offshore wind turbines in the South China Sea at a depth of nearly 30 m. Tripod caisson foundations have become increasingly important in China owing to the development and application of offshore wind turbines. Most studies have focused on installing a tripod foundation [16,17]. Jeong et al. [18] investigated the behavior of a tripod caisson foundation under cyclic lateral loads in silty sand and found that partial-to-undrained conditions may develop in actual applications during load processing. A simplified oblique parabola-like failure envelope was proposed by Barari et al. [19]. Using three-dimensional finite element analysis, Kim and Oh [20] investigated the group effect of tripod caisson foundations in clay.

The placement of a tower at different positions of a tripod foundation induces eccentricity, as shown in Fig.1, and affects its bearing capacity. The loading direction of the tripod substructure may be different for an offshore wind turbine owing to the different structural forms and marine environments [21]. However, no relevant literature has been published on the bearing capacities of eccentric special-shaped tripod caisson foundations subjected to lateral loads in different directions in silty clay. Therefore, research on the bearing capacity of special-shaped tripod caisson foundations offers new significant perspectives to researchers and designers.

In this study, model tests were conducted to assess the bearing capacities of tripod caisson foundations subjected to eccentric lateral loads in silty clay. The lateral load–rotation curves of five special-shaped tripod suction foundations were plotted owing to their geometric symmetry to analyze the bearing capacities at loading angles ranging from zero to π. The ultimate lateral capacities of the traditional and eccentric tripod caisson foundations were compared and analyzed using a polar diagram. By analyzing the displacement of the caissons, we determined the positions of the rotation centers during the loading tests. The water drainage condition was assumed to be fully undrained to determine the effect of suction under the lid of the caisson on the lateral capacity of the tripod caisson foundations.

3 Experimental equipment and test program

Kelly et al. [22] recommended that, in most cases, small-scale experimental test results should be scaled to the field using a dimensionless analysis method for suction caissons under lateral loads. The total weight of the wind turbine, except for the foundation, was neglected based on the assumption that the weight is low compared to the relatively larger applied horizontal loads [23]. The silty clay used in the model tests was obtained from the East China Sea, the largest offshore wind farm in China (Hua Neng Ru farm).

A series of small-scale model tests were conducted in a soil tank made of reinforced concrete. The tank was 1.72 m long, 0.76 m wide, and 0.72 m high. A gravel cushion with a thickness of 5 cm overlay was placed on the bottom of the soil tank as a drainage channel (Fig.2). The soil and gravel cushion were separated by a double-layer geotextile to prevent the loss of fine silty clay particles. The water tank controlled the liquid level to be approximately 3 cm higher than the mudline to maintain soil saturation.

Fig.3(a) shows the silty clay analyzed using scanning electron microscopy (SEM, the scanned image is shown in Fig.3(b)). The soil comprised 11% sand, 63% silt, and less than 26% clay-size particles. The particle-size distribution curve is shown in Fig.4 for the silty soil, with a specific gravity of 2.74. The liquid and plasticity limits of the silty clay were 31.2 and 16.3, respectively. A concrete mixer was employed to mix the soil sample with water to a slurry state and pour the mud water mixture into the soil tank. Because of the flow plastic state of the specimen, a bag filled with water was selected as a heaped load for the preloading consolidation. Tests were performed on the complete consolidation of the specimen. The test soil had an average effective gravity γ′ of 8.2 kN/m³ and an effective internal friction angle φ of 6.3°. The undrained shear strength (Fig.5) indicated that, comparatively, reasonable consistency existed between the soil specimens, and the variation between samples could be attributed to slight inhomogeneity. Further geotechnical tests on the prepared soil samples showed that the soil had a permeability coefficient of 1.62 × 10⁻⁶ m/s.

Fig.6 shows the prototype tripod caisson foundation composed of three suction caissons and the upper steel structure used in the model tests. In the 1g small-scale model test, the suction caisson was generally modeled as a rigid body, ignoring internal forces and deformation of the foundation [24,25]. The suction caisson was a steel thin-walled cylinder with a diameter D = 12 cm and height L = 18 cm. The thicknesses of the lid and wall of the caisson were 1 and 0.2 cm, respectively. Four upper steel structures had different locations of connection to the loading rod to assess the eccentric lateral-bearing capacity of the tripod caisson foundations. The loading rod and the upper steel structure were made of stainless steel with a diameter of 14 mm, with the stiffness sufficiently high to be considered rigid for the tests.

The model test setup for the tripod caisson foundation is illustrated in Fig.2. The anti-overturning bearing capacity of a suction caisson can be revealed by analyzing the bearing failure mechanism of an offshore foundation when e > 3D (where e is the loading height) [26]. Model tests were performed under displacement control at 0.01 mm/s using a servo-loading system located 3L above the loading rod. The lateral and vertical displacements of the foundation were measured using five linear variable differential transformers (LVDTs). Three negative pressure sensors connected to the drainage outlet of the foundation lid recorded the pressure in the suction caissons. The applied lateral load was measured using a force transducer fixed on top of the servo cylinder at 50 Hz in the experimental tests.

Before the 1g model tests, the foundation was placed in the designated position of the soil using a jack. The LVDTs and negative pressure sensors were installed at the corresponding positions. The test started after the foundation was allowed to stand for 1 h to prevent excess pore water pressure around the wall during installation. The servo-loading system was turned on to make the pressing head contact with the stress point. At the same time, the data-collecting instrument collected the values of the load, displacement, and pressure at an acquisition frequency of 50 Hz. Fifteen model tests were conducted to investigate the lateral bearing capacities of offshore wind turbines with tripod caisson foundations. Fig.7 shows a schematic of the loading direction and location, where the caisson spacing s of tripod caisson foundations is 2D in this study. Five different loading locations (s_a/s_p) of rod were observed. The test scheme of tripod caisson foundations is presented in Tab.1, where B1 is the single-suction caisson. Note that for s_a = s_p/3, the geometry of the top view of the regular tripod caisson foundation is symmetric in the direction of π/3.

4 Model test results

4.1 Lateral load–rotation curve

By using the results of the LVDTs measuring the lateral displacements of the loading rod, the rotation θ (rad) of the tripod caisson foundations can be determined. Fig.8 shows the relationship curves between the lateral loading and rotation of the tripod caisson foundation at different loading angles. During the initial loading period, the soil exhibited elastic characteristics, and the lateral load–rotation curve could be represented by a line model with a steep slope. It is evident that the initial stiffness of the load–rotation curve of the tripod caisson foundation far outweighs that of a single-suction caisson (B1). When the loading angle was zero, the horizontal load suddenly increased to 0.009 rad owing to unexpected instrument jittering during the test. The initial stiffness of the eccentric foundation at s_a = 2s_p/3 varied significantly with an increase in the loading angle β, as shown in Fig.8(d). The mechanical behavior of tripod foundations shows typical characteristics of work-hardening plasticity [27,28]. As the rotation of the foundation increased, the lateral load–rotation curves exhibited a double-piecewise linear response and showed no clear yield point. This phenomenon was also observed in the three-dimensional finite element simulation of traditional tripod caisson foundations in clay conducted by Hung and Kim [29]. As shown in Fig.8(c), the lateral capacity of the tripod caisson foundation is significantly higher than that of the single-suction caisson foundation. For β = π/3, the lateral loads of B1 applied were 0.110, 0.144, 0.114, 0.122, and 0.155 times those of T0R2, T1R2, T2R4, T3R2, and T4R2 at θ = 0.01 rad, respectively. Regardless of the location of the load, the loading angle significantly influenced the bearing capacity of the foundations, particularly for eccentric tripod caisson foundations. For loading location s_a = 0, the maximum and minimum H/(γ′D³) of the eccentric tripod caisson foundation were 3.26 of β = 0 and 2.40 of β = 5π/6 at a rotation of 0.005 rad, respectively. When the loading angle was 0°, the anti-overturning bearing capacity was relatively high. The dimensionless lateral bearing capacity of T2R1 of 2.55 was 82.5% of that of T2R0, whereas the rotation of the foundation was 0.006 rad.

4.2 Ultimate lateral capacity of tripod caisson foundations

The ultimate lateral bearing capacities of the foundations were obtained using the tangent intersection method, in which two tangential lines were used along the initial and latter portions of the load–rotation curve [20,28,30]. The load corresponding to the intersection point above the two tangential lines was regarded as the ultimate lateral capacity (Fig.9).

The results for the ultimate lateral capacity obtained using the tangent intersection method were plotted together to further compare the influence of the loading angle on the foundation bearing capacities. The polar diagram of the ratio (H_ult,t/(3H_ult,s)) between the tripod foundation and the single-suction caisson for the ultimate lateral capacity is shown in Fig.10, where H_ult,t and H_ult,s are the ultimate lateral capacities of the tripod caisson foundation and single-suction caisson, respectively. Compared to the eccentric foundation, the traditional tripod caisson foundation (s_a = s_p/3) had a relatively high ultimate lateral capacity in the omnidirectional loading angle. Therefore, the traditional layout scheme of the tripod foundation is advantageous for the anti-overturning bearing capacity. However, H_ult,t/H_ult,s of s_a = 0 is the same as that of s_a = s_p/3 when the loading angle is equal to 0.65π. The bearing capacity shape of the eccentric tripod caisson foundation with s_a = 0 is close to elliptical, and the ultimate lateral capacity of 2.30 for β = 0 is 1.11 times that of 2.08 for β = π. When the loading angle is zero, the most unfavorable condition exists in the loading location of s_a = s_p. Using the displacement finite element analyses, Stergiou et al. [31] found that the traditional tripod caisson foundation was in its most unsafe condition at a loading angle of 0°. This phenomenon also occurred in this study, and the ratio of the ultimate lateral capacity had a minimum value of 2.42 at β = 0.

Fig.11 depicts the relationship between the dimensionless ultimate lateral capacity and the loading location for tripod caisson foundations. The dimensionless ultimate bearing capacity of the tripod caisson foundation decreases with increasing s_a/s_p under the eccentric lateral load when β = 0. The mathematical formula for H_ult,t/(γ′D³) and s_a/s_p was derived via fitting analysis and can be expressed as follows:

(1)\frac{H_{\text{ult},\text{t}}}{{\gamma }^{\prime }{D}^3}=2.251+0.457\frac{s_{\text{a}}}{s_{\text{p}}}-1.2314{\left(\frac{s_{\text{a}}}{s_{\text{p}}}\right)}^2,

where the adjusted R-squared value was 0.982. Two peaks appeared in the curve of the dimensionless ultimate lateral capacity of the foundation when the loading angles were π/3 and 2π/3. The tripod caisson foundation was found to be under the most unsafe condition when the loading location was s_a = s_p/6.

4.3 Positions of rotation centers

The rotational center of the foundation is shown in Fig.2. In Fig.2, z_p is the horizontal distance of the foremost foundation in the loading direction, and d_p is the depth of the rotation center. The displacements measured by two horizontal LVDTs on the loading rod and three vertical LVDTs on the lids of caissons I, II, and III are denoted as l_b, l_t, s_vI, s_vII, and s_vIII, respectively. The positions of the instantaneous rotation centers of the tripod caisson foundation subjected to an eccentric lateral load can then be determined using Eq. (2):

(2){\mathit{\text{z}}}_{\text{p}}=\frac{l_{\text{b}}{h}_{\text{t}}-h_{\text{b}}{l}_{\text{t}}}{l_{\text{t}}-l_{\text{b}}},

(3)d_{\text{p}}=\frac{F_{\mathrm{s}\mathrm{v}\mathrm{I}}{S}_{\text{FP}}}{P_{\left(\mathrm{s}\mathrm{v}\text{II}\vee \mathrm{s}\mathrm{v}\text{III}\right)}-F_{\mathrm{s}\mathrm{v}\text{I}}},

where h_t and h_b are the heights of the top and bottom LVDTs from the ground surface, respectively. F_svI is the vertical displacement of the caisson I, P_{(svII ˅ svIII)} is the vertical displacement of caisson II or III, S_FP is the center distance between the caissons I and II (or III) in the loading direction.

Fig.12 shows the positions of the instantaneous rotational centers of the tripod caisson foundations subjected to an eccentric lateral load when the loading direction is π/3. The rotational center moved to the ground surface with the deflection of the tripod caisson foundation. The dimensionless depth z_p/L values of the rotation center ranged from 0.68 to 0.92 when the bearing capacity reached the limit. Similarly, Zhu et al. [32] found that the depths of these instantaneous rotation centers for single-suction caisson were approximately 0.8L below the ground surface. The horizontal distance d_p of the foundation varied in a larger range. d_p is equal to 0.27D and 1.58D when s_a = 2s_p/3 and s_a = s_p, respectively.

4.4 Pressure under caisson lid

Soil drainage somewhat influences the suction under the lid of the caisson subjected to a lateral load. Jeong et al. [18] observed that the drained condition of soil exists based on the following criteria for the normalized penetration velocity (V):

(4)V=\frac{vD}{c_{\text{v}}},

where v is the loading rate (0.01 mm/s in the model test), and c_v is the vertical coefficient of consolidation for soil. For silty clay, Robertson et al. [33] considered c_v equal to 0.072 cm²/min, which is the value used in this study. In these experiments, V was 10, which is close to the maximum under undrained conditions (V > 10) based on the tests conducted by House et al. [34].

Fig.13 shows the pressure under the lid against the rotation of the foundation. It should be noted that the pressure under the lid of caisson II is not drawn owing to a similar value to caisson I when the loading angle is zero. A diagram of the tripod caisson foundations is shown in Fig.14. Caisson III tended to pull up at β = 0. Hence, suction was generated in caisson III, and an increase in uplift resistance was observed during load processing; this increase helps in resisting lateral loads induced by the wind and waves. The dimensionless pressure P/(γ′D) increased with the rotation of the foundations, and its trend was similar to that of the load–rotation curves. P/(γ′D) of caisson I first increased and then tended to be a stable value of 4.08 with increasing rotation when s_a = s_p. The dimensionless pressure value in caisson I (4.00) is 2.99 times that in caisson III (1.34). The value of the suction in caisson III slightly increased after reaching approximately 1 kPa at different loading locations, indicating that the space between the soil and caisson showed less significant variation under the undrained condition (Fig.14). In the theoretical studies on the lateral capacity of single-suction caissons, Sun et al. [35] and Li et al. [36] neglected the separation between the soil plug and the lid. Therefore, the soil plug and caisson can be regarded as a body in subsequent theoretical analyses of the eccentric lateral bearing capacity of a tripod caisson foundation.

5 Conclusions

In this study, a series of model tests were conducted on the bearing capacities of tripod caisson foundations subjected to eccentric lateral loads in silty clay. The following conclusions were drawn.

1) The initial stiffness of the load–rotation curve of tripod caisson foundations significantly exceeds that of a single-suction caisson. Regardless of the location of the load, the loading angle significantly influenced the bearing capacity of foundations, particularly for eccentric tripod caisson foundations.

2) Compared to the eccentric foundation, the traditional tripod caisson foundation (s_a = s_p/3) has a relatively high ultimate lateral capacity at the omnidirectional loading angle. Therefore, the traditional layout scheme of tripod foundations has more advantages in terms of anti-overturning bearing capacity. The traditional tripod caisson foundation was under the most unsafe condition at a loading angle of 0°.

3) The dimensionless depth of the rotation center ranges from 0.68 to 0.92 as the bearing capacity reaches the limit. The suction increases with the rotation of the foundation, and its trend is similar to that of the load–rotation curves. The soil plug and caisson can be regarded as a body in subsequent theoretical analyses of the eccentric lateral bearing capacity of the tripod caisson foundations.

References

[1] Park J W, Sim S H, Yi J H, Jung H J. Development of temperature-robust damage factor based on sensor fusion for a wind turbine structure. Frontiers of Structural and Civil Engineering, 2015, 9(1): 42–47

[2] Zhan Y G, Liu F C. Numerical analysis of bearing capacity of suction bucket foundation for offshore wind turbines. Electronic Journal of Geotechnical Engineering, 2010, 15(10): 76–81

[3] Chen F, Lian J, Wang H, Liu F, Wang H, Zhao Y. Large-scale experimental investigation of the installation of suction caissons in silt sand. Applied Ocean Research, 2016, 60: 109–120

[4] Wu Y Q, Li D Y, Yang Q, Zhang Y K. Resistance to skirt-tip with external bevels of suction caissons penetrating clay. Ocean Engineering, 2022, 249: 110909

[5] Yan S W, Zhang J J, Chu J, Guo W, Huo Z L. Analytical and experimental studies on installation of a suction caisson with tampered tip in clay. Marine Georesources and Geotechnology, 2017, 35(3): 435–440

[6] KourkoulisRGeorgiouIGazetasG. Seismic response of suction caissons: Effect of two-directional loading. In: 6th International Conference on Earthquake Geotechnical Engineering. Christchurch: ISSMGE, 2015

[7] Sukumaran B, McCarron W O, Jeanjean P, Abouseeda H. Efficient finite element techniques for limit analysis of suction caissons under lateral loads. Computers and Geotechnics, 1999, 24(2): 89–107

[8] Liu M, Lian J, Yang M. Experimental and numerical studies on lateral bearing capacity of bucket foundation in saturated sand. Ocean Engineering, 2017, 144: 14–20

[9] Kou H, Yang D, Zhang W, Wu Y, Fu Q. Model tests on performance of offshore wind turbine with suction caisson foundation in sand. Marine Georesources & Geotechnology, 2020, 38(8): 980–988

[10] Al-Janabi H A, Aubeny C P. Experimental and numerical investigation of the performance of piles and suction caissons subjected to inclined cyclic loading in cohesive soils. Journal of Geotechnical and Geoenvironmental Engineering, 2022, 148(6): 04022036

[11] Ibsen L B, Larsen K A, Barari A. Calibration of failure criteria for bucket foundations on drained sand under general loading. Journal of Geotechnical and Geoenvironmental Engineering, 2014, 140(7): 04014033

[12] Taiebat H A, Carter J P. A failure surface for caisson foundations in undrained soils. In: Proceedings of the 1st International Symposium on Frontiers in Offshore Geotechnics. Perth: CRC Press, 2005, 289–295

[13] Wang J, Liu R, Yang X, Chen G. An optimised failure envelope approach of bucket foundation in undrained clay. Ships and Offshore Structures, 2021, 16(sup2): 42–55

[14] Basack S, Dutta S, Saha D, Das G. Power generation by offshore wind turbines: An overview on recent research and developments. WSEAS Transactions on Power Systems, 2021, 16: 254–261

[15] Ochmański M, Mašín D, Duque J, Yi H, Lizhong W. Performance of tripod foundations for offshore wind turbines: A numerical study. Géotechnique Letters, 2021, 11(3): 230–238

[16] Zhang P, Ding H Y, Le C H. Installation and removal records of field trials for two mooring dolphin platforms with three suction caissons. Journal of Waterway, Port, Coastal, and Ocean Engineering, 2013, 139(6): 502–517

[17] Zhang P, Ding H, Le C. Model tests on tilt adjustment techniques for a mooring dolphin platform with three suction caisson foundations in clay. Ocean Engineering, 2013, 73: 96–105

[18] Jeong Y H, Ko K W, Kim D S, Kim J H. Studies on cyclic behavior of tripod suction bucket foundation system supporting offshore wind turbine using centrifuge model test. Wind Energy (Chichester, England), 2021, 24(5): 515–529

[19] Barari A, Glitrup K, Christiansen L R, Ibsen L B, Choo Y W. Tripod suction caisson foundations for offshore wind energy and their monotonic and cyclic responses in silty sand: Numerical predictions for centrifuge model tests. Soil Dynamics and Earthquake Engineering, 2021, 149: 106813

[20] Kim S R, Oh M. Group effect on bearing capacities of tripod bucket foundations in undrained clay. Ocean Engineering, 2014, 79: 1–9

[21] Wang B, Li Y, Lv N, Zhu B B, Li W. Analysis of working condition and load direction for tripod substructure of offshore wind turbine. Applied Mechanics and Materials, 2014, 454: 27–33

[22] Kelly R B, Houlsby G T, Byrne B W. A comparison of field and laboratory tests of caisson foundations in sand and clay. Geotechnique, 2006, 56(9): 617–626

[23] Villalobos F A, Byrne B W, Houlsby G T. Model testing of suction caissons in clay subjected to vertical loading. Applied Ocean Research, 2010, 32(4): 414–424

[24] Li D, Ma S, Zhang Y, Chen F. Experimental studies on differences of penetration between modified suction caisson and regular suction caisson in clay. Ships and Offshore Structures, 2021, 16(2): 112–119

[25] Bienen B, Klinkvort R T, O’Loughlin C D, Zhu F, Byrne B W. Suction caissons in dense sand, part I: Installation, limiting capacity and drainage. Geotechnique, 2018, 68(11): 937–952

[26] Ma P, Liu R, Lian J, Zhu B. An investigation into the lateral loading response of shallow bucket foundations for offshore wind turbines through centrifuge modeling in sand. Applied Ocean Research, 2019, 87: 192–203

[27] Houlsby G T, Byrne B W. Design procedures for installation of suction caissons in clay and other materials. Geotechnical Engineering, 2005, 158(2): 75–82

[28] Zhu B, Zhang W L, Ying P P, Chen Y M. Deflection-based bearing capacity of suction caisson foundations of offshore wind turbines. Journal of Geotechnical and Geoenvironmental Engineering, 2014, 140(5): 04014013

[29] Hung L C, Kim S R. Evaluation of combined horizontal-moment bearing capacities of tripod bucket foundations in undrained clay. Ocean Engineering, 2014, 85: 100–109

[30] Mansur C I, Kaufman R I. Pile tests, low-sill structure, Old River, Louisiana. Transactions of the American Society of Civil Engineers, 1958, 123(1): 715–743

[31] Stergiou T, Terzis D, Georgiadis K. Undrained bearing capacity of tripod skirted foundations under eccentric loading. Geotechnik, 2015, 38(1): 17–27

[32] Zhu B, Kong D Q, Chen R P, Kong L G, Chen Y M. Installation and lateral loading tests of suction caissons in silt. Canadian Geotechnical Journal, 2011, 48(7): 1070–1084

[33] Robertson P K, Sully J P, Woeller D J, Lunne T, Powell J J, Gillespie D G. Estimating coefficient of consolidation from piezocone tests. Canadian Geotechnical Journal, 1992, 29(4): 539–550

[34] House A, Randolph M, Watson P. In-situ assessment of shear strength and consolidation characteristics of soft sediments. In: Proceedings of the OTRC 2001 International Conference. Houston, TX: Offshore Technology Research Centre, 2001, 52–63

[35] Sun X Y, Luan M T, Tang X W. Study of horizontal bearing capacity of bucket foundation on saturated soft clay ground. Rock and Soil Mechanics, 2010, 31(2): 667–672

[36] Li D, Ma S, Zhang Y, Chen F. Lateral bearing capacity of modified suction caissons determined by using the limit equilibrium method. China Ocean Engineering, 2018, 32(4): 461–466

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