# The Practice and Development of T-Bar Penetrometer Tests in Offshore Engineering Investigation: A Comprehensive Review

^{1}

^{2}

^{3}

^{4}

^{5}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Development of Marine Penetrometer Deployment Technology and T-Bar Penetrometer

^{2}and a test water depth of 50 m [33].

- The high pore water pressure during penetration testing in a high-pressure environment on the seabed and the low strength of the soft soils on the seabed compared to the soft soils on the seabed has a greater impact on the sensitivity of the penetration resistance during testing.
- There is a significant correction for unequal area effect and uncertainty in the overburden stress correction on penetration resistance.

^{2}projected area steel T-bar penetrometer (10 times the size of a standard CPT). The cross-sectional area of the connecting rods should not exceed 15% of the projected area of the T-bar penetrometer, nor should the diameter exceed the diameter of the T-bar penetrometer. Additionally, the surface of the T-bar penetrometer should be lightly sandblasted.

## 3. Analysis of T-Bar Full-Flow Penetration Test Results

#### 3.1. Analytical Solution of the Resistance Factor

_{u}) is one of the most crucial indicators for analyzing the strength properties and stability of the soils, as well as one of the most important parameters for marine soft soil engineering. Haneng et al. (2014) demonstrated that the shape of the T-bar penetrometer resembles a cylindrical pipe, and that the undrained shear strength derived from the penetration test was more accurate for use as a strength parameter in the design of subsea pipelines and risers in practical marine engineering [34,41]. The results of the model tests and field tests by Weemees et al. (2006) and Yafrate et al. (2007) showed that the L/D ratio (length–diameter ratio) of the T-bar penetrometer should be 4–10 (i.e., the projected area of the T-bar penetrometer is 6.4–15 times the area of the standard cone), which does not affect the dimensional resistance to penetration, and recommended that the L/D ratio of the T-bar penetrometer should generally be greater than 4 [42,43]. Low and Randolph et al. (2010) analyzed the results of the undrained shear strength tests conducted at several soft soil sites in Australia and concluded that the T-bar penetrometer has a good reliability in measuring the undrained shear strength of in situ and remodeled soft soils on the seabed [44]. The experimental studies by Yafrate et al. (2009) showed that the T-bar penetrometer can estimate the remodeled soil s

_{u}and Sensitivity S

_{t}, and proposed a series of equations to estimate the relevant design parameters for soft soils [45]. Lunne et al. (2010) analyzed the test results from multiple subsea soft soil sites around the world and discovered that the strength measured using full-flow penetrometer was influenced by strength anisotropy, and that the relationship between the resistance factors of the soft soil remodeling and in situ soils varied primarily with S

_{t}, independent of the properties such as the mechanical strength of the soft soil [32].

_{T-bar}of the T-bar penetrometer can be estimated by using the plasticity theoretical solution of the full-flow theory and the modified penetration resistance q

_{T-bar}obtained from the test to estimate s

_{u}as follows:

_{m}is the measured penetration resistance, u

_{0}is the static pore water pressure, and α is the static area ratio; A

_{s}is the cross-sectional area of the connection axis; and A

_{p}is the projected area of the horizontal axial direction of the tactile penetrometer. Randolph made some small modifications to the above equation, which did not result in significant changes to the calculations and eliminated the necessity for the accurate measurement of u

_{2}for the T-bar penetrometer [6].

_{T-bar}based on the plasticity theory and derived their upper limit solution for the friction coefficient α on the surface of the penetrometer and their linear fit [6,46].

_{T-bar}from 9.14 (α = 0) to 11.86 (α = 1), and it is generally accepted that a light sandblasting of the penetrometer surface would result in an α of 0.4, with Low suggesting the N

_{T-bar}value of 10.5. Randolph et al. give the variation of the resistance factor with the friction coefficient α for the T-bar, ball, and cone penetrometers, as shown in Figure 5 [6].

_{T-bar}values were larger when comparing the experimental solution to the theoretical analytical solution for the N

_{T-bar}values measured in the vane shear tests and laboratory tests [6]. Randolph analyzed this phenomenon and suggested that the main factors influencing the difference between the theoretical and experimental solutions for N

_{T-bar}were sensitivity, strain softening, and strain rate.

_{T-bar}was based on the theoretical lower and upper bound solutions for a cylindrical plane strain object moving through a rigid plastic medium [47]. Figure 7 demonstrates the upper bound mechanism for both the cylinder and sphere [49]. Figure 8 illustrates the resistance factor N

_{T-bar}values for the strain rate correlation and strain softening effects of the T-bar penetrometer [41].

#### 3.2. Numerical Simulation

_{u,ref}is the value of the resistance factor at the strain rate γ

_{ref}= 1%/h.

_{us}and sui are the softened strength and initial strength, respectively; δ

_{rem}is the damage factor value for soft soils at full remodeling and is the ratio of the shear strength of fully remodeled soils to the shear strength of de-primed soils, which is the reciprocal of the sensitivity S

_{t}; and ξ

_{95}is the cumulative plastic shear strain corresponding to the remodeled soils when the remodeling damage reaches 95%.

#### 3.3. Laboratory Model Test

- 1.
- Development of the calibration laboratory model tank test

**Figure 17.**The University of Oklahoma calibration chamber. (

**a**) Schematic diagram of the University of Oklahoma calibration chamber; (

**b**) picture of University of Oklahoma calibration chamber [61].

- 2.
- Boundary state control for calibration tank tests

_{v}is the axial stress, and σ

_{h1}~σ

_{hn}are the transverse stresses, i.e., the force states in the horizontal direction at different locations of the soil sample, which can be controlled.

- 3.
- Factors influencing the calibration tank test

- Boundary effects

- Size effect

#### 3.4. In Situ Test

#### 3.4.1. Cyclic Penetration Tests

_{u}of the soft soil gradually decreases; as reflected in the result, the penetration resistance gradually drops and stabilizes. A graph of the decay of the penetration resistance with the increasing number of penetrations can be made as depicted in Figure 22; the calculated curve and the measured data are compared and analyzed, and on this basis, the parameters δ

_{rem}and ξ

_{95}are used to calibrate [49]. After one lifting cycle, the undrained shear strength of the soft soil produces a decrease of approximately 10%, and generally, after a process of 10 cycles, the soft soil reaches a fully remodeled state, and the undrained shear strength is stabilized. In the derivation of the cyclic resistance, the penetration resistance is normalized by the initial resistance for each cycle. As the soil begins to soften during the first penetration, the final normalized resistance is typically greater than the true value of δ

_{rem}.

#### 3.4.2. Variable Rate Penetration Experiments

_{v}is the vertical coefficient of consolidation for soft soils.

## 4. Application of the T-Bar Penetrometer for Marine Soft Soil Engineering

#### 4.1. Evaluation of the Undrained Shear Strength of Soft Marine Soils

_{T-bar}obtained in these tests, as shown in Table 5, where data a are from Lunne [69], data b are from Randolph [18], and data c are from the authors of this paper. The authors of this paper agree with Lunne and Randolph that the N factors derived empirically from s

_{u}were found to be in the range of 7.2–14.3 for the T-bar [18,69]. To support the determination of the empirical N

_{T-bar}values in the Wenzhou, China test site, the vane shear tests (VSTs) were set at a distance of 1 m from each T-bar penetration test by the authors. A site-specific resistance factor N

_{T-bar}can be estimated from a linear-fitted slope of s

_{u}versus q

_{net}(Figure 24) for the Wenzhou test site based on the VSTs measured strengths, as the reference strengths increase linearly with depth. The calculated average for the resistance factor N

_{T-bar}of the spot determined by the VSTs data is 12.0, which is consistent with the study conducted by Lunne [69].

_{u}can be derived from the ratio of the penetration resistance and the resistance factor through Equation (10) [70,71] as follows:

_{T-bar}and N

_{kt}are the resistance factors for the T-bar and CPTU, respectively. The numerical solution based on the numerical analysis can be used to estimate the undrained shear strength of soft soils based on the penetration resistance, but the numerical solution cannot take into account all the factors affecting the variation of the penetration resistance under actual conditions and does not have a high degree of reliability when applied in practice. Therefore, it is necessary to correct the theoretical numerical solution to obtain the empirical equation by employing the experimental solution obtained from site-specific tests on multiple sites.

_{u}, and q

_{net}is also summarized.

#### 4.2. Sensitivity Evaluation of Marine Soft Soils

_{t}can be calculated from the in situ undrained shear strength s

_{u}and the fully remodeled undrained shear strength s

_{ur}measured by the full-flow cycle penetration test of the full-flow penetrometer using Equation (11).

_{in}is the penetration resistance at the initial penetration, and q

_{rem}is the penetration resistance at the end of the complete remodeling cycle.

_{T-Bar}, with the value of N

_{T-bar}decreasing as the sensitivity of the soil increases. Dejong et al. (2010) summarized the empirical equation for the resistance factor N

_{T-bar}with the sensitivity S

_{t}from the experimental result [16].

_{T-bar,rem}and the sensitivity of the soil [43].

_{T-bar}, the sensitivity S

_{t}of the vane shear test, and the extraction factor of the T-bar penetration test. The curve of Equation (6) in Figure 27a is the fitted curve corresponding to Equation (12). Despite the large dispersion in the data, Equation (6) still fits well for soft soil sensitivities of less than 20 (Figure 27a), but there is a large error in Equation (12) for soft soils with high sensitivities.

_{T-bar}of the penetrometer increases with the increase of q

_{in}/q

_{ext}, and has the following relationship:

_{T-bar}versus q

_{in}/q

_{ext}.

^{2}values of 0.95, with a minor increase in the prediction confidence compared with Equation (13) (Figure 28). The results of soil remolding by the full-flow penetrometers were examined through cyclic testing and field vane shear tests at all test sites.

#### 4.3. Discussion and Conclusions

_{T-bar}and q

_{ball}) are correlated with the undrained shear strength values. Moreover, the inferred undrained shear strength derived from the T-bar (or ball) penetration resistance appears to provide a robust predictive basis for assessing the bearing capacity of foundation elements, as illustrated by Watson (1999) [73].

Geotechnical Problem | Depth Below Seabed (m) | Comment | Applicability–Reliability | |||
---|---|---|---|---|---|---|

CPTU | T-bar, ball (Fitted with Pore Water Pressure Sensors) | |||||

Soil Profiling | Soil Parameters Interpreted | Soil Profiling | Soil Parameters Interpreted | |||

Backfilled trenches: upheaval buckling | 0–1 | Extremely soft material may be encountered | Soil profile ^{1,2} | γ ^{2}, u ^{2}, OCR ^{3}, K_{0} ^{4,5}, s_{u} ^{2,3}, s_{ru} ^{5}, S_{t} ^{2,3}, c’ ^{3,4}, φ’ ^{3,4}, G_{max} ^{4}, E ^{5}, G ^{5}, M ^{5}, k ^{2–4}, c_{h} ^{2,3} | Soil profile ^{3} | u ^{2}, OCR ^{3}, s_{u} ^{1,2}, s_{ru} ^{1,2}, S_{t} ^{1,2}, k ^{2−4}, c_{h} ^{2,3} |

Pipeline–riser soil interaction | 0–3 | Very soft material may be encountered | Soil profile ^{1,2}Classification ^{2} | γ ^{2}, u ^{2}, OCR ^{3}, K_{0} ^{4,5}, s_{u} ^{2,3}, s_{ru} ^{5}, S_{t} ^{2,3}, c’ ^{3,4}, φ’ ^{3,4}, G_{max} ^{4}, E ^{5}, G ^{5}, M ^{5}, k ^{2−4}, c_{h} ^{2,3} | Soil profile ^{3} | u ^{2}, OCR ^{3}, s_{u} ^{1,2}, s_{ru} ^{1,2}, S_{t} ^{1,2}, k ^{2−4}, c_{h} ^{2,3} |

Seabed templates, penetration, stability, settlements | 0–10 | - | Soil profile ^{1,2}Classification ^{2} | γ ^{2}, u ^{2}, OCR ^{3}, K_{0} ^{4,5}, s_{u} ^{2,3}, s_{ru} ^{5}, S_{t} ^{2,3}, c’ ^{3,4}, φ’ ^{3,4}, G_{max} ^{4}, E ^{5}, G ^{5}, M ^{5}, k ^{2−4}, c_{h} ^{2,3} | Soil profile ^{3} | u ^{2}, OCR ^{3}, s_{u} ^{1,2}, s_{ru} ^{1,2}, S_{t} ^{1,2}, k ^{2−4}, c_{h} ^{2,3} |

Geohazards; slope stability | 0–10/100 | Use of T-bar, ball, and vane may be limited to 40 m depth | Soil profile ^{1,2}Classification ^{2} | γ ^{2}, u ^{2}, OCR ^{3}, K_{0} ^{4,5}, s_{u} ^{2,3}, s_{ru} ^{5}, S_{t} ^{2,3}, c’ ^{3,4}, φ’ ^{3,4}, G_{max} ^{4}, E ^{5}, G ^{5}, M ^{5}, k ^{2−4}, c_{h} ^{2,3} | Soil profile ^{3} | u ^{2}, OCR ^{3}, s_{u} ^{1,2}, s_{ru} ^{1,2}, S_{t} ^{1,2}, k ^{2−4}, c_{h} ^{2,3} |

^{1}: high reliability;

^{2}: high-moderate reliability;

^{3}: moderate reliability;

^{4}: moderate-low reliability;

^{5}: low reliability; γ: soil unit weight; u: in situ pore pressure; OCR: overconsolidalion ratio; K

_{0}: coefficient of earth pressure at rest; s

_{u}: undrained shear strength; s

_{ur}: remolded undrained shear strength; S

_{t}: sensitivity; c’, φ’: effective stress shear strength parameters; E, G: Young’s and shear modulus; M: constrained modulus; G

_{max}: small strain shear modulus; k: coefficient of permeability; and c

_{h}: coefficient of consolidation.

## 5. Summary and Outlook

- 1.
- An analysis of the theoretical solution of the T-bar penetrometer data. In practical applications, the interpretation of the T-bar penetrometer test data to predict the undrained shear strength and sensitivity of soft soils mainly relies on empirical formulas. However, the evaluated parameters of soft soils through the empirical relationship method lack reliability due to the absence of a large amount of reliable test data. This problem can be solved by gaining a deeper understanding of the mechanism of the T-bar full-flow test evaluation system and the derivation of a more accurate theoretical analytical solution.
- 2.
- The numerical simulation of the T-bar full-flow penetrometer. Recently, the numerical simulation of the T-bar penetrometer is proposed by researchers, which considers the effects of the strain rate, strain softening, and strength anisotropy. However, it is difficult to restore the soil material and the penetration process in the simulation process nowadays, and further development of numerical techniques is needed.
- 3.
- The laboratory model experiment of the T-bar penetrometer. Most of the present research on laboratory model experiments is focused on the traditional CPTU testing of sandy soils, while the research on the penetration mechanism of the T-bar full-flow penetrometer of soft soil is still insufficient.
- 4.
- The T-bar penetrometer field experimental research. The good performance of the T-bar penetrometer technology depends on the large number of accurate field test data, which are used for repeated verification and calibration. In recent years, the T-bar penetrometer technology has mainly been used in Europe and the United States, and the test results are usually available for these areas. However, in many Asian countries, such as China, the research and application of the T-bar penetrometer technology is still in its infancy. Therefore, a large number of field tests still need to be conducted to verify the applicability of the T-bar penetrometer in soft coastal soils in Asian countries.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

- Baumert, H.Z.; Simpson, J.; Simpson, J.H.; Sündermann, J. Marine Turbulence: Theories, Observations, and Models; Cambridge University Press: Cambridge, UK, 2005. [Google Scholar]
- Guo, Z.; Jeng, D.-S.; Guo, W.; Wang, L. Failure mode and capacity of suction caisson under inclined short-term static and one-way cyclic loadings. Mar. Georesources Geotechnol.
**2018**, 36, 52–63. [Google Scholar] - Guo, Z.; Zhou, W.; Zhu, C.; Yuan, F.; Rui, S. Numerical simulations of wave-induced soil erosion in silty sand seabeds. Engineering
**2019**, 7, 52. [Google Scholar] - Lei, H.; Lu, H.; Wang, X.; Ren, Q.; Li, B. Changes in soil micro-structure for natural soft clay under accelerated creep condition. Geotechnology
**2016**, 34, 365–375. [Google Scholar] [CrossRef] - Lei, H.; Xu, Y.; Jiang, M.; Jiang, Y. Deformation and fabric of soft marine clay at various cyclic load stages. Ocean Eng.
**2020**, 195, 106757. [Google Scholar] [CrossRef] - Randolph, M.; Cassidy, M.; Gourvenec, S.; Erbrich, C. Challenges of offshore geotechnical engineering. In Proceedings of the 16th International Conference on Soil Mechanics and Geotechnical Engineering, Lahore, Pakistan, 7–8 December 2022; p. 123. [Google Scholar]
- Shan, Y.; Meng, Q.; Yu, S.; Mo, H.; Li, Y. Energy based cyclic strength for the influence of mineral composition on artificial marine clay. Eng. Geol.
**2020**, 274, 105713. [Google Scholar] [CrossRef] - Yang, Y. Research on Penetration Mechanism and Application of Ball Penetrometer in Offshore Engineering. Master’s Thesis, Southeast University, Nanjing, China, 2018. [Google Scholar]
- Guo, Z.; Yu, L.; Wang, L.; Bhattacharya, S.; Nikitas, G.; Xing, Y. Model tests on the long-term dynamic performance of offshore wind turbines founded on monopiles in sand. J. Offshore Mech. Arct. Eng.
**2015**, 137, 041902. [Google Scholar] [CrossRef] - Guo, Z.; Hong, Y.; Jeng, D.-S. Structure–Seabed Interactions in Marine Environments. J. Mar. Sci. Eng.
**2021**, 9, 972. [Google Scholar] [CrossRef] - Jewell, R.A. The mechanics of reinforcede bankments on soft soils. Geotext. Geomembr.
**1988**, 7, 237–273. [Google Scholar] - Lunne, T.; Andersen, K.H.; Low, H.E.; Randolph, M.F.; Sjursen, M. Guidelines for offshore in situ testing and interpretation in deepwater soft clays. Can. Geotech. J.
**2011**, 48, 543–556. [Google Scholar] - Lei, H.; Lu, H.; Liu, J.; Zheng, G. Experimental study of the clogging of dredger fills under vacuum preloading. Int. J. Geomech.
**2017**, 17, 04017117. [Google Scholar] [CrossRef] - Lei, H.; Liu, X.; Wang, P.; Liu, J.; Hu, Y. Experimental investigation of influence of air-boost pressure and duration on air-boost vacuum preloading consolidation. Int. J. Geomech.
**2021**, 21, 04021088. [Google Scholar] [CrossRef] - Duan, W.; Cai, G.; Liu, S.; Puppala, A.J.; Chen, R. In-situ evaluation of undrained shear strength from seismic piezocone penetration tests for soft marine clay in Jiangsu, China. Transp. Geotech.
**2019**, 20, 100253. [Google Scholar] [CrossRef] - Dejong, J.; Yafrate, N.; Degroot, D.; Low, H.E.; Randolph, M. Recommended practice for full-flow penetrometer testing and analysis. ASTM Geotech. Test. J.
**2010**, 33, 137–149. [Google Scholar] - Randolph, M. Characterization of soft sediments for offshore applications. Proc. ISC-2 Geotech. Geophys. Site Charact.
**2004**, 2004, 10017599903. [Google Scholar] - Lunne, T.; Powell, J.J.; Robertson, P.K. Cone Penetration Testing in Geotechnical Practice; CRC Press: Boca Raton, FL, USA, 2002. [Google Scholar]
- Duan, W.; Congress, S.S.C.; Cai, G.; Liu, S.; Dong, X.; Chen, R.; Liu, X. A hybrid GMDH neural network and logistic regression framework for state parameter–based liquefaction evaluation. Can. Geotech. J.
**2021**, 99, 1801–1811. [Google Scholar] [CrossRef] - Duan, W.; Congress, S.S.C.; Cai, G.; Zhao, Z.; Liu, S.; Dong, X.; Chen, R.; Qiao, H. Prediction of in situ state parameter of sandy deposits from CPT measurements using optimized GMDH-type neural networks. Acta Geotech.
**2022**, 17, 4515–4535. [Google Scholar] [CrossRef] - Cai, G.; Liu, S.; Peng, P.; Yang, Y. Theory and Engineering Application of Marine In Situ Testing Technology, 1st ed.; Science Press: Beijing, China, 2021. [Google Scholar]
- Liu, X.; Shen, J.; Yang, M.; Cai, G.; Liu, S. Subsurface characterization of a construction site in Nanjing, China using ERT and CPTU methods. Eng. Geol.
**2022**, 299, 106563. [Google Scholar] [CrossRef] - Zhang, W.; Liu, K.; Wang, D.; Zheng, J. Coefficient of consolidation measured by cone penetration tests in overconsolidated cohesive soils. Ocean Eng.
**2023**, 276, 114301. [Google Scholar] [CrossRef] - Lin, J.; Hou, X.; Cai, G.; Liu, S. Uncertainty analysis of axial pile capacity in layered soils by the piezocone penetration test. Front. Earth Sci.
**2022**, 10, 443. [Google Scholar] [CrossRef] - Zhou, H.; Randolph, M.F. Resistance of full-flow penetrometers in rate-dependent and strain-softening clay. Géotechnique
**2009**, 59, 79–86. [Google Scholar] [CrossRef] - Liu, K.; Wang, D.; Zheng, J. Numerical study of piezoball dissipation test with penetration under partially drained conditions. Comput. Geotech.
**2023**, 159, 105469. [Google Scholar] [CrossRef] - Guo, X.; Nian, T.; Gu, Z. A fluid mechanics approach to evaluating marine soft clay strength by a ball full-flow penetrometer. Appl. Ocean Res.
**2021**, 116, 102865. [Google Scholar] [CrossRef] - Li, C.; Yu, L.; Kong, X.; Zhang, H. Estimation of undrained shear strength in rate-dependent and strain-softening surficial marine clay using ball penetrometer. Comput. Geotech.
**2023**, 153, 105084. [Google Scholar] [CrossRef] - Yu, L.; Yang, Q.; Zhang, J. Undrained bearing capacity of irregular T-bar by the lower bound method in clay. Appl. Ocean Res.
**2020**, 105, 102409. [Google Scholar] [CrossRef] - Guo, X.; Nian, T.; Zhao, W.; Gu, Z.; Liu, C.; Liu, X.; Jia, Y. Centrifuge experiment on the penetration test for evaluating undrained strength of deep-sea surface soils. Int. J. Min. Sci. Technol.
**2022**, 32, 363–373. [Google Scholar] [CrossRef] - Yang, Y.; Zhou, X.; Zhou, M.; Zhang, X. The behavior of ball penetrometer in soft-over-stiff soil deposits. Ocean Eng.
**2023**, 273, 114011. [Google Scholar] [CrossRef] - Lunne, T. The CPT in offshore soil investigations-a historic perspective. Proc. CPT
**2010**, 10, 71–113. [Google Scholar] - Cai, G.; Liu, S.; Puppala, A.J. Comparative performance of the international piezocone and China CPT in Jiangsu Quaternary clays of China. Transp. Geotech.
**2015**, 3, 1–14. [Google Scholar] [CrossRef] - Hanzawa, H.; Tanaka, H. Normalized undrained strength of clay in the normally consolidated state and in the field. Soils Found.
**1992**, 32, 132–148. [Google Scholar] [CrossRef] - Li, S.M. Research on the Mechanical Structures of CPT System on Seabed of Shallow Ocean Area. Ph.D. Thesis, Jilin University, Changchun, China, 2005. [Google Scholar]
- Shi, Y.H. Key Technology Research of the Cone Penetration Test (CPT) on Seabottom. Master’s Thesis, Ocean University of China, Qingdao, China, 2005. [Google Scholar]
- Chung, S.F.; Randolph, M.F.; Schneider, J.A. Effect of penetration rate on penetrometer resistance in clay. J. Geotech. Geoenviron. Eng.
**2006**, 132, 1188–1196. [Google Scholar] [CrossRef] - Kelly, R.; O’Loughlin, C.; Bates, L.; Gourvenec, S.; Colreavy, C.; White, D.; Gaone, F.; Doherty, J.; Randolph, M.F. In situ testing at the national soft soil field testing facility, Ballina, New South Wales. Aust. Geomech. J.
**2014**, 49, 15–28. [Google Scholar] - Randolph, M.; Hefer, P.; Geise, J.; Watson, P. Improved seabed strenght profiling using T-bar penetrometer. In Proceedings of the Offshore Site Investigation and Foundation Behaviour: New Frontiers—Proceedings of an International Conference, London, UK, 22–24 September 1998. [Google Scholar]
- Kelleher, P.; Randolph, M. Seabed geotechnical characterisation with a ball penetrometer deployed from the portable remotely operated drill. In Proceedings of the 1st International Symposium on Frontiers in Offshore Geotechnics, Lisse, Switzerland, 15 August 2005; pp. 365–371. [Google Scholar]
- Randolph, M. Analytical contributions to offshore geotechnical engineering. 2nd McClelland Lecture. In Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, France, 2–6 September 2013. [Google Scholar]
- Weemees, I.; Howie, J.; Woeller, D.; Sharp, J.; Cargill, E.; Greig, J. Improved techniques for the in-situ determination of undrained shear strength of soft clays. In Proceedings of the Sea to Sky Geotechnics, 59th Canadian Geotechnical Conference, Vancouver, BC, Canada, 1–4 October 2006; pp. 1–4. [Google Scholar]
- Yafrate, N.J.; DeJong, J.T.; DeGroot, D.J. The influence of full-flow penetrometer area ratio on penetration resistance and undrained and remoulded shear strength. In Proceedings of the Offshore Site Investigation and Geotechnics: Confronting New Challenges and Sharing Knowledge, London, UK, 11–13 September 2007. [Google Scholar]
- Low, H.E.; Lunne, T.; Andersen, K.H.; Sjursen, M.A.; Li, X.; Randolph, M.F. Estimation of intact and remoulded undrained shear strengths from penetration tests in soft clays. Géotechnique
**2010**, 60, 843–859. [Google Scholar] [CrossRef] - Yafrate, N.; Dejong, J.; Degroot, D.; Randolph, M. Evaluation of Remolded Shear Strength and Sensitivity of Soft Clay Using Full-Flow Penetrometers. J. Geotech. Geoenviron. Eng.
**2009**, 135, 1179–1189. [Google Scholar] [CrossRef] - Martin, C.M.; Randolph, M.F. Upper-bound analysis of lateral pile capacity in cohesive soil. Géotechnique
**2006**, 56, 141–145. [Google Scholar] [CrossRef] - Randolph, M.F.; Houlsby, G.T. The limiting pressure on a circular pile loaded laterally in cohesive soil. Geotechnique
**1984**, 34, 613–623. [Google Scholar] [CrossRef] - Randolph, M.; Martin, C.; Hu, Y.J.G. Limiting resistance of a spherical penetrometer in cohesive material. Geotechnique
**2000**, 50, 573–582. [Google Scholar] [CrossRef] - Einav, I.; Randolph, M.F. Combining upper bound and strain path methods for evaluating penetration resistance. Int. J. Numer. Methods Eng.
**2005**, 63, 1991–2016. [Google Scholar] [CrossRef] - Zhou, H.; Randolph, M.F. Numerical investigations into cycling of full-flow penetrometers in soft clay. Géotechnique
**2009**, 59, 801–812. [Google Scholar] [CrossRef] - Klar, A.; Pinkert, S. Steady-state solution for cylindrical penetrometers. Int. J. Numer. Anal. Methods Geomech.
**2010**, 34, 645–659. [Google Scholar] [CrossRef] - Zhou, H.; Randolph, M. Effect of shaft on resistance of a ball penetrometer. Géotechnique
**2011**, 61, 973–981. [Google Scholar] [CrossRef] - Randolph, M.F.; Andersen, K.H. Numerical analysis of T-bar penetration in soft clay. Int. J. Geomech.
**2006**, 6, 411–420. [Google Scholar] [CrossRef] - Fan, Q.; Luan, M.; Liu, Z. Numerical simulation of penetration resistance of T-bar penetrometer in soft clay. Rock Soil Mech.
**2009**, 30, 2850–2854. [Google Scholar] - Parkin, A. The calibration of cone penetrometers. In Proceedings of the International Symposium on Penetration Testing (ISOPT-1. 1), Orlando, FL, USA, 20–24 March 1988; pp. 221–243. [Google Scholar]
- Ghionna, V.; Jamiolkowski, M. A critical appraisal of calibration chamber testing of sands. In Proceedings of the 1st International Symposium on Calibration Chamber Testing, New York, NY, USA, 28–29 June 1991; pp. 13–39. [Google Scholar]
- Holden, J. The calibration of electrical penetrometers in sand. Nor. Geotech. Inst. Intern. Rep.
**1976**, 55, 345–354. [Google Scholar] - Tcheng, Y. Fondations profonds en milieu pulverulent a diverses compacities. Ann. De I’Institut Tech. Du Batim. Et Des Trav. Publics Sols Et Fond.
**1966**, 54, 219–220. [Google Scholar] - Villet, W.C.; Mitchell, J.K. Cone resistance, relative density and friction angle. In Proceedings of the Cone Penetration Testing and Experience, St. Louis, MO, USA, 26–30 October 1981; pp. 178–208. [Google Scholar]
- Pournaghiazar, M.; Russell, A.; Khalili, N. CPT in unsaturated soils using a new calibration chamber. In Proceedings of the 2nd International Symposium on Cone Penetration Testing, Huntington Beach, CA, USA, 9–11 May 2010. [Google Scholar]
- Tan, N.K. Pressuremeter and Cone Penetrometer Testing in a Calibration Chamber with Unsaturated Minco Silt; The University of Oklahoma: Norman, OK, USA, 2005. [Google Scholar]
- Huang, A.-B.; Hsu, H.-H. Cone penetration tests under simulated field conditions. Geotechnique
**2005**, 55, 345–354. [Google Scholar] [CrossRef] - Parkin, A.; Lunne, T. Boundary Effects in the Laboratory Calibration of a Cone Penetrometer for Sand. Presented at the 2nd (European Symposium on Penetration Testing (ESOPT II); Amsterdam, The Netherlands, 24–27 May 1982; pp. 1–7. [Google Scholar]
- Salgado, R.; Mitchell, J.; Jamiolkowski, M. Cavity expansion and penetration resistance in sand. J. Geotech. Geoenviron. Eng.
**1997**, 123, 344–354. [Google Scholar] [CrossRef] - Schnaid, F.; Houlsby, G.T. An assessment of chamber size effects in the calibration of in situ tests in sand. Geotechnique
**1991**, 41, 437–445. [Google Scholar] [CrossRef] - Wesley, L.D. Interpretation of calibration chamber tests involving cone penetrometers in sands. Geotechnique
**2002**, 52, 289–293. [Google Scholar] [CrossRef] - House, A.; Oliveira, J.; Randolph, M.F. Evaluating the coefficient of consolidation using penetration tests. Int. J. Phys. Model. Geotech.
**2001**, 1, 17–26. [Google Scholar] [CrossRef] - DeJong, J.T.; Yafrate, N.J.; DeGroot, D. Evaluation of undrained shear strength using full-flow penetrometers. J. Geotech. Geoenviron. Eng.
**2011**, 137, 14–26. [Google Scholar] [CrossRef] - Lunne, T.; Randolph, M.; Chung, S.; Andersen, K.; Sjursen, M. Comparison of cone and T-bar factors in two onshore and one offshore clay sediments. In Frontiers in Offshore Geotechnics (Proc. ISFOG-1, Perth); Taylor & Francis Group: London, UK, 2005; pp. 981–989. [Google Scholar]
- Jorat, M.; Mörz, T.; Schunn, W.; Kreiter, S.; Moon, V.; de Lange, W. Geotechnical Offshore Seabed Tool (GOST): A new cone penetrometer. In Proceedings of the 3rd International Symposium on Cone Penetration Testing, Las Vegas, NV, USA, 12–14 May 2014; pp. 207–215. [Google Scholar]
- Tand, K.; Funegard, E.; Warden, P. Predicted/measured bearing capacity of shallow footings on sand. In Proceedings of the International Symposium on Cone Penetration Testing (CPT’95), Linköping, Sweden, 4–5 October 1995; pp. 589–594. [Google Scholar]
- Oliveira, J.; Almeida, M. Pore-pressure generation in cyclic T-bar tests on clayey soil. Int. J. Phys. Model. Geotech.
**2010**, 10, 19–24. [Google Scholar] [CrossRef] - Watson, P. Performance of Skirted Foundations for Offshore Structures. Ph.D. Thesis, The University of Western Australia, Crawley, Australia, 1999. [Google Scholar]
- Colreavy, C. Use of Piezoball Penetrometers for Measuring Shear Strength and Consolidation Characteristics of Soft Soil. Ph.D. Thesis, University of Western Australia, Perth, Australia, 2017. [Google Scholar]

**Figure 1.**Schematic diagram of the internal structure of the CPTU [17].

**Figure 2.**Full-flow penetrometers (T-bar, ball, and plate) [25].

**Figure 4.**T-bar and ball penetrometer and full-flow of soil during penetration. (

**a**) T-bar and ball penetrometer; (

**b**) soil full-flow [40].

**Figure 5.**Plasticity solution of resistance factor with a surface friction coefficient for three types of penetrometers [6].

**Figure 6.**Stress characteristic fields for T-bar (

**left**) and ball (

**right**): interface friction coefficient, α = (

**a**) 0, (

**b**) 0.5, (

**c**) 1 [48].

**Figure 7.**Upper bound mechanism for both cylinder and sphere [49].

**Figure 8.**Resistance factor N

_{T-bar}values for strain rate correlation and strain softening effects of T-bar penetrometer [41].

**Figure 9.**Numerical simulation meshing of T-bar full-flow penetrometer [52].

**Figure 10.**Change of shear strength due to strain softening during T-bar full-flow penetration: specific values of normalized resistance, N = (

**A**) 8.3, (

**B**) 8.17, (

**C**) 7.62, (

**D**) 8.24 [52].

**Figure 11.**Effect of strength change before and after penetration via T-bar penetrometer. (

**a**) Penetration 2.5 D; (

**b**) penetration 3D [50].

**Figure 12.**Influence of the number of cycles of penetration on the change in strain distribution [50].

**Figure 13.**Distribution of the extent of remodeling soils affected by T-bar full-flow penetrometer considering the effect of strain rate correlation [50].

**Figure 14.**Cloud chart of vertical stress of soil mass (

**a**) before penetration and (

**b**) after penetration [8].

**Figure 15.**Horizontal stress nephogram of soil mass (

**a**) before penetration and (

**b**) after penetration [8].

**Figure 16.**Specific diagram of the calibration tank. (

**a**) CRB flexible double-walled calibration tank; (

**b**) University of New South Wales calibration tank [58].

**Figure 18.**Calibration tank test with 5 different boundary states [57].

**Figure 19.**Boundary state BC5 for the 5th calibration tank test [62].

**Figure 20.**Boundary condition effects of the CPT calibration tank test for two boundary conditions, BC1 and BC3 [63].

**Figure 21.**The T-bar penetrometer cyclic penetration test [49].

**Figure 22.**Normalized penetration resistance decays as the cyclic penetration test proceeds [49].

**Figure 23.**Standard and unstable rate cone penetration test [18].

**Figure 24.**Relationship between net penetration resistance and undrained shear strength at the Wenzhou test site.

**Figure 25.**Variation of T-bar, ball, and CPTU resistance factors N with depth, undrained shear strength, and net penetration resistance [70].

**Figure 26.**Distribution of resistance factors for various probes at the Onsoy site in Norway. (

**a**) Histogram of N

_{T-bar}distribution with normal distribution probability density function; (

**b**) normal distribution probability density function (PDF) for three probes with resistance factor N [70].

**Figure 27.**Relationship between the resistance factor N

_{T-bar}and (

**a**) the sensitivity of the vane shear test S

_{t}and (

**b**) the extraction factor q

_{in}/q

_{ext}[43].

**Figure 28.**Relationship between the sensitivity of the vane shear test S

_{t}and the extraction factor q

_{in}/q

_{ext}.

**Table 1.**Summary of the main development of marine penetrometer deployment technology [32].

Penetration Mechanism/ Main Penetration Equipment | Date | Equipment | Company | Notes |
---|---|---|---|---|

Discontinuous push Hydraulic cylinder | 1972.3 | Dead weight operated from platform | NGI, Norway/McClelland, Houston, Texas, USA | Max 4 m penetration reached in dense sand |

1972.3 | Seacalf | Fugro, The Netherlands | 25 m penetration reached in 130 m water depth | |

1974 | Stingray | McClelland, Houston, Texas, USA | Push on drill pipe, not on cone rod | |

1976 | Diving bell | Delf Soil Mechanics Laboratory (Deltares) | 600 kN reaction force, 60 m penetration achieved | |

1991 | SCOPE | Geo, Denmark | Self-leveling | |

Continuous push | 1983 | ROSON | APvandenBerg/ D’Appolonia | Roller wheels |

1984 | Modified BORROS rig | McClelland, Houston, Texas, USA | Synopticated hydraulic cylinders | |

1984 | Wheel drive Seacalf | Fugro, Netherlands | Roller wheels | |

2010 | DeepCPT | Gregg Drilling & Testing Inc., California, USA | Suction anchor; 200 kN thrust capacity, 10 and 15 cm ^{2} cones | |

Coiled rod (on full size rods) | 2000 | Penfeld | IFREMER, France | Self-powered by lead batteries. Can penetrate to 30 m |

Seabed drilling Test and sampling rigs | 2001 | PROD | Benthic, Australia | Rods stored in carousel on sea bottom |

Combined rig | 1997 | Searobin | Fugro, The Netherlands | Can take sample to 1 m and perform 10 cm ^{2} CPT to 2m in one deployment |

2001 | Geoceptor | Geo, Denmark | Can take sample to 6 m and perform 10 cm ^{2} CPT to10 m in one deployment | |

Minirigs | 1992 | Seascout | Fugro, The Netherlands | Coiled rod, wt < 1 ton, 1 cm ^{2} cone penetrometer |

1999 | MiniCPT | Gregg Drilling & Testing Inc., California, USA | Coiled rod; 2 cm^{2} conesup to 12 m penetration | |

2000 | Neptune | DATEM, UK | Coiled rod, 5 and 10 cm^{2}cones; up to 20 m penetration | |

ROV mounted | 1983 | Mini Wison | Fugro, The Netherlands | 1 m stroke, 5 cm^{2} conepenetrometer |

Production Companies | Type of Touch | Equipment Model | Max Penetration Reached Depth (m) |
---|---|---|---|

A.P. van den Berg Corp., Heerenveen, The Netherlands | Downhole CPT | Wison-APB downhole mode deep-sea CPT system | 3000 |

A.P. van den Berg Corp., Heerenveen, The Netherlands | Seabed CPT | Roson seabed mode deep-sea CPT system for the seabed | 4000 |

Geomil Corp., Moordrecht, The Netherlands | Seabed CPT | MANTA seabed mode CPT system | 2000 |

Datem Corp., Sleaford, UK | Seabed CPT | Neptune 5000 Standard Marine CPT | 3000 |

Fugro Corp., Leidschendam, The Netherlands | Seabed CPT | SEACALF seabed mode CPT system | 4000 |

**Table 3.**Calibration tank system statistics [55].

Calibration Tank (Inventor or Unit) | Design Time | Calibration Tank Type | Soil Sample Size | Boundary Conditions | |||
---|---|---|---|---|---|---|---|

Diameter (m) | Height (m) | Radial Boundaries | Bottom | Top | |||

National Roads Australia | 1969 | Double wall | 0.76 | 0.91 | Flexibility | Bedding | Rigid |

University of Florida, USA | 1971 | Double wall | 1.20 | 1.20 | Flexibility | Bedding | Rigid |

Monash University, Australia | 1974 | Double wall | 1.20 | 1.80 | Flexibility | Bedding | Rigid |

Norwegian Institute of Geotechnical Engineering | 1979 | Double wall | 1.20 | 1.50 | Flexibility | Bedding | Just |

Italian Electricity Commission | 1982 | Double wall | 1.20 | 1.50 | Flexibility | Bedding | Rigid |

1982 | Double wall | 0.60 | 1.00 | Flexibility | Bedding | Rigid | |

ISMES Laboratory, Italy | 1986 | Double wall | 1.20 | 1.50 | Flexibility | Bedding | Rigid |

University of California, USA | 1975 | Single wall | 0.76 | 0.80 | Flexibility | Rigid | Rigid |

University of Texas, USA | 1984 | Single wall | Square: 2.1 × 2.1 × 2.1 | Flexibility | Flexibility | Flexibility | |

1993 | Single wall | 0.60 | 1.20 | Flexibility | Bedding | Rigid | |

2008 | Single wall | 1.37 | 2.13 | Flexibility | Bedding | Rigid | |

University of Houston, USA | 1991 | Single wall | 0.76 | 2.54 | Flexibility | Bedding | Bedding |

North Carolina State University, USA | 1991 | Single wall | 0.94 | 1.00 | Flexibility | Rigid | Rigid |

University of Louisiana, USA | 1992 | Double wall | 0.55 | 0.80 | Flexibility | Flexibility | Rigid |

Gouda Group Canada | 1991 | Single wall | 1.40 | 1.00 | Flexibility | Rigid | Bedding |

Virginia Tech, USA | 1987 | Single wall | 1.50 | 1.50 | Flexibility | Rigid | Rigid |

University of Grenoble, France | 1991 | Single wall | 1.20 | 1.50 | Flexibility | Bedding | Bedding |

University of Oxford, UK | 1988 | Single wall | 0.90 | 1.10 | Flexibility | Bedding | Rigid |

University of Tokyo, Japan | 1988 | Single wall | 0.90 | 1.10 | Flexibility | Rigid | Rigid |

Clarkson University, USA | 2006 | Single wall | 0.51 | 0.76 | Flexibility | Rigid | Rigid |

University of Sheffield, UK | 1991 | Single wall | 0.79 | 1.00 | Flexibility | Rigid | Flexibility |

2003 | Single wall | 0.40 | 0.42 | Flexibility | Bedding | Rigid | |

Cornell University, USA | 1991 | Single wall | 2.10 | 2.90 | Flexibility | Rigid | Rigid |

American Waterways Experiment Station | 1991 | Single wall | 0.80–3.00 | 0.6 × X | Flexibility | Rigid | Rigid |

National Chiao Tung University, Taiwan | 1991 | Double wall | 0.51 | 0.76 | Flexibility | Rigid | Rigid |

1998 | Single wall | 0.79 | 1.60 | Flexibility | Rigid | Bedding | |

1988 | Double wall | 0.20 | 0.36 | Flexibility | Bedding | Rigid | |

Osaka University, Japan | 2008 | Double wall | 1.40 | 1.45 | Flexibility | Rigid | Bedding |

Technical University of Gdansk, Poland | 2006 | Double wall | 0.53 | 1.00 | Flexibility | Bedding | Rigid |

University of Oklahoma, USA | 2002 | Single wall | 0.61 | 0.45–1.42 | Flexibility | Bedding | Rigid |

University of New South Wales, Australia | 2010 | Single wall | 0.46 | 0.80 | Flexibility | Bedding | Rigid |

**Table 4.**Four boundary conditions for the calibration tank test [57].

Boundary Conditions | Vertical | Horizontal | ||
---|---|---|---|---|

Stress/σ_{v} | Strain/ε_{v} | Stress/σ_{h} | Strain/ε_{h} | |

BC1 | Constant | -- | Constant | -- |

BC2 | -- | 0 | -- | 0 |

BC3 | Constant | -- | -- | 0 |

BC4 | -- | 0 | Constant | -- |

**Table 5.**Empirical values of resistance factors N

_{T-bar}obtained by the University of Western Australia and Southeast University (in this paper) at different sites.

Location | N_{T-bar-DSS},Average | N_{T-bar-DSS},Rang | N_{T-bar-FVT},Average |
---|---|---|---|

Burswood, Australia | 11.9 ^{b} | - | 10.9 ^{b} |

Onsoy, Norway | 11.9 ^{a}, 12.5 ^{b} | 11.0–13.4 ^{a} | 11.6 ^{b} |

Coastal Australia | 12.4 ^{b} | - | 11.3 ^{b} |

West African Coastal Region | 12.2 ^{b} | - | 12.7 ^{b} |

Watchet Bay, Canada | 13.0 ^{a} | - | - |

Wenzhou, China (this paper) | - | - | 12.0 ^{c} |

^{a}Norwegian Geotechnical Institute tests: Lunne et al. (2005) [69];

^{b}University of Western Australia tests: Randolph (2004) [18];

^{c}Southeast University tests: The authors (in this paper).

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |

© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Qiao, H.; Liu, L.; He, H.; Liu, X.; Liu, X.; Peng, P.
The Practice and Development of T-Bar Penetrometer Tests in Offshore Engineering Investigation: A Comprehensive Review. *J. Mar. Sci. Eng.* **2023**, *11*, 1160.
https://doi.org/10.3390/jmse11061160

**AMA Style**

Qiao H, Liu L, He H, Liu X, Liu X, Peng P.
The Practice and Development of T-Bar Penetrometer Tests in Offshore Engineering Investigation: A Comprehensive Review. *Journal of Marine Science and Engineering*. 2023; 11(6):1160.
https://doi.org/10.3390/jmse11061160

**Chicago/Turabian Style**

Qiao, Huanhuan, Lulu Liu, Huan He, Xiaoyan Liu, Xuening Liu, and Peng Peng.
2023. "The Practice and Development of T-Bar Penetrometer Tests in Offshore Engineering Investigation: A Comprehensive Review" *Journal of Marine Science and Engineering* 11, no. 6: 1160.
https://doi.org/10.3390/jmse11061160