Progress Reports: December 2005 June 2005 December 2004 June 2004 December 2003 June 2003 December 2002 June 2002 December 2001Suction Caissons and Vertically Loaded Anchors
Performance of Suctions Caissons Used to Anchor Structures in Very Deep WaterOBJECTIVE: Suction caissons are being used increasingly as seafloor anchorages for deepwater offshore exploration and production platforms. Data are needed to improve and validate analytical models and design practices. Large-scale data are scarce, and available laboratory data do not address all issues important to the design and installation of suction caissons.
The objective of this research is to perform experiments with small prototype suction caissons in normally consolidated clays, such as encountered in the Gulf of Mexico and other offshore locations. The goals include the study of design issues such as the effect of self weight versus suction penetration, limiting ratio of penetration to diameter during suction installation, consolidation (set-up) times after installation, the influence of internal stiffeners on capacity, effects of loading rates on capacity under axial loading, the effect of cyclic axial loading on capacity, range of capacities under lateral loading with differing durations of loading (drained versus undrained loading), effect of mooring line angle on lateral capacity, effect of the mooring line attachment location, and other relevant effects.
These data are being used in companion projects to develop and validate analytical and design methods for this technology. Potential benefits to the offshore industry and regulatory agencies will stem from the greater reliability of future designs.
APPROACH: Small scale experiments are being conducted in a laboratory. Suction caisson models with a diameter of 100 mm, length of about one meter, and a wall thickness of 0.8 mm (ratio of diameter to wall thickness similar to a full-scale caissons) are being used. The experiments are being conducted in test beds of clay that are made in large tanks. The test bed soil is kaolinite, which was selected to allow deposition from slurry with acceptable consolidation times (about 9 months) and still obtain sediment thick enough to allow testing. The test beds are prepared by mixing the clay and water in an initial tank until the slurry is uniform, and then pumping it into the main tanks. A number of experiments can be performed in a single test bed.
DEPLOYMENT OF RESULTS: The data from these experiments are being used in companion projects to develop and validate analytical and design methods for suction caissons. The experiments and results will be documented in a final report.
PROJECT DURATION: 6 years
PROJECT PLAN FOR YEAR 6 (2004-2005):
Previous Results: Previous test have focused on axial tensile loading and lateral loading. For axial load tests, the caissons were installed using both dead weight, and a combination of dead weight and suction. Pore water pressures were measured to determine set-up time. Axial tensile tests were performed at both short set-up times and after set-up had occurred with the top vented and sealed. Lateral loading tests involved application of essentially horizontal loading. The depth of load application was varied. Tests were performed with both short set-up times and set-up times sufficient to have full drainage, and with the top vented and sealed.
Scope of Work for 2004-2005:
Measurements of Clay Strengths Analysis of the capacity of a suction caisson under vertical and/or lateral loads requires knowledge of the shearing strength of the surrounding clay. However, experience shows that there is no such thing as “the shearing strength”, meaning that measurements using different practical tests yield different strengths. Devices used for field measurements include triaxial compression, field and laboratory vanes, quasi-static cone, and tee-bar tests. Laboratory tests are being conducted with a cone, field vane, and tee bar. Tests in triaxial compression will be investigated although such tests cannot be performed with samples at the water contents encountered in the tank because the soil samples slump under their own weight. Tests to date indicate substantial differences in the “shearing strengths” measured using different devices. Measured side and tip capacities are normalized using the measured strengths so the choice of testing method in the field is important and the effect of testing method on calculated capacity must be understood.
Measurement of Behavior Under Inclined Loading Initial experiments were for entirely vertical or entirely horizontal loading. An apparatus has been completed that allows experiments to be conducted with loads at an angle to simulate actual field applications. Testing will now focus on loading angles in the range of 10 to 60 degrees to explore the actual shapes of load-interaction diagrams.
Separation of Components of Resistance Among the many difficulties in laboratory and field tests, one of the more difficult has been the separation of capacities into components from end bearing, shear on the outside, and shear on the inside. This is particularly difficult for rapid loading with the caisson top sealed (the usual case offshore) because the tip capacity is important and seems generally unknown. Tests will be conducted with a suction caisson composed of two, concentric, very thin aluminum tubes which are sealed at the bottom to prevent intrusion of clay between the walls. The total load in each tube will be measured to allow separation of load transferred on the outside from the load transferred on the inside and at the tip. The inner tube will be strain-gauged to estimate the variation of load with depth, and can provide an estimate of the tip load by extrapolation.
Bender Elements Bender elements are small plates that are attached to a base, e.g., a suction caisson, and are caused to vibrate. The resulting waves are picked up by another bender element, and the shearing modulus can be determined from the time period involved in the wave propagation. With funding from non-OTRC sources, a student is using bender elements to determine the evolution of shear modulii in tank 4 as the clay consolidates. Data collected to date, clearly show the increase in shearing modulus as consolidation occurs. This work may show that bender elements can be used to estimate the time rate of consolidation in clays around suction caissons, and thus the time rate of build up of capacity.
Anticipated Results: A set of high quality laboratory experiments that provide a better understanding the in place performance and installation of suction caissons, and can be used to develop and improve analysis models and design methods. The experiments and results will be documented in a final report.
PRINCIPAL INVESTIGATOR (S) & OTHERS INVOLVED IN PROJECT:
PI(s): Roy E. Olson and Robert B. Gilbert, University of Texas at Austin.
Date: December, 2005
Project Title: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
MMS Project: 362 TO Numbers: 16169/35980
PI: Roy E. Olson and Bob Gilbert
COTR: A. Konczvald
Estimated Completion Date: Completed August 31, 2005
Project Description:
The project involved: (1) preparation of large tanks of normally consolidated clay in a laboratory environment, (2) design and construction of small-scale suction caissons, (3) performance of a suite of tests to measure the behavior of suction caissons under axial, lateral, and inclined loading with the soil drained and undrained, with the top cap open and sealed, with a range of set-up times, and (4) to work with others doing theoretical analyses at both the University of Texas and Texas A and M University, to facilitate the development of design methods.Progress:
The project has been completed. A final report is being completed. A partial draft was submitted to MMS as requested.
Reports & Publications:
M.S. theses, Ph.D. dissertation, and technical publications in the open literature are listed below. Other publications are in the writing stages.
Theses
Pedersen, Robert C. (2001), “Model Offshore Soil Deposit: Design, Preparation, and Characterization”, Univ. of Texas, Austin (May)
Mecham, Elliott C. (2001), “A Laboratory for Measuring the Axial and Lateral Load Capacity of Model Suction Caissons”, University of Texas, Austin (December).
Luke, Adam M. (2002), “Axial Capacity of Suction Caissons in Normally Consolidated Kaolinite”, University of Texas, Austin (January).
Coffman Richard A. (2003), “Horizontal Capacity of Suction Caissons in Normally Consolidated Kaolinite”, M.S. Thesis, University of Texas, Austin (December).
Vanka, Sandeep K. (2004), “Laboratory Tests to Estimate Strength Profile of Normally Consolidated Kaolinite”, M. S. Thesis, University of Texas, Austin (December).
Dissertations
El-Sherbiny, Rami M. (2005), “Performance of Suction Caisson Anchors in Normally Consolidated Clay”, Ph.D. dissertation, University of Texas, Austin, August
Technical Publications Arranged Chronologically
Olson, R. E., A. F. Rauch, A. F. Tassoulas, C. P. Aubeny, and W. R. Murff (2001), “Toward the Design of New Technologies for Deep-Water Anchorages”, International Symposium on Offshore and Polar Engineering, Scavenger, Norway, June
Rauch, A. F., Olson, R.E., Mecham, E. C., Pedersen, R.C. (2001). "A Laboratory Facility for Testing Model Suction Caissons." Proc., OTRC 2001 Intl Conf. on Geotechnical, Geological, Geophysical Properties Deepwater Sediments, Houston, TX, April. pp. 198-216
Pedersen, R. C., R. E. Olson, and A. F. Rauch (2003), “Shear and Interface Strength of Clay at Very Low Effective Stress”, ASTM Geotechnical Testing Journal, Vol. 26, No. 1, paper GTJ200310648-261
Rauch, A. F., R. E. Olson, A. M. Luke, and E. C. Mecham (2003), “Measured Response During Laboratory Installation of Suction Caissons”, International Symposium on Offshore and Polar Engineering, Honolulu, Hawaii, p. 780-787
Luke, A. M., A. F. Rauch, R. E. Olson, and E. C. Mecham (2003), “Behavior of Suction Caissons Measured in Laboratory Pullout Tests”, Proc. OMAE03, 22nd International Conference on Offshore Mechanics and Arctic Engineering, Cancun, Mexico, Paper 37023
Olson, R. E., A. F. Rauch, A. M. Luke, D. R. Maniar, J. T. Tassoulas, and E. C. Mecham (2003), “Soil Reconsolidation Following Installation of Suction Caissons”, Offshore Technology Conference, Houston, paper 15263
Luke, A. M., A. F. Rauch, R. E. Olson, and E. C. Mecham (2003), “Components of Suction Caisson Capacity Measured in Axial Pullout Tests”, Deepwater Mooring Systems: Concepts, Design, Analysis and Materials, OTRC (Offshore Technology Research Center) Specialty Conference, Houston, TX
Olson, R. E., A. F. Rauch, E. C. Mecham, and A. M. Luke (2003), “Self-Weight Consolidation of Large Laboratory Deposits of Clay”, Proc., 12th PanAmerican Conf. on Soil Mech. and Geot. Engr., MIT, Vol. 1, pp. 703-708
Coffman, R. A., R. M. El-Sherbiny, A. F. Rauch, and R. E. Olson (2004), “Measured Horizontal Capacity of Suction Caissons”, Proc., Offshore Tech. Conf., Houston, Paper 16161
Luke, A. M., A. F. Rauch, R. E. Olson, and E. C. Mecham (2005), “Components of Suction Caisson Capacity Measured in Axial Pullout Tests”, Journal of Ocean Engineering, Elsevier (in press)
El-Sherbiny, R. M, Olson, R. E., Gilbert, R. B, and Vanka, S. K. (2005), “Capacity of suction caissons under inclined loading in normally consolidated clay”, Proceeding of the International Symposium on Frontiers in Offshore Geotechnics, Perth, Australia, September
Date: June, 2005
Project Title: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
MMS Project: 362 TO Numbers: 16169/35980
PI: Roy E. Olson and Robert B. Gilbert
COTR: A. Konczvald
Estimated Completion Date: August 2005
Project Description:
Suction caissons have gradually replaced pile foundations as anchors for floating offshore structures in deep water. Early designs for suction caissons were based on experience with piles but there was a need to verify, and perhaps alter, these design procedures. Centrifuge studies have been used extensively because they can be performed quickly as part of design phases of individual projects. Our goal was a more systematic, and longer term, investigation in which we performed laboratory-scale tests on caissons with lengths approaching a meter and diameters around 100 mm. The caissons were instrumented more thoroughly than was feasible using the smaller caissons used in most tests in centrifuges and the properties of our soil deposits were measured in detail. Finally, our data were used in a companion project in which sophisticated finite element analyses were performed. Our measurements were used to guide the theoretical analyses and verify the results.
Progress:
This project terminates in August 2005. During this project we performed the following studies:
The entire collection of experiments is in the process of being summarized and analyzed, collectively, in a Ph.D. dissertation which should be submitted prior to the conclusion of this project in August.
- We consolidated clay from slurries in large tanks and monitored the progress of consolidation. The measurements were used in the finite element analyses to establish initial conditions prior to caisson installation.
- We installed caissons both by self weight and using suction.
- We performed tension tests on the caissons with a range of setup times to ascertain the required minimum time for essentially full setup.
- We extracted caissons with both sealed tops and open tops and observed the different failure modes.
- We performed tests using axial tensile loads, and by loading on the sides.
- For the lateral loading tests we applied loads at differing depths and at a range of angles to obtain experimental interaction diagrams.
- We measured pore water pressures on both the interior and exterior in an effort to understand caisson behavior.
- We built a double-walled caisson which allowed independent measurements of the loads on the exterior and the interior in an effort to resolve questions about side shears and end bearing.
- We strain-gauged the inner and outer walls to obtain evidence of the distribution of side shear with depth, on both the inner and outer surfaces.
Reports & Publications:
Vanka, S. K. R. (2004), “Laboratory Tests to Estimate Strength Profile of Normally Consolidated Kaolinite”, M.S. thesis, Univ. of Texas, December.
El-Sherbiny, R. M. (2005), Ph.D. dissertation in progress, anticipated submission in August 2005.
Luke, A., A. F. Rauch, R. E. Olson and E. C. Mecham (2005), “Components of Suction Caisson Capacity Measured in Axial Pullout Tests”, Ocean Engineering, Vol. 32, pp. 878-891.
El-Sherbiny, R. M., R. E. Olson, R. B. Gilbert, and S. K. Vanka (2005), “Capacity of Suction Caissons Under Inclined Loading in Normally Consolidated Clay”, Intern. Symposium on Frontiers in Offshore Geotechnics, (in press, conference in September).
Date: December, 2004
Project Title: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
MMS Project: 362 TO Numbers: 16169/35980
PI: Roy E. Olson and Bob Gilbert
COTR: A. KonczvaldEstimated Completion Date: August 2005
Project Description: The objective of this research is to measure and interpret the response of suction caisson foundations when subjected to axial and lateral loads. Data are being obtained from laboratory tests on caissons installed in deposits of soft clay. Relatively large laboratory deposits of clay, which are normally consolidated like typical Gulf of Mexico clays, are used in the tests. Our clay test beds are among the largest ever used for tests of this kind and provide a unique opportunity to measure the behavior of caissons in soft clays. To maximize the reliability of the measurements, we are using caissons that measure 100 mm in diameter by 860 mm long, sizes that are substantially larger than have been used in most other laboratory studies. We are now working in our fourth soil test bed. The tests currently concentrate on two aspects of the problem: (1) Caissons are being loaded at various angles from the horizontal to determine the “interaction curve”. (2) A new double-walled caisson is being developed in the hopes that it will be possible to separate measurements of the side capacity on the outside, side capacity on the inside, and the tip capacity. This new caisson has very thin walls so the combination of the two walls will still produce a caisson with a ratio of wall thickness to caisson diameter that is not greatly different from ones in practical use. The walls are being strain gauged to determine the variation of load with depth.
The collected data are being used with finite element analyses performed on a different project, and limiting equilibrium analyses performed at Texas A & M University, in an effort to calibrate theoretical models with experimental measurements, and thus provide both useful design programs and to indicate the possible accuracy of these codes. Currently, the limiting equilibrium code looks like it is performing well in comparison with the measurements.
Progress: Recently, nineteen tests were completed with loading ranging from horizontal to vertical. These tests seem to confirm predictions with the limiting equilibrium model being developed at Texas A&M University. Comparisons with the more refined finite element analyses are in progress. The double-walled caisson has been designed, components obtained, and preliminary experiments with the instrumentation system are nearly finished. The caisson should be ready for testing in January. It has been known in the field for decades that the measured undrained shearing strength of clays depends on the state of stress in the tests. Because different tests are in use (field vane, cone, T bar, triaxial compression with laboratory samples, and recently a ball in situ test) there is a problem as to which test should be used in design and how to correlate different test with some standard. We are currently nearing completion of a series of different tests, on undisturbed soil and remolded soil, to help clarify these differences.
Reports and Publications Not Reported Previously:
Luke, A. M. A. F. Rauch, R. E. Olson, and E. C. Mecham (2005), “Components of suction caisson capacity measured in axial pullout tests”, Journal of Ocean Engineering (in press).
Coffman, R. A., El-Sherbiny, R. M., Rauch, A. F., and Olson, R. E. (2004). “Measured horizontal capacity of suction caissons.” Paper No. OTC 16161, Proc., 2004 Offshore Technology Conference, Houston, Texas, May, 10 pages.
Coffman, Richard A. (2003). “Horizontal capacity of suction caissons in normally consolidated kaolinite.” M. S. Thesis, University of Texas at Austin, December.
Reports and Publications in Progress
Vanka, S. (2004), title not finalized, M.S. thesis, University of Texas, December.
El-Sherbiny, R. (2005), title not finalized, Ph.D. dissertation, University of Texas.
El-Sherbiny, R. M., R. E. Olson, and R. B. Gilbert (2005), title not finalized, Intern. Symposium on Frontiers in Offshore Geotechnics, Perth, Australia, (abstract accepted)
Date: June 2004
Project Name: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
Project Number: 362 Task Order: 16169
Principal Investigators: Roy E. Olson and Alan F. Rauch
Estimated Completion Date: September 2005
Project Description:
The objective of this research is to measure and interpret the response of suction caisson foundations subjected to axial and lateral loads. Data are being obtained from laboratory tests on caissons installed in deposits of soft clay. Relatively large laboratory deposits of clay, which are normally consolidated like typical Gulf of Mexico clays, are used in the tests. Consolidation requires about 8 months. The clay test beds are among the largest ever used for tests of this kind and provide a unique opportunity to measure the behavior of caissons in soft clays. The caissons measure 100 mm in diameter by 860 mm long, and are substantially larger than have been used in most other laboratory studies. The collected data are being used to verify theoretical models of suction caisson capacity being developed in other OTRC projects. The research results will lead to an improved understanding of caisson behavior and support the development of rational analytical methods.
Progress:
To date, we have prepared three test beds; a fourth has been mixed and is currently consolidating. We had previously performed more than twenty tests that focused on axial insertion and pullout behavior.
Tests in the first soil test bed concentrated on characterizing axial load response, because axial capacity appears to govern design in many field applications. Subsequent tests in the second test bed measured the behavior and capacity of the caisson when horizontal loads were applied at different locations along the lower half.
Recently, nine tests were completed with horizontal loads applied rapidly at various positions along the lower half of the caisson. The results show a peak capacity when the load is applied at a depth equal to about two-thirds of the penetration depth of the caisson, or somewhat lower. These measured horizontal capacities were compared to predictions from plasticity solutions and finite element simulations developed by other OTRC collaborators at the University of Texas and Texas A & M University. The agreement between the predictions and experimental results was good.
We are now working in the third soil test bed, and concentrating on inclined loadings applied to the caisson below the mudline that are typical of field conditions. The direct measurement of inclined loads will be particularly valuable, since design calculations for caissons subjected to inclined loads are based on the predicted axial and horizontal load capacity.
Reports & Publications:
Coffman, R. A., El-Sherbiny, R. M., Rauch, A. F., and Olson, R. E. (2004). “Measured horizontal capacity of suction caissons.” Paper No. OTC 16161, Proc., 2004 Offshore Technology Conference, Houston, Texas, May, 10 pages.
Luke, A. M., Rauch, A. F., Olson, R. E., and Mecham, E. C. (2003). “Behavior of suction caissons measured in laboratory pullout tests.” Paper No. OMAE2003-37023, Proc., 22nd Intern. Conf. on Offshore Mechanics and Arctic Eng., ASME, Cancun, Mexico, June, 9 pages
Olson, R. E., Rauch, A. F., Mecham, E. C., and Luke, A. M. (2003), “Self-weight consolidation of large laboratory deposits of clay.” Proc., 12th Panamerican Conf. Soil Mechanics and Geotechnical Eng., Cambridge, Massachusetts, June, pp. 703-708
Luke, A. M., Rauch, A. F., Olson, R. E., and Mecham, E. C. (2003), “Components of suction caisson capacity measured in axial pullout tests.” Proc., OTRC 2003 Intern. Symposium: Deep Water Moorings; Concepts, Design, Analysis and Materials, Zhang and Mercier (eds.), Houston, Texas, October, pp. 1-12
Coffman, Richard A. (2003). “Horizontal capacity of suction caissons in normally consolidated kaolinite.” M. S. Thesis, University of Texas at Austin, December
Date: December 2003Project Name: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
TEES Project Number: 32558-58876 MMS Task Order: 16169 MMS Project Number: 362
Principal Investigators: Roy E. Olson and Alan F. Rauch
Estimated Completion Date: August 2005
Project Description:
The objective of this research is to measure and interpret the response of suction caisson foundations when subjected to axial and lateral loads. Data are being obtained from laboratory tests on caissons installed in deposits of soft clay. Relatively large laboratory deposits of clay, which are normally consolidated like typical Gulf of Mexico clays, are used in the tests. Our clay test beds are among the largest ever used for tests of this kind and provide a unique opportunity to measure the behavior of caissons in soft clays. To maximize the reliability of the measurements, we are using caissons that measure 100 mm in diameter by 860 mm long, sizes that are substantially larger than are typically used in most other studies in laboratories. The primary focus of initial tests was is to study the behavior of caissons subjected to vertical or lateral loads separately but current work deals with the typical field conditions involving inclined loading. Tests in the first soil test bed concentrated on characterizing axial load response, because axial capacity appears to govern design in many field applications. Subsequent tests in the second test bed were performed to measure the behavior and capacity of the caisson model when horizontal loads were applied at different locations along the lower half. The collected data are useful in verifying theoretical models of suction caisson capacity, because design calculations for caissons subjected to inclined loads are based on the predicted axial and horizontal load capacity. The research results will lead to an improved understanding of caisson behavior and support the development of rational analytical methods.
Progress:
The tests are being conducted using an instrumented 100-mm diameter, aluminum model caisson in a 1.2-meter thick test bed of normally consolidated kaolinitic clay that is prepared from slurry in large steel tanks. The consolidation process requires about 8 months. To date, we have prepared three of these test beds. We had previously performed more than twenty tests that focused insertion and pullout behavior.
Recently, nine tests were completed with horizontal loads applied rapidly at various positions along the lower half of the caisson model. The results show a peak capacity when the load is applied at a depth equal to about two-thirds of the penetration depth of the caisson, or somewhat lower. These measured horizontal capacities were compared to predictions from plasticity solutions and finite element simulations developed by other OTRC collaborators at the University of Texas and Texas A & M Universities. The agreement between the predictions and experimental results was good.The next test series, which will begin soon in the third soil deposit, will involve inclined loads applied to the caisson below the mudline.
Reports & Publications:
Luke, A. M., Rauch, A. F., Olson, R. E., and Mecham, E. C. (2003). “Behavior of suction caissons measured in laboratory pullout tests.” Paper No. OMAE2003-37023, Proc., 22nd Intern. Conf. on Offshore Mechanics and Arctic Eng., ASME, Cancun, Mexico, June, 9 pages
Olson, R. E., Rauch, A. F., Mecham, E. C., and Luke, A. M. (2003), “Self-weight consolidation of large laboratory deposits of clay.” Proc., 12th Panamerican Conf. Soil Mechanics and Geotechnical Eng., Cambridge, Massachusetts, June, pp. 703-708
Luke, A. M., Rauch, A. F., Olson, R. E., and Mecham, E. C. (2003), “Components of suction caisson capacity measured in axial pullout tests.” Proc., OTRC 2003 Intern. Symposium: Deep Water Moorings; Concepts, Design, Analysis and Materials, Zhang and Mercier (eds.), Houston, Texas, October, pp. 1-12
Coffman, Richard A. (2003). “Horizontal capacity of suction caissons in normally consolidated kaolinite.” M. S. Thesis, University of Texas at Austin, December
Date: June, 2003
Project Name: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
Project Number: 32558-58876 Task Order: 16169
Principal Investigators: Roy E. Olson and Alan F. Rauch
Estimated Completion Date: 8/31/04
Project Description:
The objective of this research is to measure and interpret the response of suction caisson foundations when subjected to combined axial and lateral loads. Data are being obtained from laboratory tests on model caissons installed in tanks of soft clay. To obtain more reliable measurements, we are using caisson models that measure 100 mm in diameter by 860 mm long, larger than the models used in most other studies of this kind. Tests are being conducted in relatively large deposits of clay that are normally consolidated, like typical Gulf of Mexico clays. Our clay test beds are probably among the largest ever used for tests of this kind and provide a unique opportunity to measure the behavior of caissons in soft clays. While a major focus of the project is the behavior of caissons under lateral loading, theoretical studies have indicated that axial capacity will govern in many applications with combined lateral and axial loads. As a result, tests completed so far have concentrated on characterizing axial load capacity. Lateral load tests are currently underway. The research results will lead to an improved understanding of caisson behavior and support the development of rational analysis methods.
Progress:
· The model tests are being conducted in 4-ft thick deposits of normally consolidated kaolinite clay that are prepared from slurry in large steel tanks. To date, we have prepared two of these test beds and a third is consolidating. The consolidation process requires about 8 months.
· Developed computer codes to predict consolidation of the test bed soils. Designed and built an instrumentation system to monitor consolidation through the measurement of pore water pressures, soil water contents, and surface settlements.
· Developed and performed laboratory tests to measure properties of the clay at very low stress levels, as needed to interpret the model test results. Also developed test methods to measure the profile of undrained shear strength in the consolidated test bed soil.
· Designed and constructed a 4-inch diameter, aluminum model caisson. Designed, manufactured, and calibrated an instrumentation system for electronically recording applied loads, pore water pressures, and caisson displacements.
· Constructed fixtures and hardware needed for axial and lateral load tests. We are currently working to implement a computer-controlled loading device, for better control during testing.
· Developed analytical methods and software to process the caisson test results. Various components of the measured capacity, such as side resistance, can now be studied.
· Performed more than twenty tests to measure axial insertion and pullout behavior. We now have data on the effects of self-weight insertion versus suction insertion, the time required for soil reconsolidation after insertion, the effects of vented-top versus sealed-top withdrawal, and the effect of rapid (undrained) versus slow (drained) extraction.
· Recently began conducting lateral load tests, with horizontal loads applied at various positions along the lower half of the caisson model.Reports & Publications (since 2001):
Olson, R. E., Rauch, A. F., Gilbert, R. B., Tassoulas, J. L., Aubeny, C. P., and Murff, J. D. (2001). “Toward the design of new technologies for deep-water anchorages.” Proc., 11th International Offshore and Polar Engineering Conf., ISOPE-2001, Vol. IV, Stavanger, Norway, June, pp. 643-649.
Rauch, A. F., Olson, R. E., Mecham, E. C., and Pedersen, R. C. (2001). “A laboratory facility for testing model suction caissons.” Proc., OTRC 2001 International Conf., Geotechnical, Geological and Geophysical Properties of Deepwater Sediments, Houston, Texas, April, pp. 198-216.
Pedersen, R. C. (2001). "Model offshore soil deposit: Design, preparation, and characterization." M.S. Thesis, University of Texas at Austin, May.
Mecham, E. C. (2001). “A laboratory for measuring the axial and lateral load capacity of model suction caissons." M.S. Thesis, University of Texas at Austin, December.
Luke, Adam M. (2002). “Axial capacity of suction caissons in normally consolidated kaolinite.” M. S. Thesis, University of Texas at Austin, August.
Pedersen, R. C., Olson, R. E., and Rauch, A. F. (2003). “Shear and interface strength of clay at very low effective stress.” Geotechnical Testing J., ASTM, Vol. 26, No. 1, March, pp. 71-78.
Olson, R. E., Rauch, A. F., Luke, A. M., Maniar, D. R., Tassoulas, J. L., and Mecham, E. C. (2003). “Soil reconsolidation following the installation of suction caissons.” Paper No. OTC 15263, Proc., 2003 Offshore Technology Conference, Houston, Texas, May, in press.
Rauch, A. F., Olson, R. E., Luke, A. M., and Mecham, E. C. (2003). “Measured response during laboratory installation of suction caissons.” Proc., 13th International Offshore and Polar Engineering Conf., ISOPE-2003, Honolulu, Hawaii, May, in press.
Olson, R. E., Rauch, A. F., Mecham, E. C., and Luke, A. M. (2003). “Self-weight consolidation of large laboratory deposits of clay.” Proc., 12th Panamerican Conf. Soil Mechanics and Geotechnical Engineering, Cambridge, Massachusetts, June, in press.
Luke, A. M., Rauch, A. F., Olson, R. E., and Mecham, E. C. (2003). “Behavior of suction caissons measured in laboratory pullout tests.” Paper No. OMAE2003-37023, Proc., 22nd International Conf. on Offshore Mechanics and Arctic Engineering, ASME, Cancun, Mexico June, in press.
Luke, A. F., A. F. Rauch, R. E. Olson, and E. C. Mecham (2003). “Components of suction caisson capacity measured in axial pullout tests.” Offshore Technology Research Center International Symposium on Deep Water Moorings: Concepts, Design, Analysis and Materials (abstract accepted, manuscript in preparation).
Date: November 15, 2002
Project Name: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
Project Number: 32558-58876 Task Order: 16169
Principal Investigators: Roy E. Olson and Alan F. Rauch
Estimated Completion Date: August, 2004
Project Description:
The objective of this research is to measure and interpret the response of suction caisson foundations when subjected to combined axial and lateral loads. Data is being obtained from laboratory tests on model caissons installed in tanks of soft clay. To obtain more reliable measurements, we are using caisson models that measure 100 mm in diameter by 860 mm long, larger than the models used in most other studies of this kind. Tests are being conducted in relatively large deposits of clay that are normally consolidated, like typical Gulf of Mexico clays. Our clay test beds are probably among the largest ever used for tests of this kind and provide a unique opportunity to measure the behavior of caissons in soft clays. While a major focus of the project is the behavior of caissons under lateral loading, theoretical studies have indicated that axial capacity will govern in many applications with combined lateral and axial loads. As a result, tests completed so far have concentrated on characterizing axial load capacity, but lateral load tests will begin soon. The research results will lead to an improved understanding of caisson behavior and support the development of rational analysis methods.
Progress:
· The model tests are being conducted in 4-ft thick deposits of normally consolidated kaolinite clay that are prepared from slurry in large steel tanks. Clay in the first tank has been consolidated and used for axial loading tests, clay in the second tank is ready for testing.
· Developed computer codes to predict consolidation of the test bed soils. Designed and built an instrumentation system to monitor consolidation through the measurement of pore water pressures, soil water contents, and surface settlements.
· Developed and performed laboratory tests to measure the consolidation and shearing properties of the clay at very low stress levels, as needed to interpret the model test results. Also developed penetration test methods to measure the profile of undrained shear strength in the consolidated test bed soil.
· Designed and constructed a 4-inch diameter, aluminum model caisson. Designed, manufactured, and calibrated an instrumentation system for electronically recording applied loads, pore water pressures, and caisson displacements.
· Constructed fixtures and hardware needed for axial loading tests. The apparatus is now being refurbished to improve stiffness and versatility for lateral loading tests.
· Developed analytical methods and software to process the caisson test results. Various components of the measured capacity, such as side resistance, can now be studied.
· Performed more than twenty tests to measure axial insertion and pullout behavior. We now have data on the effects of self-weight insertion versus suction insertion, the time required for soil reconsolidation after insertion, the effects of vented-top versus sealed-top withdrawal, and the effect of rapid (undrained) versus slow (drained) extraction.Reports & Publications (includes only documents since 2001):
· Olson, R. E., A. F. Rauch, R. B. Gilbert, J. L. Tassoulas, C. P. Aubeny, and J. D. Murff (2001). “Toward the design of new technologies for deep-water anchorages.” Proc., 11th International Symposium on Offshore and Polar Engineering, Stavanger, Norway, June.
· Pedersen, R. C. (2001). "Model offshore soil deposit: Design, preparation, and characterization." M.S. Thesis, University of Texas at Austin.
· Rauch, A. F., R. E. Olson, E. C. Mecham, and R. C. Pedersen (2001). “A laboratory facility for testing model suction caissons.” Proc., OTRC 2001 International Conf., Geotechnical, Geological and Geophysical Properties of Deepwater Sediments, Houston, April, pp. 198-216.
· Mecham, E. C. (2001). “A laboratory for measuring the axial and lateral load capacity of model suction caissons." M.S. Thesis, University of Texas at Austin.
· Luke, Adam M. (2002). “Axial capacity of suction caissons in normally consolidated kaolinite.” M. S. Thesis, University of Texas at Austin.
· Pedersen, R. C., R. E. Olson, and A. F. Rauch (2003). "Shear and interface strength of clay at very low effective stress." Scheduled to appear in the Geotechnical Testing J., ASTM, March.
· Olson, R E., A. F. Rauch, E. C. Mecham, and A. M. Luke (2003). “Self-weight consolidation of large laboratory deposits of clay.” 12th Panamerican Conference on Soil Mechanics and Geotechnical Engineering, Boston (final manuscript under review).
· Luke, A. M., A. F. Rauch, R. E. Olson, and E. C. Mecham (2003).”Behavior of suction caissons measured in laboratory pullout tests.” 22nd Intern. Conf. on Offshore Mechanics and Arctic Engineering (abstract accepted, manuscript in preparation).
· Rauch, A. F., R. E. Olson, A. M. Luke, D. R. Maniar, J. L. Tassoulas, and E. C. Mecham (2003). “Soil reconsolidation following the installation of suction caissons.” Offshore Technology Conference (abstract submitted, manuscript in preparation).
· Luke, A. F., A. F. Rauch, R. E. Olson, and E. C. Mecham (2003). “Components of suction caisson capacity measured in axial pullout tests.” Offshore Technology Research Center International Symposium on Deep Water Moorings: Concepts, Design, Analysis and Materials (abstract submitted, manuscript in preparation).
· Rauch, A. F., R. E. Olson, A. M. Luke, and E. C. Mecham (2003). “Measured response during laboratory installation of suction caissons.” 13th Intern. Symposium on Offshore and Polar Engineering (abstract accepted, manuscript in preparation).
Date: June 2002
Project Name: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
Task Order: 16169 Project Number: 58876
Principal Investigators: Roy E. Olson and Alan F. Rauch
Estimated Completion Date: August 2002
Project Description:
The objective of this research is to measure and interpret the response of suction caisson foundations when subjected to combined axial and lateral loads. Data is being obtained from laboratory tests on model caissons installed in large tanks of soft clay. To obtain more reliable measurements, we are using caisson models that measure 100 mm in diameter by 860 mm long, larger than the models used in most other studies of this kind. Tests are being conducted in relatively large deposits of clay that are normally consolidated, like typical Gulf of Mexico clays. Our clay test beds are probably among the largest ever used for tests of this kind and provide a unique opportunity to measure the behavior of caissons in soft clays. While a major focus of the project is the behavior of caissons under lateral loading, theoretical studies have indicated that axial capacity will govern in many applications with combined lateral and axial loads. As a result, tests this year concentrated on characterizing axial load capacity. Lateral load tests will begin in the fall of 2002. The research results will lead to an improved understanding of caisson behavior and support the development of rational analysis methods.Progress:
· In previous years, work on the project resulted in the design, construction, and development of the testing tanks, model caisson, instrumentation, and data acquisition system. The first tank was filled with clay and allowed to consolidate. The consolidation time was about nine months. Extensive measurements were made of the clay's properties at appropriate stress levels. One publication (in press) on shearing properties of the clay showed remarkably high effective friction angles at the stress levels in our tank. Consolidation measurements in the tank revealed some unexpected aging effects that are currently under investigation.
· During this year, more than twenty tests were performed with the model caisson to measure axial insertion and pullout behavior. To develop techniques and instrumentation without disturbing soil in the main tank, preliminary testing was performed in smaller tanks of clay. From tests in the main tank, we now have data on the effects of self-weight insertion versus suction insertion, the time required for soil reconsolidation after insertion, the effects of vented-top versus closed-top withdrawal, and the effect of rapid (undrained) versus slow (drained) extraction. In addition, a second test bed was mixed and consolidated in preparation for continued testing next year.Reports & Publications:
· Olson, R. E., Rauch, A. F., Gilbert, R. B., Tassoulas, J. L., Aubeny, C. P., and Murff, J. D. (2001). “Toward The Design of New Technologies for Deep-Water Anchorages.” Proc., 11th International Offshore and Polar Engineering Conf., ISOPE-2001, Stavanger, Norway, June.
· Rauch, A. F., Olson, R. E., Mecham, E. C., and Pedersen, R. C. (2001). “A Laboratory Facility for Testing Model Suction Caissons.” Proc., OTRC 2001 International Conf., Geotechnical, Geological and Geophysical Properties of Deepwater Sediments, Houston, April, pp. 198-216.
· Pedersen, R. C. (2001). "Model Offshore Soil Deposit: Design, Preparation, and Characterization." M.S. Thesis, University of Texas at Austin, May, 98 pp. (Mr. Pedersen is now employed by ExxonMobil.)
· Mecham, Elliott (2001), “A Laboratory for Measuring the Axial and Lateral Load Capacity of Model Suction Caissons”, M.S. thesis, University of Texas at Austin, December, 174 pp.
· Luke, Adam (2002), "Axial Capacity of Suction Caissons in Normally Consolidated Kaolinite", M.S. thesis, University of Texas at Austin, June.
· Iskander, M. G., S. El-Gharbawy, and R. E. Olson (2002),”Performance of Suction Caissons in Sands and Clays, Canadian Geotechnical Journal, scheduled to appear in April.
· Pedersen, R. C., R. E. Olson, and A. F. Rauch (2003), “Shear and Interface Strength of Clay at Very Low Effective Stresses”, ASTM, Jour. of Geotechnical Testing, paper was accepted in final form early in 2002 and is scheduled to appear in March 2003.
· Abstracts have been, or will soon be, submitted to the 2003 Pan American Conference on Soil Mechanics and Geotechnical Engineering, the 2003 Offshore Technology Conference, and the 2003 International Symposium on Offshore and Polar Engineering.
Date: December 1, 2001
Project Name: Performance of Suction Caissons used to Anchor Structures in Very Deep Water
Task Order: 16169 Project Number: 58876
Principal Investigators: Roy E. Olson and Alan F. Rauch
Estimated Completion Date: August 2002
Project Description:
The objective of this research is to acquire experimental data on the behavior of suction caisson foundations when installed in soft clays and loaded laterally by mooring lines from floating structures. The offshore oil industry is currently designing suction caissons to anchor floating exploration and production platforms in the deep waters of the Gulf of Mexico. Unfortunately, there is a paucity of data on suction caisson behavior, especially for long, slender caissons subjected to inclined lateral loads like those being planned. We are working with laboratory-scale caisson models (100 mm diameter by 1-m long) that will be installed by suction into large tanks of normally consolidated clay and then loaded to failure under a variety of conditions. This project will yield detailed experimental data to clarify caisson behavior and provide the basis for developing and validating analytical and design methods for this technology.
Progress:
· The model tests are being conducted in 4-ft thick deposits of normally consolidated kaolinite clay that are prepared from slurry in large steel tanks. Two such test tanks have been assembled and filled with clay.
· Developed computer codes to predict consolidation of the test bed soils.
· Designed and built an instrumentation system to monitor consolidation through the measurement of pore water pressures, soil water contents, and surface settlements.
· Consolidation in the first tank of soil is complete. The second tank was filled with the kaolinite slurry in June 2001; consolidation in that tank should be complete in another 2-3 months.
· Developed laboratory methods and performed tests to measure the consolidation and drained shearing properties of the clay at very low stress levels. Also developed penetration test methods to measure the profile of undrained shear strength in the consolidated test bed soil. These soil properties are critical to proper interpretation of the model test results.
· Designed and constructed a 4-inch diameter, aluminum model caisson.
· Designed, manufactured, and calibrated an instrumentation system for electronically recording applied loads, pore water pressures, and caisson displacements during each model test.
· Developed analytical methods and software to process the caisson test results. Various components of the measured capacity, such as side resistance, can now be studied.
· Testing of model caissons is underway in the first test bed. The initial series of tests is concentrating on the axial pullout capacity, which may limit caisson capacity at high load angles.Reports & Publications:
· Olson, R. E., Rauch, A. F., Gilbert, R. B., Tassoulas, J. L., Aubeny, C. P., and Murff, J. D. (2001). “Toward the design of new technologies for deep-water anchorages.” Proc., 11th International Offshore and Polar Engineering Conf., ISOPE-2001, Stavanger, Norway, June.
· Rauch, A. F., Olson, R. E., Mecham, E. C., and Pedersen, R. C. (2001). “A laboratory facility for testing model suction caissons.” Proc., OTRC 2001 International Conf., Geotechnical, Geological and Geophysical Properties of Deepwater Sediments, Houston, April, pp. 198-216.
· Pedersen, R. C., Olson, R. E., and Rauch, A. F. (accepted). "Shear and interface strength of clay at very low effective stress." Submitted to Geotechnical Testing J., ASTM.
· Pedersen, R. C. (2001). "Model offshore soil deposit: Design, preparation, and characterization." M.S. Thesis, University of Texas at Austin. (Mr. Pedersen is now employed by ExxonMobil.
· Mecham, E. C. (2001). "A laboratory facility for measuring axial and lateral capacity of model suction caissons." M.S. Thesis, University of Texas at Austin.