A laboaratory testing program was initiated to investigate potential changes in stiffness for soils in the touch down point region of a Steel Catenary Riser (SCR). The tests were performed using a T-bar apparatus, a device normally used to determine the shear strength of clay soils. The normalized stiffness obtained with the T-bar was found to match previous results obtained with pipe tests for an unload-reload cycle of loading and helped confirm that using a normalized approach with the smaller-sized T-bar could produce meaningful results. The focus of the testing program was to determine the normalized stiffness of the soil under high amplitude cyclic loading conditions and then under lower amplitude loading after a waiting period of about 24 hours. The normalized soil stiffness was compared at a consistent displacement level in all cases. As expected the large amplitude cyclic loading produced large changes in the soil stiffness. One test where the T-bar was observed to separate from the soil resulted in a further reduction the soil stiffness. For this test the stiffness was reduced by a factor of about 33 relative to the intial undisturbed load-reload stiffness of the soil. The soil stiffness did recover after the 1day waiting period. However, this stiffness remained lower than the initial unload reload stiffness by a factor of 4. This observation could impact fatigue analyses when the soil stiffness for a fatigue event must be evaluated after prior large amplitude cyclic loading.

A comprehensive laboratory testing program provided geotechnical parameters for detailed three-dimensional, non-linear finite-element analysis of the performance of the Maleo Producer mat-supported jack-up platform under seismic loading. This paper presents the results of this program for 16 resonant column tests and 12 cyclic direct simple shear tests performed on samples from a soil boring drilled nearby the Maleo Producer at a location in the Madura Sea, offshore Indonesia, in 2007. As background, the extent of in situ data, static laboratory data, and dynamic data is discussed, followed by description of generalized soil conditions interpreted from the data. Results of piezocone penetration tests (PCPT's), seismic cone penetration tests (SCPT's), soil index properties, in situ vertical stress history, and normalized static shear strength properties are presented. The program of dynamic laboratory testing is summarized, and detailed results of the testing are shown. Finally, the field and laboratory data are integrated to develop profiles of maximum shear modulus and minimum damping. The reference strain concept (Hardin and Drnevich, 1972) is used to normalize and combine resonant column and cyclic direct simple shear data; examples of the resulting modulus reduction and damping curves are illustrated. Extent of In Situ and Laboratory DataA number of exploratory boreholes and in situ tests were performed for investigation of the stability of the foundation of the Maleo Producer. This paper focuses on the dynamic testing of samples recovered from the uppermost 100 m of the soil profile. PCPT data and SCPT data obtained are also presented. All of the detailed data discussed in this paper follow from explorations performed in January 2007. These explorations were located within a circle of 13-m diameter. Scope of advanced laboratory data.Thirty-two thin-walled tube samples, recovered during the 2007 fieldwork, were packaged and shipped to Houston, Texas, for advanced laboratory testing. The tubes were x-rayed, and the x-rays were reviewed to select the highest quality samples for advanced testing. The advanced testing program includes 16 one-dimensional consolidation tests (ASTM D4186), 21 K o -consolidated direct simple shear tests (ASTM D6528), 6 K o -consolidated undrained triaxial compression tests (ASTM D4767 with modifications), 2 K o -consolidated undrained triaxial extension tests (ASTM D4767 with modifications), 16 isotropically-consolidated resonant column tests (ASTM D4015), 12 K o -consolidated cyclic direct simple shear tests (ASTM D6528), and numerous classification and index tests (ASTM D422, D854, D2850, and D4318) (ASTM, 2007). Other geotechnical data.Standard geotechnical laboratory test data and cone penetration test data from a boring program performed in 2003, and located about 130 m to the south, were also considered as part of our study; however, these data are not reported here. Likewise, shallow cone data collected around and nearby the footprint of the mat foundation of the Maleo Produce...

The authors examined the results of 172 CKoU direct simple shear (DSS) tests. Their research has led to four important conclusions. Firstly, the test results confirm observations by other investigators that an acceptable correlation does not exist between the shear strength ratio, cu/?'v, and plasticity index, Ip. Secondly, consolidation pressure has a greater effect on cu/?'v than Ip and should be considered when evaluating DSS test results for use in a normalized soil parameter (NSP) procedure such as SHANSEP (stress history and normalized soil engineering properties). Thirdly, correlating cu/?'v results from DSS tests with only Ip could lead to either overestimating or underestimating in-situ undrained shear strength when employing an NSP procedure. Lastly, the authors demonstrate that correlations of DSS measured soil undrained shear strength, consolidation pressure and water content can provide a useful tool for evaluating in-situ undrained shear strength. Introduction Over the past thirty years, the DSS test has become widely used in geotechnical investigations, particularly in deepwater regions. The results of these tests are typically employed in some type of NSP procedure to evaluate in-situ undrained shear strength of clay deposits. The NSP procedure known as SHANSEP1 is a common method employed to perform this task. However, because of the expense and the considerable duration of testing associated with the SHANSEP procedure, laboratory testing is typically limited to a few tests within soil units defining the soil stratigraphy being evaluated. Subsequently, the results are often correlated with Ip To interpolate between SHANSEP test intervals to define the interpreted shear strength profile. A common correlation used to interpolate data between SHANSEP test intervals is that of the strength ratio, cu/?'v, and Ip. However, the authors' experience has been that a very poor correlation exists between cu/?'v and Ip when evaluated over a wide range of Ip common to offshore soils. This same opinion has been expressed by other investigators.2,3 To assess the reliability of the cu/?'v and Ip correlation, the authors examined the results of 172 DSS specimens tested in a normally consolidated state (OCR = 1). These tests were performed by five different geotechnical laboratories with extensive experience in performing SHANSEP-type testing. The soil specimens are from geotechnical site investigations conducted in six different offshore regions of the world. The plasticity characteristics of the 172 specimens examined in this study are presented in Fig. 1. This plasticity chart reveals that most of the specimens are highly plastic (CH) clays with liquid limits as high as 143 percent and Ip values as high as 101 percent. There are also several lower plasticity (CL) clays with Ip values ranging from 14 to 29 percent as well as some elastic silts (MH) and organic (OH) clays that fall below the A-line. The database does not include highly sensitive, cemented, or highly structured samples. Prevailing Strength Ratio - Ip Correlation In 1957, Skempton4 proposed the following correlation for normally consolidated clays based on field vane test results: (Mathematical equation available in full paper)

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