Soft Clay Dynamic Characteristics for Madura Straits From Advanced Geotechnical Tests
Authors: Spikula Daniel Robert , Garmon Steve 
Published: October 2008

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 Data

A 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 Ko-consolidated direct simple shear tests (ASTM D6528), 6 Ko-consolidated undrained triaxial compression tests (ASTM D4767 with modifications), 2 Ko-consolidated undrained triaxial extension tests (ASTM D4767 with modifications), 16 isotropically-consolidated resonant column tests (ASTM D4015), 12 Ko-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 Producer were studied but not shown here. Soil conditions revealed by all of the explorations were found to be consistent throughout the project area.