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A high-density polyethylene (HDPE) geogrid soil-reinforced dry-cast concrete block retaining wall 6.3-m high was designed using the K-stiffness method as part of a highway-widening project southeast of Seattle, Washington. The amount of reinforcement needed for the original wall design using the K-stiffness method was approximately 50% of that required using the AASHTO simplified method. This paper describes the construction, instrumentation program, and interpretation of the measurements. Geogrid strains were measured using strain gauges and extensometers attached to reinforcement layers. An extensive materials testing program was conducted to characterize the backfill soil properties and geogrid stiffness properties and to calibrate strain gauge readings. The reinforcement loads deduced from the measured strains are compared with Class A, B, and C1 predictions using the AASHTO simplified and K-stiffness methods. These comparisons demonstrate that the simplified method significantly overestimated reinforcement loads, whereas the K-stiffness method provided estimates that were consistent with the measured results. This paper describes lessons learned, the influence of construction activities on wall performance, and the limitations of both methods in estimating connections loads. [ABSTRACT FROM AUTHOR]

Centrifuge models of soft-clay deposits were shaken with suites of earthquake ground motions to study site response over a wide strain range. The models were constructed in an innovative hinged-plate container to effectively reproduce one-dimensional ground-response boundary conditions. Dense sensor arrays facilitate back-calculation of modulus-reduction and damping values that show modest misfits from empirical models. Low-amplitude base motions produced nearly elastic response in which ground motions were amplified through the soil column, and the fundamental site period was approximately 1.0 s. High-intensity base motions produced shear strains higher than 10%, mobilizing shear failure in clay at stresses larger than the undrained monotonic shear strength. The authors attribute these high mobilized stresses to rate effects, which should be considered in strength-parameter selection for nonlinear analysis. This nonlinear response deamplified short-period spectral accelerations and lengthened the site period to 3.0 s. The nonlinearity in spectral amplification is parameterized in a form used for site terms in ground-motion prediction equations to provide empirical constraint unavailable from ground-motion databases. [ABSTRACT FROM AUTHOR]

Accurately predicting peak penetration resistance qpeak during spudcan installation into sand overlying clay is crucial to an offshore mobile jack-up industry still suffering regular punch-through failures. This paper describes a series of spudcan penetration tests performed on medium-loose sand overlying clay and compares the response to existing centrifuge data from tests performed on dense sand overlying clay. Together these data demonstrate that punch-through is a potential problem for both dense and loose sand overlying clay soil stratigraphies. Using this experimental database, a failure-stress-dependent model has been modified to account for the embedment depth, and the depth of occurrence of qpeak is shown to be a function of the sand thickness Hs. The model then was recalibrated, taking these findings into account, for a larger range of material properties and ratios of sand thickness to spudcan diameter (Hs=D). Finally, the performance of the modified and recalibrated model is verified by comparing its predictions with those calculated using current guidelines. The comparisons show that the modified model yields more accurate predictions of qpeak over the range of Hs=D ratios of practical interest, which when used in practice will potentially mitigate the risk of unexpected punch-through on sand overlying clay stratigraphies. [ABSTRACT FROM AUTHOR]

Interpretation of experimental and field cone penetration test (CPT) data from across a broad range of stress conditions requires defining the dependence of the measurements on overburden stress and other influencing factors. This paper examines three possible methods for overburden normalization of CPT tip resistance in sand at the same state parameter or same relative state parameter. The three methods for determining state-based normalized tip resistance at a reference overburden stress of 101.3 kPa (1 atm) are evaluated against calibration chamber test data for four well-studied clean sands. The CPT data from the calibration chamber tests are corrected for chamber boundary effects using two different methods to illustrate the effect this step has on derived relationships. The CPT data are further normalized to a common lateral earth pressure coefficient to illustrate the effect of this step. The three methods for state-based overburden normalization were evaluated for bias and dispersion against the calibration chamber data, including their dependence on the applied chamber correction relationship. The dependence of state-based overburden normalized tip resistances on the crushing behavior of the clean sand was evaluated by examination of one-dimensional limiting compression curves for these four sands. Finally, correlations for estimating the state parameter or relative state parameter from the state-based overburden normalized tip resistance were developed and evaluated based on the examined data. [ABSTRACT FROM AUTHOR]