California Department of Transportation

This research’s goal is to develop recommendations for improving the interlayer (“bond breaker”) used between jointed plain concrete pavement (JPCP) slabs and lean concrete base (LCB). A full-scale test track was built and monitored to study the slab-base interaction. The test track included four independent slabs, one with asphalt concrete (AC) base and three with LCB and one of the following interlayers: curing compound, geotextile, and microsurfacing. The curing compound interlayer represents current practice in California, U.S., for JPCP with LCB. Test track monitoring included slab curling/warping and falling weight deflectometer (FWD) deflection. Experiment data collected from the track indicate that AC provides much better support to the slab than LCB with curing compound interlayer. When the slab curvature was very high, the corner deflection under FWD loading in the section with LCB and curing compound was up to three times larger than the corner deflection in the section with AC base. The geotextile performed similarly to the curing compound interlayer. However, the microsurfacing considerably improved the performance of the curing compound interlayer. The corner deflection in the section with LCB and microsurfacing interlayer was similar to the corner deflection in the section with AC base. This study demonstrates that, by using the appropriate interlayer, the cracking performance of JPCP with LCB can be improved and potentially match the performance of JPCP with AC base. This outcome results in the recommendation to allow continued use of LCB for JPCP construction in California if a microsurfacing or other interface with similar performance-related properties is used.

This paper evaluates the half-life performance of the first three 40 year design life jointed plain concrete pavements built in California, in the early 2000s. The projects, two on I-15 and one on I-40, have a combined total length of 420 lane kilometers (260 lane miles), are in desert areas, and have heavy truck traffic. The pavement performance evaluation used data from the California Department of Transportation (Caltrans) pavement-management system (PMS) databases, including pavement condition surveys, field data, and construction histories. An in situ evaluation of the projects done in 2022 included measurement of international roughness index (IRI), visual inspection, coring, and falling-weight deflectometer testing. Cores were extracted to explain the field performance based on the modulus of elasticity, compressive strength, electrical resistivity, coefficient of thermal expansion, water absorption, and degree of hydrations of concrete. Overall, the performance of the projects has been excellent so far: the transverse and third-stage cracking (slabs with two or more cracks) is essentially zero in all lanes, faulting is also essentially zero, longitudinal cracking is not severe, and the IRI has been stable since construction. Concrete mix designs and properties from cores correspond to durability observations. AASHTOWare Pavement ME analysis supports the excellent performance of the projects. Further, none of the three projects has required any maintenance or rehabilitation activity since their construction. The outcomes of this study support Caltrans’ adoption of 40 year designs as the standard design life of concrete pavements and encourage the consideration of longer design lives.

The probability distribution model for principal displacement accommodated on the surface main trace is a critical input to the fault displacement hazard analysis. This article presents a new model for strike-slip ruptures in the moment magnitude ( M ) range of 6 to 8.3. The new model is the outcome of a multi-year research effort to update the widely used model developed by Petersen and others in 2011. Updates include the adoption of the Fault Displacement Hazard Initiative database and enhancements to rupture and displacement data preparation. Statistical formulation and estimation have also been updated substantially. A three-parameter modified normal distribution that we refer to as the negative Exponentially Modified Gaussian distribution is adopted to model the probability distribution of the natural logarithm of principal displacement. Formulation for the mean parameter of the modified normal includes a random earthquake term, a nonlinear scaling relation with M , and an ellipse function for along-main-trace variation. The aleatory variability of the updated model now depends on M as well as site’s along-main-trace position. These updates not only significantly improve the fit to the distribution of the observed displacements but also yield reasonable 95th percentile predictions for M > 7.5 events. Alternative models representing the estimation uncertainty of the M -scaling relation are also developed. These new models are compared to the previous model in terms of percentile predictions and the calculated hazard curves. The steeper hazard curves from the new models yield a lower exceedance rate than the normal-distribution based model developed previously by Petersen and others.

A case study is presented comparing three analysis methods used in current practice to estimate earthquake-induced slope and bridge foundation displacements. The West Tower foundation of the Vincent Thomas suspension bridge in the Port of Los Angeles, California, is adopted for the study. A group of 167 steel piles supports the tower, which is located at the crest of a submerged 60-ft tall channel slope, with a relatively soft and weak clay layer near the toe. Earthquake-induced slope movements were evaluated in a prior effort as part of the California Toll Bridge Seismic Retrofit Program of the 1990s and early 2000s. At that time, pile pinning effects were considered using a simplified decoupled procedure. Dynamic response of the potential sliding mass and rigid body movement of the presumed failure wedge (considering pile pinning) were evaluated independently. Since that time, a newer simplified approach has been developed, which accounts for both the deformability of the sliding mass (dynamic response) and the potential for sliding in a coupled manner. In addition, computational efficiency has improved such that fully coupled numerical model (e.g., finite element) time history analyses are utilized more frequently in practice. In the current study, the West Tower slope and foundation movements are evaluated using all three methods described above (simplified decoupled, simplified coupled, and fully coupled finite element time history analysis). The methods are described in detail, and results are presented and compared. Results indicate that the decoupled method predicts the lowest slope and foundation displacements, followed by the coupled method. The fully coupled finite element model analysis resulted in the largest displacements (50% higher than the simplified decoupled method results).