Field observations suggest that preshaken natural sands in some seismic regions have high liquefaction resistance as a result of geologic aging and/or preshaking. This paper focuses on the young silty sand deposits located in the Imperial Valley of California. Recent deposition and intense seismic activity in the Valley suggest that preshaking is the main cause of their increased liquefaction resistance. The first part of the paper examines the liquefiable layer at the Wildlife site, which may have been deposited by flooding approximately between 1905–1907. The site was instrumented with accelerometers and piezometers in 2005, providing data over the last 10 years. The following conclusions are reached from this and from the catalog information on earthquakes before 2005: (1) Since 1907, the Wildlife layer has been subjected to approximately 60–70 earthquakes having amax≥0.1 g at the site, which caused pore pressure buildup in the layer; (2) most of these earthquakes generated excess pore pressur...

The effect of extensive liquefaction on the liquefaction resistance of heavily preshaken saturated silty sand is studied using a centrifuge experiment. The base of a 6-m homogeneous deposit was subjected to a total of 91 shaking events of different horizontal base accelerations and durations. Three event types were used in alternating patterns: mild preshaking Events A, stronger preshaking Events B, and strong liquefying Events C. The experiment was divided in two stages. In Stage One, reported in a previous publication, 66 preshaking Events A and B, were applied. In Stage Two, which is the focus of this paper, 25 additional shakings were applied which included two Events C in addition to continuing the same pattern of Events A and B. Stage One resulted in a significant increase in liquefaction resistance of the deposit. In Stage Two, extensive liquefaction produced by Events C resulted in a dramatic immediate reduction in liquefaction resistance of the deposit to a level comparable to that before...

Shear wave velocity is an important parameter for the design of geotechnical systems, particularly in seismically active areas. The availability of a reliable method for measuring shear wave velocity in centrifuge soil models is necessary in order to fully characterize the soil. The paper describes enhanced bender elements system developed at Rensselaer Polytechnic Institute. The fabrication process of bender elements in the laboratory is described in this paper. Also, the estimation of the shear wave velocity using the first arrival method is explained along with a study of near field presence in the results. To confirm the validity of the system, four centrifuge experiments were conducted on dry and saturated Ottawa F#55 sand. A comparison is performed between dry and saturated soil having the same relative density. Also, the effect of the direction of polarization of the shear wave is studied in the paper. The results are then compared to theoretical values estimated based on the literature and are found to match reasonably well; thus confirming the accuracy of the new system.

This study introduces a novel application of gene expression programming (GEP) for the reliability analysis (RA) of reinforced soil foundations (RSFs) based on settlement criteria, addressing a critical gap in sustainable construction practices. Based on the principles of probability and statistics, the soil uncertainties were mapped using the first-order second-moment (FOSM) approach. The historical data generated via a parametric study on a validated finite element numerical model were used to train and validate the GEP models. Among the ten developed GEP frameworks, the best-performing model, abbreviated as GEP-M9 ($R^2$ = 0.961 and RMSE = 0.049), in the testing phase was used to perform the RA of an RSF. This model’s effectiveness in RA was affirmed through a comprehensive evaluation, including parametric sensitivity analysis and validation against two independent case studies. The reliability index (β) and probability of failure (P_f) were determined across various coefficient of variation (COV) configurations, underscoring the model’s potential in civil engineering risk analysis. The newly developed GEP model has shown considerable potential for analyzing civil engineering construction risk, as shown by the experimental results of varying settlement values.

The paper compares two liquefaction case histories in California: (1) the response of the Wildlife site in the Imperial Valley to the 2010 El-Mayor Cucapah earthquake ($M_w=7.2$ , $a_{\max }=0.15\mathrm{g}$ ); and (2) the response of the Treasure Island Fire Station (F.S.) site in the San Francisco Bay area to the 1989 Loma Prieta earthquake ($M_w=6.9$ , $a_{\max }=0.16\mathrm{g}$ ). Both histories involve silty sand critical layers with nonplastic fines contents, $\mathrm{FC}=24–27\%$ , similar normalized shear wave velocities, $V_{s1}=145–155\mathrm{m}/\mathrm{s}$ , low cone penetration test (CPT) cone penetration resistances, and groundwater tables at essentially the same depth. The corresponding data points plot almost on top of each other on the shear wave velocity field liquefaction charts, which predict liquefaction at both sites. While Treasure Island F.S. did liquefy during the shaking, Wildlife did not and was far from liquefaction as indicated by piezometers at the site. This paper constitutes an attempt to understand the reason for these very different pore pressure responses through a detailed analysis of similarities and differences between the two histories. It is concluded that preshaking by previous earthquakes is the most probable explanation of the higher liquefaction resistance exhibited by the Wildlife site and other sites in the Imperial Valley. While the Wildlife critical layer was subjected to about 60–70 earthquakes capable of generating significant excess pore pressures between its estimated 1907 deposition and the 2010 earthquake, the Treasure Island F.S. layer was subjected to only about two earthquakes capable of doing so between deposition in the 1930’s and the 1989 earthquake. This difference is due to the very high seismic activity in the last 100-plus years in the Imperial Valley compared with a seismically quiet San Francisco Bay Area after the 1906 earthquake. The significance of the prior seismic history is corroborated by recent results from centrifuge and large-scale experiments. These results as well as the methodology developed in the paper may be helpful when analyzing the observed high liquefaction resistance of sandy sites located in other seismic regions.