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Map of southern California showing locations of WLA and GVDA and epicenters of earthquakes with magnitudes greater than 4.5 between 1932 and 1997.
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As part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES), two permanently instrumented field sites for monitoring ground motion, pore water pressure generation, ground deformation, and soil- foundation-structure interaction (SFSI), were added to the NEES equipment portfolio. The sites are the Wildlife Liquefaction Arr...
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... pore water pressure generation, ground deformation and soil-foundation-structure interaction (SFSI). The purpose of this project is to provide such data by instrument ing two field sites, the Wildlife liquefaction array (WLA) and the Garner Valley downhole array (GVDA). Both sites are located in highly seismic areas of southern California ( Fig. 1). Each site is equipped with surface and downhole accelerometers, pore pressure transducers, and inclinometers to monitor ground response and ground deformation during earthquake shaking. In addition, GVDA will be equipped with a single-degree-of-freedom structure to monitor SFSI response. When completed, the sites will become part of ...
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... levels ranging from 0.2 g to 0.4 g. The results of that analysis, noted on Fig. 9, indicate that for a peak acceleration of 0.3 g to 0.4 g, a likely occurrence, much of the granular layer would liquefy. With the nearness of the incised river, liquefaction to this extent would likely lead to ground deformation and lateral spread toward the river. Fig. 10 shows the approximate locations of instruments placed at the site. The purposes of the downhole and horizontal FBA arrays are to monitor ground response during future earthquakes. The piezometers are to monitor pore water pressure changes generated in response to ground shaking and ground deformation. The piezometers are field-proven ...
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... installed in a small instrumentation structure erected at the site, records data from all of the instruments. The recorded data is streamed from the site by radio link in near real-time to the NEES grid data GVDA is in a seismically active region and lies only 7 km from the main trace of the San Jacinto fault and 35 km from the San Andreas fault (Fig. 12). Historically, the San Jacinto is the most active strike-slip fault system in southern California. A fault slip rate of 10 mm/yr and an absence of large earthquakes since at least 1890 lead to a relatively high probability for magnitude 6.0 or larger e arthquake on the San Jacinto fault near the site in the near future. The ...
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... site. This station contains an FBA set into the rock surface and a second FBA set at a depth of 30 m. Data from this remote site is telemetered back to the main station via a radio link. Pore-pressure response within the alluvial sand and decomposed granite layers are monitored by an array of seven piezometers set at depths between 3 m to 13 m (Fig. 18). These piezometers are set in gravel packs placed at the bottoms of uncased boreholes. Bentonite chips were placed above the gravel packs to seal the boreholes. These piezometers are ParoScientific and PSA models that were set in February 2000 to replace a previous set of piezometers that had ...
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As part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES), two permanently instrumented field sites for monitoring ground motion, pore water pressure generation, ground deformation, and soil-foundation-structure interaction (SFSI), were added to the NEES equipment portfolio. The sites are the Wildlife Liquefaction Arra...
Citations
... The test structure is located in Garner Valley, California, as part of the Garner Valley Differential Array (GVDA), which is part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) (Youd, Steidl, and Nigbor 2004). It has a simple one-story structural system. ...
... The geometry of the system is shown in Figure 1. A detailed account of the structural and soil properties can be found here (Tileylioglu et al. 2011;Youd et al. 2004). To facilitate soil-structure interaction research, the structure is equipped with an advanced instrumentation plan consisting of multiple accelerometers, displacement transducers, and soil pressure sensors to record both the soil and structural responses (Youd et al. 2004), which is shown in Figure 2. ...
... A detailed account of the structural and soil properties can be found here (Tileylioglu et al. 2011;Youd et al. 2004). To facilitate soil-structure interaction research, the structure is equipped with an advanced instrumentation plan consisting of multiple accelerometers, displacement transducers, and soil pressure sensors to record both the soil and structural responses (Youd et al. 2004), which is shown in Figure 2. ...
The state-of-practice soil-structure interaction (SSI) analysis is based on analytical models with simplifying assumptions regarding the soil-structure system behavior. There is, however, a lack of validation studies of the available analytical solutions. In this study, we propose validating the existing analytical models through identifying soil-structure systems, using their real-world measured responses, and comparing the identified models to their analytical counterparts. The proposed soil-structure system identification framework is based on a Bayesian time-domain model updating and parameter estimation technique. In this paper, the proposed framework is employed for identifying a test structure located in Garner Valley, California, using its recorded response during a forced-vibration test. The estimated values of the soil-structure model parameters show a notable discrepancy with their analytical equivalents. The potential sources of this observed discrepancy are discussed, and a refined solution is proposed.
... The WLA soil deposit consists of a shallow layer of silty clay up to 2.7 m depth, underlain by a liquefiable silty sand layer up to 6.5 m depth, followed by silt and clay intercalations [34,35]. Also, it is estimated that the bedrock is around 1000 m deep [36]. ...
Nakamura and Takizawa (1990) proposed a shear strain model from experimental studies using the horizontal-to-vertical spectral ratio (HVSR) in potentially liquefiable sites. This model allows estimating the maximum surface layer shear strain during an earthquake. In this paper, the model's experimental verification is performed by analyzing more than 130 earthquakes in two monitoring centers with potentially liquefiable soils. It is concluded that the model may be used to estimate the maximum soil shear strain for earthquakes with peak ground acceleration greater than 5 cm/s2 and when the soil deposit has a soft surface layer over a rigid layer. A methodology to identify potentially liquefiable sites based on this model was proposed and tested in an alluvial soil deposit in Santiago de Cali (Colombia). The results are compared with those obtained from the liquefaction assessment using CPT and Vs, and a good match between the methodologies is observed.
... The groundwater level is shallow, fluctuating at a depth of approximately 1-1.2 m. The characteristics of the soil at the site have been amply investigated and documented (Bennett et al. 1984;Youd and Wieczoreck 1984;Vucetic 1986;Dobry et al. 1992;Youd et al. 2004). Based on radiocarbon information, the liquefiable layer is less than 230 years old, and Holzer and Youd (2007) The case histories of natural soils in Fig. 1 include data from five earthquakes of magnitudes ranging from 5.9 to 7.2 that shook the Wildlife site in the 31-year period between 1979 and 2010. ...
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 pressures but generally did not liquefy the soil (Events A); and (3) approximately 10 or 20% of all earthquakes were capable of liquefying the layer immediately after deposition (Events B). This information was used to plan a centrifuge experiment that crudely simulated the history of the Wildlife site. In this test, 66 base shakings were applied to the base of a 6-m prototype homogeneous deposit of loose saturated silty sand, with a ratio of one Event B for every 10 Events A. Events B liquefied the deposit at the beginning but not at the end of the experiment. Events A liquefied the deposit at very shallow depths at the beginning but stopped liquefying it very soon into the experiment. Finally, an Event B caused the next Event A to generate more excess pore pressures, with this effect being canceled rapidly by a couple of subsequent Events A. The lack of liquefaction by Events B after heavy preshaking in the experiment is consistent with theWildlife layer response to the 2010,Mw = 7.2, El Mayor-Cucupah earthquake, an Event B that generated only a 19% pore pressure ratio at the site.
... In recent years, Youd et al. [2] have performed some comparative studies between the records from the Wildlife site after the 1987 Elmore Ranch and Supersttion Hills earthquakes and numerical analysis. Through the comparison, Youd et al. [2] pointed out that, due to soil stiffness softening in liquefaction, spectral accelerations attenuate for periods less than 0.7 s, but for periods larger than 0.7 s, spectral accelerations are amplified. ...
... In recent years, Youd et al. [2] have performed some comparative studies between the records from the Wildlife site after the 1987 Elmore Ranch and Supersttion Hills earthquakes and numerical analysis. Through the comparison, Youd et al. [2] pointed out that, due to soil stiffness softening in liquefaction, spectral accelerations attenuate for periods less than 0.7 s, but for periods larger than 0.7 s, spectral accelerations are amplified. Similar work has been performed by Lopez [3] for the Port Island in the 1995 Kobe earthquake, the Wildlife site in the 1987 Superstition Hills earthquake, and the Treasure Island-Yerba Buena Island in the 1989 Loma Prieta earthquake. ...
... But Lopez obtained different results from those of Youd et al., except for the Wildlife site. From the results of Youd et al. and Lopez [2], we note: 1) equivalent linear models were used to model soil nonlinear response, in that pore-water pressure was not taken into account, and 2) liquefied site response is dependent on the strength of excitation, indicating that it is very difficult to use one excitation to obtain a reliable A result, because even if an estimated earthquake magnitude and source distance are given, the selected excitation will contain a number of uncertainties. ...
To understand the characteristics of seismic response at liquefied sites, a liquefiable site and a non-liquefiable site were selected, separated by about 500 m and having the same site conditions as Class D in the National Earthquake Hazards Reduction Program (NEHRP). A suite of earthquake records on rock sites are selected and scaled to the spectrum of the Joyner, Boore, and Fumal (JBF) attenuation model for a magnitude 7.5 earthquake at a distance of 50 km. The scaled records were then used to excite the two sites. The effect of pore-water pressure was investigated using the effective stress analysis method, and nonlinear soil behavior was modeled by a soil bounding surface model. Comparisons for spectra, peak ground acceleration (PGA), peak ground displacement (PGD) and permanent displace-ment were performed. Results show that the mean ground response spectrum at the non-liquefied site is close to the es-timated ground response spectrum from the JBF model, but the mean ground response spectrum at the liquefied site is much lower than the estimated ground response spectrum from the JBF model for periods of up to 1.3 s. The mean PGA at the non-liquefied site is about 1.6–1.7 times as large as that at the liquefied site, but the mean peak ground dis-placement (PGD) at the non-liquefied site has a slight difference with that at the liquefied site. The mean permanent displacements at the liquefied site are larger than those at the non-liquefied site, particularly at the liquefied layer.
... The masses of the intermediate structural elements are 1.7 and 2.0 Mg for the unbraced and braced configurations, respectively. The SFSI test structure is instrumented with triaxial and uniaxial accelerometers, shown in Fig. 4, and other sensors not used in the present research but described by Youd et al. (2004). Signals are digitally recorded at 24-bit resolution and a 200 Hz sample rate. ...
Foundation impedance ordinates are identified from forced vibration tests conducted on a large-scale model test structure in Garner Valley, California. The structure is a steel moment frame with removable cross-bracing, a reinforced concrete roof, and a nonembedded square slab resting on Holocene silty sands. Low-amplitude vibration is applied across the frequency range of 5-15 Hz with a uniaxial shaker mounted on the roof slab. We describe procedures for calculating frequency-dependent foundation stiffness and damping for horizontal translational and rotational vibration modes. We apply the procedures to test data obtained with the structure in its braced and unbraced configurations. Experimental stiffness ordinates exhibit negligible frequency dependence in translation but significant reductions with frequency in rotation. Damping increases strongly with frequency, is stronger in translation than in rocking, and demonstrates contributions from both radiation and hysteretic sources. The impedance ordinates are generally consistent with numerical models for a surface foundation on a half-space, providing that soil moduli are modestly increased from free-field values to account for structural weight, and hysteretic soil damping is considered.
... Simplified cross-section A -A 0 of sediment layers beneath WLA site interpreted from CPT data (after Youd et al.[13]). ...
... Map of new WLA site with locations of CPT soundings and proposed positions of instruments to be placed at site (after Youd et al.[13]). ...
... Liquefaction resistance of sediments penetrated by CPT 35 at WLA for a magnitude 6.5 earthquake and various level of a max (after Youd et al.[13]). ...
Instrumented sites provide essential information for understanding and modeling of ground response and ground deformation. For example, significant new lessons were learned from responses at the Wildlife Liquefaction Array (WLA) including: (1) soil softening led to lengthening of period of transmitted ground motions; (2) soil softening also led to attenuation of short-period spectral accelerations (<0.7 s); (3) amplification of long period motions (>0.7 s) occurred due to liquefaction-induced ground oscillation; and (4) ground oscillation led to a continued rise of pore water pressures after strong ground shaking ceased. A new and expanded instrumented site is being developed 70 m downstream from the old WLA site as part of the NSF Network for Earthquake Engineering Simulation (NEES). The new site has more accelerometers, piezometers and ground deformation measurement devices and the data will be streamed to the NEES-grid in near real time.
... The 1982 WLA instruments recorded accelerations above and below the liquefied layer, and pore water pressures within that layer as liquefaction developed during the 1987 Superstition Hills earthquake (Holzer et al, 1989). From these records, Youd et al. (2004) note four major lessons learned: (1) soil softening led to lengthening of period of transmitted ground motions; (2) soil softening also led to attenuation of short-period spectral accelerations (< 0.7 sec); (3) amplification of long period motions (> 0.7 sec) generated by Love waves caused high amplitude (> 100 mm) ground oscillations; and (4) these ground oscillations led to large cyclic shear deformations that continued to generate pore water pressure after strong ground shaking ceased. ...
In 2003-04, the Wildlife Liquefaction Array (WLA) was re-instrumented as part of the US National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES). This site was selected because of the need for additional field recordings, high liquefaction susceptibility, and a history of moderate and larger sized earthquakes in the region. The new and old sites are instrumented with 8 downhole accelerometers, 4 surface accelerometers, 11 piezometers, and 3 flexible displacement casings and a network of 30 survey monuments for measurement of ground deformation. The downhole accelerometers are at depths of 3 m (above the liquefiable layer), 5.5 m (within the liquefiable layer), 7.5 m (below the layer), and 30 m and 100 m. To allow ease of removal and replacement, pressure transducers at WLA are installed beneath packers installed about 600 mm above the bottom of 50-mm diameter casings with 300-mm long slotted sections and end caps at the base. SPT tests were conducted at 0.9 m intervals with the final SPT at the depth at which the slotted section is installed. No. 3 Monterey sand was placed around the lower part of the casing forming a 0.4-m to 0.6-m thick sand pack. A charge of bentonite chips was poured down the hole to form a 0.6 m to 0.9 m thick seal above the sand. The holes were then grouted the ground surface. Prior to installing pressure transducers, permeability tests were conducted in each casing by filling it with water and timing the fall of the water as it seeped into sediment surrounding the sand pack.
The east of Cali is composed of loose sand deposits with high water table levels. This condition and the high seismic hazard of the city make cyclic liquefaction one of the main hazards in the city, which may affect more than 600,000 citizens and important infrastructures such as the city’s main drinking water treatment plants. Therefore, it was decided to design and implement a seismic monitoring center to study the behavior of liquefiable soils under local seismogenic conditions, in which subduction earthquakes predominate. First, more than 130 earthquakes from two seismic monitoring centers with liquefiable layers in the USA were studied to determine the requirements for the adequate design of the monitoring center. Then, a robust geotechnical and seismic characterization of the study area including SPT, CPTu, and seismic and ambient noise tests were carried out. From this information, the specifications and location of the instruments and, in general, the characteristics of the monitoring center were defined. The monitoring center has been planned to be established in two stages, and the first one has already been built and commissioned. The implementation of the first stage allowed to adequately record 35 earthquakes from different seismogenic sources, most of them from subduction earthquakes, and to verify that the potentially liquefiable layer remains saturated throughout the year. Subsequent ground motion sensors will allow to deeply study and understand large shear strains and excess pore pressures generation in the soil deposit, as well as their relationships with different intensity measures. The experience shared herein can benefit the design, construction, and operation of other seismic monitoring centers across the world.
Instrumented field sites provide essential information for understanding and modeling ground response generated by earthquake shaking of liquefiable sites. For example, several instrumented liquefaction sites have been strongly shaken by earthquakes since 1987, including the Wildlife Liquefaction Array (WLA) in southern California and the Port Island Downhole Array (PIDA) site near Kobe, Japan, highlighted in this paper. Measured ground responses at the WLA and PIDA sites are compared with predicted ground responses that should have occurred in the absence of soil softening and liquefaction. At these strongly shaken sites, soil softening during the liquefaction process reduced short period (<0.7 sec) while increasing long period (>1.0 sec) spectral accelerations. Two new liquefaction sites are being instrumented as part of the NSF NEES program: (1) the WLA site has been reestablished with more FBA's and piezometers and more ground deformation monitoring capability; (2) a previously instrumented site, the Garner Valley Downhole Array (GVDA), is being enhanced with an additional downhole FBA, new piezometers, and a soil-foundation-structure-interaction experiment (not discussed herein). Data from these sites will be streamed to the NEES-grid in near real time.
