Vibro Replacement and Soil Mixing Ground Improvements at a Shopping Mall Site in San Diego, California, USA

A 230,000 ft2 (21,367 m2) addition was planned for construction at the Plaza Bonita shopping mall in San Diego, CA. The soil profile at the site consisted of fill soils underlain by alluvial deposits followed by San Diego Formation. The saturated loose sand layers were liquefiable and would result in significant settlement under the site design earthquake. In addition, soft clay layers would undergo excessive settlement under heavy building column loads. The geotechnical contractor proposed soil treatment with vibro replacement stone columns to mitigate the site liquefaction and to reduce static settlement under building column loads. Building design changes were ongoing and when two floors were added, soil mix columns were proposed to supplement the stone columns to accommodate the heavy column loads. The geotechnical contractor installed 305 soil mix columns to depths up to 35 ft (10.6 m), and 4,085 stone columns to depths up to 50 ft (15.2 m), across the site between November 2006 and March 2007. These ground improvement techniques reduced the excessive settlements by densification and/or reinforcement of the soils. Extensive site investigation and post treatment verification was conducted. Fifty borings and nearly 100 CPTs were performed at the site. During the production work, the shopping mall design evolved from a single storey department store to a four-storey structure, including a theatre. The geotechnical contractor met the schedule, regulatory and technical requirements while keeping up with the constant design changes to the project. This paper focuses on the design, production work, as well as dynamic and static settlement analysis derived from post-treatment CPTs performed by the geotechnical contractor

Jet Grouting for Mass Treatment to Support an Aggregate Stockpile Building over Very Soft Clays

A gravel storage building and distribution facility was planned for construction at the West Parr yard located in the Port of Richmond, California. The general subsurface profile consists of a fill layer overlying a lens of young bay mud, a soft to med stiff silty clay and clayey silt. Below that lied a deeper dense clayey sand and stiff clay layer. The ground water table elevation observed in borings was approximately 7 to 10 feet below the current ground surface. Loads in excess of 3,500 psf would be applied to these strata and relatively tight settlements tolerances were necessitated to maintain functionality of the building’s conveyor systems. Deep pile foundations were considered but due to the excessive costs and operational challenges, it was elected to implement a ground modification system, jet grout columns, to transfer the loads through the undocumented fill and young bay muds, to the more competent, stiff clay layer below

Vibro Replacement for Liquefaction Hazard Mitigation for Operational Storage Facility in Coronado, California, USA

Vibro replacement stone columns were installed for soil improvement for the construction of a 20,000-square-foot operational storage facility in Coronado, CA. The soil improvement program was conducted to meet seismic and static performance criteria for spread footings founded on improved soil. CPT testing was conducted before and after stone column construction to verify the vibro replacement program. Comparison between pre- and post-construction CPTs showed remarkable increase in the tip resistance in loose sand layers. Accounting for densification and shear reinforcement, the anticipated post-improvement liquefaction-induced settlement was reduced significantly

Estimation of Seismic Compression in Dry Soils Using the CPT

A popular method to evaluate earthquake induced settlements in dry sands is the approach proposed by Pradel (1998) which was based on standard penetration test (SPT) results and is only applicable to clean sands. A simple modification of the Pradel (1998) method is proposed based on cone penetration test (CPT) results and is extended to cover a wide range of unsaturated soils. A key parameter in the method by Pradel (1998) is the small strain shear modulus, Go, which can be estimated from the CPT or measured using the seismic CPT. The CPT can provide a continuous evaluation of seismic compression that allows the expeditious analysis of complicated soil profiles and a framework for sensitivity analyses. Soil parameters, such as soil type, fines content, and equivalent SPT blow count interpolated from CPTs, were compared with adjacent borings and related laboratory test results from a ground improvement site. Both vibro-stone columns and compaction grouting were adopted to mitigate the site seismic settlement. The proposed simple modification of the Pradel method provided a valuable tool to evaluate the effectiveness of ground improvement work

Bio-inspired geotechnical engineering: Principles, current work, opportunities and challenges

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Bio-inspired geotechnical engineering: principles, current work, opportunities and challenges

A broad diversity of biological organisms and systems interact with soil in ways that facilitate their growth and survival. These interactions are made possible by strategies that enable organisms to accomplish functions that can be analogous to those required in geotechnical engineering systems. Examples include anchorage in soft and weak ground, penetration into hard and stiff subsurface materials and movement in loose sand. Since the biological strategies have been ‘vetted’ by the process of natural selection, and the functions they accomplish are governed by the same physical laws in both the natural and engineered environments, they represent a unique source of principles and design ideas for addressing geotechnical challenges. Prior to implementation as engineering solutions, however, the differences in spatial and temporal scales and material properties between the biological environment and engineered system must be addressed. Current bio-inspired geotechnics research is addressing topics such as soil excavation and penetration, soil–structure interface shearing, load transfer between foundation and anchorage elements and soils, and mass and thermal transport, having gained inspiration from organisms such as worms, clams, ants, termites, fish, snakes and plant roots. This work highlights the potential benefits to both geotechnical engineering through new or improved solutions and biology through understanding of mechanisms as a result of cross-disciplinary interactions and collaborations

A Search for Light Fermionic Dark Matter Absorption on Electrons in PandaX-4T

We report a search on a sub-MeV fermionic dark matter absorbed by electrons with an outgoing active neutrino using the 0.63 tonne-year exposure collected by PandaX-4T liquid xenon experiment. No significant signals are observed over the expected background. The data are interpreted into limits to the effective couplings between such dark matter and electrons. For axial-vector or vector interactions, our sensitivity is competitive in comparison to existing astrophysical bounds on the decay of such dark matter into photon final states. In particular, we present the first direct detection limits for an axial-vector (vector) interaction which are the strongest in the mass range from 25 to 45 (35 to 50) keV/c$^2$

Experimental Study on the Damage of Optical Materials by out of Band Composite Laser

For the paper, experimental studies were performed on the damage of the Ge- and Si-based flat window by lasers out-of-band. The experimental results showed that lasers out-of-band can cause film damage and substrate damage to Ge and Si windows. The high-energy laser damage window mechanism mainly manifested as thermal effects. The composite laser damage thresholds for the substrate were an Si window of 21.6 J/cm2 and a Ge window of 3 J/cm2. Compared with continuous laser and long pulse laser experimental results, it was found that the use of long pulse-continuous composite constitution could effectively reduce the damage threshold. Compared to the long-pulse laser, the composite laser could achieve similar damage effects with a smaller energy density

Stress Transfer from Rocking Shallow Foundations on Soil-Cement Reinforced Clay

Equivalent-static pushover analyses with a three-dimensional (3D), nonlinear, finite-difference model are used to investigate the static and seismic stresses imposed on soil-cement grid reinforcements in soft clay profiles by overlying structures supported by shallow footings. The goal is to evaluate the potential stress concentrations in the soil-cement grid during foundation rocking and the potential for large foundation settlements associated with the local crushing of the soil-cement. The numerical analyses are first validated using data from dynamic centrifuge experiments that included cases with and without large foundation settlements and localized crushing of the soil-cement grids. The experimental and numerical results indicate that the stresses imposed on the soil-cement grid by the overlying structures must account for foundation rocking during strong shaking and stress concentrations at the soil-cement grid intersections. The numerical analyses provide reasonable predictions of the structural rocking loads and the zone of the expected crushing or lack of crushing, but underestimate the accumulation of foundation settlements when the seismic demands repeatedly exceed the soil-cement strength. The simulated moment-rotation and uplift behavior of the footings under monotonic lateral loading are reasonably consistent with the dynamic centrifuge test results. Parametric analyses using the validated numerical model illustrate how the stress transfer varies with the area replacement ratio, the thickness of the top sand layer, the properties of the bearing sand layer, and the relative stiffness of the soil-cement and the surrounding soil. A design model for estimating the stresses imposed on a soil-cement grid by rocking foundations was developed and shown to provide a reasonable basis for assessing whether or not local damage to the soil-cement grid is expected

Precise Orbit Determination and Accuracy Analysis for BDS-3 Satellites Using SLR Observations

Satellite laser ranging (SLR) is the space geodetic technique with the highest degree of range, measuring precision and distances right down to the millimeter level. Thanks to the improvement of SLR station layouts and the advance of SLR technology, in recent years, more research has been conducted to determine Global Navigation Satellite System (GNSS) satellite orbits using SLR data. The primary goal of this contribution is to investigate the accuracy of BeiDou Navigation-3 (BDS-3) Satellite precise orbit determination (POD) using solely SLR data, as well as explore the impact of various factors on that accuracy. Firstly, we used actual SLR data to make the POD for BDS-3 satellites, and the POD accuracy was positively connected with the orbital arc lengths. The 9-day median root mean square (RMS) in radial (R), along-track (T), and cross-track (N) directions were estimated at 4.7–8.2, 22.1–35.2, and 27.4–43.8 cm, respectively, for comparison with WUM precise orbits. Then, we explored the impact of SLR observations and stations on POD accuracy. For 9-day orbital arc lengths, five station or 20 observation arcs may offer an orbit with a 1 m precision. Six to eight stations or 30–35 observation arcs allow an improved orbit accuracy up to approximately 0.5 m. Furthermore, we examined how measurement errors and orbit modeling errors affect the SLR-only POD accuracy using simulated SLR data. For orbital arc lengths of 9 days, each cm of random error leads to a 9.3–11.0 cm decrease in orbit accuracy. The accuracy of an orbit is reduced by 10.1–15.0 cm for every 1 cm of systematic error. Moreover, for solar radiation pressure (SRP) errors, the effect of POD accuracy is 20.5–45.1 cm, respectively