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By Faisal Shalzad, Adnan Anwar Malik, Tadashi Maejima, Jiro Kuwano

Single helix screw piles carry most of the structural load through end-bearing if the helix is embedded in the dense bearing layer. The tip condition of the central shaft of the screw pile can be closed, closed with cutting blades, opened with flat cut, and opened with wedge shape cut and its selection is based on the insitu ground conditions. These different end conditions of the central shaft disturb the ground differently, leading to the change in bearing capacity. In this study, an attempt is made to investigate the effect of open and close-end screw piles on installation effort (installation load and torque) and bearing performance in the dense bearing layer. The model steel screw pile with a pile shaft diameter of 21.7 mm and helix diameter of 43 mm is used in this study. Test results show that the open-end screw pile required less installation effort than the close-end pile that penetrated the bearing layer by 1Dhwith an unplugged condition. Further, the open-end screw pile shows a higher bearing response than the close-end screw pile if it enters the bearing layer with an unplugged condition.

Oct 1, 2022

By Scott M. Doehla

A proposed rehabilitation of a 200,000 sf, 75-foot high steel-frame building at the former U.S. Navy Yard in Brooklyn, New York required the review of existing foundation data and an investigation of the foundations with respect to their condition. The building was constructed in stages between 1856 and 1933, including several expansions and interior equipment with isolated foundations. The building has clear spans on the order of 50 feet and at one time supported cranes allowing transport of heavy equipment through the building. The proposed rehabilitation is to include a food manufacturing center and office space having multiple stories. Original construction drawings, available from the Brooklyn Navy Yard Development Corporation?s drawing archive, were reviewed to determine the foundation system supporting the structure. The original drawings provide a window into the methods utilized during late 19th and early 20th century pile foundation construction. The review revealed that the building is supported by pile foundations ranging from timber to concrete-filled steel pipe (depending on the year of construction). Annotations including pile driving records were available on some drawings indicating the design and as-built capacity (using the ENR formula for driving resistance). An investigation consisting of test borings was performed to identify the subsurface conditions underlying the building for evaluating theoretical capacity of the piles. A test pit investigation was performed against existing columns within the structure to expose the piles and pile caps for inspection pertaining to pile condition. The test pit investigation revealed methods utilized during original construction to integrate new columns with existing floor slabs, the use of below-grade brick arches to support a floor slab, and the condition of timber piles which were likely installed up to 120 years ago. The observations made within the test pits were compared with original drawings to evaluate the accuracy of these drawings.

Jan 1, 2008

By Dean Abbondanza

"Below grade foundation design has construction issues that above grade foundations do not. These cost factors are dependent on soil conditions and vary by region, but for the most part, the process remains standard.An innovative design concept using steel sheet piles as the permanent wall element changes the traditional cost and schedule for below grade foundations. The sheet pile application reduces dewatering requirements, does not require waterproofing on the vertical walls and eliminates the cast in place concrete wall structure.Foremost, this versatile application affords both Contractor and Designer the choice of two methods of construction; conventional bottom up or top down. The top down method not only provides the savings of bottom up, but also eliminates the cost of anchors while taking the foundation out of the critical path in the early stages of construction. CONVENTIONAL FOUNDATIONSINTRODUCTIONUS construction for a conventional below grade (BG) foundation is fairly standard. Design and install the shoring system, followed by dewatering (if groundwater is present), then excavate in stages with installation of anchorage as work proceeds to final elevation. The site is graded for a waterproofing system to be placed at the base. Once the base slab is cast; forms are set for the vertical reinforced walls. After curing , waterproofing is applied to the back side. The remaining levels are constructed until ground elevation is reached. The site is backfilled and the ground floor is cast. The foundation is now complete and work on the superstructure can now begin."

Jan 1, 2005

By Murray Gamble

A new type of groundwater cutoff wall has been developed at the University of Waterloo. The Waterloo Barrier? is a steel sheet piling system that incorporates a sealable cavity at each interlocking joint. In order to prevent leakage through the joints, the sealable cavity is flushed clean and injected with sealant after the installation of the piling. The installation and sealing procedures of the Waterloo Barrier? system allow for a high degree of quality control resulting in a very low permeability cutoff wall. Based upon field installations, the bulk wall hydraulic conductivity of the Waterloo Barrier? ranges from 10-8 to 10-10 cm/sec. Recent case histories are presented in which Waterloo Barrier? vertical cutoff walls have been used to prevent the off-site migration of contaminated groundwater or soil gases. In some instances, the Waterloo Barrier? system was used in combinations of applications such as preventing the migration of contaminants, redirecting the flow of groundwater, providing structural shoring for soil excavation and aiding in site de-watering processes.

Jan 1, 1997

By Georg Breitsprecher

The technique of Stabilising Columns (product names are for example "Stabilisierungssaulen" (STS) or "Coplan Stabilisierungs-verfahren" (CSV)) is gradually becoming well accepted for ground improvement. The installation, dimensioning and quality control are standardized by DGGT (German Association for Geotechnique), working committee 2.8, of which until now only part one exists for dry columns. This paper describes the installation and testing of stabilising columns for a ground improvement project. To achieve comparable results in testing both ready mixed concrete and dry binder had been used for production.

Jan 1, 2006

By Narong Thasnanipan

This paper presents the outcome of the contest on the prediction of the static axial load capacity of diameter 1.20m bored pile founded at 46m below existing ground. The test pile was constructed by wet-processed method and instrumented with vibrating wire strain gauges. Different methods used by the contestants in prediction of load-settlement characteristics are described and compared with actual load test results. Load-displacement behavior of test pile is found to be better than expected. Major difference between prediction and actual test is the higher frictional resistance of Second Sand Layer achieved in the actual load test. The hyperbolic load transfer method used by one of the contestants was applied to back-analyze the load-displacement characteristics of the test pile at different conditions.

Jan 1, 2006

By Waddah Akili

The demand on pile installation in the offshore of the Arabian Gulf has, over the last two decades, experienced unprecedented boom, triggered by the construction of platforms, to help facilitate the production and transport of oil and gas. Available borehole data show that ground conditions for pile installation in the offshore is highly variable, resulting in misassessment of insitu conditions, leading to a huge discrepancy between ultimate pile capacities, based on design, and actual capacities after installation. The paper makes use of pile installation records derived from several platforms in the offshore of the state of Qatar, the Gulf Region. More specifically, the paper evaluates “as–installed” ultimate capacities and safety factors, recommends remedial installation procedures, and proposes a means for determining pile acceptability for piles meeting refusal short of design penetration. The paper offers what is believed to be relevant recommendations to guide the design and installation of future offshore structures; enabling the geotechnical community in the Region to solve their current offshore pile installation problems and gain an added margin of confidence regarding the ultimate capacity of installed piles.

By Kimberly Martin

The EFFC/DFI Carbon Calculator provides the deep foundations industry the opportunity to be a leader when it comes to carbon reduction. This tool was created 10 years ago in an extensive effort by the European Federation of Foundation Contractors (EFFC), DFI, member organizations and Carbone 4, a consultant with ex- perience in life cycle assessment. The tool was born out of the fact that governments and clients were asking for embodied carbon information for foundation systems, and that in- dividual companies were building their own calculators to meet these requests. To help all member organ- izations achieve compliance, and to have a sector-specific tool that is certified to the prevailing standards, EFFC and DFI agreed to partner to create the carbon calculator, which is: Excel based and, therefore, easy to learn and use Updated on a regular schedule Certified to ISO 14067, GHG Protocol and PAS 2050 Free and available for anyone to use Even though this tool is free and easy to use, most projects in the industry do not have a carbon calculation performed. The case to use the calculator is more obvious for members in places like Europe where there are stricter reporting standards and government work can be driven by sustainability over cost. In North America this is not the case, yet. Without directives from clients and governments, what can compel the industry to start regularly using this tool and care about the carbon emissions of projects during design and construction?

Nov 1, 2022

By Alessandro Bertero, Manuel Toniolo, Vincenzo Tirozzi

"The installation of foundation elements (large-diameter Bored Piles or Diaphragm Walls) for the execution of underground works to be performed through the ""Top Down"" Technique (Stations, Car Parks, Subways, Artificial Tunnels) often requires the insertion, with pinpoint accuracy, of steel or prefabricated elements within the foundation system, to provide temporary and/or permanent support to the whole structure.The future high-speed railway station of Florence Belfiore (Italy) is a perfect example; the new station will be built in the Northwest area of Florence, about two kilometers far from the existing station of Santa Maria Novella. The project envisages installation of about 500 bored piles (1200-1500-2100 mm diameter), with lengths ranging between 50 and 70 m. In the upper inner part of 250 piles, a steel pipe (weight: 15-20 tons, length: 22-25 mt.) has to be inserted with pinpoint accuracy.The “TREVI-CALATORE” system allows to install the plunge columns and adjust their position and verticality.INTRODUCTIONThe execution of underground works via the ""Top Down"" technique, train or tube underground stations, parking shafts, tunnels, often implies the need to carefully insert steel or prefabricated structures, serving as provisional/definitive pillars, into the foundation elements.The future high-speed railway station of Florence Belfiore is a perfect example; the new station will be built in the Northwest area of Florence, located about two kilometers far from the existing station of Santa Maria Novella.The new Belfiore Station is part of the new European high-speed railway network. The works related to Florence urban penetration include (figure 1):•,a 6.5 km. twin tunnel excavated via TBM/EPB, that will run beneath Florence in a north-east direction,•,passing under more than 150 buildings, many of which can be considered historic buildings, with a soil•,coverage ranging from 6 m to 20 m;•,a North portal in Rifredi area, Firenze Castello Station;•,a South portal near Campo di Marte Station (which is also the launch shaft of the TBM)•,the new Underground Station in Belfiore area."

Jan 1, 2016

By Michael Lane

With the success of their existing casino operation on the Ohio River in Lawrenceburg, Indiana, the Indiana Gaming Co., LP planned a major expansion of the current facilities. This expansion includes a second 1400+/- car parking garage, a new surface parking lot, elevated walkways, and a new floating casino that will double their present square footage and consolidate all of the gaming activity to one floor. In March of 2006 Richard Goettle, Inc. was awarded the general contract to construct a 260? x 520? boat slip for the new Argosy VII floating casino. An Open Cell® bulkhead system was specified as the means for constructing the new slip. Our contract included the purchase and installation of 300,000 square feet of PS27.5 sheet pile, excavation of 230,000 cubic yards of soil, and a 3300 square foot Mechanically Stabilized Earth wall.

Jan 1, 2008

By Zhou Haizuo, Diao Yu, Zheng Gang

"The conventional design method for the embankment supported by DM columns usually assumes the simultaneous failure of all the columns. However, the progressive failure may occur in practice, especially considering that many researches have justified the critical load of DM columns is bending moment. In this study, a finite difference method was adopted to simulate the embankment on soft clay improved by DM columns. An increasing surcharge was applied on the embankment surface to investigate the mechanism of the progressive failure of columns beneath embankment. To capture the brittle bending failure of the DM columns, the model employed a cut-off method, in which the column was separated on failed section as long as the ultimate bending failure was reached. Furthermore, high-strength DM columns were used to enhance the global stability of embankment in this study. The numerical results showed that the ultimate bending failure was first reached at the column beneath embankment toe, and then a continuous collapse extended to the column beneath the embankment shoulder. It is found that the reinforcement could be obviously effective when the reinforced area of high-strength DM columns was extended to a certain area.INTRODUCTIONDeep mixed (DM) columns have been commonly used as a soil-improvement technique to increase stability and to reduce settlement of embankment. Research on failure modes of DM columns owing to embankment fill and surcharge has been the subject of interest for a number of investigators (Miyake 1991; Kitazume 2000; Han 2005; 2006).The potential failure modes of DM column include bending, inclination, shearing, rotating, soil flowing and a combination of these modes (Kitazume and Terashi 1991; Broms 1999). Many researchers have found that bending failure of DM columns was more critical than the shear failure. A centrifuge test was performed by Kitazume (2000) and the results showed that the columns failed in bending before shear failure. In addition, several numerical computations illustrated that design method using the shear strength overestimated the stability of embankment over DM columns (Han and Huang 2005; 2006; Navin 2006; Liu 2007; Wang 1996). In practice, an equivalent shear strength method based on bending failure could better reflect the stability of embankment (Zheng 2010; China Code JGJ79-2011)."

Jan 1, 2015

By Scott A. Walker, Gabriel J. Alcantar, Brian Zuckerman, Ramin Golesorkhi

"The stadium development consists of construction of a 68,500-seat, open-air NFL football stadium for the San Francisco 49ers. The main structure will consist of a 7-story above grade steel structure supported by over 3,000 piles. Berkel and Company Contractors, Inc. (Berkel) was selected as the design-build pile contractor who used their auger pressure grouted displacement (APGD) piles for this project. During an indicator pile installation and pile load test program, fifteen piles were tested to develop installation criteria to support demands of 150kips tension and 180 kips compression. Following the indicator pile program Berkel installed 3088 piles in 30 working days. Throughout pile installation data were collected with an automated data acquisition system (DAS). During pile installation field engineers from Treadwell & Rollo observed the pile installation as well as the real-time data from the DAS. Strategic staging and pre-production planning by Berkel along with consistent collaboration with the design team created an atmosphere for a successful and on schedule project completion.IntroductionThe new San Francisco 49ers Stadium in Santa Clara, California will be a 68,500-seat facility, a rendering of which is shown in Figure 1. The main structure will consist of a 7-story above grade steel structure supported by more than 3,000 piles. The north, east and south portions of the stadium are designed as an open seating bowl, while the western portion includes open seating at the lower levels and seven-story tower which houses over 150 suites.The stadium project includes the stadium structure, as well as elevated open pedestrian walkways, commercial community space, and three new pedestrian bridges spanning a nearby by creek. Sustainable designs and innovations such as a green roof, photovoltaic panels, a ground source geothermal system, stadium-wide Wi-Fi capability, and access to public transit are provided throughout the project. The stadium is designed as an open, light, and airy structure and is surrounded by an existing amusement park, office buildings, the Santa Clara Convention Center, and the training facility of the 49ers."

Jan 1, 2015

By Paul R. Lear

Sustainability continues to be an important aspect of remediation and infrastructure projects. Deep soil mixing (DSM), a common construction and remedial technology, can easily incorporate the following sustainability best management practices (BMPs), including Minimizing Total Energy Use and Maximizing Use of Renewable Energy; Minimizing Air Pollutants and Greenhouse Gas (GHG) Emissions and Maximizing Use of Machinery Equipped with Advanced Emission; Minimizing Water Use and Impacts to Water Resources; Beneficial Reuse of Materials/Reduction of Materials and Waste Reduction; Use of Local Labor and Supplies. This paper focuses on the sustainability of DSM treatment and provide carbon footprint calculations at least one completed DSM project which used these sustainability BMPs to demonstrate the environmental impact of the sustainability.

Sep 8, 2021

By Shawna Munn, Jakub Hudler

This paper outlines the use of tunneling headwall softeyes for transit construction projects in the Greater Toronto Area (GTA) over the past decade. Due to spatial constraints, tunnel boring machines were used to construct the underground tunnels requiring the design of launch and exit shafts with headwall softeyes to facilitate tunneling operations. Variable ground conditions and shaft geometries lead to the development of innovative headwall and tunnel softeye design applications using fiber reinforced polymer (FRP) elements (beams, reinforcing bars, and tiebacks). This paper outlines the challenges and benefits associated with designing and constructing shafts using various systems. Lessons learned throughout design and construction of more than 20 structures over the past 10 years are outlined. The constructability challenges with using FRP and design performance are also discussed. For over a decade, the City of Toronto has been expanding its metropolitan transit network with a variety of new transit construction projects. Two recent projects in the Greater Toronto Area (GTA) for underground infrastructure include the Toronto York Spadina Subway Extension and the Eglinton Crosstown Light Rail Transit project. These add a total of 31 new stations and 18.6 km (11.5 miles) of underground transit (TTC 2017) (EllisDon 2016). Due to ground conditions and spatial constraints of existing surface infrastructure, these projects utilized tunnel boring machines (TBMs) to construct the underground tunnels requiring the design of various types of shafts and headwalls to facilitate underground tunneling operations. To allow for tunneling through the headwalls, these shafts were designed with “softeyes” - a section of the wall without metal reinforcement that allows the TBMs to tunnel through.

Jan 1, 2018

By Karen Dawson

Pressure-grouted helical piles support a new seven-story homeless housing center in the Coney Island neighborhood of Brooklyn, New York. The project team instrumented and statically load tested piles to as much as 1,000 kips (4.4 MN) in advance of construction to obtain the approval of the New York City Building Code officials and to verify the design. Use of pressure-grouted helical piles required additional design effort and time risk because of New York City's Construction Code Determination (CCD1) process, which is required for non- standard deep foundation types. Despite

May 1, 2022

By Joel L. Volterra

Since 1910, Mueser Rutledge Consulting Engineers (MRCE) has regularly provided professional engineering services including inspection of pile load tests. Historically, such services included on-site inspection of the driving of test piles and subsequent static load tests by qualified Geotechnical Engineers. Load testing procedures are specified by local or State Building Codes, locally the 1968 Building Code of the City of New York (1968 BCCNY). Between 1968 and 2008, the 1968 BCCNY required a minimum 48-hour hold period for standard loads per pile type, an extended 96-hour hold period for higher capacity piles, and a settlement criterion that the pile maintain a test load equal to two times the design load with less than 0.012 inches of settlement over the last 48 hours of the hold period. Effective July 2008, the new 2008 BCCNY shortened the hold period and relaxed the settlement criteria to that which is more similar to other governing codes and standards such as the International Building Code (IBC 2006) and the American Society for Testing and Materials (ASTM). MRCE implemented an automated load test monitoring system to reduce costs and to alleviate or minimize overnight and off-hour staffing for load test readings. Initially, a series of linear variable differential transformers (LVDTs) and data loggers were included in the Contractor?s load test setup to electronically record pile head settlement and where applicable, settlement of telltales installed to varying depths in the pile. A pressure gage was subsequently added in the hydraulic line, then a load cell, strain gages, and remote access using modems. The ease of the setup and modular adaptive nature of this system have proven it to be a useful tool and improved our ability to better serve our clients and manage our pile load testing services.

Jan 1, 2008

By Michael Cianchetti, Nadir Ansari, Matthew Janes

"PROJECT DESCRIPTIONThe R C Harris Filtration Plant underwent an expansion to install an underground sludge treatment capability consisting of a series of underground tanks within stepped excavations 12m (39 ft) and 10m (33 ft) deep into compact, wet sands over stiff clays and clayey silts.Concerns regarding the original structure influenced designers to set the lateral deflection limit for the proximal front footing at 4mm (1/6 in), (0.03% excavation depth). The design-build team indicated at the time of tender that the movement criteria was unattainable using the tender design. Through extensive Fast Lagrangian Analysis on Continua (FLAC) and a novel construction geometry the design-build team crafted an alternative that produced significant savings over the original concept and met deflection concerns.GEOTECHNIQUEThe hillside site drops 14.5m (47.6 ft) over a distance of 53m (174 ft) between the existing Filter Building on the north and the Services Building on the south. The soils adjacent to the Filter Building consist of 6m (20 ft) of sandy fills, to the footing elevation, over compact sands and layered dense sands and silts to a depth of 10m (33 ft) below existing footing. Beneath the silts lies a 10m (33 ft) thick stiff clayey silt, 2m (6.6 ft) of sandy silt till (containing cobbles and boulders) and an artesian gravelly sand at a total depth of 30m (98.5 ft).The tender information was deemed inadequate to accurately determine soil parameters for a finite element analysis. As a result, the design-build team performed pre-tender Cone Penetrometer Testing (CPT), including dynamic analysis. The CPT data indicated stratigraphy consistent with the conventional bore hole exploration (SPT results) however, the CPT data provided consistently superior soil strengths. The CPT data indicated the sands and silts were dense to very dense throughout their full thickness. The clayey silts below the sands were found to have shear strengths in the 100 to 200 kPa (14.5 to 29 psi) range with an Over-Consolidation Ratio (OCR) ratio of 1.5 to 2. The dynamic analysis, while low strain, indicated very competent behavior with Young’s Modulus values in the 200 to 350 MPa (29,000 psi to 51,000 psi) range. The CPT derived shear moduli and OCR values were vital in determining the soil engineering parameters used for the FLAC analyses."

Jan 1, 2007

By Anne Fagot

Because of the risk of corrosion caused by stray currents, steel foundations and steel sheet piling are generally prohibited in the vicinity of railway structures. Steel solutions are only accepted if they are shown to meet the required design working life and if this can be achieved at an acceptable cost compared to competing materials. The influence of stray currents on various steel sheet piling designs was studied using software initially dedicated to gas and pipeline industries and cathodic protection systems. It has been successfully adapted to model stray currents affecting steel sheet piling. Corrosion rates assessed using this modeling software were considerably lower than commonly expected. Zones of potential corrosion risk were identified; specific cost-effective countermeasures could be established. The developed software tool can help to optimize the design of piling solutions in the vicinity of DC railway power systems in terms of suitable countermeasures that meet structural reliability and cost requirements.

Jan 1, 2008

By Abhijit Saha

"Two analytical closed-form elastic-rigid-plastic solution methods to predict the rigid foundation behaviour on stone-column reinforced soil are compared, both of which takes into account the stone material yield within the host soil according to stress-dilatancy theory. These are the mechanistic methods developed by the author (2004, 2005) [that presently incorporates the dilatancy angle as per Schanz and Vermeer (1996)] and that developed by Pulko and Majes (2006), that takes into account the column yield as per Rowe dilatancy theory. Since optimal design of stone column necessitates optimum stress concentration on column, which is generally composed of dense gravel with/or without sand, the vertical stress on granular column is often close to its peak strength and the material dilates. To arrive at closed-form analytic solution to this complex soil-stone column interaction problem, some common assumptions like axi-symmetric soilstone column ‘unit-cell’, elastic host soil and rigid-plastic Mohr-Coulomb stone column material are combined with equilibrium and kinematic conditions. The results reflect the beneficial effect of dilatancy within the optimal range or techno-economic domain of area-ratio. The settlement predictions are compared with other analytical methods available in literature as well as with measured settlement reduction of stonecolumn reinforced ground at different subsoil conditions around the globe reported in literature.INTRODUCTIONStone columns or granular piles are frequently used in stabilization of soft clays, silts and loose silty-sands with large amount of fines. The majority of analytical methods assume infinitely wide loaded area with end-bearing columns having constant diameter and spacing that approximate to axi-symmetric conditions, and the approach is known as ‘unit-cell concept’. Several analytical solutions are available, and many of them (Aboshi et al; 1979, Balaam & Booker; 1981) are based on elastic approach considering the stonecolumn and surrounding soil as elastic materials. However, elastic methods give the ratio between the vertical stress in the column to soil (stress concentration factor) approximately equal to the ratio of constrained modulus of both materials. This ratio was found to be considerably higher than measured in the field and it is believed that elastic methods may overestimate the effects of stone columns on settlement reduction (Barksdale & Bachus, 1983). The elastic and elasto-plastic solutions presented by Balaam and Booker (1981, 1985) indicate that the problem can be idealized by assuming that the stone column is in a triaxial state and possibly yielding, such that there is no shear stress at the stone-soil interface and no yielding in the soil. Similar assumptions of stone column to be in a state of limiting equilibrium and under a triaxial stress state are considered in other methods also (Priebe; 1976, Van Impe & De Beer; 1983, Van Impe & Madhav; 1992, Saha & De; 1994, Saha; 2004, 2005, Pulko & Majes; 2006). In majority of the methods it is assumed that under load the stone-column yields at constant volume. However, the last three cases cited consider another parameter; the dilation of stone column. In Van Impe and Madhav’s (1992) and author’s (2004, 2005) method, the dilation is taken into account through the final value of the volumetric strain of column, whereas Pulko & Majes (2006) considered the stone column as Mohr-Coulomb rigid-plastic; dilating at yield in line with Rowe (1962) dilatancy theory."

Jan 1, 2015

By Arash Saeidi Rashk Olia, Dunja Perić

The increasing demand for renewable energy has attracted attention to energy geostructures as means of extracting clean geothermal energy from the ground. To further advance the understanding of soilstructure interaction in energy piles analytical solutions considering the self-weight of the pile were derived. These solutions were then incorporated in recently-derived thermomechanical weightless solutions to provide comprehensive analytical solutions for axial displacement, strain and stress in single energy piles. This was accomplished by comparing responses of energy pile under different loading scenarios that reflect presence and absence of the self-weight. Results of mechanics-based analysis revealed that the self-weight of energy piles embedded in stiff soils has no significant contribution to displacement, strain and stress that develop under thermo-mechanical loads. Overall, the significance of the self-weight contribution depends on the magnitude of thermal load as well as the soil-pile interface stiffness. The stiffness of end restraints imposed to the pile head and tip were also found to play an important role in contribution of self-weight in induced thermomechanical stresses in energy piles.

Oct 1, 2022