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Final Report: Deep Foundations on Brownfields Sites
EPA Grant Number: R825427C003Subproject: this is subproject number 003 , established and managed by the Center Director under grant R825427
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Urban Waste Management and Research Center (University New Orleans)
Center Director: McManis, Kenneth
Title: Deep Foundations on Brownfields Sites
Investigators:
Institution:
EPA Project Officer: Krishnan, Bala S.
Project Period: August 17, 1998 through May 30, 2002
RFA: Urban Waste Management & Research Center (1998)
Research Category: Targeted Research
Description:
Objective:Brownfields are often desirable building sites because of their location within or close proximity to urban areas. Construction at these sites often raises questions regarding environmental and health issues. One such question is the potential for contaminating deeper aquifers via the pile foundations often required for industrial or multi-story structures. Piles penetrating contaminated soils and driven through an aquitard to achieve end-bearing in a deeper sand aquifer may transfer or provide a migration pathway for contaminants. The current knowledge of pile/soil behavior in a contaminated soil environment is very limited. Consequently, regulatory authorities often require extensive and expensive protection measures (such as grouted casing) for piles in this situation. Thus, there is a real world need to address this topic to serve as a guide in the design of pile foundations in a brownfield environment.
The main concern is that the penetration of the contaminated zone and the aquitard by the pile will transfer and/or allow the migration of contaminants vertically. While there would be slow movement through the clay aquitard, the mechanisms created by the pile are (1) direct transfer of soils at the pile tip, which is a one-time event, (2) flow in the zone disturbed by pile-driving, including the pile/soil interface, and (3) flow through the pile material itself. The flow mechanisms are long-term phenomena. The objective of this study was to evaluate the cited mechanisms to determine if pile foundations can be used in an environmentally safe manner for a brownfield situation without special protective measures. Direct transfer was evaluated through geohydrologic calculations. The vertical transfer of flow along the pile/soil interface and the influence of the pile type was investigated through laboratory modeling. The long-term flow is the most serious potential problem. The model tests investigated the effects of pile type on flow and contaminant migration.
Summary/Accomplishments (Outputs/Outcomes):The first evaluation was of direct transfer. A simple theoretical study was carried out to evaluate the direct transfer mechanism. When a pile is driven, its tip can carry down a conical plug of the soil through which it passes. The volume of the soil plug (V) for a flat-tipped pile driven through clay is about 0.15D3, where D is the pile width/diameter. Initially, the contaminant concentration in the pore water of the plug is the same as that in the contaminated upper stratum (co). The volume of actual contaminant in the plug is the plug volume (V) times the soil porosity (n) multiplied by co. Some of the contaminated initial plug is lost during driving, especially when the pile tip passes through stronger materials.
However, regulatory concerns would be more appropriately addressed by examining
the maximum concentrations downgradient of a pile group in a flowing aquifer.
Calculations were made to determine the maximum (c/co)
values along the x-axis (cm/co). The assumed parameters
are presented on Figure 1, which also presents the results in terms of (cm/co)
versus distance from the downgradient pile face, both for a single pile and
for a 9-pile group.
Table 1 presents xo distances for various initial concentrations co of these groups, again assuming the worst case: flat-tipped piles.
| Group | MCL | Single Pile xc (meters) | 9 - Pile Group xc (meters) | ||
| (mg/L) | co = 10 mg/L | co = 1000 mg/L | co = 10 mg/L | co = 1000 mg/L | |
| Pet. Hydrocarbon | 0.34 | <1 | 3 | <1 | 10 |
| Heavy Metals | 0.015 | 1 | 20 | 4 | 80 |
| Volatile Organics | 0.005 | 2 | 45 | 8 | 180 |
This data indicates that direct transfer is negligible for all but the most highly contaminated sites, even with the worst-case assumption on the plug volume (flat pile tip). There is some reduction in end-bearing with conical tips. The effect of a conical tip on end bearing of the pile was investigated using data from Meyerhof (4). It can be shown that a conical tipped pile has the same capacity as a flat-tipped pile if its tip penetration into the sand is increased by 0.5-1.0 pile widths. This is equivalent to 1% - 2% additional pile length for typical cases, a small price to pay for regulatory acceptance. In the case of 9-pile group, using 450 conical tips decreases the distance (xc) at which cm < 0.005 mg/L for co = 1000 mg/L from over 150m to less than 10m.
For the vertical flow transfer method six model test chambers were fabricated to evaluate the influence of different pile types and field conditions. The test chamber is a PVC pipe 30.5cm in diameter with sand and clay layers placed to simulate the field conditions of a clay aquitard overlying a sand aquifer. The model pile is driven through the clay and then flow induced from top to bottom. The top sand layer distributes the in-flowing permeant uniformly before it enters the clay. The compacted clay layer simulates the aquitard. As the clay was placed, bentonite seals were placed against the chamber walls to minimize wall effects. The bottom sand layer allows collecting and draining the permeant exiting from the clay. This layer is divided by three concentric rings; each sand section has its own collection system so that edge effects on flow can be accounted for. Each segment also has a conductivity meter for measuring the salinity of its effluent. A rubber "doughnut" above the top sand applies effective overburden pressure to the sample. The permeant is supplied by a separate pressurized chamber.
The CL clay had the following characteristics: Liquid Limit = 34, Plasticity Index = 19, Fines < 0.074 mm= 76%, Clay (as 0.005 mm) =34%. The 20/40 sand had 2% fines and a d10 of 0.10mm. The contaminant was simulated by a NaCl solution (13,000mg/L), both for laboratory safety and for ease of concentration measurement. This permeant is not retarded by absorption, and at that test concentration does not alter the clay's hydraulic conductivity. To confirm this, small-scale permeability/ compatibility tests were also carried out to ascertain the effects of the salt water. The sample size was 7.62 cm. diameter and 3 to 6 cm height for rapid permeation. The procedures followed essentially ASTM D 5084. One sample was permeated first with tap water and then with salt water. The other sample was permeated only with the salt water. Neither exhibited a greatly increased hydraulic conductivity, even after more than 1600 hours of permeation, achieving 2-5 replacements of the samples' pore fluids.
The concentrations exiting from the test chambers were determined by measuring the effluent's specific conductivity, which had previously been correlated with NaCl content. Field conditions were simulated by compacting the clay at a moisture content 2% higher than its optimum in order to have a soft clay. This enables easy placement of piles in the chamber. The clay was placed in the chamber by compacting in 5 layers. The specific energy used for compaction was equivalent to reduced proctor compaction, i.e., 355.5 kJ/m3. The resulting clay had a porosity of 0.31 and 100% saturation. The effective pressure applied to the top surface was 190 kN/m2, to simulate a typical overburden. The gross vertical hydraulic gradient during the tests was about 25.
Tests were conducted on the following pile types: No pile or penetration (Control A) round wood pile, untreated penetration with a sand pile (Control B) round metal pile, round wood pile, treated H section metal pile Control B terminated 2.5 cm above the bottom sand. All piles were 2.5 cm in nominal diameter, 50 cm long and had flat tips. The wood piles were tapered slightly in accordance with ASTM D25 standards for wood piles. All piles were driven with a hydraulic press; a guide was used to keep the piles vertical. During the tests, periodic measurements were made for each bottom segment of both the amount of flow and the electrical conductivity simultaneously. Intervals for the measurements were in the order of hours for the first days and later on in days. The "breakthrough" time for the model tests was calculated using Darcy's Law as about 1000 hours. The final tests were therefore permeated about 2400 hours with water, then some 1400 hours with brine.
The data collected from the innermost ring has the greatest effect from the model pile and the least effect from any sidewall interface seepage. The model tests were therefore analysed using only the data from that inner ring.
Flow was compared by computing the effective hydraulic conductivity for the inner ring of each test from its flow-time relationships towards the end of the test, averaging the results from the two tests for each pile type. The results using water as the permeant are illustrated on Figure 3; the results for brine did not differ significantly. Clearly, the pipe and treated wood piles did not increase flow significantly over the no-pile case. For both, the effective hydraulic conductivity remained below the U.S. EPA maximum standard for recompacted clay liners: 1 x 10-7 cm/sec. The "H" and untreated wood piles showed a significant increase, and exceeded the cited standard. The difference in behavior between the pipe and "H" piles can be explained by the lateral pressures each develops during driving. The pipe displaces some 6 times the volume of soil displaced by the "H". This creates far more lateral pressure, which then has a greater tendency to seal any annulus developed during driving. Both types of wood pile are displacement-type piles, but the untreated wood is more permeable, resulting in "wicking" action in the pile material. This phenomenon was also noted by Hayman, et.al (1).
The piles' effects on contaminant transfer were evaluated using the electrical conductivities measured at the inner rings during the brine permeation phase of each test. The measure chosen was the ratio (Rc) of the change in conductivity (over background) to the input brine's conductivity over background. The results are presented on Figure 4. In that figure, c = measured conductivity, co = background conductivity, and cb = brine conductivity. They indicate that the pipe and treated wood piles had no adverse effect on contaminant transfer over that noted for the "no pile" condition. However, the "H" and untreated wood piles showed rapid and significant adverse changes in contaminant transfer. These behaviors can be attributed to the same causes as described above for flow.
The results of this study confirmed the findings of the earlier work by Hayman et.al (1),but extended them. Driven piles can be used on even " brownfields" sites without causing adverse environmental effects. However, the proper type(s) of piles must be selected to avoid such effects. The piles should be of a low-permeability material, such as steel and possibly concrete to avoid internal flow. A displacement-type pile such as wood, pipe, or "square" piles should be used to develop the lateral pressure needed to seal any annular space. Use of a pointed pile tip reduces direct transfer of contaminants to a negligible level.
Journal Articles:No journal articles submitted with this report: View all 1 publications for this subproject
Supplemental Keywords:piles, brownfields, hydraulic conductivity, contaminant transfer, groundwater contamination, soil contamination, groundwater contamination, pilings, deep foundations, aquifer, aquitard. , Geographic Area, Scientific Discipline, Waste, Brownfields, Ecology, Ecological Risk Assessment, Municipal, Environmental Chemistry, Ecology and Ecosystems, State, brownfield sites, waste minimization, urban waste, groundwater quality, New Orleans (NO), urban runoff, technology transfer, waste management, municipal waste, outreach
Relevant Websites:
Progress and Final Reports:
Original Abstract
Main Center Abstract and Reports:
R825427 Urban Waste Management and Research Center (University New Orleans)
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R825427C001 Comprehensive Evaluation of The Dual Trickling Filter Solids Contact Process
R825427C002 Issues Involving the Vertical Expansion of Landfills
R825427C003 Deep Foundations on Brownfields Sites
R825427C004 Ambient Particulate Concentration Model for Traffic Intersections
R825427C005 Effectiveness of Rehabilitation Approaches for I/I Reduction
R825427C006 Urban Solid Waste Management Videos
R825427C007 UWMRC Community Outreach Multimedia Exhibit
R825427C008 Including New Technology into the Investigation of Inappropriate Pollutant Entries into Storm Drainage Systems - A User's Guide
R825427C009 Investigation of Hydraulic Characteristics and Alternative Model Development of Subsurface Flow Constructed Wetlands
R825427C010 Beneficial Use Of Urban Runoff For Wetland Enhancement
R825427C011 Urban Storm and Waste Water Outfall Modeling
R827933C001 Development of a Model Sediment Control Ordinance for Louisisana
R827933C002 Inappropriate Discharge to Stormwater Drainage (Demonstration Project)
R827933C003 Alternate Liner Evaluation Model
R827933C004 LA DNR - DEQ - Regional Waste Management
R827933C005 Landfill Design Specifications
R827933C006 Geosynthetic Clay Liners as Alternative Barrier Systems
R827933C007 Used Tire Monofill
R827933C008 A Comparison of Upflow Anaerobic Sludge Bed (USAB) and the Anaerobic Biofilm Fluidized Bed Reactor (ABFBR) for the Treatment of Municipal Wastewater
R827933C009 Integrated Environmental Management Plan for Shipbuilding Facilities
R827933C010 Nicaragua
R827933C011 Louisiana Environmental Education and Resource Program
R827933C012 Costa Rica - Costa Rican Initiative
R827933C013 Evaluation of Cr(VI) Exposure Assessment in the Shipbuilding Industry
R827933C014 LaTAP, Louisiana Technical Assistance Program: Pollution Prevention for Small Businesses
R827933C015 Louisiana Environmental Leadership Pollution Prevention Program
R827933C016 Inexpensive Non-Toxic Pigment Substitute for Chromium in Primer for Aluminum Sibstrate
R827933C017 China - Innovative Waste Composting Plan for the City of Benxi, People's Rupublic of China
R827933C018 Institutional Control in Brownfields Redevelopment: A Methodology for Community Participation and Sustainability
R827933C019 Physico-Chemical Assessment for Treatment of Storm Water From Impervious Urban Watersheds Typical of the Gulf Coast
R827933C020 Influence of Cyclic Interfacial Redox Conditions on the Structure and Integrity of Clay Liners for Landfills Subject to Variable High Groundwater Conditions in the Gulf Coast Region
R827933C021 Characterizing Moisture Content Within Landfills
R827933C022 Bioreactor Landfill Moisture Management
R827933C023 Urban Water Issues: A Video Series
R827933C024 Water Quality Modeling in Urban Storm Water Systems
R827933C025 The Development of a Web Based Instruction (WBI) Program for the UWMRC User's Guide (Investigation of Inappropriate Pollutant Entries Into Storm Drainage Systems)
R827933C027 Legal Issues of SSO's: Private Property Sources and Non-NPDES Entities
R827933C028 Brownfields Issues: A Video Series
R827933C029 Facultative Landfill Bioreactors (FLB): A Pilot-Scale Study of Waste Stabilization, Landfill Gas Emissions, Leachate Treatment, and Landfill Geotechnical Properties
R827933C030 Advances in Municipal Wastewater Treatment
R827933C031 Design Criteria for Sanitary Sewer System Rehabilitation
R827933C032 Deep Foundations in Brownfield Areas: Continuing Investigation
R827933C033 Gradation-Based Transport, Kinetics, Coagulation, and Flocculation of Urban Watershed Rainfall-Runoff Particulate Matter
R827933C034 Leaching and Stabilization of Solid-Phase Residuals Separated by Storm Water BMPs Capturing Urban Runoff Impacted by Transportation Activities and Infrastructure
R827933C035 Fate of Pathogens in Storm Water Runoff
R87933C020 Influence of Cyclic Interfacial Redox Conditions on the Structure and Integrity of Clay Liners for Landfills Subject to Variable High Groundwater Conditions in the Gulf Coast Region