Sediment supply drives floodplain evolution in Amazon Basin

A new study of the Amazon River basin shows lowland rivers that carry large volumes of sediment meander more across floodplains and create more oxbow lakes than rivers that carry less sediment.

The findings have implication for the Amazonian river system, which may be significantly altered by proposed mega-dams that would disrupt sediment supplies.

Researchers from Cardiff University’s School of Earth and Ocean Sciences examined 20 reaches within the Amazon Basin from Landsat imagery spanning nearly 20 years (1985 to 2013).

They found rivers transporting larger amounts of sediment migrated more, and noted that channel movement did not depend on either the slope of the channel or the river discharge.

The research gives scientists insight into the contrasting behavioural properties of rivers where sediment is an imposed variable – e.g. resulting from glacial, volcanic, or human activity – and rivers were the main sediment supply is from local bank erosion.

Dr José Constantine, Lecturer in Earth Sciences at Cardiff University’s School of Earth & Ocean Sciences and lead author of the paper said: “We found that the speed at which the meanders migrated for each of the rivers studied depended on the river’s supply of sand and silt. The meanders of rivers carrying more sediment migrated faster than those carrying less sediment, and were also more frequently cut off and abandoned to form U-shaped lakes. If sediment loads are reduced — by a dam, for example — meander migration is expected to slow, and thus the reshaping of the floodplain environment is affected.

Rivers flow differently over gravel beds, study finds

River researchers used a specially constructed model to study how water flows over gravel river beds. Illinois postdoctoral researcher Gianluca Blois (left) and professor Jim Best also developed a technique to measure the water flow between the pore spaces in the river bed. -  L. Brian Stauffer
River researchers used a specially constructed model to study how water flows over gravel river beds. Illinois postdoctoral researcher Gianluca Blois (left) and professor Jim Best also developed a technique to measure the water flow between the pore spaces in the river bed. – L. Brian Stauffer

River beds, where flowing water meets silt, sand and gravel, are critical ecological zones. Yet how water flows in a river with a gravel bed is very different from the traditional model of a sandy river bed, according to a new study that compares their fluid dynamics.

The findings establish new parameters for river modeling that better represent reality, with implications for field researchers and water resource managers.

“The shallow zones where water in rivers interacts with the subsurface are critical environmentally, and how we have modeled those in the past may be radically different from reality,” said Jim Best, a professor of geology, geography and geographic information science at the University of Illinois. “If you’re a river engineer or a geomorphologist or a freshwater biologist, predicting where and when sediment transport is going to occur is very important. This study provides us with a very different set of conditions to look at those environments and potentially manage them.”

Best and postdoctoral researcher Gianluca Blois led the study at the U. of I., in collaboration with colleagues in the United Kingdom. The team published its findings in the journal Geophysical Research Letters.

The researchers used a specially constructed flume in the Ven Te Chow Hydrosystems Laboratory at Illinois to experimentally compare scenarios ranging from the traditional model of an impermeable river bottom to a completely permeable river bed – a collection of spheres that simulate gravel.

The researchers used a technique called particle image velocimetry (PIV), a widely used method for quantifying how water flows over a model river bed, pioneered at the U. of I. in the 1980s. Best and Blois developed a method to use PIV endoscopically to study, for the first time, fluid flow within the small spaces between the gravel. This allowed them to quantify flow within the river bed and link it to the stream flow above.

They found that, in the scenario that simulates a gravel bed, the patterns of flow velocity above the bed and the distribution of forces on the river bed were dramatically different from the models on which all previous work has been based. Their experimental scenarios also disproved one popular theory that explained the difference between classic models and field observations for the formation of bed topography, such as dunes.

“Bedforms formed in fine sediments are known to be substantially different from those formed in gravel beds, but we just didn’t know why,” Blois said. “People before us suggested that those differences were due to the roughness of the grains. But we introduced the bed permeability, just like real rivers. This, with our new measurement technique, allowed us to demonstrate that most of the stress variation is actually coming from fluid emerging from the permeable bed, rather than roughness.”

The maps of water flow that the experiments produced could lead to better predictive models, so that researchers can more accurately predict and study how nutrients and pollutants travel and accumulate in rivers. These new models also could provide insight into the growth and behavior of organisms that thrive in the narrow zone where river flow meets the river bed.

“For example, when salmon spawn in gravel-bed rivers, they basically make a depression in the gravel, into which they lay their eggs,” Best said. “By doing that, not only do they protect the eggs, but they create a bump in the sediment that creates a pressure distribution that would keep fine grains from going into the bed, which would be detrimental to the eggs. It’s fascinating that fish actually take advantage of these flow dynamics.”

The researchers are working with collaborators around the world to study how permeability affects turbulence above the bed, how this affects the organisms that grow in the pore spaces, and how tiny particles and dissolved substances accumulate in porous riverbeds.

“It’s going to change the way we conceptualize these systems and model them,” Blois said. “We’re trying to raise awareness of the fact that we are now able to measure the complex flow dynamics in these challenging environments, and that’s going to open up a new paradigm for river research.”

A unique approach to monitoring groundwater supplies near Ohio fracking sites

This image shows a drilling rig in Carroll County, Ohio. -  Amy Townsend-Small
This image shows a drilling rig in Carroll County, Ohio. – Amy Townsend-Small

A University of Cincinnati research project is taking a groundbreaking approach to monitoring groundwater resources near fracking sites in Ohio. Claire Botner, a UC graduate student in geology, will outline the project at The Geological Society of America’s Annual Meeting & Exposition. The meeting takes place Oct. 19-22, in Vancouver.

Botner’s research is part of UC Groundwater Research of Ohio (GRO), a collaborative research project out of UC to examine the effects of fracking (hydraulic fracturing) on groundwater in the Utica Shale region of eastern Ohio. First launched in Carroll County in 2012, the GRO team of researchers is examining methane levels and origins of methane in private wells and springs before, during and after the onset of fracking. The team travels to the region to take water samples four times a year.

Amy Townsend-Small, the lead researcher for GRO and a UC assistant professor of geology, says the UC study is unique in comparison with studies on water wells in other shale-rich areas of the U.S. where fracking is taking place – such as the Marcellus Shale region of Pennsylvania.

Townsend-Small says water samples finding natural gas-derived methane in wells near Pennsylvania fracking sites were taken only after fracking had occurred, so methane levels in those wells were not documented prior to or during fracking in Pennsylvania.

Hydraulic fracturing, or fracking, involves using millions of gallons of water mixed with sand and chemicals to break up organic-rich shale to release natural gas resources.

Proponents say the practice promises a future in lower energy prices, an increase in domestic jobs and less dependence on foreign oil from unstable overseas governments.

Opponents raise concerns about increasing methane gas levels (a powerful greenhouse gas) and other contamination involving the spillover of fracking wastewater in the groundwater of shale-rich regions.

“The only way people with private groundwater will know whether or not their water is affected by fracking is through regular monitoring,” says Townsend-Small.

The Ohio samples are being analyzed by UC researchers for concentrations of methane as well as other hydrocarbons and salt, which is pulled up in the fracking water mixture from the shales. The shales are ancient ocean sediments.

Botner’s study involves testing on 22 private wells in Carroll County between November 2012 and last May. The first fracking permits were issued in the region in 2011. So far, results indicate that any methane readings in groundwater wells came from organic matter. In less than a handful of cases, the natural methane levels were relatively high, above 10 milligrams per liter. However, most of the wells carried low levels of methane.

The UC sampling has now been expanded into Columbiana, Harrison, Stark and Belmont counties in Ohio. Researchers then review data on private drinking water wells with the homeowners. “We’re working on interacting with these communities and educating them about fracking as well as gathering scientific data, which is lacking on a very sensitive issue,” says Botner. “It can also be reassuring to receive data on their water supplies from an objective, university resource.”

The team also is seeking additional funding to begin monitoring groundwater wells near wastewater injection wells, where fracking brine is deposited after the wells are drilled.

###

Funding for Botner’s research to be presented at the GSA meeting is supported by a grant from the Missouri-based Deer Creek Foundation.

Botner is among UC graduate students and faculty who are presenting more than two dozen research papers, PowerPoint presentations or poster exhibitions at the GSA meeting. The meeting draws geoscientists from around the world representing more than 40 different disciplines.

UC’s nationally ranked Department of Geology conducts field research around the world in areas spanning paleontology, Quaternary geology, geomorphology, sedimentology, stratigraphy, tectonics, environmental geology and biogeochemistry.

The Geological Society of America, founded in 1888, is a scientific society with more than 26,500 members from academia, government and industry in more than 100 countries. Through its meetings, publications and programs, GSA enhances the professional growth of its members and promotes the geosciences in the service of humankind.

Hydraulic fracturing linked to earthquakes in Ohio

Hydraulic fracturing triggered a series of small earthquakes in 2013 on a previously unmapped fault in Harrison County, Ohio, according to a study published in the journal Seismological Research Letters (SRL).

Nearly 400 small earthquakes occurred between Oct. 1 and Dec. 13, 2013, including 10 “positive” magnitude earthquake, none of which were reported felt by the public. The 10 positive magnitude earthquakes, which ranged from magnitude 1.7 to 2.2, occurred between Oct. 2 and 19, coinciding with hydraulic fracturing operations at nearby wells.

This series of earthquakes is the first known instance of seismicity in the area.

Hydraulic fracturing, or fracking, is a method for extracting gas and oil from shale rock by injecting a high-pressure water mixture directed at the rock to release the gas inside. The process of hydraulic fracturing involves injecting water, sand and chemicals into the rock under high pressure to create cracks. The process of cracking rocks results in micro-earthquakes. Hydraulic fracturing usually creates only small earthquakes, ones that have magnitude in the range of negative 3 (−3) to negative 1 (-1).

“Hydraulic fracturing has the potential to trigger earthquakes, and in this case, small ones that could not be felt, however the earthquakes were three orders of magnitude larger than normally expected,” said Paul Friberg, a seismologist with Instrumental Software Technologies, Inc. (ISTI) and a co-author of the study.

The earthquakes revealed an east-west trending fault that lies in the basement formation at approximately two miles deep and directly below the three horizontal gas wells. The EarthScope Transportable Array Network Facility identified the first earthquakes on Oct. 2, 2013, locating them south of Clendening Lake near the town of Uhrichsville, Ohio. A subsequent analysis identified 190 earthquakes during a 39-hour period on Oct. 1 and 2, just hours after hydraulic fracturing began on one of the wells.

The micro-seismicity varied, corresponding with the fracturing activity at the wells. The timing of the earthquakes, along with their tight linear clustering and similar waveform signals, suggest a unique source for the cause of the earthquakes — the hydraulic fracturing operation. The fracturing likely triggered slip on a pre-existing fault, though one that is located below the formation expected to confine the fracturing, according to the authors.

“As hydraulic fracturing operations explore new regions, more seismic monitoring will be needed since many faults remain unmapped.” Friberg co-authored the paper with Ilya Dricker, also with ISTI, and Glenda Besana-Ostman originally with Ohio Department of Natural Resources, and now with the Bureau of Reclamation at the U.S. Department of Interior.

A new look at what’s in ‘fracking’ fluids raises red flags

Scientists are getting to the bottom of what's in fracking fluids — with some troubling results. -  Doug Duncan/U.S. Geological Survey
Scientists are getting to the bottom of what’s in fracking fluids — with some troubling results. – Doug Duncan/U.S. Geological Survey

As the oil and gas drilling technique called hydraulic fracturing (or “fracking”) proliferates, a new study on the contents of the fluids involved in the process raises concerns about several ingredients. The scientists presenting the work today at the 248th National Meeting & Exposition of the American Chemical Society (ACS) say that out of nearly 200 commonly used compounds, there’s very little known about the potential health risks of about one-third, and eight are toxic to mammals.

The meeting features nearly 12,000 presentations on a wide range of science topics and is being held here through Thursday by ACS, the world’s largest scientific society.

William Stringfellow, Ph.D., says he conducted the review of fracking contents to help resolve the public debate over the controversial drilling practice. Fracking involves injecting water with a mix of chemical additives into rock formations deep underground to promote the release of oil and gas. It has led to a natural gas boom in the U.S., but it has also stimulated major opposition and troubling reports of contaminated well water, as well as increased air pollution near drill sites.

“The industrial side was saying, ‘We’re just using food additives, basically making ice cream here,'” Stringfellow says. “On the other side, there’s talk about the injection of thousands of toxic chemicals. As scientists, we looked at the debate and asked, ‘What’s the real story?'”

To find out, Stringfellow’s team at Lawrence Berkeley National Laboratory and University of the Pacific scoured databases and reports to compile a list of substances commonly used in fracking. They include gelling agents to thicken the fluids, biocides to keep microbes from growing, sand to prop open tiny cracks in the rocks and compounds to prevent pipe corrosion.

What their analysis revealed was a little truth to both sides’ stories – with big caveats. Fracking fluids do contain many nontoxic and food-grade materials, as the industry asserts. But if something is edible or biodegradable, it doesn’t automatically mean it can be easily disposed of, Stringfellow notes.

“You can’t take a truckload of ice cream and dump it down the storm drain,” he says, building on the industry’s analogy. “Even ice cream manufacturers have to treat dairy wastes, which are natural and biodegradable. They must break them down rather than releasing them directly into the environment.”

His team found that most fracking compounds will require treatment before being released. And, although not in the thousands as some critics suggest, the scientists identified eight substances, including biocides, that raised red flags. These eight compounds were identified as being particularly toxic to mammals.

“There are a number of chemicals, like corrosion inhibitors and biocides in particular, that are being used in reasonably high concentrations that potentially could have adverse effects,” Stringfellow says. “Biocides, for example, are designed to kill bacteria – it’s not a benign material.”

They’re also looking at the environmental impact of the fracking fluids, and they are finding that some have toxic effects on aquatic life.

In addition, for about one-third of the approximately 190 compounds the scientists identified as ingredients in various fracking formulas, the scientists found very little information about toxicity and physical and chemical properties.

“It should be a priority to try to close that data gap,” Stringfellow says.

‘Fracking’ in the dark: Biological fallout of shale-gas production still largely unknown

Eight conservation biologists from various organizations and institutions, including Princeton University, found that shale-gas extraction in the United States has vastly outpaced scientists' understanding of the industry's environmental impact. With shale-gas production projected to surge during the next 30 years, determining and minimizing the industry's effects on nature and wildlife must become a top priority for scientists, industry and policymakers, the researchers said. The photo above shows extensive natural-gas operations at Jonah Field in Wyoming. -  Photo courtesy of EcoFlight.
Eight conservation biologists from various organizations and institutions, including Princeton University, found that shale-gas extraction in the United States has vastly outpaced scientists’ understanding of the industry’s environmental impact. With shale-gas production projected to surge during the next 30 years, determining and minimizing the industry’s effects on nature and wildlife must become a top priority for scientists, industry and policymakers, the researchers said. The photo above shows extensive natural-gas operations at Jonah Field in Wyoming. – Photo courtesy of EcoFlight.

In the United States, natural-gas production from shale rock has increased by more than 700 percent since 2007. Yet scientists still do not fully understand the industry’s effects on nature and wildlife, according to a report in the journal Frontiers in Ecology and the Environment.

As gas extraction continues to vastly outpace scientific examination, a team of eight conservation biologists from various organizations and institutions, including Princeton University, concluded that determining the environmental impact of gas-drilling sites – such as chemical contamination from spills, well-casing failures and other accidents – must be a top research priority.

With shale-gas production projected to surge during the next 30 years, the authors call on scientists, industry representatives and policymakers to cooperate on determining – and minimizing – the damage inflicted on the natural world by gas operations such as hydraulic fracturing, or “fracking.” A major environmental concern, hydraulic fracturing releases natural gas from shale by breaking the rock up with a high-pressure blend of water, sand and other chemicals, which can include carcinogens and radioactive substances.

“We can’t let shale development outpace our understanding of its environmental impacts,” said co-author Morgan Tingley, a postdoctoral research associate in the Program in Science, Technology and Environmental Policy in Princeton’s Woodrow Wilson School of Public and International Affairs.

“The past has taught us that environmental impacts of large-scale development and resource extraction, whether coal plants, large dams or biofuel monocultures, are more than the sum of their parts,” Tingley said.

The researchers found that there are significant “knowledge gaps” when it comes to direct and quantifiable evidence of how the natural world responds to shale-gas operations. A major impediment to research has been the lack of accessible and reliable information on spills, wastewater disposal and the composition of fracturing fluids. Of the 24 American states with active shale-gas reservoirs, only five – Pennsylvania, Colorado, New Mexico, Wyoming and Texas – maintain public records of spills and accidents, the researchers report.

“The Pennsylvania Department of Environmental Protection’s website is one of the best sources of publicly available information on shale-gas spills and accidents in the nation. Even so, gas companies failed to report more than one-third of spills in the last year,” said first author Sara Souther, a postdoctoral research associate at the University of Wisconsin-Madison.

“How many more unreported spills occurred, but were not detected during well inspections?” Souther asked. “We need accurate data on the release of fracturing chemicals into the environment before we can understand impacts to plants and animals.”

One of the greatest threats to animal and plant life identified in the study is the impact of rapid and widespread shale development, which has disproportionately affected rural and natural areas. A single gas well results in the clearance of 3.7 to 7.6 acres (1.5 to 3.1 hectares) of vegetation, and each well contributes to a collective mass of air, water, noise and light pollution that has or can interfere with wild animal health, habitats and reproduction, the researchers report.

“If you look down on a heavily ‘fracked’ landscape, you see a web of well pads, access roads and pipelines that create islands out of what was, in some cases, contiguous habitat,” Souther said. “What are the combined effects of numerous wells and their supporting infrastructure on wide-ranging or sensitive species, like the pronghorn antelope or the hellbender salamander?”

The chemical makeup of fracturing fluid and wastewater is often unknown. The authors reviewed chemical-disclosure statements for 150 wells in three of the top gas-producing states and found that an average of two out of every three wells were fractured with at least one undisclosed chemical. The exact effect of fracturing fluid on natural water systems as well as drinking water supplies remains unclear even though improper wastewater disposal and pollution-prevention measures are among the top state-recorded violations at drilling sites, the researchers found.

“Some of the wells in the chemical disclosure registry were fractured with fluid containing 20 or more undisclosed chemicals,” said senior author Kimberly Terrell, a researcher at the Smithsonian Conservation Biology Institute. “This is an arbitrary and inconsistent standard of chemical disclosure.”

Fracking flowback could pollute groundwater with heavy metals

Partially wetted sand grains (grey) with colloids (red) are shown. -  Cornell University
Partially wetted sand grains (grey) with colloids (red) are shown. – Cornell University

The chemical makeup of wastewater generated by “hydrofracking” could cause the release of tiny particles in soils that often strongly bind heavy metals and pollutants, exacerbating the environmental risks during accidental spills, Cornell University researchers have found.

Previous research has shown 10 to 40 percent of the water and chemical solution mixture injected at high pressure into deep rock strata, surges back to the surface during well development. Scientists at the College of Agriculture and Life Sciences studying the environmental impacts of this “flowback fluid” found that the same properties that make it so effective at extracting natural gas from shale can also displace tiny particles that are naturally bound to soil, causing associated pollutants such as heavy metals to leach out.

They described the mechanisms of this release and transport in a paper published in the American Chemical Society journal Environmental Science & Technology.

The particles they studied are colloids – larger than the size of a molecule but smaller than what can be seen with the naked eye – which cling to sand and soil due to their electric charge.

In experiments, glass columns were filled with sand and synthetic polystyrene colloids. They then flushed the column with different fluids – deionized water as a control, and flowback fluid collected from a Marcellus Shale drilling site – at different rates of flow and measured the amount of colloids that were mobilized.

On a bright field microscope, the polystyrene colloids were visible as red spheres between light-grey sand grains, which made their movement easy to track. The researchers also collected and analyzed the water flowing out of the column to quantify the colloid concentration leaching out.

They found that fewer than five percent of colloids were released when they flushed the columns with deionized water. That figure jumped to 32 to 36 percent when flushed with flowback fluid. Increasing the flow rate of the flowback fluid mobilized an additional 36 percent of colloids.

They believe this is because the chemical composition of the flowback fluid reduced the strength of the forces that allow colloids to remain bound to the sand, causing the colloids to actually be repelled from the sand.

“This is a first step into discovering the effects of flowback fluid on colloid transport in soils,” said postdoctoral associate Cathelijne Stoof, a co-author on the paper.

The authors hope to conduct further experiments using naturally occurring colloids in more complex field soil systems, as well as different formulations of flowback fluid collected from other drilling sites.

Stoof said awareness of the phenomenon and an understanding of the mechanisms behind it can help identify risks and inform mitigation strategies.

“Sustainable development of any resource requires facts about its potential impacts, so legislators can make informed decisions about whether and where it can and cannot be allowed, and to develop guidelines in case it goes wrong,” Stoof said. “In the case of spills, you want to know what happens when the fluid moves through the soil.”




Video
Click on this image to view the .mp4 video
This video visualizes the effects of hydrofracking flowback fluid on colloid mobilization in unsaturated sand. Included are the injection of the colloids into the sand column at the beginning of the experiment, the deionized water flush at 0.3 ml/min, the flowback water flush at 0.3 ml/min, and the flowback water flush at 1.5 ml/min. – Cornell University

Another concern arises over groundwater contamination from fracking accidents

The oil and gas extraction method known as hydraulic fracturing, or fracking, could potentially contribute more pollutants to groundwater than past research has suggested, according to a new study in ACS’ journal Environmental Science & Technology. Scientists are reporting that when spilled or deliberately applied to land, waste fluids from fracking are likely picking up tiny particles in the soil that attract heavy metals and other chemicals with possible health implications for people and animals.

Tammo S. Steenhuis and colleagues note that fracking, which involves injecting huge volumes of fluids underground to release gas and oil, has led to an energy boom in the U.S. But it has also ignited controversy for many reasons. One in particular involves flowback, which refers to fluids that surge back out of the fracked wells during the process. It contains water, lubricants, solvents and other substances from the original fracking fluid or extracted from the shale formation. High-profile spills and in some places, legal application of these liquids to land, have raised alarms. Research has linked fracking to groundwater contamination that could have major health effects. But another factor that no one has really addressed could play a role: colloids. These tiny pieces of minerals, clay and other particles are a concern because they attract heavy metals and other environmental toxins, and have been linked to groundwater contamination. Steenhuis’ team set out to take a closer look.

To simulate what would happen to colloids in soil after a fracking spill, the researchers flushed flowback fluids through sand with a known amount of colloids. They found that the fluids dislodged about a third of the colloids, far more than deionized water alone. When they increased the flow rate, the fluids picked up an additional 36 percent. “This indicates that infiltration of flowback fluid could turn soils into an additional source of groundwater contaminants such as heavy metals, radionuclides and microbial pathogens,” the scientists conclude. More research with real soils is planned.

New hi-tech approach to studying sedimentary basins

A radical new approach to analysing sedimentary basins also harnesses technology in a completely novel way. An international research group, led by the University of Sydney, will use big data sets and exponentially increased computing power to model the interaction between processes on the earth’s surface and deep below it in ‘five dimensions’.

As announced by the Federal Minister for Education today, the University’s School of Geosciences will lead the Basin GENESIS Hub that has received $5.4 million over five years from the Australian Research Council (ARC) and industry partners.

The multitude of resources found in sedimentary basins includes groundwater and energy resources. The space between grains of sand in these basins can also be used to store carbon dioxide.

“This research will be of fundamental importance to both the geo-software industry, used by exploration and mining companies, and to other areas of the energy industry,” said Professor Dietmar Müller, Director of the Hub, from the School of Geosciences.

“The outcomes will be especially important for identifying exploration targets in deep basins in remote regions of Australia. It will create a new ‘exploration geodynamics’ toolbox for industry to improve estimates of what resources might be found in individual basins.”

Sedimentary basins form when sediments eroded from highly elevated regions are transported through river systems and deposited into lowland regions and continental margins. The Sydney Basin is a massive basin filled mostly with river sediments that form Hawkesbury sandstone. It is invisible to the Sydney population living above it but has provided building material for many decades.

“Previously the approach to analysing these basins has been based on interpreting geological data and two-dimensional models. We apply infinitely more computing power to enhance our understanding of sedimentary basins as the product of the complex interplay between surface and deep Earth processes,” said Professor Müller.

Associate Professor Rey, a researcher at the School of Geosciences and member of the Hub said, “Our new approach is to understand the formation of sedimentary basins and the changes they undergo, both recently and over millions to hundreds of millions of years, using computer simulations to incorporate information such as the evolution of erosion, sedimentary processes and the deformation of the earth’s crust.”

The researchers will incorporate data from multiple sources to create ‘five-dimensional’ models, combining three-dimensional space with the extra dimensions of time and estimates of uncertainty.

The modelling will span scales from entire basins hundreds of kilometres wide to individual sediment grains.

Key geographical areas the research will focus on are the North-West shelf of Australia, Papua New Guinea and the Atlantic Ocean continental margins.

The Hub’s technology builds upon the exponential increase in computational power and the increasing amount of available big data (massive data sets of information). The Hub will harness the capacity of Australia’s most powerful computer, launched in 2013.

Ground-improvement methods might protect against earthquakes

Researchers from the University of Texas at Austin’s Cockrell School of Engineering are developing ground-improvement methods to help increase the resilience of homes and low-rise structures built on top of soils prone to liquefaction during strong earthquakes.

Findings will help improve the safety of structures in Christchurch and the Canterbury region in New Zealand, which were devastated in 2010 and 2011 by a series of powerful earthquakes. Parts of Christchurch were severely affected by liquefaction, in which water-saturated soil temporarily becomes liquid-like and often flows to the surface creating sand boils.

“The 2010-2011 Canterbury earthquakes in New Zealand have caused significant damage to many residential houses due to varying degrees of soil liquefaction over a wide extent of urban areas unseen in past destructive earthquakes,” said Kenneth Stokoe, a professor in the Department of Civil, Architectural and Environmental Engineering. “One critical problem facing the rebuilding effort is that the land remains at risk of liquefaction in future earthquakes. Therefore, effective engineering solutions must be developed to increase the resilience of homes and low-rise structures.”

Researchers have conducted a series of field trials to test shallow-ground-improvement methods.

“The purpose of the field trials was to determine if and which improvement methods achieve the objectives of inhibiting liquefaction triggering in the improved ground and are cost-effective measures,” said Stokoe, working with Brady Cox, an assistant professor of civil engineering. “This knowledge is needed to develop foundation design solutions.”

Findings were detailed in a research paper presented in December at the New Zealand – Japan Workshop on Soil Liquefaction during Recent large-Scale Earthquakes. The paper was authored by Stokoe, graduate students Julia Roberts and Sungmoon Hwang; Cox and operations manager Farn-Yuh Menq from the University of Texas at Austin; and Sjoerd Van Ballegooy from Tonkin & Taylor Ltd, an international environmental and engineering consulting firm in Auckland, New Zealand.

The researchers collected data from test sections of improved and unimproved soils that were subjected to earthquake stresses using a large mobile shaker, called T-Rex, and with explosive charges planted underground. The test sections were equipped with sensors to monitor key factors including ground motion and water pressure generated in soil pores during the induced shaking, providing preliminary data to determine the most effective ground-improvement method.

Four ground-improvement methods were initially selected for the testing: rapid impact compaction (RIC); rammed aggregate piers (RAP), which consist of gravel columns; low-mobility grouting (LMG); and construction of a single row of horizontal beams (SRB) or a double row of horizontal beams (DRB) beneath existing residential structures via soil-cement mixing.
“The results are being analyzed, but good and poor performance can already be differentiated,” Stokoe said. “The ground-improvement methods that inhibited liquefaction triggering the most were RIC, RAP, and DRB. However, additional analyses are still underway.”

The test site is located along the Avon River in the Christchurch suburb of Bexley. The work is part of a larger testing program that began in early 2013 with a preliminary evaluation by Brady Cox of seven potential test sites along the Avon River in the Christchurch area.