Risks Associated with Subsidence and Uplift Vertical Movements of the Earth’s Crust.

Risks Associated with Subsidence and Uplift

Vertical Movements of the Earth’s Crust

Introduction Small scale vertical movements Human induced or aggravated Occurring on time-scales of a few

decades Causing substantial economic

losses and societal disruption

Subsidence and Uplift Subsidence: The lowering of the land

surface due to Creation of cavities in solid rock by mining,

combustion of coal or dissolution of soluble material

The removal of fluids (water or oil) from the pore spaces of unconsolidated or poorly consolidated sediments

Uplift: changed land conditions due to expansive soils

•Loss of water in organic soils•Dissolving of subsurface limestone rock•First-time wetting of formerly dry, low-density soils•Natural compaction of soils•Underground mining•Withdrawal of ground water and petroleum

Causes of Vertical Movements

Relation between subsidence and collapseFluid withdrawn results in bed compactionEnlarging solution cavities causes collapseCollapse of mine can cause subsidence or collapse

Subsidence Underground mining is the most

widespread cause of subsidence by direct removal Coal- Illinois, North Dakota, others Salt- Kansas and New York Copper- Ducktown, TN

Removal causing changes in local or regional groundwater system either by natural or anthropogenic causes

Copper Basin, TN- Burra Burra Mine

Differential Compaction due to the Compaction of SoilsThe high-rise buildings are built on piers in bedrockThe smaller buildings are built on slab foundations ston soils, in time they settle and damage results

Chemical Weathering

Role of Acid Hydrogen ions in water pH=-Log[H+] Acid/Base

Carbonic Acid H2CO3 CO2 + H2O -> H2CO3

H2CO3 -> H+ + HCO3- (in water)

Solution weathering- Karstic Features Calcite (in limestone) dissolves in acidic water fluted (channeled) rock surface caves

Effects of Groundwater Action

Karst topography-Caves Rock usually limestone Dissolves by weakly acidic water

rainwater pH 5.5 and carbonic acid from humus Water + carbon dioxide + calcite calcium ion + bicarbonate ion Precipitation (dripstones) solution (caves) H2O + CO2 + CaCO3 Ca2+ + 2HCO3

-

Dripstone- Speleothems stalagtite stalagmite

Flowstone Sinkholes

in a Cavern System

Subsidence vs. Collapse Sinkhole

Winter Park, FL

Collapse SinkholesCollapse sinkholes are the most dramatic of the three sinkhole types; they form with little warning and leave behind a deep, steeply sided hole.  Collapse occurs because of the weakening of the rock of the aquifer by erosion and is often triggered by changes in water levels

in the surficial and confined aquifers.   

                                                                   1

Stage 2

Stage 3

Subsidence SinkholesThe progression of a subsidence sinkhole is shown below. Rainwater percolates through overlying sediments and reaches the limestone, dissolving the rock and gradually wakening its structural integrity. Gradually subsiding sinkholes commonly form where slow dissolution takes place, mostly along joints in the limestone. These sinkholes tend to form naturally and are not greatly affected by human activities.

1

Stage 2

Stage 3

Stage 4

KARST

Sinkhole in Winter Park, FL

Balancing Withdrawal & Discharge of Groundwater Pumping in a quarry or other man-

made hole or; Overpumping of g.w. for supply can

results in: Falling water table Ground subsidence

Subsidence of landcaused by extraction of groundwater in theSan Juaquin Valley, CAThe land sank 9m or30 ft in 52 years

SantaClaraBasin, CAGW w/dCaused1.2mBet.1960-1967

Greater Houston-Galveston Groundwater withdrawn by industry Petroleum Between 1906-1978 a total of 2.5m

of subsidence

Greater Houston Area

*NASA

Seabrook and Bayport, TX

Greater Houston-Galveston Withdrawl of fluids, particularly

coastal aquifers, has caused subsidence fissures, cracks, significant structural damage and flooding

NASA has constructed a hurricane-resistant facility to warehouse their moon rock collection

Venice, Italy Venice is subject to flooding by high tides

in the Adriatic Sea Between 1952-1969 Venice was sinking

due to subsidence Subsidence is caused by groundwater

pumping from 5 aquifers which reduce pore-water pressure and the fine grained sediment began compacting

In 1997 proposals for gas exploration has increased the concerns

Coal Mining If the mine workings are near the surface (few 10’s

of meters) the overlying rocks maybe too weak to support their own weight and eventually they will collapse into the mine below

This generates a series of collapse pits 2 methods of coal mining

Room and pillar…leaves behind a support system, however if the mine is shallow it can cause collapse pits

Longwall mining…the resource is removed completely as mining advances, in an active mine a hydraulic shield supports the roof. This leaves behind uniform subsidence

Subsidence pits at theSurface from collapse Of the mine workings atdepth

Room and pillar miningLeaving pillars to support surface does not work wellbecause flooding of the Mine weakens the supportSystem. Coal is porous

Coal Mining Related Damage In areas of Kentucky, Pennsylvania and W.

Virginia surface drains, culverts, underground pipes are damaged by subsidence. Ponding and flooding can occur.

Subsidence can disrupt GW flow, draining them and drying up wells and springs. Fractured aquifers may lose artesian pressure and become vulnerable to contamination.

Underground fires Carbondale, PA burned for 33 years Can cause emission of CO and CO2 to atmosphere

through fissures

Mitigating Mine Subsidence

Subsidence can be mitigated by filling the void below using mine waste or sand can be pumped through drill holes at the surface.

Development can be curtailed or only allowed after the mining operations are completed them the foundations of the structures can be built on the mine floor

Salt Mining Salt often mined by solution methods

Water is injected through wells into a salt deposit, the salt dissolves and saturated water is pumped out.

The removal of salt leaves a cavity behind and weakens the support for overlying rocks

In the 1970 an event near Detroit, MI left a pit 120m across and 90m deep; another in Saltville, VA produced 75m of subsidence; In 1974 in Hutchinson, KS a 60m sinkhole with vertical walls formed; in 1980 a lake drained in Louisiana into a salt mine after an oil drilling rig punched a hole in the mine

Hutchinson, KS 1974

Lake Peigneur, LA On Nov. 21, 1980 a drill rig punched a hole through an abandoned

shaft of a still operating multimillion dollar salt mine The mine was located 430m below the surface of Jefferson Island

salt dome. The lake drained so fast that 10 barges, a tug boat and an oil

drilling barge disappeared into a whirlpool of water, 25 hectatres of Jefferson island were also lost including a botanical garden and a $500K home

The lake immediately began refilling from waters from the Gulf of Mexico, 9 of the barges popped up to the surface

15million m3 of water entered the salt dome and the mine was lost The once shallow lake (1m) was now a deep hole in the bottom The oil company paid $30million to the mine operation, the

botanical garden and home owners were paid $13million by all other parties

Salt Mining in Western New York

Failure of a room and pillar mine in Retsof Mine Livingston Co, NY which led to the closure of the world’s largest salt mine

The salt bed was 300m below the floodplain of the Genesee R.

On March 12, 1994 a sinkhole developed on flat farmland, a bridge over a highway failed and the cause was thought to be a magnitude 3.2 earthquake

Salt Mining in Western New York

GIS analysis showed that the sinkhole was located directly above a section of the mine where a new mining method was employed, one where the pillar were 20x20 instead of 80x80 ft

The pillars failed leading to a collapse which produced the seismic event

Immediately following the creation of the sinkhole water started pouring into the mine, concrete was poured into the fractures to try to prevent the water from flowing into the mine but this failed

Subsequently 2 other sinkholes appeared, more water poured in and started dissolving the pillars, the mine was abandoned in 1996

Costs of Subsidence Sudden events like the Winter Park, FL sinkhole are

rare, but are the easiest to evaluate in monetary terms… $2 million for losses of permanent structures

Other events are more complex and develop over long periods of time such as coastal subsidence in Houston and Venice Direct and immediate costs due to permanent flooding Costs associated with measures to prevent flooding Costs that will result from future flooding In 1978 Texas A&M estimated that costs from subsidence

in Houston would be on the order of $ 32 million per year between 1969-1974

At least 9 sinkholes form in Hernando County after heavy rain Monday, June 17, 2002

Associated Press

SPRING HILL — At least nine sinkholes formed in Hernando County after heavy weekend rain.

The sinkholes opened late Friday and early Saturday, after about 5 inches of rain fell overnight. No homes were seriously threatened and no one was injured.

The biggest was about 40 feet wide and 50 feet deep. Officials also had their eyes on two depressions in a pond that appeared likely to drop.

In Orlando this month, a 150-foot-wide, 60-foot-deep sinkhole threatened two apartment buildings and forced dozens of residents to evacuate. Last month, a 10-foot-deep, 15-foot-wide sinkhole collapsed part of Interstate 4 in Lake Mary, about 15 miles north of Orlando.

And in Hernando County, sinkholes are even more common.

Long periods of drought, followed by heavy rain fall, contribute to the problem. The area's thin layer of clay to protect the limestone below doesn't help.

During 2001, Hernando County had more than 65 confirmed sinkholes.

Two more sinkholes open in Spring HillBy MARY SPICUZZA, Times Staff Writer© St. Petersburg Timespublished July 23, 2002

SPRING HILL -- Kathy Davis said she is looking forward to moving into her new home. And she is not going to let a nearby pair of 15-foot deep sinkholes get her down. "They're popping up everywhere," Davis said. "I'm not nervous about it. But I'm glad they're not on my property." Davis, 56, said she saw the sinkholes after construction workers told her that several nearby trees had sunk into the ground. She mentioned it to her daughter-in-law, Kimberly Davis, who had just moved in across the street from her future home. The Furley Avenue holes are the latest major holes in the Spring Hill area, which seems to be an especially active area for sinkholes. Assistant Fire Chief Danny Roberts said workers had enclosed an area of woods near the roadside about 100 feet wide in yellow caution tape. He said that one of the sinkholes appeared to be old but that a fresh one indicated new activity in the area. "We've been up there a couple of times checking on it," Roberts said. Stuart Glover, the president of the Hernando Builders Association, said few builders test for sinkhole activity before building. "I suppose someone could test for that," Glover said. "But it's not something most do." He said he had never seen a sinkhole open near a construction site. Kathy Davis said she was not thrilled about her neighborhood sinkhole, but she doesn't regret building a new home. "From what they tell me, all of Florida is a big sinkhole," she said. -- Mary Spicuzza can be reached via e-mail at [email protected]

Responses to Subsidence Problems: Hazard Mitigation Areal Prediction Intervention Insurance Assigning Responsibility

Areal Prediction

Geologic information in map form including GIS

Areal predicyion over cavities Given actual current distribution of subsidence;

subsidence areas in the future can be estimated by continuous monitoring including GPS

Areal prediction over aquifers that are being withdrawn Available drill-hole data for oil/water fields

GPR: Cross section showing an underground cavity nearGainesville, FL

Intervention

Map interpretation Regulation of source of extraction

Once cause and effect relationship established

Legislation creating special boards or laws to curtail or modify extraction

Insurance Protection of the public by making

insurance available Insurance premium paid reflects

level of risk as established by hazards maps or site specific insurance In Florida state legislature required that

all insurance coverage had a sinkhole clause

Assigning Responsibility

Establishment of how particular human actions are responsible for all or part of an observed subsidence based on cause and effect

Pennsylvania Coal v. Mahon, supreme court case PA tried to regulate coal in 1922 to prohibit

mining in areas where existing structures would be affected. State lost because they were seen to be infringing on rights of mine

“Act of God”; were legal establishment of responsibility has not been established

The Role of Science The Panel on Land Subsidence of the U.S. National

Research Council (NRC) (1991) recognized three information needs:

“First, basic earth-science data and information on the magnitude and distribution of subsidence [...] to recognize and to assess future problems. These data […] help not only to address local subsidence problems but to identify national problems. [...] Second, research on subsidence processes and engineering methods for dealing with subsidence […] for cost-effective damage prevention or control. […] And third, although many types of mitigation methods are in use in the United States, studies of their cost-effectiveness would facilitate choices by decision makers.”

Recognition• Subsidence is sometimes obvious• Where the frequency of well-casing

failures is high, land subsidence is often suspected and is often the cause.

• The formation of earth fissures in alluvial aquifer systems is another indication that compaction and land subsidence may be occurring.

• Other possible indicators of land subsidence include changes in flood-inundation frequency and distribution; stagnation or reversals of streams, aqueducts, storm drainages, or sewer lines; failure, overtopping or reduction in freeboard along reaches of levees, canals, and flood-conveyance structures; and, more generally, cracks and/or changes in the gradient of linear engineered structures such as pipelines and roadways.

Assessment

Mitigation

• When development of natural resources causes subsidence, governments sometimes exercise their power either to prohibit the resource development or to control it in ways that minimize damage.

• This may be done through regulation. With adequate monitoring programs and institutional mechanisms in place, optimal benefits may be achieved for both subsidence mitigation and resource development.