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Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
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OCR for page 45
3
Findings
INTRODUCTION
Efforts in three general areas are needed to mitigate the nation's subsidence problem. Fug,
a broad range of earth-science data, the data base, must be collected in order to assess locally
and regionally the incidence and potential impact from each type of subsidence. Although some
of these data are already available, they must be converted to the appropriate scale and format
to be useful. This often will require collection of additional field data S=Qn4, teCh~G~
research is needed bow to improve the capability to predict the dine, rate or magnitude,
and place of subsidence and to develop engineering designs that are resistant to subsidence
damage. And third, institutional methods of subsidence mitigation need to be evaluated for
their cost-effectiveness and suitability for each type of subsidence. Although many different
approaches have been tried in the United States, few studies of the methods themselves hake
been conducted.
Our greatest concern is that efforts to reduce-the federal deficit, which have jeopardized
the small but effective subsidence research programs disseminated throughout the federal
government, will halt scientific and technical progress at the federal level. Data and research
results from these federal programs historically have complemented state and local efforts by
establishing much of the technical basis for the recognition A subsidence potential, as well
as its prevention or mitigation. Basic earth-science data collection and research on subsidence
processes are legitimate roles for the federal government. Without funding for this work,
agencies such as the Bureau of Mines, U.S. Geological Survey, and Agricultural Research
Service are unable to provide the data and techniques required by state and local government
and industry to mitigate subsidence in a timely and cost-effective manner.
DATA BASE
Mitigation of subsidence requires many types of basic earth-science data, including ge-
ologic, hydrogeologic, soils, hydrologic, geodetic, and land-use information as well as infor-
mation on the incidence and areal distribution of the subsidence itself. Many of these data
are rc,~tinekr collected in map form by the many federal, state, and local agencies. However,
45
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46
they rarely are collected pnmanly for subsidence mitigation. Consequently, without furler
interpretation and field work, their usefulness for subsidence mitigation is limited.
Findings
In areas of the nation where geologic or hydrologic conditions conducive to subsidence
exist and activities can trigger subsidence, detailed mapping programs to identify potential
subsidence areas are needed. These should be associated with a data base developed to iden-
tify the areas of potential subsidence that includes an inventory of sizes, shapes, frequency,
predictability, and triggering mechanisms. These maps should be accompanied by the neces-
sary graphics and text to be understandable by the general public, legislators, planners, and
regulators. The information should be presented in a manner that will be useful to:
· provide guidelines for building design and codes,
· provide a basis for development of land-use planning maps as an instrumental resource
in land-use management,
· develop actuarial data for insurance purposes, and
· guide location, management, and monitoring of landfills for municipal, hazardous, and
toxic wastes.
Implementation
Primary data collection and mapping should be carried out by state geological surveys, the
U.S. Geological Survey, and the Soil Conservation Service. Special research to define mapping
criteria and identify and solve complex causes of subsidence should be the responsibility of
federal agencies such as the U.S. Geological Survey, Bureau of Mines, and Agricultural
Research Service.
TECHNICAL RESEARCH NEEDS
Technical research in two areas is needed to improve our capability to mitigate subsi-
dence: (~) prediction of specific subsidence occurrences and (2) subsidence-resistant design of
structures.
Subsidence Prediction
Although the mechanism for each of the six types of subsidence considered in this report
is generally understood, the ability to predict time, place, and magnitude or rate of subsidence
is frequently impaired by either inadequate mapping or incomplete understanding of details of
the subsidence process and difficulty in determining the parameters that control the process.
Findings
To improve our predictive capability of subsidence, the following research needs were
identified:
· Mining- monitoring of the extent of subsidence and subsurface deformation in coal
fields to provide data for the development of predictive models for subsurface conditions
peculiar to the United States
· Sinkholes remote sensing and geophysical methods to identify subsurface voids and
provide better understanding of triggering factors
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47
· Underground fluid withdrawal—methods to reliably determine the spatial distribution
of compressibility of underground fluid reservoirs before they are developed
· Natural compaction methods to predict compaction, particularly its rate
· Hydrocompaction methods to reliably identify collapsible soils and to predict mag-
nitude of settlement, particularly for routine engineering investigations
· Organic soil better methods to identify carbon content and temperature within soil
profiles; development of truck and field crops suited for high water tables
Implementation
in many cases, federal and state agencies already have the expertise and mandates to
conduct this research. However, reduced funding, particularly at the federal level, has jeopar-
dized fundamental research on subsidence processes. Before seeking additional funding, these
agencies need to establish priorities collectively and seek to improve coordination of Heir
research effort on ground failure, both with other federal agencies and with state agencies. The
U.S. Bureau of Mines has been primarily responsible for research on mining; the U.S. Geo-
logical Survey for underground fluid withdrawal, natural compaction, sinkholes, and geologic
aspects of mining; the U.S. Bureau of Reclamation for hydrocompaction; and the Agricultural
Research Service for organic soils. Agencies concerned with construction, such as the Army
Corps of Engineers, Soil Conservation Service, ant! Federal Highway Administration, should
be involved in establishing these priorities, since they frequently spend large amounts on very
specific subsidence problems.
Engineering Design and Construction
A number of engineering solutions are available to prevent or minimize subsidence
damage to structures, transportation facilities, and utilities. However, the movement and
resulting damage to structures in response to subsidence ground movements needs to be better
documented. Methods also exist to backfill underground mines and voids in soluble rock.
Little is known of the long-term effectiveness of void backfilling methods and materials.
Findings
· Mining and sinkholes. Studies of building movements and the resulting damage should
be conducted in areas subject to local colIapse, particularly mining. This would improve our
ability to design subsidence-resistant structures. Techniques and costs of presubsidence support
of buildings should be evaluated against postsubsidence damage repair. Use of geofabncs
and earn reinforcement for construction of slabs, roads, and dikes with more resistance to
subsidence damage should be examined.
The effectiveness of mine backfilling techniques and materials should be evaluated. Core
drilling, sampling, and downhole inspection using TV cameras would provide data for eval-
uation and improving procedures. Partial mine filling can reduce subsidence by reducing the
size of voids and providing lateral support for existing mine pillars. The effectiveness and
cost of this procedure should be evaluated relative to total void filling. Research on less-costly
materials handling systems, such as pumped slurry, could result in improved, cost-effective
void-filling procedures. Fiber-reinforced grout columns should be tested.
· Hydrocompaction. Cost-effective methods to stabilize colBapsible soils are needed.
Such methods need to be developed for small structures, for example, houses, as well as large
· · ~
engineering projects.
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· Organic soils. In agricultural areas, new crop varieties Hat tolerate shallow water
tables are needed. Chemical treatment can inhibit organic soil degradation.
Implementation
Although research on construction and void backfiHine can be conducted or funded bY
~ ~ _ _ ~ _ _ O
a number of agencies and Industries, it appears appropriate to assign responslullltles tor this
type of subsidence research to the U.S. Bureau of Mines. Necessary technology-transfer inputs
could be obtained by assistance from appropriate professionals and the National Institute of
Standards and Technology. Agencies concerned with roads, canals, and dams are the ones most
frequently confronted by hydrocompaction. The primary agencies are the Federal Highway
A~ninistration and Bureau of Reclamation, although there is also a role for the Federal
Housing Administration because of the explosive growth in the western part of the Sun Belt.
The Agricultural Research Service historically has had responsibility for organic soil research.
MITIGATION MEASURES RESEARCH AND IMPLEMENTATION NEEDS
Because of He diverse causes of and impacts from land subsidence, as well as the
need to consider the status quo when mitigation is necessary, mitigation measures must be, in
general, designed for each situation. General approaches to mitigation of subsidence rarely will
apply to aU types of subsidence. Another consequence of the diversity is that governmental
responsibilities for mitigation measures primarily fall to state and local governments. The
appropriate role of the federal government is to provide national coordination and information,
provide technical assistance to state and local governments, and fund research on mitigation
techniques.
Regulation of Resource Development
Introduction
When development of natural resources causes subsidence, governments sometimes find
it necessary to exercise their power either to prohibit the resource development or to control it
in ways that minimize subsidence damage.
Findings
Legislative regulation of resource development reflects a decision that the benefits of
unregulated resource development are outweighed by the harm caused. Therefore, such reg-
ulation is most appropriately considered when there is sufficient information regarding He
relationships between resource development and subsidence costs. Sufficient information of
this kind still needs to be developed.
Implementation
The federal government can encourage the development and dissemination of technolo-
gies for evaluating these relationships through programs of the appropriate agencies of the
Deparunents of Agriculture, Housing and Urban Development, and Interior. Where the federal
gove'Tunent is itself involved in resource development, it can take steps to ensure that subsi-
dence is one of He factors considered as part of the development process. Where states are
responsible for the regulation of resource development, He appropriate state agency should
consider whether procedures for addressing subsidence should be integrated win the resource
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49
development process. Such an agency may be able to accomplish this directly through ad-
ministrative regulation, or it may be necessary for state legislatures to take action through the
legislative process.
Land-Use Management and Construction Codes
Introduction
Land-use management in the United States is primarily the responsibility of state and local
governments operating within the constraints of state enabling legislation. The federal role is
limited to the collection and dissemination of information, although the federal government
may require land-use regulation as a condition of participation in a federal program, as in the
case of flood insurance.
Because of variations in subsidence characteristics, there is no general zoning approach
to the prevention or mitigation of subsidence damage. Zoning is most efficiently used where
the risk and potential cost of subsidence are high enough to offset the impacts of controlling
the use of property. Zoning can be used to restrict the use of land to levels consistent with
the hazard, but short of prohibition of all uses. Zoning win be most effective where risk is
very high or where the value of the surface land and improvements is low. Moreover, where
the zoning prohibits any use of property in a subsidence-risk area, the question will arise of
whether a taking in violation of the Fifth Amendment of the U.S. Constitution has occurred.
Where subsidence risk is very high, the most cost-effective approach may be direct acquisition
of the land affected or of the development rights of the land.
Construction techniques sometimes can be used effectively to eliminate or limit subsidence
damage, but these are now seldom used in connection with subsidence hazards in the United
States.
Findings
Research needs to be done specifically on local codes and ordinances that can be used
to reduce subsidence damage. Since the subsidence-damage problem, except in the case of
increased flooding in areas of lower elevation, is primarily economic, the costs to the community
of subsidence damage compared with those of zoning restrictions must be examined. The
relative costs of prohibition of development, limits on development, and outright purchase of
land in subsidence-nsk areas need to be examined. An optional zoning approach that should
be studied is the imposition in high-risk areas of a requirement that subsurface investigations
be undertaken and appropriate engineering measures be taken to prevent or reduce subsidence
damage.
Studies also need to be made of building code provisions that can reduce subsidence
damage. These could be applied in connection with the zoning approach suggested above.
Imp lementatz on
Because land-use and building regulation is a local responsibility, the studies recommended
above win have to be earned out by local planning agencies and by related professional groups
such as Me Planning Advisory Service of He American Planning Association. Building
codes are generally a local government responsibility, but mocle] codes are prepared by such
organizations as the Intemational Conference of Building Officials (ICBO), the Building
Officials and Codes Administrators, Inc. (BOCA), and the Sou~em Building Code Congress
International (SBCCI). These organizations should consider the inclusion of subsidence-related
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so
provisions in mode! codes, similar to ICBO's Uniform Building Code, which has provisions
for earthquake damage reduction.
Federal involvement should consist of He dissemination of information and research on
building technology by the National Institute of Standards and Technology, National Science
Foundation, and Department of Housing and Urban Development; and research of land-use
regulation by the National Science Foundation.
Market-Based Methods
Introduction
There are a few examples of effective systems for market-based methods to internalize
subsidence costs. The Surface Mining Control and Reclamation Act of 1977 requires mine
operators to reimburse surface owners for damage in some cases, and a tax on groundwater
in the Santa Clara Valley eliminates the cost advantage of groundwater over surface water.
Subsidence costs are also internalized through litigation by parties suffering damage and by
payments negotiated by resource extractors facing possible litigation.
Findings
Studies need to be ca'Tied out on the relative costs and benefits of different approaches
to resource taxation for different types of extraction that could result in subsidence. Studies
should also be made of the overall costs of resource taxation compared with leaving He
problem of cost distribution to litigation.
An approach that could effectively internalize the cost of subsidence resulting from
resource extraction would be state legislative action requiring that extractors take measures to
. · . . . ·. . . · ~ . · . ~ . · . .
prevent subsidence and be responsible under specified circumstances for subsidence damage
on the surface resulting from extraction. This approach is applied by the federal government
to some coal-mine subsidence, but its application is currently very limited.
Implementation
Cost-benefit studies could be carried out by university researchers and consultants and
funded by industry groups for whom subsidence-related litigation is potentially a significant
cost, and possibly by the National Science Foundation. Action to require resource extractors
to bear subsidence mitigation and damage costs must be taken by state legislatures.
Insurance
Introduction
Insurance is a viable form of relief for the types of subsidence Hat meet He following
criteria. An "insurable risk" is generally defined as presenting itself to a sufficiently large
and homogeneous group of exposure units to permit reasonably accurate prediction of average
losses, where He loss is definite but unpredictable in time and place and where there is no
threat of a major catastrophe of unknown proportions. Experience with coal-mine and sinkhole
subsidence, and with flooding, suggests that insurance, if properly structured and executed, may
equitably, expeditiously, and predictably provide relief for property damaged by subsidence or
by flooding aggravated by subsidence.
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51
Findings
1. Information regarding the incidence of insurable types of subsidence needs to be
developed in conjunction with property insurers in states where those types of subsidence are
widespread.
2. Basic questions regarding underwnting/coverage, claims/value, and adm~stradon/
program structure for subsidence-insurance programs should be addressed in conjunction with
any state legislative efforts to authorize such insurance. Early decisions should be made
regarding whether subsidence-insurance availability wiD be mandatory or voluntary, the type
and doBar amount of coverage to be available, and whether insurance should or should not be
interrelated with land-use controls or other mitigation measures.
3. In flood-prone rivenne and coastal areas, methodologies are needed to determine the
incremental contribution of subsidence to flooding costs, and criteria need to be developed for
establishing priorities for remapping flood zones in subsidence areas.
Implementation
The following state and federal agencies are identified to develop the information and
methodologies given above:
Finding I. state geological surveys in conjunction with the U.S. Geological Survey
Finding 2. state insurance administrators, property insurance companies doing business in
each affected state, and appropriate staff of state legislatures
Finding 3. We Federal Emergency Management Agency
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!
Representative terms from entire chapter:
resource development
