E

Geoplanning for Underground Space

Leif G. Eriksson

very now and then in consider­ ing new subsurface facilities we should take a look at where we

came from in order to appreciate where we are, so as to utilize our existing ex­ perience in meeting the requirements of the future.

The art of geoplanning, as described in this article, is a contemporary, ideal­ ized, step-by-step rationale for the op­ timal subsurface siting of a safe and cost-effective facility. It is governed by geotechnical, functional, and environ­ mental screening criteria. Geoplan­ ning is intended to illustrate a logical procedure for optimal site selection within the parameters of an incentive savings project and may be poorly adapted to an incentive spending pro­ ject. Numerous applications of geo­ planning have been made and brief ex­ amples of projects are used here to illustrate the incorporation of such varying factors as political criteria.

Leif G. Eriksson is Senior Geological En­ gineer with Ertec Western, Inc., Long Beach, California.

Underground Space, Vol. 7, pp. 387-392, 1983.

Printed in the U.S.A. All rights reserved.

Introduction

Geoplanning for underground space is a concept older than man. Natural underground space in the form of cav­ ities and caverns has long been used by a succession of occupants, from early vertebrates and primates to various species of homo sapiens. Natural un­ derground space initially provided the basic needs for survival through safe, energy efficient, and durable shelters for wild animals, mankind, livestock, and products. Man's ever-increasing demand for convenient living, natural resources, and environmentally ac­ ceptable storage space, coupled with the quest to develop cost-effective solu­ tions for sophisticated technical prob­ lems, has resulted in artifically devel­ oped (man-made) underground space as an integrated part of modern society (Fig. 1).

The geologic history of the earth poses problems in constructing a mod­ ern subsurface facility. This continu­ ously dynamic, four-billion-year geo­ logic process has created an

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Copyright © 1983 Pergamon Press Ltd.

environment without engineering con­ trol or quality assurance. Lithologic and structural changes occur unpredictably and abruptly, and it is a challenge and a responsibility to identify and de­ velop safe, economical solutions to en­ courage the utilization of under­ ground space. Every subsurface project will face unique subsurface conditions requiring multidisciplinary analyses and integration (geomechanics and hy­ drology, for example). Functional re­ quirements may impose additional constraints.

Three common objectives for suc­ cessful subsurface utilization are:

• To identify the optimal location for a safe, cost-effective subsur­ face facility within the constraints of geological-hydrogeological­ geotechnical, functional, environ­ mental, socio-economic, demo­ graphic, and political conditions.

• To verify, and modify if neces­ sary, the design and construction procedures to ensure a safe, func­ tional, and cost-effective facility.

387

388 UNDERGROUND SPACE May/june 1983

Figure 1. An underground oil storage cavern. (Photo courtesy of SKANSKA)

begins with national or large regional land masses and eventually leads to the preferred sites (Fig. 2). The process progressively increases the data base and at the same time reduces the land parcels subjected to study and ranks them. Screening criteria become suc­ cessively and increasingly more de­ tailed and specific with reductions in land parcels. The objective of each level of the geostudy is to establish pertinent screening criteria and to identify pre­ ferred or deferred regions, areas, and sites in close contact with the owner and operator (Fig. 3). Deferred re­ gions, areas, and sites should be banked for future renewed screen i ng, as screening criteria may change with tirp.e.,

The national geostudy is normally fairly insensitive to geological-hydrogeolog­ ical -geotechnical and functional screening criteria. Socioeconomic and demographic screening criteria! may prove more helpful in reducing the land parcels to preferred regions. Govern­ ment projects such as the National Waste Terminal Storage (NWTS) pro­ gram for the disposal of commercial high-level radioactive waste (see Un­

derground Space 6:4-5, Jan.-Aprill982) and the MX missile deep basing plan usually acquire the attention and im­ portance to justify a national geostudy.

The regional geostudy is based on the methodology and results of the na­ tional geostudy, with similar but more detailed screening criteria. Geological­ hydrogeological-geotechnical as well as functional screening criteria will aid further in reducing the land parcels down to preferred areas. By incorpo­ rating satellite remote sensing and other airborne investigative techniques with geological and topographical maps, re­ gional structural trends as well as the relative geologic complexity of a region may be defined. Functional require­ ments such as the existence or absence of ground water within a certain dis­

• To control, monitor, and main­ tain the function and the environ­ mental protection of an operating or decommissioned facility.

The concept of geoplanning outlines an idealized procedure to meet these objectives during three phases in pro­ ject development-the feasibility and design phase, the construction phase, and the operation and closure phase.

Geoplanning has progressed in timely concert with the increased utilization of subsurface space for different pur­ poses. Various of its concepts have pre­ viously been discussed at conferences and described in publications (by Mor­ feldt 1974 as geoprojecting and by Mor­ feldt 1976 and Bergman 1978 as geo­

planning). These contributions notwithstanding, the updated concept

of geoplanning as discussed here con­ stitutes the opinion of the author only and may differ from those of individ­ uals and organizations that have con­ tributed to this article.

Feasibility and Design Phase

Identifying the optimal location and design of the planned facility during the feasibility and design phase can be divided into three stages. Stage one in­ cludes the national, regional, and area geostudies; stage two is the site geo­ study; and stage three is the design geo­ study.

Stage One- National, Regional,

and

Area Geostudies

The first stage in geoplanning in­ volves a land evaluation screening se­ quence by indirect techniques which

tance from the surface or a minimum area of exposed rock may furnish ad­ ditional criteria to reduce land parcels.

The Strategic Petroleum Reserve (SPR) program is an interesting exam­ ple of a regional screening project, as it was capable of being supplemented by a national geostudy subsequent to a series of site geostudies (see Under­

ground Space 6:6, May- June 1982). This screening of the Gulf region resulted in the concentration of existing SPR

storage space in six salt domes, two lo­ cated in Texas and four in Louisiana. Despite the fact that ample potential storage space is indeed available in the salt domes in this region, criteria such as the mining cost of other geologic media and the location of storage space in other regions with favorable infra-

UNDERGROUND SPACE 389 May/june 1983

CONSTRUCTION

Figure 2. Geoplanning phases in the development of an underground project.

structures and potential users may warrant a greater national dispersion of strategic storage facilities.

The area geostudy evaluates pre­ ferred areas to identify preferred or deferred sites that meet the m,Yority of criteria required for optimal facility placement. It is based on interpreta­ tion, extrapolation, and evaluation of data obtained by indirect techniques such as literature reviews and contacts with professionals, authorities, agen­ cies, industry, and universities. The area geostudy establishes a ranking of sites as a basis for selecting the preferred sites. An expectation model of inferred sub­ surface conditions within the subsur­ face system (host rock mass) affected by the planned facility at the preferred sites should then be developed to assist in design and resource estimates for the site geostudy.

The area geostudy is normally very sensitive to geological-hydrogeologi­ cal-geotechnical and functional crite­ ria. Socioeconomic and demographic screening criteria may be less useful in reducing land parcels to preferred sites. Political concerns are particularly sen-

, ------------------------, I I I I

I

... w Cl

NATIONAUREGION/

AREA GEOSTUDY Data Collection and Evaluation

REGION/AREA/SITE

RANKING

<(

Iii PREFERRED

REGIONS(SI/AREA(SI/t----- - -- --- - - --- -- ---------i

SITE(S)

DEFERRED REGION(SI/AREA(SI/

SITE(S)

I I

,------------------------- I I

SITE GEOSTUDY

Screening Criteria

GEOINVESTIGATION

Data Collection

w and Evaluation

en

DEFERRED

LOCATION(SI

Bid Package and Bid Evaluation

Figure 3. Flow chart indicating the three stages in feasibility and design studies for an underground facility, according to the principles

of geoplanning.

sitive and could eliminate a site if cred­ ible and accurate information is not properly provided to concerned par­ ties.

The manageable size of the land par­ cels under study makes reconnaissance field studies a valuable means of data collection. The rock quality in surface

exposures, the ground conditions, ac­ cess, and the distance to necessary in­ frastructure are examples of screening data most effectively collected by re­ connaissance visits. Communication with local authorities, etc., may furnish additional information on the feasibil­ ity of the planned project and also al­ lows gauging local public opinion.

Stage Two-Site Geostudy

The second stage in geoplanning is the site geostudy, which is the level of study most projects achieve. It leads to the optimal siting and preliminary de­ sign of the facility, employing primar­ ily direct techniques during the geo­ investigation to characterize the host rock mass. Every underground con­ struction project requires its own tai­ lor-made investigation system. The geoinvestigation should be designed from the model of expected subsurface conditions developed in the area geo­ study. This should be systematic yet flexible to accommodate the possible need to address particular areas of im­ portance based on the continuously in­ creasing data base on subsurface con­ ditions.

Geotechnical conditions (soil and rock) and the ground water regime constitute the framework for design and

affect the construction, operation costs, and performance of every subsurface facility. It is therefore important to ob­ tain all the available information on subsurface conditions affecting or af­ fected by the planned facility. This cannot be overstressed. Designs can be created for any situation, but efficient designs can be achieved only by careful siting and layout which incorporate subsurface conditions to advantage.

The quantity and quality of subsur­ face information depends on re­ sources, applied investigative tech­ niques, the accuracy of data interpre­ tation, and the use intended for the information. Drilling is normally used to obtain information on subsurface conditions, but the information reveals conditions only at the single location where the bore takes place. Locations beyond the borehole wall can be in­ vestigated by indirect techniques such as geophysical or resistivity surveys or the extrapolation of lithologic bound­ aries and structural features, but this depends largely on the complexity of the geologic system under investiga­ tion.

Target drilling, illustrated in Figure 4, should be used to define the char­ acteristics of the weakest and most crit­ ical parameters in the host rock mass, such as discontinuities and the ground water regime. Target drilling, how­ ever, is only a vehicle for access to the host rock mass. Supplementary inves­ tigative techniques should be an inte­ gral part of the geoinvestigation to de­ termine other important parameters such as strength and stress state. Em-

ploying more than one investigative technique increases confidence in in­ vestigation results. Every investigative technique should have a clear objective and should be integrated well with other techniques so that results can be col­ lectively evaluated and supplemented as necessary to address specific issues or problems. Experience also shows that the cost of optimum investigation is far less than the cost of conservative design created by scant data.

Percussive ..drilling and rotary core drilling (Fig. 5) frequently lose subsur­ face data due to material escaping with the flushing media or to mechanical destruction of the core, sometimes re­ quiring an unnecessarily expensive design. Photographs, TV inspection, or impression packer imprints of the borehole wall may furnish directly visible, supplementary, and critical structure and lithologic information on subsurface conditions otherwise unavailable. Borehole photographs serve as a visual aid to document struc­ tural conditions in selected sections of the borehole where information is lacking due to core losses. Tv inspec­ tion permits enlarged, oriented view­ ing and logging of borehole wall fea­ tures along the entire borehole. The impression packer is expanded in se­ lected portions of the borehole and the external rubber surface of the packer records prevailing structural discon­ tinuities as impressions that can be cor­ related to location, orientation, dip, and width. Impression packer applications may be more limited than TV camera equipment due to less versatility in ob-

OVERBURDEN GROUND-WATER

WEATHERED ROCK

BOREHOLE

Q TARGET OBJECTIVES

Figure 4. The principles of target drilling.

390 UNDERGROUND SPACE May/june 1983

ing to the identification of candidate repository sites, as a project-specific screening process, serves to illustrate the compromises that a concept like geoplanning can experience in facing political realities.

Stage Three-Design Geostudy

The third stage in geoplanning leads to the design of the planned facility. This involves assistance in preparing the final design and bid documents as well as bid evaluations. Data furnished in the georeport are used to finalize facility design and numerical models predict facility performance during various modes of operation and de­ commissioning. Basing the final loca­ tion, geometrical shape, and orienta­ tion of the facility on prevailing sub­ surface conditions and their response to the facility system ensures optimal design; this reduces later, often costly attempts to resolve the intricacies of mother nature with engineered struc­ tures. During the bid process contrac­ tors may suggest design changes that should be reviewed for design impli­ cations as well as potential adverse ef­ fects on the environment for time pe­ riods during which the facility or its products may affect the human envi­ ronment.

,..... Figure 5. Core drilling for engineering characterization of rock at depth.

Construction Phase

Before commencing the construc­ tion phase seasonal ground water var­

taining host rock mass data and higher cost per unit area recorded. A wide range of indirect techniques involving subjective interpretations is also avail­ able.

During the geoinvestigation core samples should be laboratory tested to establish physical, thermo-mechanical, and chemical characteristics; selected borehole intervals subjected to in situ tests to establish hydraulic, thermal, and stress-strain characteristics; and, if nec­ essary, scaled tests performed to estab­ lish scale effects and define subsurface parameters important to the design, construction, performance modeling and operation of the planned facility.

The geotechnical feasibility of the project and anticipated site-specific subsurface conditions are contained in the georeport. Included in this report are the occurrence, frequency, ap­ proximate location and width of lith­ ologic formations and structures im­ portant to the project (Fig. 6) and the site-specific stress state and ground water regime characteristics. The abil­ ity to discern these features is limited by the characteristics and density of field

data collection points.

May/june 1983

The site geostudy is normally very sensitive to geological-hydrogeologi­ cal-geotechnical and functional con­ cerns because the two major parame­ ters affecting all underground design and construction work are the rock mass quality and the ground water regime.

By way of example we may note that the National Waste Terminal Storage Program has experienced an unpar­ alleled sequence of screening efforts on all scales, even beyond those de­ scribed in geoplanning. The continued investigative program proposed by the U.S. Department of Energy includes exceptionally detailed site characteri­ zation of the repository host rock, with comprehensive testing from caverns located at candidate repository depths. This is beyond the detail normally re­ quired for an underground facility. The NWTS screening process must fre­ quently be responsive to non -geo­ technical screening criteria rather than geotechnical ones. For example, two NWTS sites are located on government lands which display complex rock mass or ground water regime characteristics but are associated with nuclear activi­ ties. The NWTS screening process lead-

iations should be established by contin­ ualfy monitoring ground water observation stations installed during the geoinvestigation. This allows timely implementation of cost-effective de­ watering or injection systems to pre­ vent ground water problems during the construction phase. Supplementary in­ vestigation and observation stations may be required in complex geologic set­ tings or adjacent to areas of expected changes in subsurface conditions to en­ sure safe construction and operation of the planned facility.

Subsurface conditions encountered during the construction phase should be mapped or otherwise documented on a regular basis by adequately trained and experienced personnel. The in­ creasing data base on subsurface con­ ditions should be compared regularly with subsurface conditions predicted in the georeport. Major discrepancies should be evaluated and incorporated in the numerical models predicting the stability of the designed excavation and the performance of the facility, as ex­ cavation techniques and reinforce­ ments may need to be modified. A de­ tailed model of prevailing subsurface lj

UNDERGROUND SPACE 391

Figure 6. Model of subsurface conditions anticipated within the host rock mass. (Photo

courtesy of Hagconsult)

for the planned facility during the fea­ sibility and design phase, to benefit from continuously increasing knowledge of geology during the construction phase, and to maintain functional and envi­ ronmental control during the opera­ tion and closure phase of an under­ ground project. To ensur.e the successful implementation of geoplan­ ning all three phases must be devel­ oped in close interaction and with con­ fidence between the owner or operator and the other parties involved in the project. D

References

Allen, L. D., Doherty, T. J., and Fossum, A. F. 1982. Geotechnical issues and guide­ lines for storage of compressed air in excavated hard rock caverns. Prepared for the U.S. Department of Energy by Pacific North­ west Laboratory. Report no. PNL-4180 UC-94e.

Bergman, S. M. 1978. Geoplanning, a nec­ essary tool for controlled underground construction. Proceedings of the Third In­ ternational Congress of the International As­ sociation of Engineering Geology, September 1970, Madrid, Spain.

Eriksson, L. G. 1982. Geoplanning for foun­ conditions and applied reinforcements should be prepared for future refer­ ence after the construction phase.

Operation and Closure Phase

Operational and environmental safety should be monitored during the op­ eration and closure phase using sta­ tions installed during the construction phase to monitor excavation safety and rock mass response. Subsurface con­ ditions affected by the facility system should also be monitored or inspected regularly to ensure that system per­ formance complies with predictive models. With increased foundation depth, instrument limitations may re­ quire physical access to critical loca­ tions adjacent to the facility.

Conclusion

The ost of an underground instal­ lation depends on more factors than those of a corresponding surface in­ stallation. Most of these factors are in­ fluenced by geological, hydrogeologi­ cal, and geotechnical conditions at the site with respect to the function of the planned installation, whereas environ-

392 UNDERGROUND SPACE .

mental and political concerns are usu­ ally identical for surface and subsur­ face facilities.

The art of geoplanning establishes as early as possible the importance and influence of the prevailing geological conditions that would enable cost sav­ ing to be made to the tentative project. Geoplanning has the greatest potential for saving time and money for the client during the feasibility and design phase.

The design of a reliable rapid sub­ surface geoinvestigation determining the details of subsurface conditions is more important to reducing the total construction cost than any other detail of design. It must be emphasized, how­ ever, that the main objective in a sub­ surface investigation is to collect data of importance to the design and con­ struction of the planned subsurface space. High drilling production which yields poor investigative results and fails to provide necessary information inev­ itably leads to a conservative design far more expensive than one which has been based on professional investiga­ tion.

In summary, then, it can be stated succinctly that the objective of geo­ planning is to identify the optimal site

dations and facilities in soil and rock. Nar­ rative summary with illustrations from presentations in the Republic of China. Available from the author.

---. 1981. Performance assessment of the Swedish overcoring method for application at Hanford . Proprietary report to Rockwell Hanford Operations.

---. 1978. Rapid subsurface investiga­ tion system for underground openings and space. Proceedings of the Third International Congress of the International Association of Engineering Geology, September 1970, Ma­ drid , Spain.

International Society for Rock Mechanics. 1975. Recommendations on site investigation techniques. Final report.

Morfeldt, C. 0. 1976. Brief review of the method of oil storage in bedrock caverns and its de­ velopment up to date. Marketing paper.

---. 1974. Storage of oil and gas in un­ lined caverns. Presented at the Society of Petroleum Engineers European Spring Meeting, May 29-30, Amsterdam, The Netherlands.

Ninety-Seventh Congress of the United States of America. 1982. Nuclear Waste Policy Act of 1982. White House copy.

U.S. Department of Energy. 1983. Nuclear Waste Policy Act of 1982: proposed gen­ eral guidelines for recommendation of sites for nuclear waste repositories; proposed rule (10 CFR Part 960). Federal Register (Monday, February 7, 1983).

May/june 1983