Soft Sedimentary Rock Research Articles

Characterization of a Sedimentary Soft Rock by a Small In-Situ Triaxial Test

To measure the shear strength and deformability of a sedimentary soft rock, a small down-hole in-situ triaxial testing method is developed. The apparatus consists of a triaxial cell and an axial loading device which enables testing at any depth. In this method, a columnar specimen of diameter 90 mm and 285 mm height can be sheared at the bottom of a drill hole. A series of tests were conducted at a 50 m deep experimental cavern. The test gallery is contained in mudstone with some inter-bedded thin sand layers. The tests were done in three different depths in a borehole by a multiple-step loading method. The new testing method was successful to measure stress–strain relation of rock mass. The test results demonstrated that the multiple-step loading method is acceptable in mudstone formation, if an appropriate criterion for load reversal is selected to recognize the instant of failure by stress–strain relation during loading. In addition, different results for mechanical properties of mudstone rock mass were observed in the specimens contained sand layers. It is also concluded that, the same loading method is not successful if a sand layer is located in the middle of the specimen due to large damage induced in early stages of loading.

Geological disposal of high-level radioactive waste and the role of rock engineering

Japan Atomic Energy Agency (JAEA) and its predecessors have been conducting an extensive geoscientific research program since the 1970’s in order to contribute to the formation of a firm scientific and technological basis for the geological disposal of high level radioactive waste in Japan. As a part of this program, in situ experiments have been performed at the Tono Mine in soft sedimentary rocks and at the Kamaishi Mine in hard crystalline rocks. An experiment on excavation disturbance has been one of these experiments and has revealed the extent and properties of the excavation disturbed zone (EDZ) and the applicability of available measurement methods. It is suggested that mechanical excavation and controlled excavation have reduced excavation damage of the rock mass around a drift, although some improvements in the currently available methods for measuring and simulating the EDZ are essential to understand excavation disturbance in more detail. JAEA is now promoting two underground research laboratory projects in Japan; the Mizunami Underground Research Laboratory (MIU) project for crystalline rocks and t he Horonobe Underground Research Laboratory (Horonobe URL) project for sedimentary rocks. From a rock mechanical point of view, the major interest in these projects will be paid to failure phenomenon in deep underground, rock stress estimation at larger scales and long-term physical stability of underground structure. These projects are open for international collaboration.

Influence of Membrane and Filter Paper on Plane-Strain Testing of Soft Sedimentary Rock

Abstract It is recognized that the intermediate principal stress plays an important role in the strength and the stress-dilatancy relation of soft sedimentary rock. However, few plane-strain/true triaxial experiments on soft rock have been referenced in literature due to the relatively high strength of geomaterials. With a conventional plane-strain apparatus, equipped with a prefixed plane-strain confining frame, it is difficult to obtain real isotropic consolidation before shearing. On the other hand, it has been found that the influence of the membrane/covering material on a high-strength specimen cannot be ignored. In this study, therefore, an innovative plane-strain test system for soft rock, that can overcome the shortcomings of the conventional type of apparatus, and issues related to specimen preparation are introduced. The results of drained compression tests and drained creep tests, along with theoretical simulations, are reported. The influence of the membrane and the filter paper are illustrated by a simple finite element method. A combination of experimental and theoretical approaches is employed to facilitate the understanding of the mechanical behavior of soft rock.

Test on Soft Sedimentary Rock Under Different Loading Paths and its Interpretation

Tests on soft sedimentary rock under conventional triaxial and plane-strain compression and/or creep have been conducted. The purpose of the tests is to investigate the influence of intermediate principal stress that may affect the strength and dilatancy of the soft sedimentary rock under different loading paths. Meanwhile, theoretical simulations by an elasto-viscoplastic constitutive model were also conducted. Influence of membrane and filter paper was investigated using finite element analysis based on the elasto-viscoplastic model. Furthermore, particular attention was paid to the migration of excessive pore water pressure within a specimen, by continuous monitoring of the inner excessive pore water pressure of specimens and calculation with soil-water coupled finite element-finite difference (FE-FD) method. The shear strength, inherent dilatancy and creep behavior of soft rock were explained experimentally and numerically in detail.

Recent borings in limestone cobbles from Marloes Bay, southwest Wales

Limestone clasts from the beach at Marloes Sands, southwest Wales, contain slender, straight to sinuous borings cross‐cut by younger, clavate borings. The former were probably produced by sipunculids or polychaetes; the latter preserve shells of the boring bivalve Gastrochaena dubia (Pennant). Unusually, the calcareous linings of the clavate bivalve borings extend into many of the slender worm borings. Such linings are considered part of the hard parts of the producing bivalve, but the chance association of the two morphologies of borings has led to the lining becoming intimately associated with both of them. The modified linings of the bivalve borings have a similar morphology to the crypt of certain clavagellid bivalves, perhaps presenting an analogue for the morphology of a pre‐clavagellid, boring ancestor. Walls and linings in burrows and borings are of importance to the systematic ichnologist (e.g., Keighley & Pickerill 1994) and the functional morphology of the producing organism (e.g., Savrda & Smith 1996; Monaco et al. 2005). Fossil clavate borings in limestone (e.g., Gastrochaenolites Leymerie, 1842) and wood (e.g., Teredolites Leymerie, 1842) commonly have calcareous linings, which are ‘part of the hard part of the shell’ (Kelly & Bromley 1984, p. 795). The lining of the boring is secreted by the mantle and hence is part of the body fossil (Evans 1999), although such a structure preserved free of the boring can be treated as an organically generated mould of the trace fossil (table 2 in Donovan 2002). In the extreme example of crypt‐dwelling bivalves, the lining has become secondarily readapted to a life within unlithified sediment (Pojeta & Sohl 1987; Savazzi 1994, 1999). Such calcareous linings have a morphology determined by the boring. The boring/lining relationship can be modified either by the boring organism (e.g., Gastrochaenolites pickerilli Donovan, 2002) or by features of the substrate. It is the latter phenomenon that is the subject of the present paper. Interactions between invertebrates and the surrounding substrate, and modifications of the substrate by organisms forming traces are probably better known from soft sediments and related sedimentary rocks (Bromley & Ekdale 1986; Pickerill 1994), but analogous interplays are recognized from borings (e.g., Donovan 2002). Interference between borings in a hard substrate that has been repeatedly infested can produce structures of unusual topography that complicate interpretation. Herein, such associations are explored by reference to an example of calcareous linings encroaching on adjacent borings that would have been otherwise unlined. While there are probably good functional reasons for such behaviour, the resultant structure is convergent with that of a notable, and related, group of bivalves, begging the question, what evolutionary influence (if any) might be read into such accidental structures? Descriptive terminology of borings follows Hantzschel (1975). All specimens are deposited in the Nationaal Natuurhistorisch Museum Naturalis, Leiden (RGM).

Small Strain Stiffness and Non-Linear Stress-Strain Behaviour of Cement-Mixed Gravelly Soil

ABSTRACT The stiffness at small strains and non-linear stress-strain relation of compacted cement-mixed well-graded gravelly soil as well as the ageing effects were evaluated by drained triaxial compression tests on compacted moist specimens cured for different periods at isotropic and different anisotropic stress states. In all the tests, the initial stress-strain relation at small strains less than about 0.001% was essentially elastic and the initial Young's modulus, E0, was essentially the same as the Eeq value evaluated by applying unload/reload cycles under otherwise the same conditions. The Eeq values were rather independent of strain rate. The Eeq value from the first unload/reload cycle applied during otherwise continuous ML became noticeably lower than the elastic modulus evaluated at the same stress state, more as approaching the peak stress state. After a number of small unload/reload cycles and long sustained loading, the Eeq value became closer to the elastic modulus due to a decrease in the viscous effects. The ratio of E0 to the compressive strength (qmax) was similar to that of concrete but noticeably larger than those of uncompacted cement-mixed soil, sedimentary softrock and unbound gravelly soil. Both E0 and qmax increased with time by ageing, while the E0/qmax ratio decreased with time. When ML was restarted at a constant strain rate after ageing with a shear stress, the tangent stiffness became very high for a large stress range with a substantial change in the non-linearity of stress-strain relation.

Application of the material force concept to formation of discontinuities in soft sedimentary rocks

The possibility of rock joint formation from discontinuities which originate in poorly lithified sediments is presented. The mechanism for the development of these discontinuities along the maximum compressive stress Tmax is discussed and quantitatively investigated. Micro-defects (holes, cavities) may exist in sediment due to non-ideal packing. It is shown that in certain situations, a physically warranted tendency to reduce the total energy of the system splits into two separate holes which move away relative to material particles (grains) along the Tmax axis. The trace left by the moving hole is interpreted as a macro-discontinuity evolving with time into the closed mode I macro-crack. Some justifications for the mechanism are presented.

短報 揚水に伴う沿岸域堆積軟岩中の塩淡境界形状と地下水流動の変化

沿岸域における塩淡境界は,流動する地下水による移流混合の影響が大きい浅部に比べて,化石海水の拡散混合が支配的な深部の評価が難しく,現地観測と数値解析を組み合わせた評価技術の高度化が求められるようになってきた(例えば,放射性廃棄物の地層処分事業).そのためには,塩淡境界の動的な形状変化の把握が重要となるが,これまでの観測事例は浅部を対象としたものが多く,深部の現象を捉えた事例はなかった.そこで本研究は,茨城県東海村の試験地における第四系と第三系の塩淡境界を深度200mまで動態観測した.試験地ではリング状トンネル構造物(大強度陽子加速器の一部)の建設に伴ってディープウェルによる揚水工事(日量約10,000m3)が行われ,塩水が浸入する状況下にあった.まず,静的条件下の塩淡境界解析を行い,自然状態の塩淡境界形状を推定するとともに集中的な観測研究を実施する位置(塩水化が進行すると考えられる領域)を決定した.続いて,揚水工事と並行して4孔の観測井を設け,水位,電気伝導度,温度を長期観測した.その結果,第四系と第三系の塩水浸入状況の違いについて次の知見を得た.(1)電気伝導度の測定結果によると,工事開始13-22ヶ月の問に,現海水が第四系に浸入したが,第三系には浸入しなかった.遮水層は浸入層下位の不透水層で,その透水性は浸入層の1/10-1/100であった.(2)揚水工事に伴う温度プロファイルの局所的な低温化と高温化が観察された.例えば,工事開始11-12ヶ月後に現海水浸入層が低温化し,18ヶ月後には第四系と第三系の地質境界付近などで低温化した.本試験地では,第四系への現海水浸入の他に,地層に含まれる塩水が複数深度から浸入した.(3)静的条件下の塩淡境界解析で,工事前の第四系と第三系の塩淡境界を推定した.塩淡境界の位置は観測結果と一致したが,第三系の塩分濃度評価は困難であった.静的条件下の塩淡境界解析は,浅部の形状が妥当であっても,深部まで含めた評価には不十分であることが分かった.

Effect of rock type on the recruitment and early mortality of the barnacle Chthamalus montagui

Discontinuities in distribution of sessile species due to changes in available habitat have rarely been investigated. In the English Channel, soft sedimentary rocks including chalk could potentially present a barrier to eastward range extension of the southern barnacle Chthamalus montagui. To test the effect of rock type on recruitment and mortality, prepared settlement tiles of four calcareous rocks that form important platforms close to existing limits of distribution were fixed to the shore at a site in south-west England, known to have consistently high larval settlement. Prior to fixation, the roughness parameter “ R a” and Potential Settlement Sites (PSS) index was measured. Recruitment was monitored photographically on four occasions during the settlement season and subsequent mortality for 7 months after the settlement season. By the end of the settlement season, recruitment on the hard Kimmeridge Cementstone was significantly less than on the other three rock types and attributed to low surface roughness and fewest Potential Settlement Sites (PSS), yet only 28% of variance could be attributed to PSS. Post-recruitment mortality was more variable, however after 7 months there were significant differences between rock types. Simultaneous surveys of post-recruitment mortality in natural populations showed that although recruitment on chalk can potentially be high, survivorship was relatively low. Thus rock type could be influential in setting species geographical limits.

An Elasto-viscoplastic Constitutive Model with Strain-softening for Soft Sedimentary Rocks

In general, soft sedimentary rocks exhibit strain-softening and time-dependent behavior. In the present paper, an elasto-viscoplastic constitutive model for soft rocks is proposed, that can universally describe time-dependent behavior such as creep, stress relaxation and strain rate sensitivity by extending Adachi and Oka's elasto-viscoplastic model for frozen sand. It is found that the proposed model can be applied to the time-dependent behavior of a soft tuffaceous rock called Tomuro Stone under the strain rate constant triaxial compression, drained triaxial creep and undrained triaxial stress relaxation.

Submarine landforms and the reconstruction of fast-flowing ice streams within a large Quaternary ice sheet: The 2500-km-long Norwegian-Svalbard margin (57°–80°N)

Morphological interpretation of regional and detailed bathymetric data sets on the 2500-km-long Norwegian shelf from the North Sea (57°N) to Svalbard (80°N) has revealed a dynamic ice-flow pattern along the western marginof the Scandinavian and Barents/Svalbard ice sheets. About 20 cross-shelf troughs with megascale glacial lineations (MSGL; elongate ridges and grooves oriented parallel to trough long axes) are interpreted as former pathways for fast-flowing ice streams. Studies of large-scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross-shelf troughs. Less dynamic ice probably existed on shallower banks. The two largest paleo-ice streams were the Norwegian Channel Ice Stream and Bear Island Trough Ice Stream, each 150-200 km wide at the mouth. The lengths of individual MSGL vary from hundreds of meters to several tens of kilometers, and the distance between ridges varies from 0.1 to 3 km. MSGL amplitudes reach 15 m, but are commonly <10 m. The onset of MSGL and, hence, fast ice flow is generally close to the outer coast, at the border zone between crystalline rocks and softer sedimentary rocks. Transverse submarine ridges on various scales, commonly parallel to the shelf edge, reflect either the maximum ice-sheet position or the recessional pattern of the ice sheet. Lateral ice-stream moraines several tens of kilometers long have also been mapped along the sides of several cross-shelf troughs, identifying the border zone between fast ice flow and stagnant or slow-flowing ice on intervening banks.

ROCK MASS DEFORMATIONAL BEHAVIORS DURING THE EXCAVATION OF THE LARGE-SCALE NATM CAVERN IN SOFT SEDIMENTARY FORMATION

During excavation of a large-scale water storage tunnel in soft mudstone, rock deformations at the tunnel side wall have unexpectedly increased corresponding to the stepwise bench excavation. The conventional numerical analysis for designing tunnel supports could not predict such behaviors in advance. In this paper, some different numerical analyses for tunnel excavation in soft rock will be employed as the methods that can reasonably represent such rock mass mechanical behaviors. Analyses of large-scale cavern excavation in soft sedimentary rock will be carried out by them and all analysis results will be compared together with the measurement data in order to improve the prediction of tunnel deformational behaviors.

酸性堆積軟岩の風化過程における化学的・生化学的特性

Recently, the acid sedimentary soft rock that caused a collapse of the cutting ground has appeared in the surface with the road construction and the estate development. The acid soil at construction, however, must be effectively utilized as the land reclamation.The purposes of this study are to verify the importance of the biochemical oxidation of pyrite in the weathering process and to investigate the optimum pH condition for faster oxidation than in nature. First, pH, sulfate content and pyrite remaining in the acid soil that collected in the field were measured. When the ratio of pyrite remaining in the soil was less than 70 percents, pH was also lowered with the decrease in the pyrite remaining. Then, samples that added the commercial pyrite or sulfur powder were sterilized by the autoclave in order to clarify the biochemical characteristics of the acid sedimentary soft rock in the weathering. The result showed that sulfate ion was detected only in non-sterilized samples at pH below 3.5. On the other hand, sulfur powder was hardly converted at pH above 2.5. Therefore, it was confirmed that ferrous iron oxidation, given as Fe2++1/4O2+H+→Fe3++1/2H2O was the most important process in the biochemical oxidation of pyrite and its optimum pH was 2.5-3.5.

Anisotropic Behavior of Soft Sedimentary Rock and A Constitutive Model

In order to investigate the anisotropic behavior of soft sedimentary rock, a series of triaxial compression tests are performed on Tomuro stone, sampled in different directions. From the test results, it is confirmed that the deformation characteristics and strength are strongly dependent on the direction; in other words, Tomuro stone is a transversely isotropic body. The authors have developed an anisotropic elasto-plastic constitutive model which can describe anisotropic behavior through triaxial tests. The model is based on the elasto-plastic constitutive model with strain softening proposed by Adachi and Oka (1995). In the formulation of the model, a generalized Hooke's law is adopted for the elastic strain increment, and the transformation stress concept proposed by Boehler and Sawczuk (1977) is used for the plastic strain. Five independent elastic moduli are used for the transversely isotropic body, and three independent parameters are introduced for the plastic anisotropy. These parameters can be determined from the triaxial compression tests performed with specimens sampled in different directions. Comparisons between the experimental data from triaxial tests and simulated results from tests using the model indicate that the proposed constitutive model can well reproduce the direction dependent behavior of soft sedimentary rock.

封圧環境下におけるＡＥ法による原位置初期地圧測定法の開発

The acoustic emission (AE) method under a confining pressure has been developed in order to measure in-situ stress that is expected to be close to the uniaxial compressive strength or to estimate the stress from weak rock, which are very difficult to deploy the conventional AE method based on standard uniaxial loading. We have developed a special small pressure vessel by which AE event can be detected under a confining pressure. We tested the ability of the vessel to detect the Kaiser effect of AE occurrence under a confining pressure. Then, we evaluated the AE method under a confining pressure by conducting a simulation test of determination of pre-stress using a soft sedimentary rock from Tono mine in Japan. The result showed that the previous stress could be estimated under a confining pressure with reasonable accuracy of 3.3 % mean error.

Evaluation of Time-Dependent Deformation Properties of Sedimentary Soft Rock and their Constitutive Modeling

A triaxial testing system with local axial strain measurements was developed to accurately evaluate the time-dependent deformation properties of sedimentary soft rock. A series of consolidated triaxial creep tests were conducted on undisturbed samples of sedimentary silt-sandstone and mudstone. Drained creep tests, each lasting for three days, were performed at several deviator stresses in the course of drained triaxial compression. Creep axial strains measured locally at the lateral surface of the specimen were always noticeably smaller than externally measured ones, indicating significant time-dependent effects of bedding error occurring at the specimen ends. In these triaxial tests, the axial strain rate was stepwise changed during monotonic shearing to evaluate the effects of strain rate and its change on the stress-strain behaviour. It is shown that instantaneous irreversible strain and its rate uniquely control the current stress state whether the strain rate is constant or continuously changing. This isotach property is modeled in a simple model to be applied to the limited test condition examined. It is shown that this model can predict adequately the measured stress-strain-time behaviour for various time histories of strain (or stress)

放射性廃棄物地層処分 ＡＥ法とＤＲＡによる地下応力測定試験方法とケーススタディ

In this paper, firstly, we describe the detail of the methodology for the stress measurement using the AE and DRA methods. Secondly, we show the two case studies of stress measurement using the AE and DRA methods to evaluate the possibility to measure in situ stresses using rock core samples obtained from underground excavation area.In one of the case studies, rock cores were obtained from horizontal boreholes drilled into the wall of a drift excavated in soft sedimentary rock. This allowed the vertical stress variation with distance from the drift wall to be determined up to a depth of 5 m. The vertical stresses determined using rock cores varied with distance and reached a maximum of 4 ∼ 5 MPa at a distance of 2 ∼ 2.5 m from the drift, when the highest concentration of stress was expected. The vertical stress variation was consistent with calculations by the three dimensional FEM program, ANSYS. Furthermore, the stress measured by the over coring method just nearly agreed with the stress determined by the AE and DRA methods. The AE and DRA methods described in this paper should be applicable to in situ stress measurement with reasonable accuracy even in soft sedimentary rock. A delay time of up to 101 days did not affect the determination of in situ stress in soft sedimentary rock.The other case study has been focused on full stress tensor determination from a single oriented cored rock. Core was obtained from an HI cell measurement hole at Cannington mine in Australia to establish whether the complete stress tensor could be determined from AE and DRA test data. The rockmass at Cannington mine is geologically very complex, and different stress magnitudes and orientation were calculated by the HI cell even within adjacent locations along a hole axis. Two test sites were analyzed for stress measurements using cored rock. The orientation of the estimated stresses appears to match the localized orebody orientation very well. The main principal stress was found to be parallel to the orebody strike. The intermediate principal stress was parallel to the dip, while the minor principal stress was normal to the orebody. Given that the predominant geological structures in the mine are a set of strike slip faults oriented 70 / 330 and that the general slickensides on these are sub-horizontal, the conclusion that the principal stress is parallel to the strike of the orebody is geologically sound.

In-situ experiments on an excavation disturbed zone induced by mechanical excavation in Neogene sedimentary rock at Tono mine, central Japan

The excavation disturbed zone (EDZ) is defined as the rock zone where rock properties and conditions have been changed due to the processes induced by excavation, such as fracturing, stress redistribution and desaturation. Based on our results of the in situ blasting excavation disturbance experiment at the Tono mines, the rock mass around the drift behaved elastically and the excavation damage induced by blasting was considered to be a primary factor in causing a change in rock properties. The excavation damage was considered to depend on the excavation method. So we performed an excavation disturbance experiment with mechanical excavation using a boom header in the Neogene sedimentary soft rock to compare the rock property change and width of the EDZ induced by blasting. Geological observation, rock mass displacement and vibration measurement were performed during the drift excavation. Seismic refraction and tomographic surveys, borehole expansion test and hydraulic test were performed before and after the drift excavation. A low seismic velocity layer of the EDZ with a width of ca. 0.3m and a seismic velocity of 65–70% of the intact rock was detected by a seismic refraction survey along the drift wall. Deformability and hydraulic conductivity were not changed in the rock mass up to 0.3m from the drift wall. The change in rock properties and width of the EDZ was shown to depend on the excavation method. In this geological setting, the mechanical excavation method is more effective in limiting the extent of the EDZ and change in rock mass properties.

堆積軟岩での立坑掘削に伴う岩盤物性変化の現場計測による検討

A shaft with an inner diameter of 6 m has been excavated by blasting in Tertiary soft sedimentary rocks and we have estimated the changes of rock properties, such as deformation modulus, permeability and fracture frequency, of the rock around the shaft. We have performed four kinds of in-situ investigations; borehole jack test, cross-hole seismic velocity measurement, water injection test and borehole television survey. We have carried out these investigations before and after the shaft excavation in the same locations, with the same sets of equipment and through the same procedures for accurate estimation of rock property changes induced by the shaft excavation. The measurement locations have been selected in order to estimate the dependency of the excavation disturbance on the distance from the shaft wall and geological conditions such as lithology and faults. Within 0.5 to 1 m from the shaft wall, detectable property changes have been observed. In the rock zone, some kinds of deformation moduli have decreased. On the other hand, the number and apertures of fractures have increased and permeability has also increased by 2 ~ 3 orders of magnitude in the rock zone. Blasting damage is supposed to be the main factor which has induced these rock property changes considering strength and stress condition of the rock. Effectiveness of each investigation method in the estimation of excavation disturbance is also discussed.

Weathering rate of mudstone and tuff on old unlined tunnel walls

The mechanisms and rate of weathering of soft sedimentary rocks exposed along unlined tunnel walls were investigated using mineralogical, chemical and physical methods. Tunneling occurred several decades ago within the Kakinokidai Formation (middle Pleistocene) and the Kiwada Formation (lower Pleistocene) of the Kazusa Group of Chiba Prefecture, as well as within the Fukuda Formation (Miocene) of Saitama Prefecture in Japan. Since then, the walls of the tunnels have been desiccated by ventilation, sulfuric acid has been generated by pyrite oxidation, calcite and glass have been dissolved by sulfuric acid, and gypsum has crystallized on the surface of the tunnel walls. The oxidized zone was formed on the surface of the walls by the weathering. The formation of this zone and weathering rates (determined as rates of movement of the oxidation fronts) in the vadose zone are explained by the diffusion of oxygen from the surface of the tunnel walls. The relationship between the depth of the oxidation front ( l cm) and the number of years since excavation ( t year) was expressed by l=R oxi t . The R oxi values from the tunnels ranged among 5 for the middle Pleistocene sandy mudstone, 2–4 for the middle Pleistocene mudstone, 0.3 for the lower Pleistocene mudstone and 1–3 for the Miocene tuff. R oxi depends on the diffusion coefficients of oxygen and the chemical composition of rocks. The diffusion coefficients of oxygen ( D e), calculated using the R oxi and chemical compositions of the four kinds of rock above, were 10 −5 cm 2/s, 10 −7–10 −5 cm 2/s, 5×10 −8 cm 2/s and 4×10 −7–3×10 −6 cm 2/s, respectively, depending on the air permeabilities of the rocks that correlate closely with the coefficient of water permeabilities ( K). The relationship for the mudstone was log D e (cm 2/s)=0.91 log K (cm/s)−0.71. The values of D e for the tuff were smaller than for the mudstone due to the smaller air porosities of 0.01–0.04.