Horizontal Borehole Research Articles

Interpretation of pressure recovery curves recorded simultaneously in different sections of a horizontal well borehole

A new approach to carrying out and interpreting hydrodynamic investigations of horizontal wells is proposed. The problem of determining the flow parameters of an inhomogeneous oil reservoir is considered. As the initial information, the pressure recovery curves recorded simultaneously in different sections of the horizontal well borehole are used.

雪山横穴空洞式熱交換システムの開発に関する研究（イチゴ育苗ハウスへの雪冷房システムの利用）

In the cold climate and deep snow regions in the winter season of Japan, it has been advanced to utilize the snow as the cold energy source for air conditioning in summer. In this study, a system to extract the chilled air directly from the snow mound of several thousand ton through a horizontal borehole in it is proposed. Some troubles caused by mud in the snow melting water can be avoided by means of transferring heat from the melting water to the supply air. The thermal design for the heat exchange of this system is carried out by theoretical means and verified by the practical experiment. According to results of the experiment, it is proved sufficiently that the theoretical thermal design method predicts appropriate values of the system. The snow cooling system has been applied to a strawberry seedling greenhouse with 270m2 as a practical experiment. And predicted values and experimental results are 9.90 kW as the cooling power gained from the snow mound using two blowers needed 0.8 kW totally.

Interpretation of pressure recovery curves recorded simultaneously in different sections of a horizontal well borehole

Interpretation of pressure recovery curves recorded simultaneously in different sections of a horizontal well borehole

Numerical analysis of the influence of in-seam horizontal methane drainage boreholes on longwall face emission rates

Abstract High methane emissions originating from the active face areas and from the fractured formations overlying and underlying the mined coalbed can adversely affect both safety and productivity in underground coal mines. Since ventilation alone may not be sufficient to control the methane levels in the longwall mining environment, gob gas ventholes have become a standard supplementary methane control option in many mines. As mines progress into deeper and gassier coalbeds, or as longwall panel size increases, ventilation and gob gas ventholes together may not be sufficient to maintain methane levels within statutory limits. To decrease the risk associated with methane emissions under these circumstances, in-seam horizontal methane drainage is often used to reduce the gas content of the coalbed prior to mining. Horizontal methane drainage borehole completion designs, drilling strategies, and degasification lead times may need to be adjusted for site-specific conditions due to mine design, geology, and the gas content of the coalbed. This study investigates different horizontal methane drainage borehole patterns, borehole lengths, and degasification times prior to and during panel extraction to evaluate their effectiveness in reducing methane emissions using a “dynamic” 3D reservoir modeling of a 381-m wide longwall panel operating in the Pittsburgh coalbed. Results of this study showed that dual and tri-lateral boreholes are more effective in decreasing emissions and in shielding the entries compared to fewer shorter, cross-panel, horizontal boreholes parallel to the longwall face. Modeling results showed that after 12 months of pre-mining methane drainage, the average longwall face emission rates can be reduced by as much as 10.3 m 3 /min and 6.8 m 3 /min using tri- and dual-lateral boreholes, respectively. It was also shown that if pre-mining methane drainage time is short, it is important to continue methane drainage during the panel extraction to maximize reductions in longwall face emissions since additional face emission reductions achieved during this period can be comparable to pre-mining degasification.

Experimental studies of the interactions between anaerobically corroding iron and bentonite

In the horizontal emplacement concept (KBS-3H) for the disposal of radioactive waste, which is being developed in Sweden and Finland, copper canisters will be surrounded by bentonite buffer and placed in perforated steel containers in long horizontal boreholes in the crystalline bedrock, at a depth of ≈500 m. Under the chemical conditions in a deep repository, it is possible that the release of iron from the steel containers could influence the physico-chemical properties of the bentonite, for example, by exchange of the interlayer ions. In order to gain further insights into this process, an experimental study was undertaken, to investigate the mode of iron uptake into bentonite and the extent of changes induced in the basic physico-chemical properties of bentonite. The samples were taken from long-term anaerobic corrosion tests of carbon steel or cast iron in compacted bentonite (Na/Ca-bentonite: Volclay MX-80, ∼4% Fe 2O 3) in contact with a simple artificial groundwater at 30 °C or 50 °C. A range of analytical techniques was applied to samples of corrosion product on carbon steel and cast iron and to the bentonite surrounding the corroding specimens. Corrosion products and bentonite samples were analysed using scanning electron microscopy (SEM), electron microprobe analysis (EPMA), Raman spectroscopy, X-ray diffraction (XRD) and Mössbauer transmission spectroscopy. In addition, the bentonite samples were analysed using Fourier transform infra-red spectroscopy (FTIR), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) and selected area electron diffraction (SAED), exchangeable cation analysis and cation exchange capacity (CEC) measurements. Hydraulic conductivity and swelling pressure were also measured. From visual observation, the corrosion product formed on the carbon steel in bentonite was less voluminous than that formed on steel in artificial porewaters with no bentonite, although previous work showed that the corrosion rates were slightly higher in the presence of bentonite. The Raman spectroscopy analysis showed that corrosion products on the surface of carbon steel and cast iron consisted of an inhomogeneous mixture of magnetite, hematite and goethite. The predominant species was magnetite. In the bentonite, the concentration of iron decreased with increasing distance away from the iron–bentonite interface, with local iron concentrations as high as 20 wt% in some experiments. The total iron content of the bentonite in contact with corroding carbon steel wires increased by several percentage points during the experiments and the cation exchange capacity of the bentonite was reduced. After contact with corroding steel wires the hydraulic conductivity of MX-80 increased substantially. The results of the analyses were consistent with ion exchange of Fe 2+ ions with Na + ions in the montmorillonite interlayer positions but the exact chemical location of all the additional Fe 2+ ions is currently uncertain. There was no evidence for the transformation of montmorillonite to an iron-rich clay mineral phase.

Measurement of thermally-induced pore-water pressure increase and gas migration in the Opalinus Clay at Mont Terri

In order to gain a better understanding of coupled thermo-hydro-mechanical (THM) processes in indurated clays as host rock for the disposal of high-level radioactive waste, a heating experiment named HE-D is being conducted in the Opalinus Clay at the Mont Terri Rock Laboratory in Switzerland. An electric heater equipment of 5.4 m length was installed in a horizontal borehole of 30 cm diameter and 14 m length. The surrounding rock has been heated from the temperature of 15–43 °C at the heater/rock interface over the first 3 months and to 100 °C over further 8 months, respectively. The second heating phase is going for a total period of 12 months until June 2005. Following that, a cooling phase will be carried out by shutting-down the power supply for 6 months. Finally, the dismantling is scheduled for the beginning of January 2006. During the experiment, the temperature, pore-water pressure, gas migration, and deformation in the clay rock have been monitored by means of more than 80 instruments installed in 24 boreholes. Significant thermal effects have been observed. In the heated region at distances of 0.8–1.4 m to the heater, the pore-water pressure increased from 0.7–1.2 MPa to 3–4 MPa. The responses of the host rock in terms of pore-water pressure and deformation were simulated by several modelling teams with use of different codes. Preliminary results of the measurements and the calculations are presented.

Effects of an off-centered tool on dipole and quadrupole logging

An acoustic logging tool in inclined or horizontal boreholes may be placed apart from the center and produce additional complicated wavefields. We investigate the effects of an off-centered tool on monopole, dipole, and quadrupole logs due to off-centering of the tool. In recent logging tools, monopole, dipole, and quadrupole logs can be obtained by adding or subtracting responses at four monopole (pressure) receiver arrays at right angles. We examine the responses of the four monopole receiver array system for three directions of eccentricity: inline direction of the dipole source (Off [Formula: see text] case), crossline direction (Off [Formula: see text] case), and [Formula: see text] to the dipole source (Off [Formula: see text] case). To simulate responses at each receiver array, we use the discrete wavenumber method. In a dipole tool positioned on the borehole axis, the inline receiver arrays have only the flexural wave while the cross receiver arrays have zero response. However, an off-centered dipole source produces nondipole modes as well as the dipole mode. For all cases with a dipole source, the dipole mode was enhanced by subtracting responses at one of the inline receiver arrays from those of the other receiver array, and we could extract the formation shear velocity. Similar to the dipole source, an off-centered quadrupole source introduces additional nonquadrupole modes. The quadrupole mode was enhanced by subtracting the sum of responses at receiver arrays below negative poles of a quadrupole source from the sum of responses at receiver arrays below positive poles for all cases. In addition, the formation shear velocity was obtained from the time semblance calculation.

Hydromechanical modelling of pulse tests that measure fluid pressure and fracture normal displacement at the Coaraze Laboratory site, France

In situ fracture mechanical deformation and fluid flow interactions are investigated through a series of hydraulic pulse injection tests, using specialized borehole equipment that can simultaneously measure fluid pressure and fracture displacements. The tests were conducted in two horizontal boreholes spaced 1 m apart vertically and intersecting a near-vertical highly permeable fault located within a shallow fractured carbonate rock. The entire test cycle, both the initial pressure increase and subsequent pressure fall-off, was carefully monitored and used for the evaluation of the in situ hydromechanical behaviour. The field data were modelled using both distinct-element and finite-element modelling techniques, in two and three dimensions. Field test data were evaluated by plotting fracture normal displacement as a function of fluid pressure, measured at the same borehole. The curves for the normal displacement of the fracture as a function of fluid pressure showed hysteresis loops, in which the paths for loading (pressure increase) and unloading (pressure decrease) are different. By matching this behaviour, the fracture normal stiffness and an equivalent stiffness (Young's modulus) of the surrounding rock mass were back-calculated. Evaluation of the field tests by coupled numerical hydromechanical modelling showed that the pressure-increase path of the normal displacement-versus-pressure curve is highly dependent on the hydromechanical parameters of the tested fracture and the stiffness of the matrix near the injection point, whereas the pressure-decrease path is influenced by mechanical processes within a larger portion of the surrounding fractured rock.

LWD for Imaging, Wellbore Placement, and Formation Evaluation

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 17646, "LWD for Imaging, Wellbore Placement, and Formation Evaluation," by J.C. Rasmus, SPE, C. Esmersoy, SPE, J. Seydoux, and A. Hawthorn, Schlumberger, prepared for the 2005 Offshore Technology Conference, Houston, 2-5 May. Logging-while-drilling (LWD) measurements are widely available for a variety of applications. Many of the first generation LWD measurements are similar to those obtained traditionally with wireline methods. However, there are measurements available now that are either complementary or are entirely unique compared with traditional wireline measurements. Introduction LWD borehole-seismic measurements can enable placing the bit on the seismic map or producing a seismic-impedance map ahead of the bit while drilling the well. These measurements provide accurate depth determination of drilling targets and identification of pore-pressure transgressions. LWD ultradeep-resistivity (UDR) measurement technology meets the requirements for geosteering at the reservoir level by use of subseismic resolution. Its major applications include delineation of the oil/water contact (OWC) and distance to reservoir caprock and bottom shale. Well Placement Since the emergence of LWD in the 1980s, the industry wanted a reliable while-drilling borehole-seismic measurement. However, several technical roadblocks prohibited its realization until recently. These difficulties included the nature of and required accuracy of the measurement, timing issues, sensors, automation, and the lack of an electrical connection between the downhole tools and the surface in a while-drilling configuration. Technological solutions to these road-blocks have since been found. Seismic-while-drilling data are delivered in real time to make critical decisions while a well is being drilled. They also replace intermediate wireline check-shot surveys, eliminating the need to stop the drilling process and pull drilling equipment out of the hole for the duration of a survey. Real-time accurate positioning of a horizontal borehole within a reservoir can be performed with standard LWD tools. However, a limitation of these measurements is the relatively small volume of investigation with traditional LWD sensors, which typically probe no deeper than 1 m into the formation. Therefore, unpredictable geological events are, in many cases, detected too late to allow proactive geosteering decisions. A prototype LWD resistivity tool was developed with a much larger radial response that allows detection of lithology features and fluid contacts that are tens of meters away from the borehole. The tool has a modular design with separate transmitter and receiver subassemblies that can be placed a large distance away, anywhere in the bottomhole assembly (BHA). The main output is estimated distance to boundaries indicated by resistivity contrasts. These distances are computed through inversion of a formation model in real time. On the basis of tool measurements, determining the optimum formation model and its related parameters allows proactive geosteering decisions and pro-vides significant geological insight into the reservoir structure.

On drilling directions for optimizing horizontal well stability using a dual-porosity poroelastic approach

Horizontal wells are often drilled in pay zones, where formations frequently contain dominant natural fractures. For characterizing such reservoirs the dual-porosity poroelastic model appears to be relevant to assess stresses as well as flow fields. Traditionally, various combinations of elastic, elastoplastic and poroelastic models are employed to predict wellbore stability and calculate mud weight windows. However, the majority of such models are either limited to the case of vertical wells, or unsuitable for applications to naturally fractured porous formations. A novel wellbore model, based on the dual-porosity poroelastic theory, has been developed, which can effectively simulate the coupled processes of fluid flow and rock deformation in fractured porous formations. The numerical implementation of the theoretical model leads to a pseudo-three-dimensional generalized plane strain finite element model specialized in analyzing borehole stability problems. The numerical model not only performs the effective stress and fluid pressure analyses, but also conducts the mud weight calculation and optimizes the drilling direction. The model has been further applied to analyze the stability of horizontal wells with open-hole completion, drilled parallel or perpendicular to the maximum horizontal stress direction. Results show that horizontal borehole stability depends strongly on the in-situ stress state and borehole orientation: the horizontal wells drilled in the maximum stress direction in a strike slip faulting stress regime are usually more stable during both drilling and production.

Geophysical characterisation of a rockslide in an alpine region

A combination of geophysical methods has been used for the characterisation of a rockslide area, located in the Graie Alps, NW of Italy, where the construction of a roadway tunnel has been planned. Electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and spectral analysis of surface waves (SWM) have been adopted to determine the overburden thickness and the geometry of the sliding surfaces. The geomechanical characterisation of rock mass was performed by means of horizontal seismic profiles (HSP) and sonic log in a horizontal borehole. The results have been calibrated by comparing the geophysical responses with the geological evidence derived from boreholes and with the movements recorded using inclinometric probe. Moreover, borehole geophysics results were validated by the results of laboratory measurements performed on core samples. The integration of geophysical and geotechnical results allowed the definition of a subsoil model for the investigated area and provided the necessary data for the design of the roadway tunnel. The study shows that surface and borehole geophysical techniques could be an efficient and cost-effective tool in rockslide investigations.

Strainmeters at Moxa observatory, Germany

Since 1997, two quartz tube strainmeters at the Geodynamic Observatory Moxa, located 30 km south of Jena, are used to observe long-period horizontal deformation signals. Both strainmeters are 26 m long with orientations NS and EW and are installed in a gallery. To this system a third component was added in 1999, which connects the ends of the quartz tubes diagonally. This component is realised as a laser strainmeter, running through a 38 m long horizontal borehole. The first data analyses show high signal-to-noise ratios for the tidal frequencies and also the free oscillations caused by the Sumatra earthquake in December 2004 are clearly detectable. It can be shown that the quartz strainmeter extending in EW direction generally contains significant more noise induced by barometric pressure than the NS-component. The laser strainmeter record shows strong influences of changing barometric pressure, due to the fact that the beam does not run in a vacuum. This influence is reduced in the higher frequencies by sealing the ends of the horizontal borehole with high quality glass. In addition, the observations are clearly temperature dependent and the influence of rainfall could be verified by two irrigation experiments.

Observations of preferential flow during a liquid release experiment in fractured welded tuffs

To better understand preferential flow in fractured rock, we carried out an in situ field experiment in the Exploratory Studies Facility at Yucca Mountain, Nevada. This experiment involved the release of ~22 m3 of ponded water (at a pressure head of ~0.04 m) over a period of 7 months, directly onto a 12 m2 infiltration plot located on a fractured welded tuff surface. As water was released, changes in moisture content were monitored along horizontal boreholes located in the formation ~19‐22 m below. Distinct flow zones, varying in flow velocity, wetted cross‐sectional area, and extent of lateral movement, intercepted the monitoring boreholes. There was also evidence of water being diverted above the ceiling of a cavity in the immediate vicinity of the monitoring boreholes. Observations from this field experiment suggest that isolated conduits, each encompassing a large number of fractures, develop within the fractured rock formation to form preferential flow paths that persist if there is a continuous supply of water. In addition, in fractured welded tuffs the propensity for fracture‐matrix interactions is significantly greater than that suggested by existing conceptual models, in which flow occurs along a section of fracture surfaces. An overriding conclusion is that field investigations at spatial scales of tens of meters provide data critical to the fundamental understanding of flow in fractured rock.

Vadose Zone Characterization and Monitoring Beneath Waste Disposal Pits Using Horizontal Boreholes

Vadose zone characterization and monitoring immediately below landfills using horizontal boreholes is an emerging technology. However, this topic has received little attention in the peer‐reviewed literature. The value of this approach is that activities are conducted below the waste, providing clear and rapid verification of containment. Here we report on two studies that examined the utility of horizontal boreholes for environmental characterization and monitoring under radioactive waste disposal pits. Both studies used core sample analyses to determine the presence of various radionuclides, organic compounds, or metals. At one borehole site, water content and pore‐water chloride concentrations were also used to interpret vadose zone behavior. At another site, we examined the feasibility of using flexible membrane liners in uncased boreholes for periodic monitoring. For this demonstration, these retrievable liners were air‐injected into boreholes on multiple occasions carrying different instrument packages for environmental surveillance. These included a neutron logging device to measure volumetric water at regular intervals, high‐absorbency collectors that wicked available water from borehole walls, or vent tubes that were used to measure air permeability and collect air samples. The flexible and retrievable liner system was an effective way to monitor water content and measure in situ air permeability. The high‐absorbency collectors were efficient at extracting liquid water for contaminant analyses even at volumetric water contents below 10%, and revealed tritium migration below one disposal pit. Both demonstration studies proved that effective characterization and periodic monitoring in horizontal boreholes is both feasible and adaptable to many waste disposal problems and locations.

Analysis of the hydration of a bentonite seal in a deep radioactive waste repository

A deep geological repository for nuclear waste requires the backfilling and sealing of shafts and galleries to block any preferential path for radioactive contaminants. The paper presents the coupled hydromechanical analyses of an in situ test carried out in the HADES underground laboratory in Mol, Belgium. The test examines the effectiveness of an expansive clay seal in a horizontal borehole specifically drilled for this purpose. The analysis covers the phase of seal hydration up to saturation and subsequent pore pressure equilibration. Hydraulic and mechanical constitutive laws suited to expansive clay materials have been chosen for the analyses with all the parameters determined independently of the in situ test. A quite good agreement has been found between test observations and computed results suggesting that the numerical formulation employed is able to reproduce the main features of a real sealing system.

A case study of the pore water pressure fluctuation on the slip surface using horizontal borehole works on drainage well

The infiltration of rainfall reduces shear strength on the slip surface by increasing pore water pressure, resulting in increased landslide movement. Although pore water pressure fluctuation is an important factor influencing landslide activity, it is difficult to observe its mechanism at various depths of the slip surface because of the complex hydrogeological structure. This study aims to examine the pore water pressure fluctuation in shallow and deep strata of the slip surface. The rainfall, pressure head and drainage rate were observed at the Tairasawa landslide before and after the drainage well work. The pressure heads were measured in the vertical observation borehole with a screened section at the depth of slip surface. The horizontal drain borings of drainage well were drilled for confining groundwater in a screened section at the same depth of slip surface. After drilling a horizontal drain boring, the pore water pressure on the slip surface was reduced and the decreasing volume in the deep stratum was larger than that in the shallow stratum. The effects of horizontal drain boring could be easily evaluated by comparing the decrease in pore water pressure before and after the works. Furthermore, the decrease in pore water pressure on the slip surface shows two significant characteristics. First, the variation in pore water pressure corresponds to drilling depth and seepage water in a horizontal drain boring. Second, the decreasing effects of pore water pressure can be clearly seen when the drilling direction of a horizontal drain boring is near the vertical observation borehole.

A method for evaluating horizontal well pumping tests.

Predicting the future performance of horizontal wells under varying pumping conditions requires estimates of basic aquifer parameters, notably transmissivity and storativity. For vertical wells, there are well-established methods for estimating these parameters, typically based on either the recovery from induced head changes in a well or from the head response in observation wells to pumping in a test well. Comparable aquifer parameter estimation methods for horizontal wells have not been presented in the ground water literature. Formation parameter estimation methods based on measurements of pressure in horizontal wells have been presented in the petroleum industry literature, but these methods have limited applicability for ground water evaluation and are based on pressure measurements in only the horizontal well borehole, rather than in observation wells. This paper presents a simple and versatile method by which pumping test procedures developed for vertical wells can be applied to horizontal well pumping tests. The method presented here uses the principle of superposition to represent the horizontal well as a series of partially penetrating vertical wells. This concept is used to estimate a distance from an observation well at which a vertical well that has the same total pumping rate as the horizontal well will produce the same drawdown as the horizontal well. This equivalent distance may then be associated with an observation well for use in pumping test algorithms and type curves developed for vertical wells. The method is shown to produce good results for confined aquifers and unconfined aquifers in the absence of delayed yield response. For unconfined aquifers, the presence of delayed yield response increases the method error.

Tunnel construction right below a controlled industrial waste landfill

The 1340-m Kozuka Tunnel, located in a section between Shin-Tamana Station (provisional name) and Kumamoto Station along the Kagoshima route of the Kyushu Shinkansen line, is being excavated using heading and bench and New Austrian Tunneling Method (NATM) methods. A controlled industrial waste landfill operated by the Kumamoto municipal government is located right above the midpoint of the Tunnel. The clearance below the landfill with an embankment height of about 40 m is about 4 m. A weak boundary layer between the Aso pyroclastic deposit and Ko-kinpozan rock needs to be excavated. Thus, construction conditions are extremely severe over a length of about 60 m. Adverse effects of tunnel excavation on the bottom (waterproof membrane) of the landfill and leakage of turbid water from industrial waste would have immeasurable impact on surrounding environments. In the section under such unique conditions, a pipe roof (composed of 13 steel pipes of a 800-mm diameter and a 66-m length) was applied, and side drifts and NATM were adopted. In order to select an optimum pipe roofing method before tunneling, the geology in the section under the landfill and the location of the waterproof membrane under the landfill were explored using horizontal boreholes and ground-penetrating radars. As a result, the Unclemole-Super method was adopted because it could satisfy such requirements as excavating the strata containing hard boulders with diameters of 1.0-2.0 m, preventing collapse of excavated face for installing the pipe roof and limiting the alignment error under 1/500 of the pipe length. The pipe roof was completed successfully with the maximum alignment error being 1/2200 of the roofing pipe length. The Tunnel is now being excavated using side drifts and NATM. Construction is strictly monitored. Standard settlements have been defined and settlements are being measured by inclinometers installed in the pipes. This paper describes pipe roof construction and construction control plans that are being implemented while the Tunnel is being excavated using side drifts and NATM. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Harnessing the catastrophic inrush of water into new Yungchuen Tunnel in Taiwan

The New Yungchuen Tunnel, located in northeast Taiwan, is a single-track railway tunnel with a length of 4433 m. The project area is tectonically active and the bedrocks are composed of slate, metasandstone, schist, marble and amphibolites, etc. In the planning stage, its construction was known to be challenging, according to comprehensive geological investigations and experience of constructing the original Yungchuen Tunnel which suffered from severe collapse, water inrush and squeezing problems in the 1970s. In the early 1990s, the route of the New Yungchuen Tunnel was set to the west (toward the hillside) of the original Yungchuen Tunnel to avoid the potential influence of ground water and unfavorable geological conditions. The top heading method was designed for excavating the tunnel. The support system included shotcrete with mesh, steel ribs and rockbolts. Auxiliary measures such as the use of a drainage tunnel, a pipe roof, cement and chemical grouting were prepared, and tunnel seismic prospecting and pilot drilling were requested during tunneling. On October 24, 1998, when the tunnel has been excavated to 1812 m from the south portal, a mass of water gushed out from the working face at 25 ton/min initially, and later at 80 ton/min. More than 15,000 m3 of collapsed debris came out in the water, burying more than 540 m of the supported tunnel. After extensive investigations the inrush of water was associated with the marble layer, which was covered with opening joints and consisted of fractured rocks. The very high water pressure, 5.0 MPa measured in a place with overburden around 260 m only, originated from the west mountain range and attacked the tunnel through some highly permeable passageways in marble layer. The gouge filled fractured zone or faulty zone in the boundary between the marble and schist, was destroyed and caused the tunnel to collapse. The thickness of marble layer near the original proposed line is about 70 m and diminishes to the east. Following more than sixty discussions on budget, possible environmental impact, tunneling-related and operational risks, and the temporal constraints on the Eastern Railway Improvement Project, the philosophy of ''draining the far and grouting the near'' was proposed. The tunnel route in hazard section was modified to the east with maximum distance of 70 m. Widespread horizontal boreholes with total lengths of 2970 m are installed for drainage. Two bypasses with total length of 1917 m were excavated as testing pilots and drainage galleries. Umbrella grouting with bitumen, cement and chemical materials were used for sealing up the groundwater. Reinforced concrete lining with maximum thickness of 1.0 m was installed to sustain the potential water pressure. Observing facilities for water pressure, discharge, tunnel convergence and surrounding rock displacement, and the support stresses were set up. The monitoring program was implemented not only during construction, but for a period after the tunnel was operational. The tunnel was broken through on September 5, 2002 after extensive investigations and reinforcements. Completely overcoming the effects of the catastrophic water inrush section took approximately four years. The philosophy of ''draining the far and grouting the near'' worked very well. Although the project cost increased from 22.4 to 44.0 million USD, the tunnel was opened on time in May 2003. The improved eastern railway, with a total length of 337 km is contributing the high efficiency of the flow of traffic. (A) Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

The aging of gypsum in underground mines

The aging properties of gypsum extracted from two underground mines in France (Livry–Gargan and Grozon) have been highlighted by means of observation performed using scanning electron microscopy on samples taken along horizontal boreholes drilled through to the middle of several pillars. The aging process is exhibited by the presence of traces of dissolution (edges of the dissolved crystals, corroded crystalline surfaces, important intra- and intercrystalline space). These dissolution figures decrease in number and in intensity from the wall heading towards the middle of the pillar. The “older” pillars display a greater number of dissolution traces than the “more recent” pillars. Then, the role of the aging has been assessed by determining various physical and mechanical parameters on cylindrical samples of 38 mm in diameter and 76 mm in height, machined from the set of drilled boreholes. The following parameters have been quantified: density, grains density, total porosity, porosity accessible to water, intrinsic permeability to nitrogen, velocity of ultrasonic compression and shear waves, dynamic Young's modulus, dynamic Poisson's ratio, uniaxial compressive strength and static Young's modulus. Significant variations in parameter values between the wall and the middle of the pillar were recorded and recognized as being strongly correlated with the intensity of dissolution traces, and hence with gypsum aging.