Use Of Boreholes Research Articles

Estimating water content in an active landfill with the aid of GPR

Landfill gas (LFG) receives a great deal of attention due to both negative and positive environmental impacts, global warming and a green energy source, respectively. However, predicting the quantity of LFG generated at a given landfill, whether active or closed is difficult due to the heterogeneities present in waste, and the lack of accurate in situ waste parameters like water content. Accordingly, ground penetrating radar (GPR) was evaluated as a tool for estimating in situ water content. Due to the large degree of subsurface heterogeneity and the electrically conductive clay cap covering landfills, both of which affect the transmission of the electromagnetic pulses, there is much scepticism concerning the use of GPR to quantify in situ water content within a municipal landfill.Two landfills were studied. The first landfill was used to develop the measurement protocols, while the second landfill provided a means of confirming these protocols. GPR measurements were initially completed using the surface GPR approach, but the lack of success led to the use of borehole (BH) GPR. Both zero offset profiling (ZOP) and multiple offset gathers (MOG) modes were tried, with the results indicating that BH GPR using the ZOP mode is the most simple and efficient method to measure in situ water content. The best results were obtained at a separation distance of 2m, where higher the water content, smaller the effective separation distance. However, an increase in water content did appear to increase the accuracy of the GPR measurements. For the effective separation distance of 2m at both landfills, the difference between GPR and lab measured water contents were reasonable at 33.9% for the drier landfill and 18.1% for the wetter landfill. Infiltration experiments also showed the potential to measure small increases in water content.

THE VEGETATION RESOURCES OF BOTSWANA'S SAVANNAS: AN OVERVIEW

ABSTRACT The current status of the vegetation resources of Botswana's savannas is evaluated. However, a lack of systematic data providing sufficiently detailed information on vegetation cover has meant a reliance on site specific data making national level aggregation difficult. At the national level, the importance of vegetation resources in the subsistence livelihoods of the largely poor rural population is evidenced by the large percentage of rural households below the poverty datum line (PDL). This is despite Botswana having the second fastest rate of economic growth in the world in 2000, after Mozambique, mainly as a result of a shift from an agricultural to a mineral-based economy. The continued reliance of the rural population on the savannas has resulted in an increase in the woody biomass component of the vegetation cover that appears to have occurred through the processes of bush encroachment in response to reduced grass cover. This change in vegetation cover has resulted from changing land use, which in turn is primarily the result of the very large increase in the number of grazers (predominantly cattle) and the related decrease in the number of browsers (predominantly wildlife, antelopes). The process has been continuing over the last 40 years at least. In addition, complex changes have resulted from the increased use of boreholes which have allowed the colonisation of previously uninhabitable areas. Population growth has also had a significant impact even though the preliminary results of the recent population census showing a reduced growth rate of 2.38% compared to 3.25% in the previous census in 1990 (Botswana Government, 1991 and 2002). Despite the importance of the savannas to the people of Botswana, most of the services provided by savannas to their inhabitants are not valued and hence do not exist in national or international accounting systems designed to assess sustainability. Therefore, many of the critical services provided by the savanna vegetation are largely or totally ignored in policy making. This is primarily important to the local inhabitants who continue to see either policy failures or a complete lack of policy development aimed at successfully improving their welfare. The rural poverty in Botswana is clear evidence of the continuing failure of developmental policy in sub-Saharan Africa to make progress in assisting its rural and often even urban populations, to achieve significant levels of development even when national wealth may be increasing. The lack of rural development may partially be a result of the under-investment in the stocks of natural capital of which savannas are an important component. It is important for Botswana and other countries in the region to understand how to value the services provided by savannas properly and in doing so develop balanced policies that will allow savanna vegetation to be sustainably exploited and developed.

99/03085 Use of bore-holes to determine the range of a drainage zone of methane

99/03085 Use of bore-holes to determine the range of a drainage zone of methane

Efficient use of boreholes for rock mass investigations

Efficient use of boreholes for rock mass investigations

Drinking water sources, mortality and diarrhea morbidity among young children in Northern Ghana

In the Upper East Region of Ghana, considerable resources have been invested in the provision of boreholes. As part of the Ghana Vitamin A Supplementation Trials' Survival Study which was carried out in one of the districts of the Upper East Region between January 1989 and December 1991, data were collected over a period of one calendar year on the drinking water sources used by approximately 13,000 mothers/guardians of over 20,000 children and on the morbidity and mortality experiences of these children. These data were used to describe seasonal and geographical variations in drinking water sources; to look for other predictors of water source use; and to establish whether the drinking water source was associated with the risk of child death or the period prevalence of diarrhoea among young children. Boreholes were used as the main source of drinking water by about 60-70% of respondents. They were used slightly more frequently in the dry season. In the rainy season, the use increased of more traditional sources such as rainwater or holes dug in stream beds. The use of boreholes was greatest in the northern zone of the study area and was more common in those who had had some formal education and were of higher socioeconomic status. Some association was found between reported drinking water source and diarrhoeal morbidity, although this association appeared to be seasonal. No significant association was found between drinking water source and child mortality.

Further development of a high-frequency seismic source for use in boreholes : Baria, R; Jackson, P D; McCann, D M Geophys ProspectV37, N1, Jan 1989, P31–52

Further development of a high-frequency seismic source for use in boreholes : Baria, R; Jackson, P D; McCann, D M Geophys ProspectV37, N1, Jan 1989, P31–52

Interborehole acoustic measurements in site investigation

Summary Interborehole acoustic measurements are made by transmitting a pulse of sound energy from one borehole to another. Analysis of the recorded signals can provide useful information on ground conditions between and beneath the boreholes. This includes the location of boundaries between different rock and soil types, and an assessment of geotechnical properties in certain cases. A sparker source of energy has been developed for use in boreholes, giving a repetitive pulse shape. The received signal may contain direct, refracted and reflected arrivals, which can be timed. These times are converted to apparent velocities and a vertical scan of two boreholes presented as an apparent velocity versus depth curve. Two case histories from the Dinorwic hydro-electric scheme in North Wales and from Whatley Quarry near Frome in Somerset, illustrate the nature of the interpretation process, and the quality and distribution of the additional geological data that can be achieved. Interborehole scanning has certain advantages over conventional surface seismic refraction; for example, in the detection of low velocity layers at depth. It does of course have its limitations, in the theoretical, interpretational and the practical senses. With these limitations minimized, interborehole acoustic measurements can be a very useful addition to site investigation.

Borehole analysis for copper and nickel using gamma-ray resonance scattering

A technique has been developed for the in-situ determination of copper and nickel in boreholes using γ-ray resonance scattering. A radioisotope is chosen so that in the gaseous state its γ rays resonantly scatter via an excited state of the wanted element. This makes the process highly specific to the wanted element. Results are presented for the determination of copper and nickel in 7.5–20 cm diameter simulated boreholes using gaseous sources of 65ZnI2 and 60CoBr2, respectively. A probe design suitable for use in boreholes of diameter ≳ 14 cm is described. The resonance photopeak count rate with this probe in a 15 cm diameter borehole was 5 counts/s per 5 Ci 65Zn for a sample containing 1 wt.% copper. The background under the photopeak was 5 counts/s while the count rate at lower energies due to Compton scattered radiation was about 10 k counts/s. The estimated counting time for the determination of 0.5 wt.% copper to ±0.1 wt.% in boreholes is about 50 s which permits logging speeds of about 0.6 m/min for examination of a 0.5 m strata width. Similar results have been obtained for nickel. Variations in factors such as rock density, borehole diameter and probe location will affect the probe count rates but in most field situations the combined errors from these sources should not exceed ±20% of the elemental concentration. Compared to the various other nuclear methods of analysis the γ-ray resonance technique is shown to have many advantages for the analysis of copper and nickel, particularly copper. The use of a resonance probe in a 15 cm diameter borehole drilled by one of the coreless drilling techniques will offer the following advantages over diamond-core drilling: (1) drilling costs are reduced by at least half, (2) a prompt measure of elemental concentration is obtained; cores generally take at least a week for transport and analysis, (3) the rock sampled by a resonance probe is ≈ 20 times the 2–3 kg/m sampled by diamond drilled cores.

Author's Reply:

The authors welcome Dr Wurzel's contribution concerning radioactive tracers and look forward to reading the paper he is preparing on their use in crystalline rocks in Rhodesia. A guide book on “Nuclear Well Logging in Hydrology”, shortly to be published by the International Atomic Energy Agency in association with the International Hydrological Decade, with which one of us (DAG) is associated, reviews the techniques comprehensively. However, the author's paper was concerned with the recognition of fissure flow using non-radiometric techniques which are of general application and do not suffer from the somewhat restrictive attitude of some territories to the use of radio tracers in water supply wells, even in the small quantities which are necessary; this has been recognised as a problem in the U.S.A. where a brine injector was developed as an alternative (Scott Keys 1968). The technical advantages of a tracer free from density effects are fully recognised both at high and low velocities, especially at the low end, near the diffusion rate. One of us has been associated with the United Kingdom Atomic Energy Authority in the development of a prototype, single-point radio tracer injection probe for use in boreholes (Anon. 1968). Severe calibration problems were encountered which resulted in part from the density effect, although Scott Keys (1967) commented that such effects may not be significant. Certainly other errors may be more significant, including those due to the position of the injector in relation to the centre of the borehole, to variations in borehole diameter and

Use of boreholes to measure the stresses in sedimentary rocks

Use of boreholes to measure the stresses in sedimentary rocks

Earth Pressure Control in Mines by Stress Measurement

Much effort has been made for the earth pressure control in metal mines as well as in limestone mines where the ores are mined by the room and pillar method. To obtain the fundamental data for the earth pressure control in these mines the measurement of the variation in stress in the rock has been made by the photoelastic stressmeter under the authors' guidance. Recently the absolute stress has come to be measured by the stress-relief technique to supply more substantial data.These measurements have been made mainly on the rock surface around underground openings, where the cracks initiated by excavation are frequently found. Although the measurement has served not a little for the earth pressure control, it is desired that the measurement of the rock stress will be made possible at the points at considerable distances apart from the wall surface by making use of boreholes. However no method to determine the stress in the rock from the measurements made in the boreholes has yet been established. The authors have therefore investigated this problem. The first part of this paper describes the results obtained.Based on the theory of elasticity, they have deduced formulae to be used in determining the amount of stress in the rock (1) from the changes in diameter, (2) from the strains on the bottoms of boreholes and (3) from the strains on the wall of a borehole. The application of these formulae in terms of the measured values gives the observation equations, and their solution yields the estimation required of the stress in the rock in question. The minimum number of boreholes that afford the necessary data for determining the amount of stress in the rock has been discussed by examining the rank of the matrix made up of the coefficients of the observation equations.Subsequently two practical examples of stress measurements are described. In the Nakatatsu mine, the absolute stresses on the walls of a number of drifts around the Stope 4-5 of the Nakayama pit were measured, from which it was discussed whether or not the rock around the shaft situated near the stope would fail by extracting the ore completely. The original stress state, which seems to depend more on the orogeny rather than the topography, was estimated. Judging from the stress concentration that might appear after a complete mining, it was found that complete extraction of ore would be allowed.In the Hikawa mine, the main haulage drift had been driven through the deep strata in the Tobo district before any other excavation was made. For the purpose of obtaining the data for the design of mining, the stresses on the wall of the drift were measured along the drift. Then the original stress states were determined mathematically, which were taken into consideration in the design of the mining. On the other hand, this measurement presented the data about the stress state in the rock in a mountain district as well as about the influence of faults on the stress state.

MAGNETIC WELL LOGGING

The need for control data in interpretation of surface magnetometer surveys has led to the development of borehole instruments for measuring magnetic susceptibility and total magnetic field in situ. The susceptibility instrument is an alternating current induction device, and by separation of the quadrature components simultaneous recording of the magnetic susceptibility and the electrical conductivity is possible. The susceptibility log has many features that depart from ordinary electric logs. The instrument has a sensitivity of the order of [Formula: see text] cgs units and sufficient contrast has been found in the sediments to yield a log of considerable lithologic character. This magnetic character suggests the use of the susceptibility tool in the field of special well logging, particularly for geologic correlation, and for tracer studies. The general assumption that the magnetic susceptibility of the sediments is sufficiently low compared to basic igneous rocks so that sedimentary rocks have little effect on surface magnetometer measurements has been verified. Since the magnetic susceptibility and electrical conductivity logs are made with an induction instrument, an electrolyte is not required in the hole and the logs are independent of the drilling fluid, except that the conductivity log is influenced by highly conductive muds. The total field log is made with a three element self‐orientating saturable core magnetometer that has been developed for borehole use. This log has not been used extensively. In addition to reflecting changes in polarization of the formations, it is influenced by formation susceptibility. Logs have been made of the total field going into and through igneous plugs. The paper presents examples of these logs along with a brief description of the instruments developed to produce them.