This article discusses the various steps that the authors feel are necessary to the successful progression of an engineered
project sited in karst terrain. The procedures require a multidisciplined approach with liaison and cooperation among the
various parties to the project.
Initially, the prospective owner must have sufficient understanding of the potential engineering problems to incorporate the
engineering geologist into the early stages of any planned acquisition. The first step in an investigation should include
a review of the available geologic information, aerial photo interpretation, consultation with the State Geological Survey,
and a geologic reconnaissance of the prospective site and surrounding area.
A go-no-go decision as to purchase can often been made at an early time. Although, in some instances, more study is needed
for a particularly intriguing property.
The second stage should consider the various planning alternatives that are feasible based upon the limited available information.
At this stage planning/purchase decisions can be made as to purchasing options, value of the property, design constraints,
and the possible economic penalties that could be associated with the potential site construction. Various planning and construction
alternatives should be considered in this phase of the work.
The third stage should include a site investigation program of moderate size, consisting of test pits and/or exploratory borings.
The borings should be drilled using water as the drilling fluid, with an experienced crew and qualified technical inspection.
The authors find the use of geophysical techniques can be extremely misleading unless used in conjunction with exploratory
drilling. Successful evaluations using geophysical procedures occur only under ideal conditions.
The geotechnical viability of the plan and preliminary design should be investigated in the fourth phase. Additionally, the
physical parameters required for the design of structures founded atop cavities can be obtained at this time. Several support
schemes which incorporate cavity roof thickness, rock strength, and cavity space are discussed.
Possible construction procedures include excavation and dental concrete, grouting, piers or piles to sound rock, or moving
to another area. The relative economies of these procedures are discussed in relation to the size and depth of the soil or
rock cavity, possible future cavity formation, magnitude of loading and acceptable safety factors. 相似文献
Spatial relations between land use and groundwater quality in the watershed adjacent to Assateague Island National Seashore,
Maryland and Virginia, USA were analyzed by the use of two spatial models. One model used a logit analysis and the other was
based on geostatistics. The models were developed and compared on the basis of existing concentrations of nitrate as nitrogen
in samples from 529 domestic wells. The models were applied to produce spatial probability maps that show areas in the watershed
where concentrations of nitrate in groundwater are likely to exceed a predetermined management threshold value. Maps of the
watershed generated by logistic regression and probability kriging analysis showing where the probability of nitrate concentrations
would exceed 3 mg/L (>0.50) compared favorably. Logistic regression was less dependent on the spatial distribution of sampled
wells, and identified an additional high probability area within the watershed that was missed by probability kriging. The
spatial probability maps could be used to determine the natural or anthropogenic factors that best explain the occurrence
and distribution of elevated concentrations of nitrate (or other constituents) in shallow groundwater. This information can
be used by local land-use planners, ecologists, and managers to protect water supplies and identify land-use planning solutions
and monitoring programs in vulnerable areas. 相似文献
The process of pressure solution is defined as the dissolution of materials under high stress at grain-to-grain contacts and precipitation at interfaces under low stress. The kinetics of this process are still poorly understood mainly because of the large timescales involved. In this research, the Surface Forces Apparatus (SFA) technique was coupled with an optical interference technique for in situ visualization of the nanoscale deformations and thickness changes. The SFA was used to measure the forces (or pressures) and distances between two solid surfaces pressed together with a thin film between them. Using the SFA, combined with geological observations, we are studying the short-range colloidal forces between surfaces of mica and silica at the nanoscale such as van der Waals, electrostatic, and hydration forces.
This study involves two cases, the symmetric case of mica in contact with mica and the asymmetric case of a quartz surface in contact with mica. Our results reveal highly subtle effects depending on the nature and concentration of the counterions present in the solution either of Na+, Ca2+, or mixtures of these ions, as well as on the pH. For the symmetric case, the equilibrium interactions of force F or pressure P versus fluid film thickness T have been measured between the mica surfaces across aqueous films in the thickness range from T = 25 Å down to contact separations around T = 0 Å, and depend on the solution conditions and applied lithostatic pressure. Measurements have also been made of the rates of diffusion of ions through such ultra-thin films and on the precipitation and growth of ionic crystallite layers on the surfaces. Our results show that the diffusion coefficient of hydrated sodium is two orders of magnitude lower than the diffusion of water into mica–mica cleavage and a factor of 40 lower than the coefficient of sodium ions in bulk water.
For the asymmetric case, the dissolution of the quartz surface was observed to be dependent on the interfacial fluid composition and pH, the externally applied ‘lithostatic’ pressure, and the type of crystalline structure exposed to the mica surface. Our experiments also show that there is an initial stage after fresh solution is added in which the spacing between the surfaces increases, however, the thickness started decreasing steadily after approximately 4 h of exposure independently of the crystallinity of the quartz surface. For a particular set of conditions, the process eventually slows down and reaches equilibrium after some time, but a further increase in pressure restarts the dissolution process. This is also true for the addition of fresh interfacial solution during the experiment after a period of thickness fluctuation. These results are consistent with the observation that pressure solution of quartz is greatly enhanced with the presence of mica. 相似文献
Summary An evaluation of the impacts of weather on pollution, specifically, ozone and total suspended particulates concentration
for Summer, is examined in four cities in the U.S.: Birmingham, Cleveland, Philadelphia, and Seattle. These cities were selected
because of their different climate regimes and their generally good pollutant and meteorological datasets. This paper uses
a synoptic climatological approach, which combines a number of atmospheric factors, to better identify the relationships between
atmospheric pollution and climatological conditions. Synoptic events represent holistic units of atmospheric conditions which
commonly occur at a given locale, and possess specific weather and pollution characteristics. A number of weather variables,
including temperature, are used in the development of a synoptic index, which can be used to identify synoptic events associated
with specific pollution episodes. Results from the analysis illustrate that there is a substantial difference in pollution
loads under different synoptic patterns, and that the cities do have substantially different relationships.
Information from this study could be used to assist in the analysis of the differential impacts of weather and pollution upon
human morbidity. Specific information as to the linkages between the synoptic weather patterns, pollution concentrations,
and human health could be used in the development of weather/health watch-warning systems to alert the public that a synoptic
episode is imminent.
Received September 18, 1998 相似文献
Exposure from groundwater contamination to aquatic receptors residing in receiving surface water is dependent upon the rate of contaminated groundwater discharge. Characterization of groundwater fluxes is challenging, especially in coastal environments where tidal fluctuations result in transient groundwater flows towards these receptors. This can also be further complicated by the high spatial heterogeneity of subsurface deposits enhanced by anthropogenic influences such as the mixing of natural sediments and backfill materials, the presence of subsurface built structures such as sheet pile walls or even occurrence of other sources of contaminant discharge. In this study, the finite volume point dilution method (FVPDM) was successfully used to characterize highly transient groundwater flows and contaminant mass fluxes within a coastal groundwater flow system influenced by marked tides. FVPDM tests were undertaken continuously for more than 48 h at six groundwater monitoring wells, in order to evaluate groundwater flow dynamics during several tide cycles. Contaminant concentrations were measured simultaneously which allowed calculating contaminant mass fluxes. The study highlighted the importance of the aquifer heterogeneity, with groundwater fluxes ranging from 10−7 to 10−3 m/s. Groundwater flux monitoring enabled a significant refinement of the conceptual site model, including the fact that inversion of groundwater fluxes was not observed at high tide. Results indicated that contaminant mass fluxes were particularly higher at a specific monitoring well, by more than three orders of magnitude, than at other wells of the investigated aquifer. This study provided crucial information for optimizing further field investigations and risk mitigation measures. 相似文献
Meteorological and oceanographic data from ships of opportunity are the largest contributor to the world’s ocean surface database and thus are extensively used to estimate the change in climatic properties over the world’s oceans during the previous 150 years. The importance of these data for climate change studies underscores the need to fully understand the error associated with averages of these data. The sampling error problem is especially acute for ship data due to the fact that ships are moving platforms and, thus, report observations from constantly varying locations with time. This paper develops a theoretical framework for assessing the averaged sampling error associated with monthly, 1°×1° latitude-longitude box averaged ship data. It should be noted that the time-space distribution of ships within the averaging domain strongly affects the sampling error. This is shown in our derivation. The framework developed here can be used to improve upon existing methods for estimating the sampling error associated with three-dimensional box averages of meteorological and oceanographic data obtained from ship records. The framework is complimentary to existing methods of assessing biases and random error due to instrumentation, recording, etc. It is demonstrated mathematically that the uncertainty due to incomplete sampling is primarily a trade off between of the number of observations and their relative locations within the box as well as the inherent time-space correlation structure of the variable of interest. This work differs from other studies in that the three-dimensional interdependence of data is taken into account in deriving an expression for the sampling error. 相似文献