Artesian Pressure Research Articles

Hydrology, Water Chemistry and Ecological Relations in the Raised Mound of Cowles Bog

SUMMARY (1) The Cowles Bog National Natural Landmark and the wetlands between the dunes near the south shore of Lake Michigan, in Indiana, contain plant species that are typical of circum-neutral fens. (2) The distribution of eight, rather sharply delineated, vegetation types correlates most strongly with water level variations resulting from the presence of a 4.1-ha convex peat mound. (3) A network of shallow ground-water wells installed in the wetland has identified an upwelling of water under artesian pressure at sites underlying the mound. (4) The well-buffered water, containing high concentrations of inorganic solutes, is derived from an aquifer that is recharged on an upland moraine and is confined beneath a clay till sheet. (5) A breach in this clay layer beneath the mound allows water to flow upward and radially outward as the hydraulic head is dissipated in the overlying marl and peat. (6) The marl and organic lake sediments in the wetland were formed during the Nipissing level of ancestral Lake Michigan (4000-6000 years ago) when the wetland basin was probably a small bay of the lake. (7) The peat mound developed when the lake level fell from the Algoma through to modern times. This increased the difference in hydraulic head and increased spring flows, which in turn induced peat formation.

Topographic Fluctuations Across a Spring Fen and Raised Bog in the Lost River Peatland, Northern Minnesota

(1) A topographic survey was conducted with both laser and electronic levels across a spring fen, a raised bog and the water track (fen) between them, in the Lost River Peatland of northern Minnesota. (2) The survey demonstrated that the spring fen consisted of a peat mound whose slopes were steeper than that of the bog. (3) Three successive surveys in 1982 and 1983 showed altitudinal changes in benchmarks fixed in trees relative to a base level on a power-line pylon located in the water track. Nearly all benchmarks rose, with the greatest rises occurring near the centres of the raised bog (11 cm) and spring fen (6 cm) in contrast to very slight rises across the water track. (4) The most likely explanation for this altitudinal change is a swelling of the sub-surface peat in response to artesian fluid pressure generated by regional hydraulic gradients. (5) Very precise determinations of altitude are thus possible with a laser or electronic level on an unstable peat substrate, providing great care is taken in surveying techniques.

Discussion on ‘The influence of ground and groundwater geochemistry on construction in the middle east’ by P. G. Fookes, W. J. French & S. M. M. Rice

Dr A. N. James and Mr A. L. Little write: Dr Fookes and his co-authors are to be congratulated on a valuable and interesting paper which is similar to work in Saudi Arabia for which the writers of this present discussion were responsible during 1977 and 1978. The present writers were concerned with geotechnical aspects of certain structures being designed for the Royal Commission of Jubail and Yanbu, under whose authority the very large Jubail Industrial Complex was being constructed. Many of the structures were to be situated on the sabkha areas near Jubail and Al abd Allahand on the Arabian penninsula some 25 km north of the sabkha Al Riyas which has been briefly described by Johnson et al. (1973). The present authors had access to extensive investigations of the Jubail sabkha area made by a number of different organizations including: Al-Muhandis Nizar Kurdi, Arabian Engineering Bureau, Sir Alexander Gibb & Partners, Dames and Moore & Basil Geotechnics, Binnie & Partners, Consulting Engineering Office Soilmafco, Pacific Consultants Inc. and Saudi Fugro Ltd. Information available from these investigations was used during the design stages of a variety of large and small structures with different load bearing and settlement requirements. During the review stages of the project it became apparent that effects of artesian water were an important consideration for all the foundation designs. This aspect of foundation design and construction on sabkha has received very little attention previously although it is mentioned briefly byOwles and Bowman (1981). The artesian pressures

Weathering and slope stability on Upper Carboniferous mudrocks in south-west England

Summary Natural landslides are a common occurrence on inland slopes of Upper Carboniferous strata in south-west England. They range from shallow, translational slides to earthflows, and usually involve soils above and belonging to the zone of completely weathered mudrock. Solifluction was more active in periglacial conditions (due to softening by excess surface water) and formed widespread clayey head deposits found mainly on lower slopes. Translational sliding is more characteristic of temperate environments and locally may be initiated by artesian groundwater pressures on the base of silty clay soils of low permeability where these overlie pervious weathered rock. These slides may develop downslope into earthflows when seepage of groundwater produces softening. The clay soils do not have a high activity or plasticity on the whole, due to the high diagenetic grade of the underlying mudrocks whose non-swelling clay mineralogy they inherit. Measurements of the residual shear strength of the slipped soil at one site shows a curved strength envelope with ϕ′ r falling to about 15° at high normal effective stress, but with values up to 30° at low stresses. The significance of the variation with normal stress of ϕ′ r and c′ r in the analysis of the stability of very shallow landslides makes it important to determine accurately both the laboratory strength and in situ effective stress at low overburden stresses. The direct observation of unstable or susceptible areas before the main ground investigation may be aided by electrical resistivity surveying. Stabilization can usually be achieved by drainage measures, but complete removal of unstable soils is sometimes necessary.

Groundwater control by drainage gallery at Aberfan, South Wales

Abstract The Aberfan (Merthyr Vale) tip, which failed with disastrous consequences in 1966 (HMSO, 1969), was constructed above rocks subjected to artesian pressures. Two-thirds of the tip were removed after the failure and sub-surface drainage measures have been installed to secure the remainder. These include a drainage gallery, the construction and performance of which are the subject of this paper. The ‘factor of safety’ of a critical slope of the tip has been improved to an acceptable value by a reduction in the artesian pressures within the rock. Investigations before and during construction indicate that water moves towards the seat of the 1966 failure in a 20 m wide flexure in the rock adjacent to a hitherto unrecorded minor fault. It appears that tensional strains created by past mining have been concentrated within this structure the existence of which must be added to the other previously established factors which contributed to the failure. The profound anisotropy within the aquifer caused by this geological structure and mining history is demonstrated by the fact that an estimated 25% of the water entering the potential groundwater catchment is released from a length of aquifer equivalent to less than 1% of the available spring line.

The investigation and control of groundwater at Ysbytty Reservoir, Gwynedd

Abstract During early site investigations for an underground water storage reservoir at Ysbytty near Caernarfon-North Wales groundwater under artesian conditions was encountered. A subsequent investigation, including pumping trials from two large diameter boreholes, was conducted in order to establish the feasibility of reducing the artesian pressures during and after construction. The parameters thus defined enabled a scheme to be devised for dealing with groundwater during construction, utilising the wells installed during the investigation, and for the detailed design of an under-floor drainage system as part of the permanent works. A further problem concerned the effects of prolonged draw-down of the water table below the adjacent clay-lined open service reservoir. Recharge wells were installed to maintain the water table and groundwater levels in the immediate vicinity were monitored throughout construction. The under-floor drainage system for the new reservoir was designed and installed, incorporating porous pipes in a stone filter layer. Its function is to prevent uplift of the reservoir under all working conditions; a gravity outlet drain eliminated the need for permanent pumping.

Rising groundwater levels in cities

Abstract It is well documented that groundwater levels in a number of cities in this country and abroad have been rising over the past few years. Parts of central London are experiencing rises of one metre per year, while in Paris, previously dry basements are now affected by severe flooding. The extraction of good quality water from city wells for a variety of industrial and domestic purposes led to a general lowering of groundwater levels from the early 1800s. During the period of depressed groundwater levels development within restricted city centre sites required higher buildings with deeper basements and foundations. Communication networks also moved underground to ease congestion at the surface. A large percentage of this work was carried out during a period when the groundwater was tens of metres below ground level; a situation accepted as being stable at the time. Consequently the effect of a higher water table was often not considered in the geotechnical design of structures. Within central London the water table is still very deep and may not cause problems for years to come. In Birmingham the situation is more critical and the rise in groundwater level is already causing problems. Computer model predictions play a leading role in predicting tomorrow’s groundwater levels. Evidence suggests that groundwater levels in the near future will attain those of natural conditions. The effect that these levels will have on current structures requires assessment. Simplified calculations for the London area show that the bearing capacity of deep basement foundations and piles could be reduced by 25’30% if the rise in groundwater level continues. High levels of sulphates have been recorded during recharge experiments and these will produce adverse effects on unprotected foundations. Problems with high artesian pressure during construction are also likely if the aquifer is confined. These is an urgent need to assess the geotechnical risk to engineering structures with respect to the rising groundwater levels. This should be carried out now so that problems can be properly anticipated and solutions developed in good time.

The Borah Peak, Idaho Earthquake of October 28, 1983—Hydrologic Effects

Spectacular groundwater effects accompanied the October 28, 1983 Idaho earthquake (Ms = 7.3). Groundwater discharge increased from many springs and base flow of major rivers significantly increased over an 18,000 km2 region. In the epicentral area a 35-m surge in artesian pressure produced spectacular bursts of muddy water from carbonate bedrock hills at Chilly Buttes. This pressure surge was also manifested as a 1.4-km long zone of large sand boils erupted through the valley alluvium. At Smith's Fish Hatchery, sediment eroded by the surge of water clogged the fresh spring-water supply inlet pipes and led to suffocation of the entire crop of trout. North of the epicentral area a major warm springs dried up for 8 days and then recommenced flowing at an ever increasing rate until it stabilized at about 9 times the pre-earthquake flow. This flow of about 1400 l/s caused severe bank erosion of pastureland until diverted into an artificially excavated channel. At Clayton Silver Mine, 50 km north of the epicenter, increased seepage into the underground mine workings overwhelmed the mine-pump capacity and flooded the 330-meter level within 14 hrs. Thirty kms south of the epicenter a 200,000 m3 mudflow was apparently caused by increased spring flows. The valley fill failed two days after the earthquake and devastated a 3.5-km reach of Lupine Creek valley. Similar coseismic and post-seismic hydrologic effects were reported in studies of the 1952 Kern County, California earthquake, and the 1959 Hebgen Lake, Montana earthquake. Several mechanisms for these hydrologic phenomena are considered, but the most plausible cause is the sudden release of elastic strain in aquifer rocks. Sudden strain release of elastic rebound increases pore pressure in some confined aquifers thus leading to increase in discharge from springs that contribute to the base flow of major rivers.

Optimal management of a confined groundwater system

Dynamic programming is applied to a relatively simple economic and hydrologic model of a confined aquifer system in Southwest Montana to determine an optimal interseasonal allocation schedule. The derived decision rule demonstrates the economic advantage of maintaining a confined groundwater system. While localized intraseasonal loss of the artesian pressure may occur, it is important to maintain this pressure from year to year because of its role in reducing extraction costs. The welfare gap, as measured by differences in the net present value of economic returns to the basin under an optimal use policy versus an uncontrolled, “common pool” situation, is not trivial. Sensitivity analysis indicates that assumptions about uniformity of land productivity, vis-à-vis their impact on the shape of the returns function, the discount rate, and the level of electric power rates are particularly critical with respect to the magnitude of the commonality problem.

Cast-in-place bored piles on soft rock under artesian pressures : Sharma, H D; Sengupta, S; Harron, G Can Geotech JV21, N4, Nov 1984, P684–698

Cast-in-place bored piles on soft rock under artesian pressures : Sharma, H D; Sengupta, S; Harron, G Can Geotech JV21, N4, Nov 1984, P684–698

Safety first in frozen bore : Dadson, J New Civ Engr25 Oct 1984, P26–27, 31

Nitrogen ground freezing has become necessary to overcome very confused ground conditions over some 55 m of the 6 km long, 2.44 m internal diameter concrete lined tube needed to provide an alternative water supply for London should the River Thames become polluted. At the site, running sands and silt are under considerable artesian pressure. Claquage grouting was tried but was needed to be supplemented by ground freezing. Nitrogen freezing was chosen in preference to brine because it stiffens the ground within 48 hours. Health precautions, which are vigorously enforced, are divided into two types, above and below ground. There is little danger of nitrogen asphyxiation above the ground, but cold burns provide a more serious threat, and the use of leather gloves is compulsory. Maintenance of freeze around the shield is carried out during the shift changeover period and no general freezing is carried out within 4 m of the face when working. Only one man is allowed in the tunnel to measure oxygen deficiency at a start of a shift. Good communications between the face and the freezing operation are essential to ensure nitrogen is not fed to a pipe which has been cut at the face. (TRRL)

Cast-in-place bored piles on soft rock under artesian pressures

This paper outlines the geotechnical investigations and axial compression, pullout, and lateral pile load tests that were carried out at a site where cast-in-place bored concrete piles were installed. These piles were designed to bear on top of soft weathered rock surface that was under artesian pressures. Pile load test results have been compared with theoretically calculated pile capacities. It has been found that in areas of high artesian pressures in bedrock axial compressive pile load capacities theoretically estimated by conventional methods were significantly higher than the values obtained from load tests. Recommendations have been made that representative exposed bedrock samples be tested to determine their undrained strength, and these values be used for estimating theoretical pile capacities. Construction problems encountered during pile installation, such as locating the top of weathered bedrock without penetrating through water-bearing layers that were under artesian pressures, are presented briefly and a solution provided to install belled piles on top of bedrock is discussed. Key words: bored concrete piles, construction problems, load tests, soft weathered rock under artesian pressures, ultimate pile load capacities.

Heart Mountain, Wyoming--Blocks in a Collapsing Volcanic Pile: ABSTRACT

The Heart Mountain was caused by volcanic collapse and not free sliding. These huge blocks could hang together if immersed in volcanics, but not in air. Block separation is logical during sideward volcanic collapse, but inertia and the rate required make free sliding untenable. Lack of erosion of the fault surface requires instant burial if free sliding was the cause. However, if the detachment was part of a volcanic collapse, the fault surface was never exposed. Free-moving blocks would gouge the delicate Grove Creek pavement, but the equal loading by a glacier-like collapse of volcanics would allow this stratigraphy to remain intact. Nothing in present experience moves free blocks on so large a scale on that flat a surface, especially up and over a transgre sive ramp in a free setting. A collapsing volcanic pile propelled by its profile of repose, not by the slope under it, would allow movement. Earthquake vibration is ineffective in a free slide, but extremely effective in collapsing a weak pile. The Reef Creek structure is an imbrication; the South Fork is an unloading bulge. A long dip slope with a basin-facing monocline below it, a large young volcanic pile, seismicity, a swampy toe, and artesian pressure combined to cause failure. It may have been steady-state, incremental, or catastrophic, the latter being favored. End_of_Article - Last_Page 947------------

Boise Geothermal System, Western Snake River Plain, Idaho: ABSTRACT

The Boise geothermal system lies in an area of high heat flow along the northern margin of the western Snake River plain. Exploratory drilling for petroleum and geothermal water, seismic reflection profiling, and regional gravity data permit construction of a detailed structure section across the western plain. A faulted acoustic basement of volcanic rocks lies at depths of 2,400 to 6,000 ft (730-1,830 m) beneath late Cenozoic lacustrine and fluvial deposits in the center of the plain. Volcanic rocks of the acoustic basement are typically basalt out in the plain, but the acoustic basement along the north margin in the vicinity of Boise is largely silicic volcanic rock. Geologic mapping and geothermal well data have provided information on the late Cenozoic geologic units nd structures important to the understanding of the Boise geothermal system. The main geothermal aquifer is a sequence of rhyolite layers and minor arkosic and tuffaceous sediment of the Miocene Idavada Volcanics. The aquifer is confined by a sequence of impermeable basaltic tuffs. The aquifer has sufficient fracture permeability to yield 150°-170°F (65°-76.6°C) hot water for space heating at a rate of 600 to 1,200 gpm from wells drilled in the metropolitan area, north of the Boise River. In this area the rhyolite lies at a depth of 900-2,000 ft (274-610 m). Artesian pressure typically lifts water to an elevation of about 2,760 ft (840 m). A conceptual model of recharge assumes percolation driven by the topographic head to a depth of more than 7,000 ft (2,135 m) benea h the granitic highlands northeast of the city. Heated water convects upward through northwest-trending range-front faults. End_of_Article - Last_Page 955------------

The distribution and engineering significance of superficial deposits in the Upper Clydach Valley, South Wales

Summary Abernant Colliery, in the South Wales Coalfield, disposes of 300 000 tonnes of washery waste each year onto the floor of the Upper Clydach valley. Rockhead is deeply buried by 20–60 m of superficial deposits which consist of a Lower silty stony clay, Middle bedded silts, sands and clays, and an Upper silty stony clay. The Lower silty stony clay, up to 30 m thick, is of variable composition and is probably a glacial melt-out till. The Middle bedded deposits, thickest in the middle of the valley, were probably laid down immediately after the ice had melted. The Upper silty stony clay, 5 to 15 m thick, may have been largely laid down in the form of valleyside mudflows at the same time as the Middle bedded deposits were being formed, but there is also some evidence of movement of surface layers by solifluction. The presence of water-bearing Middle bedded deposits has caused engineering problems in spoil-heap construction and a slip which occurred in 1981 was in part caused by high artesian pressures in silts and sand in these beds. Many simple, low-gradient valley floor slopes in South Wales conceal highly complex drift successions. While the near-surface material may be strong, it may overlie weak, water-saturated material at a few metres depth.

Dewatering cofferdam for the trident submarine drydock : Forrest, J B Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981, V1, P123–126. Publ Rotterdam: A. A. Balkema, 1981

Abstract : The dewatering cofferdam for the TRIDENT nuclear submarine drydock at Bangor, Washington, presented many challenges. These included water depths up to 25 meters, artesian pressures 10 to 13 meters above mean sea level, difficult pile driving conditions, and the potential for seismically induced liquefaction of the fill in the cofferdam cells. Design ground motions of 0.15 g dictated that fill densities exceed 75% density index. Deep compaction was achieved using a large vibratory probe. Inclinometer, strain gage, and optical survey measurements on the sheet piles and extensive piezometric data was obtained. Significant observations were that (1) deep cell compaction can markedly increase fill density without increasing lateral cell pressures unduly, and (2) maximum interlock tension may be well below the one-quarter height of exposed sheeting as often assumed in design. (Author)

Relation of concealed faults to water quality and the formation of solution features in the Floridan aquifer, northeastern Florida, U.S.A.

Abstract Geological and hydrological information on the Floridan aquifer in northeastern Florida indicates that isolated occurrences of water having relatively high chloride concentration in the upper part of the aquifer may be associated with buried faults. Water having chloride concentrations of more than 700 mg l −1 occurs in the deeper zone of the aquifer at depths below ∼ 600 m below sea level in the coastal and east-central part of the study area. This deep salty water is under higher artesian pressure than water in the shallower, generally freshwater zones, but it is restricted from moving upward by relatively impermeable dolomite beds. Two buried faults with vertical displacements of 30–45 m are in areas where relatively high concentrations of chloride have been detected in water in the upper part of the aquifer. Geochemical, artesian pressure, and water temperature data show that the source of the relatively high concentrations of chloride in water in the upper part of the aquifer is from the deeper zone. This indicates that the faults may have breached the dolomite confining beds and allowed the upward movement of salty water from the deeper zone. The upward movement of mineralized water along the faults may also have formed some of the solution features found in the aquifer near the faults. In this area, freshwater in the upper part of the aquifer is normally saturated with respect to calcite and dolomite. However, water from wells tapping the upper part of the aquifer near the faults is not fully saturated suggesting that the mixing of deep mineralized water with shallower freshwater produces a mixture that is not saturated with respect to these minerals and allows for the dissolution of limestone in the aquifer near the faults. Dissolution of limestone may also be occurring at the freshwater-saltwater interface in the deeper zones of the aquifer.

Howe lake: a hydrodynamic blowout structure

Howe Lake (formerly called "Goudie Lake") is an unusual feature of southeast Saskatchewan. Almost perfectly circular (diameter 295 m), it is much deeper (26 m) than almost any other prairie lake. Initially noted in 1952, numerous investigations culminated in deep drilling and geophysical programs in the 1969–1976 period. The lake is the surface expression of a deep, funnel-shaped depression filled with coarse colluvium at the bottom and finer material near the top. A central pipe extends to a depth of at least 138 m. Radiocarbon dates and the history of deglaciation give evidence that the structure was formed between 12 000 and 12 500 years BP, shortly after the last ice sheet melted in the area. The structure was probably formed by a hydrodynamic blowout of water from the Mannville Group 400 m below surface. Extreme overpressure of water in the Mannville Group was probably induced by recharge from meltwater of the continental glacier then standing a few kilometres to the north of Howe Lake. The blowout was initiated at Howe Lake by fractures in the subsurface, related to a salt solution-collapse structure. Howe Lake probably served as a valve controlling the artesian pressure in the Mannville Group over a large area, until the active ice margin had retreated northeastward exposing lower elevation discharge areas. Hydrodynamic blowouts provide another process for the origin of breccia-filled pipes.

Ground‐Water Flow Systems and Stability of a Slope

AbstractShoreline recession on the Great Lakes has caused millions of dollars worth of property damage in the lake bordering States and Canadian provinces. A variety of projects have been funded to study the erosion problem. The general conclusion of these studies is that wave action at the base of the bluff is the most important basic cause of bluff‐top retreat. The purpose of this study was to investigate the role of various physical processes in causing bluff erosion. One part of the study was to ascertain the role of ground water in bluff stability. In this study, along a certain stretch of the Lake Michigan shoreline, 9 to 10 m (27 to 30 ft) per year of bluff‐top recession that is not correlated to toe erosion was recorded. Heads were measured in 25 piezometers and a complex ground‐water flow system was defined at this site. A glacial sand unit that is under artesian pressure was found 5 m (15 ft) above the toe of the bluff. Another “perched” system was observed in a fractured till unit at the top of the bluff. Water‐table fluctuations have been recorded over a year and fluctuations of up to 13 m (39 ft) in the lower sand unit were measured. These fluctuations were found to have a significant influence on bluff stability. Pore pressures calculated from field measurements, along with the effective strength parameters of the soil units, were then used in the slope stability analysis to determine safety factors.Ground‐water flow systems are found to be highly complex at the land‐lake interface due to the inhomogeneities of the glacial materials that compose the bluffs. Furthermore, these complex ground‐water flow systems influence the stability of the upper part of the bluffs. Because of the complexities, extrapolation of results to other stretches of the shoreline is difficult. However, methodologies and the awareness of how water‐table fluctuations and multi‐layered ground‐water flow systems affect slope stability can be of help in other field situations.

Ground freezing aids Swiss tunnel construction : Aerni, K; Mettier, K Tunn Tunnlg, V13, N3, April 1981, P52–P53

Ground freezing, currently gaining in popularity, was selected as the most suitable method of providing ground stability in the moraine section of an urban motorway tunnel under Zurich where clearance under some of the buildings was as little as 6 M. The ground consists of interbedded marl and sandstone (freshwater molasse), and an area of well compacted moraine with inclusions of non-cohesive silty sand material and the presence of some water under an artesian pressure of up to 3 bar. (Author/TRRL)