IES940009A2 - Process of using controlled refrigeration to stabilise &¹strengthen water & soil, immobilise water portable materials¹& construct structures - Google Patents

Abstract

The invention deals with the problems of constructing permanent ice structures, soil stabilisation on waterlogged sites & protecting against earthquake damage particularly on sites containing thixotropic materials. The invention involves a process of embedding conduits containing refrigerant in soil or water, laying an intermediate layer on the site of insulating material, laying surface water collection & runoff channels, an upper or outer layer on the site of armour coating or facing materials and passing refrigerant throught the conduits in a controlled manner to freeze the water & soil, surface run off water excluded, thereby strengthening & stabilising the water & soil, immobilising materials and enabling the construction of permanent ice structures even in regions where temperatures are above the freezing point of water. The invention is used for constructing permanent ice structures, immobilising water portable contaminants or thixotropic muds or clays & protecting existing constructions against earthquake damage.

Description

PROCESS OF USING CONTROLLED REFRIGERATION TO STABILISE & STRENGTHEN WATER & SOIL, IMMOBILISE WATER PORTABLE MATERIALS & CONSTRUCT STRUCTURES PATENT APPLICATION BY PADRAIG MC ALISTER, AN IRISH CITIZEN OF 63 THORMANBY LAWNS, HOWTH, COUNTY DUBLIN ·*“ ®4 000 9 This invention concerns a construction process consisting of embedding conduits containing refrigerant in the soil or water of sites containing water, water soluble contaminants or contaminants capable of being carried by water, laying an intermediate layer on the site of insulating material, laying surface water collection & runoff channels & an upper or outer layer on the site of hard standing, armour coating or facing materials and passing refrigerant throught the conduits to freeze the water & soil, thereby strengthening & stabilising the water, the soil, immobilising contaminants and constructing structures. The system of controlled refrigeration & conduits near the interface between the soil or water being treated & the insulating material, is used to maintain any water present, surface runoff excluded, in the form of ice, in a solid state and consequently immobile, dimensionally stable & structurally strong enough to render the site & its structures usable for useful load bearing purposes. The surface water runoff channels are used as is normal. Such types of process are not known at present. There are some partly similar features in ice rinks and there may be adventitious partial similarities in roads in Arctic or Antarctic regions. There are however none where the arrangement is of the type described in this application.

In the case of ice rinks, while the Ice is refrigerated and capable of carrying the weight of humans, it is uninsulated & unarmoured for any permanent structural application. In the case of Arctic and Antarctic roads there is no artificial refrigeration & no insulation. In the case of deliberate ice constructions in Arctic in Antarctic regions the processes used are different & do not involve the same control of refrigeration, temperature, stresses & water permeabiity. These existing types of bodies are unsuitable for any of the purposes for which this invention is suitable. In particular they are restricted to purposes involving low compressive stresses or to naturally cold climates and to use in simple and obvious load bearing applications such as ice skating or constructions in very cold regions at times when the temperature is such that the ice is naturally in the solid state.

It is the object of this invention to provide a treatment of the afore mentioned general type whereby the above cited disadvantages are eliminated & the potential useful load bearing applications of contaminated, waterlogged & earthquake prone sites are realised. In particular it is an object to realise the ability to treat sites contaminated MO0O9 with water portable contaminants so that they are capable of safe structural use, pending permanent disposal of any contaminants. It is also an object to treat land or water sites to strengthen & stabilise them & use the method to construct permanent structures on such sites. It is also an object to treat sites prone to earthquakes or containing thixotropic clays or muds so that they are frozen solid & the energy absorbtion capacity greatly enhanced, thereby improving the capacity of any structures on them to withstand tremors or other earth disturbances.

According to the invention there is provided a treatment comprising a surface load bearing or facing layer which may be of any of the normally used materials cited in the literature such as metal, ashphalt, tarmacadam, tile, brick, reinforced concrete, unreinforced concrete, earth, sand, or stone, any of the normally suitable surface water collection & runoff channels, an intermediate layer of insulating material which may be of any of the normally used materials cited in the literature, such as cement, concrete, stone, earth, sand, wood, plastic foam, or treated urban waste and a lower site layer within which is embedded a system of conduits for refrigerant near the interface with the insulating material. This system of conduits and refrigerant & artificial refrigeration is used to maintain any water present, surface runoff water excluded, in the form of ice at a temperature below the freezing point of the water present less 1 degree Celsius for each 10 million pascals of stress experienced by the ice at its most stressed point.

It has been surprisingly discovered by the inventors research that this treatment results in a loadbearing capacity throughout the site in the range .7 to 2.5 newtons/square millimetre for a surprisingly small lifetime cost. This loadbearing capacity is suitable for a number of practical applications, it has also been surprisingly discovered that the treatment over time enables the refrigerant conduits to freeze any naturally ocurring water in the site soil area down to basement rock or water impermeable subsurface strata, without freezing surface runoff water, thereby enabling successful rigid bonding of all site soil & water to the basement strata on which it is resting, without the need for piles or grouting, even for basement rocks which are waterlogged, fissured, earthy, sandy, peaty or muddy or covered with loose gravel, stone or thixotropic materials, thereby created a structurally rigid, strong & watertight bond, while maintaining clean runoff water on top. It has also ζ π η o g been surprisingly discovered by the inventors research that the cost of maintaining certain types of site in this condition and structurally sound, for the sites for which the treatment is especially suitable, is smaller than the cost of alternative soil stabilisation or contaminant immobilisation treatments or construction processes.

The present state of the art in ice constructions is described in USSR patents 858617, 859229, 924227, 924237, 1016426, 1059050, 1092241, 1130665, 1130667, 1145082, 1146360, 1194964, 1206372, 1318639, 1342969, US patents 3675429, 3738114, 3742715, 3750412, 3804543,3849993,3863456, 3909992,4021972,4055052, 4094149, 4205928, 4242012, 4325656, 4432669, 4456072, 4695194, 4808036, Japanese patent 297598 & Canadian patent 1066900. These are, with the exception of the Japanese patent, for processes using natural cooling in a very cold climate. None of the processes described in any of these patents are suitable for climates where temperature exceeds the water freezing point for any significant length of time. The Japanese process is proposed as a method for burying large structures such as nuclear power plants & involves deliberately melting the ice as this is done. None of the existing processes for ice constructions meet the requirements for a calculatable controllable bearing stress or pressure for a site or structure or identify the best method which can be used by design engineers skilled in the state of the art to construct a permanent ice structure capable of structural use anywhere in the world.

The present state of the art in soil stabilisation is described in Irish patent 51969 issued in 1987. In that patent the treatment using concrete, other materials and plasticizers is described. The methods described are perfectly good methods but costly in terms of materials, particularly for very wet, waterlogged or submerged sites.

The present state of the art in treatment of contaminated sites is also extensively described in the literature. The principal method is removal of the soil and its incineration to destroy contaminants. This is also a perfectly good but very costly method in time & energy particularly for very wet or waterlogged sites.

In the case of earthquake protection, the literature cites a particular technical problem in protecting water logged ground, particularly ground containing thixotropic clays or muds & presently the literature cites no ® 4 0 0 0 9 satisfactory treatment for such ground capable of rendering it structurally stable during earth tremors.

Using the process described in this specification, the technical problems on all these types of site can be successfully treated, material costs of treatment are considerably reduced and sites can be more quickly used for some useful purposes thereby realising useful income.

The best method of employing the process according to this invention is a function of the loadbearing strength required, the slope or submergence of the site, the basement rock depth & contours & the type of technical problem to be treated.

The loadbearing strength of the site is increased by reducing the temperature of the frozen layer of the site below the threshhold local liquefaction point. This threshhold is the point at which traffic vibrations or earth tremors generate pressure peaks in the subsurface resulting in local ice liquefaction. As ice locally liquifies & is refrozen by the artifical refrigeration system, small scale local creep or contaminant movement could take place, if the compressive strength of the residual unliquified loadbearing portion were inadequate for the load, or if the local liquefaction were to permit small scale movement downhill or spreading. This is the glacier flow mechanism. In order to prevent this, the site temperature below local freezing is controlled so that at such high pressure points liquefaction & contaminant mobilisation does not take place. This is done by calculating the pressure peak by any of the methods cited in the road traffic or earth science literature and reducing the design site temperature by 1 degree Celsius for each 10 million pascals of pressure at the pressure peak. Whether ice temperature is reduced in advance of calculated pressure peaks by way of prior sub cooling of the site or dealt with as pressure peaks arise is a matter for designer choice based on the local expected frequency & duration of earth tremors or traffic vibrations.

In the case of traffic, the best method of dealing with traffic generated stresses is as follows. The dynamic pressure peaks experienced under heavy duty vehicles on modern skid resistant surfaces have a characteristic frequency in cycles/second of the vehicle speed in metres/second divided by the size of the road surfacing stone in metres. For .02 metre gravel & vehicle speed of 100 kilometres/hour the characteristic frequency is 1389 cycles per second. The pressure peak *40009 s produced by rubber tyres at this frequency is given by the relationship modulus X amplitude X frequency. For example with an amplitude of .001 metres & a rubber modulus of 700 kilonewtons per square metre the pressure peak is 972 kilonewtons per square metre or 972,000 pascals. Using the relationship cited above of 1 degree reduction per 10 million pascals, a temperature reduction of .1 degree Celsius is calculated to best cope with this technical problem. For the pressure peaks typically to be expected from traffic other than such high velocity heavy duty traffic, this reduction of .1 degrees below local freezing is also adequate.

With the exception of certain specialised applications such as quarry exit roads, the pressure peak on an actual site is more likely to be determined by small earth tremors than by vehicular traffic. It is clear also from this analysis that typical earth tremor generated pressure peaks of a magnitude of 30 million pascals will initiate local liquefaction of a site held at 3 degrees Celsius below the local freezing point by transmitting the pressure peaks of ground vibrations into the site.

The best method of using the invention in the case of earth tremor prone sites is as follows. The pressure peak expected from the expected tremor is calculated. For tremors below a 30 million pascal pressure peak the 3 degree reduction cited above will prevent any liquefaction. Tremors above a pressure peak of 30 million pascals or major tremors will liquefy part of the ice. However such earth tremors are always of short duration. Not all of the ice will be liquefied and the refrigeration system will remove large amounts of mechanical energy as heat. In earthquake prone regions the energy absorbed from the design tremor during its duration is also calculated and the proportion of ice liquefied calculated for the expected duration of the tremor. This will generally be a small proportion, typically less than 10% because of the low thermal equivalent of mechanical energy, the high latent heat of melting of ice & the short duration of tremors. When this proportion is calculated, an additional allowance is made by the designer for this potential liquefaction of some site ice due to tremors, to maintain the structural integrity in any structure built on the site, or on a raft on the site, either by prior subcooling of all the site ice, or by freezing this calculated vulnerable % of the site area as an excess over the 100% calculated to t ^40009 maintain structural integrity from other considerations. The choice of which is the best method on a particular site will also be influenced by the local site characteristics, raft design if any, geothermal heat flux and is a matter for site specific design by the design practitioner skilled in that art using the invention as described here & the normal design tools. The slope of the site or depth of submergence is also an important consideration. The best method of dealing with slope differences or submergence according to this invention is by calculating the additional pressure at the lowest point on the site created by the total heigth of site material above that point to the highest structurally connected point and calculating the lithostatic pressure created by this height of site material above this lowest point. The design temperature for the ice at this lowest, most stressed point is then further reduced according to the relationship already mentioned of 1 degree Celsius per 10 million pascals of stress.

This is also the best method of using the invention for site points submerged below the waterline.

The temperature employed in refrigeration is a function of firstly the design site temperature calculated as above for different points on the site. These differences can be controlled by any of the normally available control mechanisms. Secondly design refrigeration temperature also depends on whether the water present is fresh or locally saline, or if saline what the dissolved salt is, according to the scientific data published on freezing point depression caused by dissolved salts. Calcium chloride inclusions are to be avoided at all costs as they reduce the required refrigeration temperature greatly & add to costs significantly. For fresh water & the more common seawater saline environments, typical site normal & additional refrigeration temperatures required for the best method are given in the following table of example temperature reductions.

For minimum ice strength of .7 newtons/square millimetre, Degrees Celsius below zero required Fresh water ice Seawater ice For salinity environment With vertical stress 400 tonnes/ sq. metre With heavy traffic vibrations With 30 million pascal ground shock wave Total reduction below zero Celsius required .4 .1 2.2 .4 .1 3.5 .7 * *40009 The refrigeration system used can be any of the normally suitable systems, but an indirect system using sodium chloride brine pumped though plastic piping will normally be preferred on economic grounds. The particular insulating material employed, the armour material employed & the reinforcement added to any site slope or submerged point before freezing are matters for the choice of the designer.

The embodiments in the following examples are calculated on the requirement of a minimum site compressive strength requirement of .7 newtons/square millimetre minimum, a seawater environment & a level unsubmerged site not prone to traffic or earthquake stresses. However the method described in the invention is obviously not limited to such sites and it is left to the discretion of the design engineer skilled in the practice of the art, to adapt the method of the invention to different requirements.

Example 1 An embodyment in which the armour is gravel or stone chippings, the insulator is the site soil itself, the refrigeration conduits are plastic piping, the site soil core is maintained at a temperature below minus 2.2 degrees Celsius less 1 degree for each 10 million pascals of pressure to be experienced by the ice at its most stressed point and the resultant body is freeze bonded at its base to the basement rock is especially suitable and useful for immobilising water portable contaminants on contaminated sites or sites used in dams, land reclamation, polder construction, flood control, construction of artificial land in water or for airport runways.

Example 2 An embodyment in which the armour is lightweight concrete, the insulator is plastic foam, refrigeration ducts are lightweight metal or plastic tubing, the core ice is maintained at a temperature below minus 2.2 degreesCelsius less 1 degree for every 10 million pascals of pressure to be experienced by the ice at its most stressed point, the treatment has insulation, armour & refrigeration ducts at boundaries to water courses as weli as the surface & and the resultant body is freeze bonded to the basement rock is especially useful for and suitable for soil stabilisation of waterlogged sites or flood control barriers in or near lakes, streams or offshore in the sea, protection from storm damage, -** *4 σσ ο 9 making flood prone quarries permanently safe from drowning accidents & reclaiming land areas near watersides.

Example 3 An embodyment in which the armour is concrete, the insulator is plastic foam on top of site soil, the refrigeration conduits are iron piping laid in holes drilled vertically down around an existing building or site containing thixotropic clays or muds & entending downwards to the basement strata, the site soil core is maintained at a temperature below minus 2.2 degrees Celsius less 1 degree for each 10 million pascals of pressure to be experienced by the ice at its most stressed point and the resultant frozen soil body is freeze bonded at its base to the basement strata is especially suitable and useful for protection of buildings & dams in earthquake prone areas or areas containing thixotropic clays or muds.

Two methods for applying the process according to the invention will be described. In both cases after applying the process, sufficient continuing refrieration to absorb both energy absorbtion from traffic, sensible heat leakage in from the atmosphere and geothermal flux from the earth's core, is provided & sufficient spare refrigeration capacity installed to absorb the energy from the earth tremor used in the design basis without loss of structural integrity.

In the first method the site soil & water is frozen in a series of stages and when ready for final armouring, the refrigerant ducts are placed in their final position before final freeze binding of the site area to basement rock. During the ice formation process care is taken to prevent the build up of undue stress concentrations by monitoring site stress & controlling the rate of refrigeration and temperature gradients particularly between the upper and lower parts of the site. Stress concentrations are also monitored & controlled by a careful choice of the location & spacing of the refrigerant piping between the inner and outer parts of the site. If a particularly strong construction is desired at a point, reinforcement is added to that site point before freezing & removal of refrigerant pipes to the next stage or ievel to be frozen. Each subsequent stage or level consists of freezing the site a further section or level and repeating the process until the total site area & depth required is frozen.

The final step consists of closing off the frozen sections & layers with the finally positioned system of refrigerant conduits, adding the insulation layer and finally the load bearing layer together with water runoff £ ®40009 channels on upper & outer surfaces, following which the site will be freeze bound in Situ to the basement rock. This process of freeze binding level by level is especially useful where the site basement rock levels are uneven or for submerged construction of embankments or dams in free water such as lakes, rivers or the sea.

The second method of construction to be described consists of constructing the frozen loadbearing layer from the top. This is especially suitable for construction on land but may also be carried out on a waterbed. This is carried out in a smaller number of stages by placing the refrigeration conduits in their final position, isolating the site area for freezing by a suitable canopy to control the temperature of the site to be frozen, treating any free water as desired, pumping a slushy water phase into site voids and passing refrigerant through the coils to freezeup the frozen top site layer to a thickness suitable for the loads being considered. When the desired top site frozen thickness is reached the site is topped off by insulating it with the insulating material chosen together with water runoff channels on upper & outer surfaces & armouring it with the loadbearing material chosen.

It is clear from this that the invention gives the designer freedom to match any site basement rock or subsurface strata shape, including sites submerged in water to any practical depth & that the refrigerant system will gradually freeze the site down to any desired level by controlling the amount of refrigeration. The method can therefore if desired bind the base of any site rigidly to the basement rock or to water impermeable strata. Any water in the rock fissures or impermeable strata can be frozen & will expand by about 9% on freezing. This will result in watertight adhesion of the site even to irregularly shaped & fissured basement rock or impermeable strata areas and is especially suitable for earthquake prone areas or areas such as limestone rock areas where rock can be extensively fissured. This feature is also especially suitable for treating sites beside rivers, lakes, canals, seashores or municipal refuse dumps where only part of the site is naturally enclosed to begin with.

Any surface water from rain or other precipitation can be dealt with by any of the usual methods, as being isolated from the frozen layer by the armour & insulation it can runoff into drains in the normal way. Furthermore not having contacted any contaminated soil, this runoff ¢40009 water will be clean & meat discharge requirements without further treatment, even from sites contaminated with water soluble contaminants.

Claims (5)

1. A process for immobilising water & water portable materials present in the water & soil of land or water, by the process of embedding conduits for refrigerant in the soil or water of a site & using this system of conduits, refrigerant & controlled refrigeration to reduce & maintain the soil & water of the site at a temperature below the freezing point of water present, less 1 degree Celsius for each 10 million pascals of stress experienced in the site at stressed points, together with an intermediate layer of any of the normally suitable insulating materials, an upper layer of any of the normally suitable load bearing or facing materials & any of the normally suitable surface water collection & runoff channels.

2. A process for stabilising & strengthening the soil or water of wet or waterlogged sites or constructing ice structures to a minimum bearing strength of .7 newtons/square millimetre by the same process.

3. A process for stabilising & strengthening the soil or water of earthquake prone sites or sites containing soils potentially prone to thixotropic behaviour after experiencing disturbance, to a minimum compressive strength of .7 newtons/square millimetre & a minimum energy absorbtion capacity of 335 joules/gramme of ice present after freezing, by the same process.

4. A process of water & soil stabilisation & strengthening, structure construction or water portable material immobilisation, substantially as described herein with reference to the examples & embodyments described.

5. Soil or water when stabilised or strengthened or materials when immobilised or structures when constructed according to the process of any of claims 1 to 4.