Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
  • E02D3/12—Consolidating by placing solidifying or pore-filling substances in the soil
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D35/00—Straightening, lifting, or lowering of foundation structures or of constructions erected on foundations

Definitions

• the present disclosure is generally related to a method and systems for elevating areas. More particularly, the present disclosure relates to systems and methods for the subterranean injection of solids that are of biological origin including divided wood, algae and plant material for example saw dust, wood chips, trimmings, leaves, and grasses.
• An advantage of elevation of terrain and structures using subterranean injection of solids is that there is no disturbance of the actual use or characteristics of the existing structures when elevation or subterranean mechanical enhancement is done. Additionally, structures can be elevated a little at a time as needed once the rate of sea level rise is understood or more accurately predicted. This spreads the cost of protecting structures over potentially many years rather than requiring that the entire cost be borne at one time.
• Lignocellulosic material when used herein, is a short-hand for any biomass material or lignocellulosic material and is understood to be plant material and explicitly includes up to 100% leaves, grass-trimmings, wood pulp, rice-husks, corn stover or any plant-based product including wood ash and biochar which have undergone reactive processing.
• Pyrolysis is a form of reactive processing employing application of heat and, similar to combustion, may yield more carbon-rich solid materials such as carbon-containing ash or more concentrated carbon-containing materials sometimes known as biochar.
• Lignocellulosic material is meant as a short-hand for all photosynthesizing organisms and so is intended to also include phytoplankton and algae though these organisms do not necessarily synthesize cellulose or lignin. In some islands or coastal areas, the most ready source of plant materials available for subterranean injection may be algae.
• wood chips is used as a shorthand for any comparable biomass based material with a fibrous nature.
• the term “height” is occasionally used to describe the least of three dimensions of an aperture, for example. It is not meant to be restrictively be applied to altitude or dimension normal to the surface of the ground but rather is intended to indicate the smallest of three dimensions of a three dimensional shape.
• the height of a vertical aperture may thus project horizontal to the surface of the earth in this sense.
• the height is also meant to indicate the space between two surfaces. Because the surfaces will usually be somewhat curved, the height at one part of an aperture will point in one direction while the height at another part of the aperture with a different orientation will point in a different direction.
• the present disclosure relates to an apparatus and process to protect structures and terrain from inundation as well as to gain potential improvements in seismic performance during earth tremors. Expansion of terrain or island formation is also enabled by the systems and methods disclosed herein. Aspects of the disclosed systems and methods include selection of depth, spacing and diameter of holes to be drilled. Other aspects of the disclosed system include selection, formulation, preparation, concentration and injection of lignocellulosic-based slurries into subterranean spaces. Measurement and adjustment of surface altitude, site monitoring and the techniques used to achieve desired final surface topography are also important aspects. The apparatus used to achieve these goals is an additional aspect of the present disclosure.
• An objective of the present disclosure is to reduce the cost of elevating terrain, earthworks, structures of every description including roadways, bridges, buildings, and homes with little or no damage or cost of reconstruction. Terrain may be expanded, and new islands may be formed where previously no dry land existed.
• An additional object of the present disclosure is to gain additional valuable benefits relative to the use of mineral solids or sediments as described in Germanovich and Murdoch.
• the subterranean injection of lignocellulosic material may gain advantages such as the alteration of the mechanical character of the ground to improve seismic performance.
• Lignocellulosic material may also be injected into a subterranean space to provide a space to accept fluid or gas.
• a method for altering a characteristic of the ground comprises the steps of preparing a lignocellulosic material, suspending the lignocellulosic material in a slurry to create a lignocellulosic slurry, creating a fluid movement of the lignocellulosic slurry, resuspending a portion of the lignocellulosic slurry with the fluid movement, and injecting the lignocellulosic slurry below a surface of the ground.
• the lignocellulosic material comprises a buoyant force on the order of approximately +/- 0.2 g/cc or less.
• the lignocellulosic material comprises an intrinsic particle density of approximately 0.8 to about 1.2 g/cc.
• the lignocellulosic material comprises a molecular density of approximately 1.45 to about 1.55 g/cc.
• the lignocellulosic material is selected from a group consisting of saw dust, divided wood, plant material, wood chips, wood pulp, rice husks, com stover, wood ash, biochar, trimmings, leaves, grasses, grass trimmings, phytoplankton, algae, and biomass materials.
• a method of subterranean injection of lignocellulosic material comprises the steps of selecting a suitable location for terrain protection, accomplishing surface elevation documentation, and placing surface elevation and inclination change sensors on a surface.
• the method of the present invention further comprises the steps of determining a desired depth of prospective subterranean solids, determining a desired orientation of prospective subterranean solids, determining at least one subterranean injection location, and creating an injection well to enable a transfer of solids from the surface to the determined desired depth of the prospective subterranean solid.
• the method of the present invention further comprises the steps of creating a subterranean aperture by injecting fluid under pressure into the subterranean space, and injecting lignocellulosic material into the aperture by injection of an aqueous slurry.
• Figure 1 illustrates a method for the protection of structures with subterranean injection of lignocellulosic solids
• Figure 2 illustrates a method of pre-selecting lignocellulosic materials for injection
• Figure 3 illustrates optional varieties of slurry formation apparatus
• Figure 4 illustrates slurry placement technique option A wherein a single well aperture is expanded with fluid and subsequently filled with a single variety of lignocellulosic solids and then relaxed;
• Figure 5 illustrates slurry placement technique option B employing a dual well aperture and directional bulk flow with reverse flow sweeping cycle
• Figure 6 illustrates slurry placement technique option C dual well aperture injection with material interchange to add a different variety of solids in reverse flow
• Figure 7 illustrates a hypothetical resort uplift example
• Figure 8 illustrates a hypothetical highway elevation project with bulk flow.
• Figure 9 illustrates two varieties of soil anchoring mechanisms that can apply compression to the soil.
• Figure 10 illustrates in more detail soil anchoring mechanisms that can apply compression to the soil as well as inject fluid into an area of the soil above the lower anchor.
• Figure 11 illustrates a soil anchor that can apply either compression or tension to an area of soil intermediate between two anchor sections
• Figure 12 illustrates how an array of soil anchoring devices may be applied in combination to alter the way in which a subterranean aperture is shaped, filled and compressed to facilitate escape of supernatant fluid.
• the present disclosure provides techniques and apparatus to enable the protection of terrain and structures from inundation by ground level elevation as well as to protect structures from seismic events by altering the mechanical character of the ground.
• Terrain may be expanded, and islands may be formed if the process is used in shallow marine areas.
• the present disclosure comprises in one aspect a method 10 of protecting structures with subterranean injection, including a sequence of steps as illustrated in Figure 1.
• the process starts at step 15 and proceeds to a first step 20 wherein selection of a suitable location is done where the advantages of structural or terrain protection from inundation or seismic events or both may be advantageous.
• step 30 surface elevation documentation is next accomplished in conjunction with the placement of surface elevation and inclination change sensors.
• step 30 the process proceeds to step 40 w/here a determination of the desired depth and orientation of prospective subterranean solids is done by evaluation of soil borings or other information about local geotechnical character of the site.
• step 50 a determination of the number of subterranean injection locations is done which will best accomplish the elevation of ground and contouring of surface or alteration of local soil mechanical properties as desired.
• step 60 a creation of an injection well is done which will enable transfer of solids from the surface to the selected subterranean depth.
• this will entail drilling, direct piercing, sonic drilling, or auguring to the appropriate depth.
• Placement of pipe or tubing from the surface to the bottom follows if not used in the process of creating the well.
• the well bore may then be sealed to the pipe or tubing so as to ensure that fluids pumped into the injection well cannot simply flow back to the surface or other substrata around the pipe or tubing via the well bore.
• This sealing may often be accomplished through the use of cementitious sealing plugs, polymer foams, reactive grouts or inflatable plugs that isolate the fluid and pressure at the base of the hole from that of the well bore. Placement of equipment to monitor the subterranean conditions such as a pressure transducer may also be done as needed. Connection of the well to the fluid preparation, pressurization, movement, monitoring and control systems is done.
• step 70 creation of a subterranean aperture is accomplished by injection of fluid under pressure into the subterranean space.
• This step may involve the use of high-pressure jets to help direct the shape of formation of the aperture or additives to increase the fluid viscosity and reduce aperture leak off of injection fluid.
• step 80 expansion of the subterranean aperture is next accomplished by the injection of fluid under pressure.
• step 90 placement of lignocellulosic materials in the aperture is completed with the injection of an aqueous slurry.
• T hen at step 100, rinse of slurry materials from transfer piping with the aqueous solution is done as needed.
• release of excess liquid from the aperture is next allowed which is called relaxation.
• This may be done by allowing fluid to leak out into adjacent subterranean structures or the fluid may be removed at the surface by release of pressure or by controlled pumping.
• the aperture surface settles over the included solid fill and can compact the subterranean solid fill.
• This relaxation allows the included solids to bear the weight of the overburdening earth rather than for the fluid surrounding the solids to bear this weight. With time subterranean fill will also become more thoroughly saturated with fluid increasing the density of individual fill particles and potentially causing them to swell.
• step 120 assessment is completed of alterations in surface elevation and inclination changes.
• the process concludes at step 130.
• process steps 60-120 may be repeated any number of times to elevate and shape the terrain. Larger areas may require that a large number of wells be created and any given well may undergo injection, material distribution, and relaxation cycles multiple times.
• aqueous slurry injected in the lignocellulosic placement at step 90 is created and controlled on a separate apparatus which is further described.
• a separate apparatus which is further described.
• lignocellulosic material is understood to include lignocellulosic materials of all descriptions with or without reactive processing which originated from plants or other photosynthetic organisms as stated earlier.
• An object of the present disclosure is to describe systems and methods to reduce the cost for protection of structures and terrain from inundation.
• This cost reduction derives from a number of different improved aspects of the disclosed systems and methods relative to the use of mineral solids or sediments to elevate terrain and structures as described in Germanovich and Murdoch.
• These improved aspects include at least the following: Transportation cost of solids to be injected is significantly reduced, Slurry preparation costs are reduced, Slurry injection management and subterranean distribution of solids is simplified, and Certain costs associated with location surface preparation and post-injection clean-up are eliminated. More details on achieving by the presently disclosed systems and methods of each of these cost reduction advantages and their importance follows.
• the minimum requisite volume of solids exceeds this number because the edges of the elevated area must be tapered down to meet the old surface of the earth.
• the taper volume requires additional solids with the quantity dependent on the slope of the taper. For very large areas of elevation the volume of solids required approaches this minimum volume per area due to the diminishing significance of this edge effect.
• the minimum volume also exceeds this minimum value because a given volume of solids when measured as delivered to the surface location will compact and densify after placement in a subterranean space and exposure to compaction forces such as the mass of the soil overburden the solids will support.
• the delivered cost associated with a new location where the solids are desired is largely determined by the cost of transporting the solids from the site of removal to the locations where the solids are desired. This cost is most frequently defined for bulk materials by density.
• the bulk density of chipped lignocellulosic plant materials is variable but frequently in the range of 0.15 to 0.35 g/cc while mineral solids such as sand and sediment are frequently in the bulk density range of 1.5 to 2.0 g/cc.
• the bulk density includes the open space between particles and perhaps the water that may fill them and so is lower than the particulate or intrinsic density.
• a truck or other transportation device is usually allowed a certain maximum mass to transport and thus the volume transportable at this maximum mass may be expected to be inversely proportional to the densities of the materials. It is expected that the delivered price of lignocellulosic materials will range from one tenth to one quarter the cost of sand, soil or sediment because a comparable volume of the mineral materials would require four to ten times as many truck trips to transport. By converting the bulk densities of lignocellulosic material and also sediment to volumetric ranges delivered per truck shipment the lower transportation cost advantage of lignocellulosic material becomes apparent.
• a low-cost mineral fill material for example the dredge spoils and sediment referenced by Germanovich and Murdoch would contain unwanted coarse and problematic materials, for example large rocks, metal cans, rope and branches as may have accumulated at the bottom of navigational channels or elsewhere.
• dredge spoils are pumped, very large centrifugal slurry pumps are needed to pass the majority of these large contaminants.
• the large foreign materials would require removal before subterranean injection. This removal could be done in either a dilute aqueous vibratory screening operation or in stagewise cyclonic or gravity settling equipment.
• Lignocellulosic fill materials are an extremely attractive alternative to mineral fill.
• a significant advantage of the subterranean injection of lignocellulosic material as described herein is that they have high porosity and lower density while in some cases retaining high mechanical strengths.
• the porosity enables these alternative solids to form slurries that do not settle as rapidly as mineral solids of comparable dimension.
• Sand and other dense mineral materials often have particulate (intrinsic) solid density of about 2.7 g/cc and thus settle readily in water at a rate determined by their particle size and the viscosity of the water within which they are suspended.
• Biological origin solids may float in water, be neutrally buoyant or sink based on porosity of their structure and the degree of water saturation of these air-filled pores.
• Most wood materials and similarly porous biological materials may have a pressure dependent buoyancy in fluid. Increased pressure will progressively collapse included air space and shift these materials toward higher apparent densities as they approach their molecular density.
• the molecular density eliminates porosity effects.
• the molecular density of lignocellulosic materials is approximately 1.45 -1.55 g/cc dependent on the ratio of lignin to holocellulose. Thus, they may sink or float in an aqueous media depending on wetting and the volume of the included vapor space.
• Lignocellulosic material may alternatively be made to sink, or float based on pressure, duration of exposure to the liquid, and agitation. Lignocellulosic materials that have undergone reactive processing vary in their densities and porosity depending on the conditions of the reactive process.
• Lignocellulosic materials inevitably contain some fraction of sand, soil and other mineral material as incidental contamination. Some lignocellulosic materials such as algae gathered in coastal areas will often contain contaminants such as plastic and other foreign materials. In many cases, these inclusions do not change their fundamental character and suitability for subterranean injection. In fact, the inclusions may make it desirable to use the contaminated materials for subterranean injection rather than other potential uses such as surface soil enhancement.
• Improved slurry management tools can be important when seeking to inject slurries with larger particle sizes.
• Biological sourced materials have buoyant forces in water that may be either positive or negative and generally of a magnitude less than 25% as large as most mineral materials of comparable size. Often these buoyant forces are instead about +/- 0.2 g/cc or less depending on the relative quantity of included gas in the plant cell structure. This low buoyancy or sinking force enables slurries to be stable with particles that are dramatically larger.
• a slurry of lignocellulosic materials or biologically sourced material (collectively called lignocellulosic material but understood to also include 0-100% leaves, grass, or any other plant material, also called “biomass”) performs very differently in a water slurry in comparison to mineral slurries that commonly have intrinsic particle densities of approximately 2.7 g/cc. Wood chip slurries do not consolidate and solidify after settling in the way that mineral or rock/soil materials are observed to do. As an example, a mixture of minus 60 mesh sand with 20% clay soil from Marin County California after settling in a 200 ml glass jar cannot be completely resuspended with vigorous shaking unless the jar is inverted numerous times. The solid mixture settles with larger particles at the bottom and progressively finer material toward the upper portion of the settled mass.
• a slurry of fine particles (8-20 micron) magnetite is observed to form a solid-like plate and cannot be resuspended without recrushing and intense shearing. This behavior may be characterized as partial cementation.
• a mineral slurry is a minus 40 mesh clinoptilolite zeolite which also compacts after settling and partially cements. Hard physical scraping and agitation is enough to partially resuspend this material.
• additives which increase the viscosity must often be used.
• Common additives for hydraulic fracturing slurries used to deliver mineral proppants into petroleum well geological structures include polyacrylamide and polysaccharides such as guar gum.
• the particle size of the proppants must be small and the viscosity of the fluid sufficient to enable transport of the proppant horizontally into the fracture without proppant settling or screening out.
• Additives such as guar gum, xanthan gum or fine particle size clay minerals that increase the fluid viscosity may reduce the rate that gases can migrate through the fluid by reducing convective currents and by immobilizing gas bubbles so that they may not freely move in the fluid.
• decomposition by manipulating the pH of the wood chip environment or by adding inhibitors or biocides.
• Another mode to reduce decomposition would be to enrich the environment with the products of decomposition whether those products are organic acids, CO 2 , methane or other constituents.
• Some decomposition of wood chips is inevitable, and this may result in the presence of vapor bubbles in the subterranean space from accumulation of CO 2 and methane to accompany any residual nitrogen or other constituents of residual air. If decomposition reaction products are retained in the wood environment and not allowed to exit, the degradation rate must ultimately decline. Saturation with reaction products such as hydrogen sulfide gas in the case of near-anaerobic decomposition by sulfur utilizing microorganisms can ultimately stop degradation and poison microorganisms responsible for decay.
• reaction rate decline due to the buildup of reaction products is fermentation of sugar-containing fluids by yeast. Elevation of alcohol content in wine or beer will ultimately stop further biological decomposition of sugars to alcohol. Limiting availability of necessary reactants or nutrients and buildup of reaction products will both limit decomposition of lignocellulosic materials in a subterranean environment.
• the solubility of gases such as oxygen, carbon dioxide, and methane in the aqueous fluid surrounding submerged lignocellulosic particles is an important determinant of decomposition reaction rate.
• the quantity of reducible reactants such as oxygen for aerobic decomposition or sulfate, iron, manganese and nitrate ion for partially anoxic decomposition determines whether the whole lignocellulosic material can be decomposed and to a large extent how rapidly that decomposition will occur.
• lignin component of lignocellulosic materials does not degrade and the rate of decomposition of holocellulose which is the combination of the carbohydrates cellulose and hemicellulose that makes up cell walls in plant material is greatly reduced.
• Anoxic decomposition of carbohydrates involves methanogens consuming low molecular weight acidic molecules that are produced by other microbes.
• Anoxic decomposition produces a mixture of carbon dioxide and methane gas. If the reaction products are allowed to accumulate the reaction may be slowed or stopped, as mentioned earlier. In a subterranean environment the condition is effectively always anoxic below the water table or more than a meter underground if dense soils are present.
• Coastal or riparian areas subject to inundation are often anaerobic due to close proximity to the subterranean water table.
• Lignocellulosic materials pumped into a subterranean space of adequate depth or below the local water table are generally only subject to anaerobic decay assisted by methanogenic microbes once initial oxygen available in pore spaces are consumed. This anaerobic decay can only proceed to the extent that reaction products (wastes) can exit the subterranean space.
• Carbon dioxide and methane can migrate as gases through subterranean spaces. Gases such as oxygen, methane and carbon dioxide are significantly less soluble in water when sodium chloride and other salts are present. Because of this brackish water like sea water can slow delivery of reactants and removal of wastes for microbes decomposing lignocellulosic materials and thus increase the longevity of these materials in a subterranean space.
• the determination of a minimum depth of injection to ensure that wood chip materials will persist in the subterranean environment guides depth selection.
• the wood chips must be injected below the permanent anaerobic surface level or horizon of the soil.
• the elevation below ground surface of the transition to anaerobic and anoxic conditions will be different for each soil type and geographic region.
• the anaerobic depth varies with local water table depth, soil compaction and soil type.
• the anaerobic depth will be the lessor of: 1) The local water table as determined by soil cores or one skilled in local hydrology, 2) 1 meter below an area of soil with 20% or less void space as determined by soil cores, 3) The depth at which redox testing of soil chemistry performed using direct measurement by one skilled in the art shows a reducing condition, and 4) 5 m deep if the soil is fine grained such as silt or clay.
• soil with 20% void space or less is too compacted to allow air passage and so can stop air penetration to zones below.
• the presence of iron as Fe(II) as opposed to Fe(III) indicates a reducing soil environment and can signal to one skilled in the art that soil at and below that depth will be anaerobic.
• Direct measurement of the redox potential of the soil to indicate a reducing environment is an alternative method to signal an anoxic state because of anaerobic conditions or consumption of nearly all available oxygen by soil components.
• This anaerobic depth may be considered a minimum distance below ground level needed to avoid wood chip decomposition by aerobic microorganisms but soil stability for structures may require injection still deeper as further defined below.
• the desired level of wood chip compaction by the overburdening soil will establish a deeper minimum depth for material placement if structures are to be supported by the injected lignocellulosic material.
• the indicated injection depth would therefore need to be below the anaerobic transition horizon and also the minimum depth to achieve adequate compaction.
• the physical properties of fibric peat soil including its friction angle and shear strength increase with increasing consolidation pressure. This is true with other varieties of organic fibrous materials.
• the consolidation pressure would be about lOOkPa and the shear strength and friction angle of a compressible wood chip layer would often be on a par with or in excess of the shear strength and friction angle of clay or silt soils.
• clay soil types would be reinforced by a layer of wood chips.
• Biomass materials come in a very broad variety of characteristics and selection of a fibrous material with particle size in the range of 2 mm to 25mm would best serve this reinforcement character. Deeper injection than the minimum depth determined above is economically advantageous if fewer well bores are desired and a greater injection quantity per well is sought. Geotechnical engineers must be consulted to determine depth required beneath any structure with more than two stories. An injection depth of 5 m is a practical minimum and 100 meters is considered a practical maximum depth of injection.
• Saturated wood chips are highly porous and subject to significant compaction as the depth of the overburden increases and thus normal stress state of the woodchip soil increases. Fully saturated wood chips will undergo some additional compaction due to creep and thus the level of porosity and hydraulic conductivity will decline over time until a steady state is reached. The level of creep consolidation will increase with increasing depth due to higher loads from the overburdening soils.
• Lignocellulosic material when placed in water often has sequestered vapor (mostly air) held inside residual plant structure that can gradually escape. The process of this gas escaping from plant tissue may be through physical replacement by water. This pushes vapor bubbles out. Another form of escape is through dissolution in the fluid.
• Oxygen is approximately twice as soluble in water as is nitrogen and air contains only approximately 21% oxygen gas but 78% nitrogen. Available oxygen will be consumed by aerobic lignocellulosic decay organisms. It is thus expected that the vapor bubbles inside the wood structure will more rapidly be depleted of oxygen than they are depleted of nitrogen.
• lignocellulosic particles will resist decomposition longer and thus it is desirable to pump larger Lignocellulosic particles into subterranean spaces.
• Green waste and wood chipping operations create a range of particle sizes.
• Uniformly fine lignocellulosic materials such as sawdust of perhaps 2 mm length by 1 mm width can be quite easy to suspend in an aqueous slurry.
• Sawdust requires more energy to produce and thus once limited supplies of “waste” sawdust materials are exhausted, sawdust would be a much more expensive form of lignocellulosic materials for slurries than coarse chips.
• Sawdust sized material also has a lower bulk density than coarser materials which in turn means a given mass of sawdust will require more water to slurry than a comparable mass of coarser lignocellulosic material.
• Sawdust is also more compressible than more coarsely sized lignocellulosic materials such as bulk wood chips produced by tree trimming services.
• a 100 mm thick aperture filled with a sawdust slurry might thus need to lose much water during the relaxation stage mentioned in the sequence of steps for injection to place materials in a subterranean aperture.
• This relaxation step allows the injected solids to begin to support the full weight of the overburdening earth.
• the quantity of water lost from the aperture during relaxation by a wood chip slurry with average particle size of 20 mm might be half that lost in a similar relaxation conducted on a sawdust slurry of average particle size 2 mm if both slurries were formed with a similar dry volume of sawdust and woodchips.
• the ability to slurry and inject large particles of lignocellulosic materials has the advantages of significantly lower size-reduction costs, slower degradation in a subterranean environment, lower water required to form slurries, and consequently lower water loss requirement during relaxation of the filled subterranean aperture space.
• the near-neutral buoyancy of lignocellulosic materials is advantageous in this regard. It is expected that particles up to or indeed in excess of 25 mm in any dimension may be pumpable with appropriate pump systems such as progressive cavity or piston pumps that include large check valves. Well piping diameter must be at least four times the diameter of the largest particles.
• Subterranean apertures may be of any orientation, vertical, inclined, horizontal or any complex intermediate shape. Horizontal apertures when filled serve most effectively to elevate the surface of the ground. Slurry flow in a horizontal space poses important challenges. As the fluid flows in a horizontal direction, solids denser than the fluid (which usually has a density close to that of water) will sink until they reach the floor of the aperture. To reduce the rate at which solids settle the viscosity of the fluid may be increased or the size of the solids may be reduced. As the viscosity of the suspending fluid increases, the requisite difference in pressure between the starting point of the fluid and its ultimate endpoint along a horizontal plane increases. Pumping more viscous fluids requires more energy than less viscous fluids over a similar path. A more viscous slurry will prevent solids from settling and also from excessive contact friction with edges of solids such as encountered in sharp pipe bends or tight underground spaces.
• Additives such as guar or xanthan gum or mixtures of the two as well as fine clay materials like sodium bentonite clay can increase the viscosity of fluid and help avoid screen outs or immobilization of solids at tight transitions or bends.
• a mineral solid slurry must be maintained at an adequate agitation velocity or the solids will settle unless the solids content is high enough to result in a thick paste or mud.
• the thin slurry will fill the subterranean aperture with a large volume of water which will still contain fine clay particles and be quite dirty in appearance and potentially able to pollute surface water. Though the thin slurry is quite pumpable it will not carry adequate solids to prop up the terrain and the extra water will require a long period to escape the aperture. Relaxing the aperture so that the solids are bearing the weight of the overburden may take a long time. Reuse of a given aperture space may be challenging because the fine clay particle may clog the pores of the space around the solids as the additional water attempts to exit during relaxation. Therefore, relaxation may take progressively longer and eventually the aperture may not function for additional injections.
• the thick mud will result in a high pressure differential between the injection point and the peripheral extent of the aperture.
• This pressure differential results from the Bingham plastic rheological nature of the mud and may distort the shape of the aperture.
• the distorted shape may result in the central or material entry portion of the aperture filling with a disproportionate quantity of the solids while the periphery has much less material.
• a thick mud is also potentially a major contamination issue for the surface area around the well in the inevitable event of a spill.
• Lignocellulosic slurries by comparison are quite easy to sort, manage and use in a subterranean injection operation. They may be preselected to include only particles of a certain size range with trommels or vibratory screeners without need for drying or fines management systems. Lignocellulosic materials are not generally considered problematic or contamination when spills occur on the surface. They may often be removed with rakes, brooms, leaf blowers, or vacuums. They may also be intentionally placed on the surface to act as a weed controlling mulch or landscaping material. When structures are elevated, the surface placement of residual lignocellulosic mulches, for example wood and bark mixes, creates a particularly beneficial habitat for methanotrophic bacteria.
• the placement of mulch on the surface of an elevated area may be considered an important part of the process of ensuring that little or no methane escapes to the atmosphere. It is during the first few years after placement of the subterranean fill when whatever anaerobic evolution of methane from the subterranean space is highest. Methane produced by anaerobic organisms is generally understood to peak shortly after placement and decay thereafter in the ensuing few years.
• the water used to produce a lignocellulosic slurry does not generally become contaminated as water that is used to make a mud or mineral slurry is observed to become filled with fine muddy clay particles. If freshwater is used for slurry formation, there is generally no contamination issue on the surface in the case of slurry water spills and therefore no reason to expend effort avoiding surface water spills. Mineral slurry systems would require surface protection systems to trap the water and recover and potentially haul it away after use. This activity adds substantially to the cost of using the mineral slurry for terrain elevation. No such cost is associated with the use of a lignocellulosic slurry except perhaps in unusual cases.
• Figure I illustrates a method 10 of Protecting Structures with Subterranean Injection of Lignocellulosic Solids.
• FIG. 1 illustrates a method for preparing lignocellulosic materials. As illustrated, the process starts at step 200 and proceeds to step 210, where the materials are pre-selected to include the variety or varieties of lignocellulosic materials that are most desirable and those other constituents of the slurry to be formed subsequently.
• T hen at step 220, the slurry is formed, an optional post-selection process may be utilized and the slurry is brought to the desired solids level.
• step 230 the slurry is pressurized.
• the slurry components are methodically placed in a subterranean space using a sequence of steps which best enables construction of the subterranean solids mass that is most suitable.
• the pre-selection process at step 220 is guided by knowledge of how different materials contribute to the slurry formation and subsequent solids placement using the slurry.
• Lignocellulosic materials may be selected based on species of plant material, size or shape of plant material, porosity of plant material, degree of water saturation, or degree of decomposition. Additional slurry components such as finely divided mineral solids, chemicals, binding agents and viscosity adjustment agents such as guar gum, cross-linkers and breakers, which are used in hydraulic fracturing, may also be beneficial in the slurry or may be desired in the ultimate solid mass to be placed in a subterranean location.
• Peat soils are notoriously poor at supporting structures. Peat is a decomposed form of lignocellulosic material, Fibric peat soils are less decomposed and contain fibers that serve to enhance their shear strength. The normal force applied to the sample compacts the fibric peat and its shear strength as measured by the direct shear test also rises. At or near the surface where there is little compaction pressure the shear strength of peat soils is very low and so these soils are problematic for structure foundations. However, at depths of 5 meters the compaction pressure arising from support of the overburdening soil would make the soil shear strength adequate for fibric peats in some circumstances. Less aged lignocellulosic materials would be expected to follow a similar pattern. More fibrous materials may be desirable at shallow depths and less fibrous materials may be selected for deeper injections.
• the aspect ratio or length to width ratio for fibrous lignocellulosic materials significantly affects their strength. Short fibers do not impart as much strength as do long fibers in wood fiberboard products. The strength of wood also varies dramatically with and against the grain of the wood.
• lignin The portion of the holocellulose component of lignocellulose may eventually decompose in an anaerobic environment but lignin is generally persistent. Most lignocellulosic biomass will remain even after many thousands of years. The ratio of lignin to holocellulose varies by type of lignocellulosic material as it does with algae and phytoplankton. Most algae for example have little to no lignin and some may have no cellulose.
• the slow, partial anaerobic decomposition of lignocellulosics will produce methane and carbon dioxide.
• Most soils contain plant roots that decompose anaerobically and the methane produced feeds methanotrophic organisms in the upper, more oxygenated layer of the soil.
• Most of the soil produced methane from subterranean plant decomposition does not enter the atmosphere but is instead consumed by methanotrophic microbes before this occurs. Underneath some structures there would be little to no methanotrophic activity and so lower methane emissions are desirable underneath structures in comparison to under adjacent open or plant covered terrain.
• the presently disclosed systems and methods exploit the unique capabilities of lignocellulosic material subterranean injection to protect structures can be most efficacious when used at the very lowest cost because many billions of cubic meters of injection solids must be placed to protect many millions of structures. Doubtless lignocellulosic materials will be used with chemical viscosity control as important embodiments but it is the enablement of the simplest and lowest cost slurries which in the end will be a primary contribution of the presently disclosed systems and methods.
• the slurry formation apparatus blends the lignocellulosic materials which may have minor contaminants as mentioned herein with the water which may optionally be brackish and any desired additives such as viscosity control agents or others mentioned earlier to form a slurry with a controlled solids content for presentation to a pump.
• Option A is a batch system in which fixed amounts or solids and the liquid are blended with an agitator, ribbon mixer or by tumbling as in a batch cement mixer. The batch is pumped into the aperture, the valve is closed and a new batch is prepared.
• Slurry formation Option B illustrates the use of a novel device called a centrifugal concentrator for floats.
• the concentrator allows delivery to the injection pump of lignocellulosic materials that float in water (at surface pressure conditions) and enables control over the slurry concentration.
• the concentrator creates a spinning mass of wet lignocellulosic material that remains in place above the pump suction.
• the raw solids and any additives are delivered to a fluid level-controlled tank.
• a self-priming slurry pump as illustrated in the figure or (other pump variety) then delivers wetted materials that are entrained in the water to the concentrator positioned above the injection pump suction and flowing through a preferably pneumatic pinch valve.
• Slurry formation Option C includes all the equipment of Option B with the addition of a hydrocyclone on the tangential return line from the floats concentrator.
• This hydrocyclone removes dense solids that sink in the aqueous fluid.
• the sink materials will typically contain small diameter particles and particles with high aspect ratio. Sand, gravel and coarse heavies will also deliver at this location. Smaller diameter lignocellulosic materials will typically saturate with water more quickly and their density will rise.
• These sinking particles may be delivered to a second pump, for example a progressive cavity pump.
• Both a floats and a sinks stream can be delivered simultaneously to different well locations in dual product mode. These locations may optionally feed different apertures or may feed an expanded aperture in different locations as explained later.
• the dual outlet configuration can be used in conjunction with a grinding circuit.
• the floats product (coarse) that delivers to the apex of the first centrifugal concentrator can be dewatered and returned to a grinder for further size reduction.
• the denser and more fine sinks product may be delivered in a concentrated state to a slurry pump for injection. This creates a safer and less energy intensive way to produce fine particles for a slurry. It reduces overgrinding and dust generation as well as energy use while still creating a reliable fine particle concentrated slurry at the hydrocyclone discharge.
• the cone angle of the hydrocyclone may be made larger, for example from an industry standard 20 degree included angle to a higher included angle such as 30-90 degrees. The larger this angle the larger will become a rotating bed of dense material awaiting discharge from the apex.
• a level sensor in the small feed cone above the dense discharge pump may be used as a control signal to adjust the diameter of the pneumatic apex.
• a low pump feed level would result in a signal to increase the apex diameter by reducing the air pressure in the pneumatic apex of the hydrocyclone.
• As the discharge volume decreases, more rotating material in the bed will instead be re-entrained by the flow of fluid exiting the vortex of the hydrocyclone with residual float solids in the feed and will report back to the initial slurry tank.
• a unique character of this slurry formation option operating in dual product mode is that the relative amount of production of both the floating (coarse) material and the denser sinking material will vary to a significant extent with the relative rate of their withdrawal by their respective pumps. Therefore, if more dense material is required the dense removal pump rate may be increased and this will have the effect of raising the percentage of the feed that reports to dense material because the size of the rotating bed of material is smaller and more solids will join the bed at the margin of material close to the sink/float cut point of the feed.
• apex or vortex diameter in the floats selection concentrator and the cone angle, vortex finder diameter, and apex diameter of the dense selection hydrocyclone enables controlled partition of many varieties of lignocellulosic feeds.
• Each variety of Lignocellulosic material may be partitioned into a more buoyant light (and often coarse) fraction and a more dense heavy (and often fine) fraction over a wide range of ratios of floats/heavy flow splits.
• the floats concentrator can be bypassed and the dilute slurry pump made to feed only the hydrocyclone as shown in slurry formation apparatus option D. If the hydrocyclone is used as in this option a sinking particle stream alone is available and any floats will be returned to the dilute slurry tank. This optional configuration is useful when only fully saturated fine products that sink are desired in the slurry placement and this mode is a single product mode.
• the level of concentration of the slurry depends on the variety of the pump to be used in addition to the flow rate required to open the subterranean aperture and the requisite pressure.
• a centrifugal slurry pump is an attractive option if injection pressures measured at the surface are 500 kpa or lower.
• Centrifugal pumps will have significant pressure limitations when high pressures are required to create fractures but the pressure required to fill an open aperture is often significantly lower than that required to create a fracture.
• Centrifugal pumps work well in situations where the formation aperture to be filled with solids is quite porous and at a depth shallower than 23 m. Centrifugal pumps work better on lower solid volume fraction and so more water per given volume of solids placed in the aperture must escape the structure to allow the solids to carry the overburden.
• a head box can also be used in unusual situations where a 20-50 m high tower or hillside is immediately adjacent to the injection location.
• the water and the solids are combined in a box opening at the top of a vertical pipe. This avoids the problem of solids passing through a mechanical pump but is only useful when a large supply of water and solids are available at an altitude significantly above the injection altitude.
• a head box is not useful to supply the usually high pressures of fracture formation as mentioned above for centrifugal pumps
• a positive displacement pump enables higher injection depths with higher slurry solids loadings.
• Piston pumps such as those used to pump concrete and stucco are quite suitable for injection with solids up to perhaps 25 mm in size for very large pumps but more frequently around 15 mm.
• Progressive cavity pumps are a very good choice if solids are perhaps up to around 10 mm.
• Progressive cavity pumps can be reversed to pull fluid out of a well while still providing backpressure to the fluid. In this way, they can be used to meter flow out of a pressurized aperture. Still other pumps available to those skilled in the art may prove useful for this purpose.
• a pneumatically compressed bladder subsequent to the pump may be a particularly effective check valve variety for trouble-free passage of large solid particles.
• the pneumatic bladder may be inflated after the pump positive stroke to reseal the subterranean pipe from backflow and the bladder may be deflated to enable the passage of a subsequent charge of slurried solids. This may be carefully and automatically timed for best effect.
• Figure 4 is a single well, single material placement.
• Figure 4 also shows aperture enlargement with fluid pumping to open the aperture size adequately to avoid problems when a primary lignocellulosic solids injection particle size is larger than the initial dimension of the aperture height which may create a solids flow problem.
• This is the simplest placement strategy and may be used to initiate subterranean lignocellulosic injection operations at a site where plans include multiple well locations and multiple materials for placement.
• Figure 4 also illustrates the process of aperture relaxation with leak off of fluid into the subterranean structure.
• the single well injection strategy typically results in a subterranean orientation of fill materials that is roughly symmetrical about the injection well location as illustrated. Subterranean structures and conditions may substantially alter the material placement away from this generalized symmetrical pattern in any given specific well location.
• the first important piece of information that must be understood about any given location is the level of porosity of the geotechnical structure at the injection site.
• the structure will be so porous that the injection pressure will not rise to indicate that a fracture is forming because the permeability of the injection zone exceeds the capacity of the pumping system at the pressure requirement associated with that depth.
• Viscosifying agents such as clay are added in Germanovich and Murdoch but an excellent option is fine particle size lignocellulosic materials such as those which may be continuously produced by a dense solids removal hydrocyclone such as that described in slurry formation Option C or D. These fine materials can beneficially reduce water leak-off rates by plugging the pores of the subterranean structure particularly during fluid leak off when the aperture grows quite large.
• lignocellulosic solids may be chosen such as grass and leaves or algae to more efficiently block water escape from very permeable structures. This type of consideration helps inform the material pre-selection step of the slurry placement sequence.
• the Option B placement strategy illustrated in Figure 5 is directional bulk flow with backpressure.
• an array of wells may be used to create a large horizontal aperture under an area where adjacent wells are in hydraulic communication with the same subterranean space. In this way the overburdening earth can rise and fall as a slab in the ideal case.
• Slurry solids in Germanovich and Murdoch mineral solids are described
• the substitution of porous lignocellulosic slurry particles enables the ensuing invention of a different way to utilize the array of wells.
• the adjacent well may be used to actively draw the slurry water out of the formation.
• the lignocellulosic solids of most types will settle or float relatively quickly when flow velocity slows as they move away from the injection well and into the aperture. As they do so a nearly clear liquid space will open toward the center of the flow depth because material will move toward the roof or the floor of the aperture space but away from the middle.
• a mixed float and sink material will yield an open space in the center between a raft and a pad.
• a uniformly floating material will result in an open space below the raft.
• a uniformly sinking injection solid will result in a space above the pad. The floating particles will form more dense entangled rafts and the sinking particles will form more dense entangled pads.
• the inward most particles will be those that are the most neutrally buoyant and therefore the most easy to dislodge and move horizontally. If the rafts or pads are thickened in areas around the aperture, representing uneven solids fill, the free channel space in these thickened areas will be diminished and the gap will be tighter.
• Germanoch and Murdoch propose, with lignocellulosic particles the excess water in the aperture formation can be directly pumped out of the adjacent well by reversing the flow of the progressive cavity screw pumps or switching the check valve directions on piston pumps.
• This reversal of the pump direction provides the opportunity to maintain the elevated pressure in the formation using feedback control of the pump flow rates.
• the exit pump flow rate may be increased to bring the pressure back into the control range.
• the solids-feed well pressure transducer provides a signal that increases the slurry feed rate as the pressure falls. This enables a bulk flow of slurry to move from the first well to the adjacent well sweeping solids along with it. This increases the control over where the solids move in the formation and how far they may be made to travel.
• the bulk flow of fluid may be thought of as a fluid rake that both makes more uniform the distribution of solids which have accumulated in thicker rafts or pads and carries solids farther.
• the water may be removed from the aperture as the pressure of the formation is rapidly released by slowly drawing water up each well until the pressure falls satisfactorily at each well or excessive solids appear in the fluid at that well. This accelerates the relaxation process for the system of wells.
• the well can be near the edge of a one-sided filling aperture rather than generally in the middle of the solid fill of an aperture. This improves the ability to demarcate edges of elevated areas more precisely. Solids are swept toward one side of the well by adjacent wells which pull fluid and so direct the flow of placed solids. This is useful for example when a highway is to be elevated but the surrounding terrain is not. It is also helpful to shrink the area of uplift produced on a land parcel and avoid the tilting of adjacent structures which are not to be elevated. Directional bulk flow also enables better economy with injection solids consumption.
• Option C Directional bulk flow with backpressure and material interchange.
• This option has the same capabilities as Option B with the enhancement that it can inject either a floats- concentrated product or a sinks-concentrated product because a preselection process has created these two available lignocellulosic feeds.
• Option C produces a concentrated dense (sinks) product and a concentrated buoyant (floats) product, as described earlier. If the initial well, for purposes of illustration, injects floats, the adjacent wells can inject sinks. Such a scenario is illustrated in Figure 6. Floats contain predominantly solids that will form a floating raft in the expanded aperture space and importantly leave a relatively clear path for water to flow toward the bottom of the aperture space.
• the adjacent wells can inject sinks which have predominantly solids which will form a sinking pad.
• the alternation of these two varieties of well solids creates the opportunity to more rapidly and efficiently fill the whole height of the aperture with first one material and then finish off the fill process with the alternative missing complimentary material.
• the fill process can efficiently feather the solids together enabling more rapid fill while still enabling the alternating sweep process to level up the solids placement.
• the subterranean injection of lignocellulosic material has substantial novel benefits including: Improvement in the seismic performance of elevated structures, Very long term sequestration of atmospheric carbon which has been incorporated into plant solids, Elimination of fire and pollution risk associated with combustion of plant lignocellulosic material, and Potential Seismic Benefits.
• Soil liquefaction in earthquakes results when soils lose strength and stiffness as a result of applied stress. It is mostly observed in water-saturated, loose, sandy soils. The applied stress causes particles of soil to lose contact with one another and the soil water pore pressure to rise. Mechanisms for desaturating soils are described (Cheng Shi et al 2019 Soil Desaturation Methods for the Improvement of Liquefiable Ground IOP Conf. Ser.: Mater. Sci. Eng. 562 012015 and Microbe-based Soil Improvement Method JP2012092648 A) which discuss methods for introducing gas bubbles in the soil. The gas bubbles can compress during a seismic event as water pore pressure begins to rise and significantly enhance soil resistance to liquefaction.
• Gas bubbles introduced into the soil structure as described above whether by their presence in the interstices of wood chips or other biomass pores or through the slow decomposition of the wood chips to form CO 2 or methane will also compress in response to rising pore pressure in surrounding saturated soil. This is expected to protect the soil from liquefaction to some extent.
• wood chips are compressible and can rebound if stress is reduced. If a time variable and high level of stress is applied normal to planar mass of wood chips the compression of the chips would be expected to alter the maximum stress level transmitted to the soil or rock on the opposite side. If the stress is applied at a frequency, the presence of the springy wood chip plane might be expected to alter the frequency of the stress transmitted across the plane under many circumstances.
• a saturated porous body of wood chips enables movement of water in response to variations in soil stress.
• the presence of vapor space within the wood chips can enable small local movement of water to compress the trapped vapor instead of moving the stress freely through the soil or rock structure.
• the wood chip body can allow small movement of water toward lower resistance regions for example upward movement of water in a vertically oriented plane of wood chips. This enablement of movement introduces a level of viscous dissipation to the soil or rock.
• the fundamental mechanical character of the ground structure beneath a construction can be altered with these characteristics in mind.
• the strategic application of wood chip layers in different orientations such as vertical, horizontal, inclined, cupped or bent can represent one variable to be engineered.
• the stacking of these planes or shapes in any given dimension can create intricate distributed reinforcement.
• the porous layer of wood chips may be used to provide a protective channel through which water is directed around, underneath or away from an area.
• the thickness of the layer or in various parts of a given layer and the variety of biomass within regions will materially alter the stress and strain behavior and porosity of a body of wood chips. This may be thought of as adjusting the spring constant of the ground for various applications of stress.
• the center of a layer may be of one character while the periphery is of a different character.
• the viscous dissipation character and the dimension within which the dissipation is most pronounced may also be thoughtfully adjusted.
• the quantity of sequestered vapor which plays an important role in enabling dissipative movement of water and of the ground may be adjusted by selecting different types of wood chips (biomass) whether by selecting those which possess more isolated vapor or those types which decompose to a saturation level of vapor and thus renew any vapor that may be lost with time.
• a very small addition with time of additional nutrients, oxygen or microbes may also be used to tune vapor inclusion or regeneration.
• the ground structure can thus be tuned in a variety of ways to protect structures from frequencies of ground movement to which those structures are most vulnerable.
• the frequency, direction and intensity of stresses applied by seismic events to structures may in these ways be engineered.
• the ground may be designed to be most protective of planned or existing structures.
• a building or structure may thus be tuned in conjunction with its ground structure to provide the most cost-effective protection from seismic ground movement or liquefaction or from damage caused by the movement of water within the ground such as that which can cause sinkholes.
• Controlling the extraction of reaction products as mentioned above can be used as a mechanism to regulate decomposition rate and the formation of new gas bubbles.
• Controlling the extraction of reaction products as mentioned above can be used as a mechanism to regulate decomposition rate and the formation of new gas bubbles.
• In addition to adding oxygen, or required nutrients such as fixed nitrogen or phosphorus may be expected to maintain desirable gas bubbles in a subterranean wood chip area to enable continued protection from ground movement or rapid increase in pore water pressure.
• areas may be simultaneously protected from rising sea level or subsidence of land below sea, lake or river levels as well as from ground movement events and liquefaction of soil. Elevation of areas protects from rising relative water levels while altering soil mechanical nature gives additional protection from ground movement such as earthquakes.
• An island resort, illustrated in Figure 7 is facing inundation due to sea level rise and there is no available mineral fill material locally.
• a large nearby lagoon hosts extensive algal growth due to local use of fertilizers to grow food and coconuts.
• the lagoon also serves as a catchment for some floating plastic debris which is unsightly.
• the decaying algae washes up daily contaminated with fine floating plastic in large moist piles and creates noxious odors as it dries and decays in the sun.
• the eight wells were drilled and a 100 mm well pipe was cemented and sealed in place with a capillary pressure transducer placed at the base of each pipe to allow accurate measurement of aperture pressure.
• a level controlled tank on one edge of the yard supplied seawater for well slurry preparation and injection.
• a batch slurry preparation area for the partially dehydrated algae which was collected from a beach on the lagoon at a distance of 150 meters from the resort was used for the 20 meter injections.
• a common piping system for the four algae wells was buried in a shallow trench running to each well.
• a second coconut and cocopalm grinding area 150 meters from the resort was utilized to supply the four shallow wells close to the resort building.
• a manual well selection system for each well type could supply pump pressure to any given well while sealing the three others.
• a 20 MPa high pressure jet pump was used with a rotatable pressure pipe to score the lithified reef stone at the base of each 20 m well in a 360° arc to a radius of 50 cm to initiate the aperture.
• the jet pipe with the nozzle removed was then temporarily placed with a removable pressure packer at the base of the hole to protect the well piping from high pressure.
• the base of the well was pressurized with the jet pump using a pressure relief at a maximum pressure of 3 MPa.
• the lithified reef stone began to crack as the pressure was slowly elevated and as the crack opened the aperture formed at the base of each well.
• the jet pump hardware and packer were removed.
• a progressive cavity pump delivered the prepared slurry to the wells at about a 12% solids content by volume.
• Monthly injection was done because the particle size of the material required larger spaces for penetration so lifts of less than 14 mm did not yield good solids flow. Elevation was done as required to maintain the building level with the elevating yard and avoid unacceptable tilting or differential elevation that might damage the building.
• the slurry piping was rinsed after each injection cycle for both wells.
• a San Francisco Bay area highway was built on ground constructed after the 1906 earthquake by filling in a portion of the bay. It crosses a portion of a meandering old stream bed that ran through a salt march into the bay.
• the highway is particularly subject to damage from seismic soil liquefaction and lateral spreading. This area has undergone extensive subsidence and with rising sea level faces inundation routinely several times a year during king tide or storm events. It was decided to elevate the highway.
• the approximately one hectare, 30 x 300 m rectangular space beneath the roadway was selected for elevation.
• the starting elevation of the highway was 0.3 m with a uniform level grade.
• the geotechnical profile of the area includes a relatively uniform dredged fill to a depth of 5 meters over a sandy consolidated bay mud profile that extended to 30 meters, followed by a cemented mudstone layer to a depth of 50 meters Based on this information, elevation apertures at a depth of 30 meters were selected to intersect with the mudstone interface.
• the fill strategy would require relatively frequent injections of high uplift thickness.
• a grid of 30 wells on four lines spaced 10 meters apart on a 5 meter staggered grid was selected.
• a total of 120 wells would be required.
• the close spacing of the wells was necessary to ensure that by pressurizing the wells the roadway could be lifted as a slab to avoid local bending that might fail the paving surface.
• the well layout along the roadway and example slurry injection bulk flow sequence are shown in Figure 8.
• the first pipe manifolded the odd numbered wells on the southern shoulder vertical wells.
• the third pipe manifolded the odd numbered inclined wells under the southern lane.
• the sixth pipe manifolded the even numbered inclined wells under the northern lane.
• the seventh pipe manifolded the odd vertical wells on the northern shoulder.
• the eighth pipe manifolded the even vertical wells on the northern shoulder.
• a progressive cavity pump was installed on each of the eight lines that could run in either forward direction or reverse direction.
• Each well had a separately actuated pneumatic valve.
• These wells were also joined with a piping system run in a trench.
• a sophisticated automatic well selection system could supply pump pressure to any given well while sealing all the others wells along that particular manifold line. All solids were supplied from either a Northeast or Southeast slurry forming station.
• the fir bark had few binding problems in the piping and so the less saturated float product worked quite well despite incomplete saturation with water.
• the system operated using baywater.
• the dilute slurry pump drove the centrifugal floats concentrator and the hydrocyclone.
• a progressive cavity pump delivered the prepared slurry to the wells at about a 20% solids content by volume. Injections were done every week. During each injection cycle the floats material was first injected under the lanes while the 3 adjacent wells westward of that well were used to sequentially withdraw water to sweep the fill material first toward the Southwest, then toward the West, then toward the Northwest. After this the sinks material was injected in the shoulder well and the two adjacent westward wells were sequentially used to withdraw fluid. In this way the heavy material was allowed to flow in the gaps left after the floats product was injected under the lanes. This accelerated the process of filling the aperture and increased the penetration of the material by virtue of the bulk flow. The time required to relax the wells was also reduced.
• the roadway elevation project provided a degree of base isolation to the highway which reduced the transmission of seismic energy to the highway.
• the increased vapor bubbles created by the slow decomposition of the fir bark migrated upward through the shallow dredge fill profile which was most vulnerable to liquefaction as well as upward through the sandy bay mud.
• the presence of these bubbles reduced the tendency for soil pore pressure to rise with seismic activity and so reduced the likelihood of liquefaction of the soil.
• a mechanism for providing variable back-pressure to the subterranean aperture is provided.
• a hydrocyclone style separator or other similar centrifugal solids separation device on the flow of liquid exiting the underground space may be utilized.
• a hydrocyclone style separator will provide a variable back pressure that increases with liquid flow rate.
• the diameter of the hydrocyclonic separator and its inlet and outlet sizes may be altered to adjust the amount of pressure required to drive a given flow through the unit. In this way, a level of back-pressure may be used that is adequate to maintain the size of the subterranean aperture.
• the formula for the requisite volume of flow that is delivered to the subterranean aperture includes make-up water.
• This make-up water may be utilized to account for a volume of fluid that may be lost from the subterranean aperture to the surrounding soil structure.
• the following formula may be satisfied.
• the volume of the aperture must increase and at the end of an injection process, the aperture’s volume will decline as the additional liquid added escapes.
• the deposited solids are compressed by the mass of the overburden of soil above. While solids are being added to the aperture, the added solids will displace liquid that was added to increase the size of the aperture.
• the anionic polyacrylate solution reduced the rate of the clay particle collapse, requiring more than twice the time of the tap water.
• the sodium bentonite slurry did not collapse the clay but instead partially hydrated and softened it over a much longer period of time. After agitating the anionic polyacrylate solution with the clay particle the clay particle broke apart completely and was more strongly suspended in the liquid than were clay and water alone.
• Injection of a gas into the subterranean aperture is an excellent way to protect the roof from direct exposure to water that can cause clay to lose cohesion and fall from the roof.
• the injection of a gas stream may be done by blending with the entering liquid steam or as a separate stream into the aperture space. This gas may then collect at the upper surface and partially shield the roof from exposure to penetrating water. It is desirable to limit oxygen exposure over the long term to the chips which can accelerate degradation. If the gas stream is enriched in nitrogen and thus depleted of oxygen this is advantageous. Air itself is a nitrogen-enriched gas and the roughly 21% oxygen will rapidly be depleted if no new oxygen is supplied once the aperture is sealed. The active compression of the aperture by anchor devices may serve to eliminate much of this gas before aperture sealing.
• a first requirement to be tested is whether a given thickening system can be pumped.
• the novel active deposition process here described as directional bulk flow introduces a second requirement that the lignocellulosic solids will accumulate in the aperture.
• the settling time for the solids must therefore be higher than the time required to transport the fluid with the solids from the aperture entry to the aperture fluid removal location.
• Pulp fiber that has been subjected to a lignin removal operation often for incorporation into paper is an attractive thickening agent. It is widely available at low cost and may be sourced in the form of recycled paper or cardboard and repulped in wet-blending devices which are known to those skilled in the art.
• Our laboratory testing of pulp fibers suspended by blending mixed recycled office paper in a Vitamin 5000 blender at various concentration in 400 ml beakers with a Brookfield viscometer using a #2 RVT spindle at 10 and 100 rpm are given in Table 1 below where 2% pulp concentrations begin to exceed acceptable viscosity of around 3000 cp at low shear rates.
• Microcrystalline cellulose is quite expensive to purchase and so coarser pulp fibers such as are used in conventional paper may be more cost-effective.
• Pulp fiber that has been reduced in lignin content has the advantageous property of shear thinning for easier pumping but also gives a minimum yield stress to enable solids settling.
• a wood chip of insufficient size or buoyancy differential from the fluid will thus not settle if the fluid has a high yield stress to enable particle movement.
• This creates the possibility of a non-settling slurry which greatly facilitates free slurry flow avoiding clogs and screen-outs which block flow. This is particularly advantageous when injection without fluid removal from an aperture is desired because bulk slurry flow to an aperture discharge location places a limit on the minimum settling rate to avoid lignocellulosic material exiting the aperture.
• Table 1 illustrates that pulp fiber slurries have different viscosities at different shear rates.
• the shear rate in a centrifugal separation device is high and so the lower viscosity of pulp at 100 rpm shear rates is more relevant.
• When a fluid is pumped into an aperture the higher viscosity at 10 rpm is more comparable. This creates a surprising advantage that can be exploited because pulp fibers when used as a thickener can be subsequently removed by a centrifugal separator from the fluid for potential reuse. The pulp solids settle more quickly with the lower apparent viscosity in the higher shear environment.
• a pulp-containing viscous slurry can be injected at one location of the aperture to expand and shape the aperture and stabilize the aperture roof with clays, polyacrylate or polyacrylamide sealants. This same slurry can be removed at a different or multiple different locations once the shape of the aperture is perfected.
• the pulp thickeners can be passed through a hydrocyclone or other centrifugal separator while back-pressure is maintained to ensure the aperture stays open.
• the fluid can be returned to the aperture with a different viscosity that is lower once some of the pulp has been removed by the separator.
• This fluid then has a lower viscosity that is designed to allow deposition and settling of lignocellulosic materials that are now introduced and suspended in the slurry.
• Polysaccharide thickeners can’t be easily removed and must be either diluted, chemically broken apart or discarded. A more viscous fluid is desirable during the aperture formation and expansion process but a less viscous fluid is needed later to enable lignocellulosic solids deposition in the aperture so that settling rates are not too high.
• cellulose pulp thickener with fluid extraction after aperture shaping while aperture shape is maintained by back-pressure enables both solids and liquids to be separated and recovered independently for reuse.
• the aperture forming fluid viscosity may be high while the same fluid may be used with a lower viscosity later for deposition of solids.
• Polysaccharide gums such as guar or xanthan gums are known to increase the viscosity of fluids but they are costly. It was discovered that by using a combination of 1% pulp fibers and 1% guar polysaccharide gum, a synergistic benefit appeared enabling stable suspension of a lignocellulosic material more than 50% of which did not pass a 6 mm screen.
• a centrifugal separation device such as a hydrocyclone accelerates deposition of coarse solids including sand and coarse lignocellulosic materials.
• Bentonite clay thickeners are shear thinning and thus their apparent viscosity declines when they pass through a high shear environment inside a hydrocyclone.
• a hydrocyclone may be used to alert operators that one of several conditions will require adjustment: the deposition fluid viscosity may require reduction to expedite lignocellulosic settling rates, the size or degree of water saturation of the incoming prepared lignocellulosic materials may require increase, or alternatively additional exit wells locations might be simultaneously used so as to increase the areal fraction of the aperture through which liquid passes. Increasing the number of exit wells used increases the apparent area of the aperture and thus increases residence time for settling of particles.
• An additional alternative to reduce the population of coarse lignocellulosic particles in the exiting flow is to reduce the total fluid entry and exit flow rates.
• the location of the active aperture determines the area where solids deposition underground will occur.
• the balance of forces in the subsoil space determines the location where the aperture will form or persist. These forces are partially determined by the initial stress state of the soil. In one arrangement, these forces may be adjusted by altering the stress state of the soil.
• a crack can form when the forces that are normal to the dimension of the crack holding the soil together reach zero at the edge as the crack propagates.
• Aperture geometry may be actively altered by a system that changes the force magnitude or direction with time in different locations.
• the viscous fluid can optionally contain some combination of nearly 50% by mass fine mineral material whether from recycle of fluid exiting the aperture or from addition of up to 12% bentonite clay.
• the fluid may also contain from 40-1000 ppm anionic polyacrylate, 0.1-2% cellulose pulp subjected to lignin removal operation, or polysaccharide gums at a concentration of 0-1% for example guar or xanthan gum.
• the use of any of these viscosifying materials solely or in combination can achieve the goal of enabling the injected material to act as a fluid jack to increase the local height of the aperture to accommodate lignocellulosic solid particles wherein more than 50% by mass of the material does not pass a 5 mm square opening screen.
• weights placed in specific locations on the top layer of soil affect aperture shape.
• weights can be placed around an injection in a ring pattern. The force exerted on top of the soil from these weights increases the pressure necessary to inject material through the volume of soil lying under the ring pattern at the injection depth. This can create an aperture with a higher vertical to horizontal displacement ratio due to the injected material aligning in a vertical column due to the resistance generated by the external pressure created by the weights.
• a vertically oriented anchoring device such as a shaft, tube, cable or other similar structure may pass through the upper portion of the soil profile and be anchored in the ground beneath the plane of an existing, proposed or possible aperture zone. Applying a tensile force to the vertical oriented anchoring device creates a compressive load downward on the space where the aperture zone might be and provides a closing force on this space.
• the vertical distance between the points of application of the lower and upper reaction forces determines the areal extent in the horizontal plane of the soil zone influenced by the applied load as is understood by the science of Soil Mechanics.
• Anchoring devices of various types both above and below the zone to be under compression may be used including soil nails, augers and anchoring plates that pivot to anchor into soil when tension is applied.
• One anchoring method that may be used is to drive a single large auger into the ground with a threaded section on the superterranean portion of the auger central pipe or cylinder. A platform or plate can then be made to apply pressure to the soil as a nut is tightened on the threaded section as depicted in Figure 9A.
• Figure 9B depicts an alternative technique employing a cable as the tensile member creating the compressive force.
• the cable may be inside tubing to avoid contamination of the cable and pulleys with soil.
• a single cable may pass down to pulleys underground or a stub cable or chain connected to the subterranean anchor may rise to the surface where a surface mounted tensioning arrangement may attach to it.
• the surface mounted device for applying tension to the vertically rising stub cable or chain is thus protected from contamination by soil.
• a cable has the capacity to apply tension to a number of such soil anchors at once using a single cable winch as an actuator. They can also be placed with precision similar to the weight method described earlier.
• a sequence of anchoring systems like cables or screws for applying force have the advantage of “sewing” the ground together as there is an upward force applied from the anchoring auger and a downward force from the superterranean tightening mechanism.
• a single 3,000 kg cable winch can create 6,000 kg compressive force on each anchored cable because there would be 3,000 kg on each of two cables passing to the subterranean anchor. If the same cable passed through 20 cable anchors in a line stretching over a 100 m, it would create 1,176 kN force or the equivalent of parking 5 fully loaded 24 metric ton trucks in a line at the push of a button. Other varieties of techniques could be used to compress screw type or hydraulic soil force application systems automatically.
• a 1,1176 kN force applied along a 100 m line, arc, or circle will likely stop an aperture from opening and also close one along the line that is already open. This enables careful shaping of elevated spaces and the dynamic flow of solids within a filled or filling aperture.
• two small augers can be driven in the ground on either side in a horizontal plane of an anchoring plate with a threaded rod above it. Connecting these and then tightening a bolt downward against the anchoring plate causes a downward force on the plate. This increases the pressure on the volume of soil underneath the plate which force is translated to an upward tension on the two horizontally adjacent augers in the soil.
• This particular method does not involve perforating the soil directly in the area where the downward force is applied but instead perforating the soil some distance to either side horizontally of the compressive force application.
• Figure 10 (A) illustrates in more detail a compressive soil anchor and 10(B) shows a soil anchor with a slurry injection discharge at the upper end of the auger anchor that enables rotation to clear plugs which may form when injecting biomass materials.
• the placement of the subterranean discharge port normal to the axis of the anchoring device assists in reduction of plugging and enables higher fluid velocity in a selected direction.
• the addition of a liquid pressure jet operating at 7-38 MPa assists in pushing the injected slurry forward if applied such that the jet impinges on the fluid after the solids have begun moving outward from the axis of the well and into the aperture.
• the jet may be used to clear plugged material and assist cleaning along with the rotating normally oriented discharge port mentioned earlier.
• Figure 11 illustrates a soil anchor that does not employ a surface mounted footing to locate the upper reaction force but instead a second concentric auger soil anchor which may be located at any distance between the soil surface and the lower soil anchor by a separate rotary placement operation. In this way, the location of application of the reaction force may be altered in the vertical dimension. Both a compressive force and an opening or tensile force may be created between the upper and lower soil anchors by employing any of a variety of methods to create differential movement of the lower and upper soil anchors.
• a second soil anchor such as an auger which can be placed a precise distance above a lower anchor enables application of compressive and tensile forces to alter the tendency of apertures to either open or close.
• Tensile forces encourage opening and compressive forces encourage closing or reduce the tendency to open.
• an area of subsoil can be in compression and moments later after adjustments are made to the mechanism, it may be in tension or the level of compression may be dramatically reduced relative to surrounding soil.
• Dynamic aperture shaping is thus enabled as well as direct movement of aperture fluids from one area to another area without pumping fluid in or out of the aperture at the surface.
• Removal of fluid is accomplished while maintaining back-pressure to support the aperture height.
• This can be done using a reversible pump such as a progressive cavity or a peristaltic pump whose rate is adjusted to maintain adequate back pressure or by a hydrocyclone device which increases back-pressure intrinsically as flow rate increase.
• An additional way for this to occur is to discharge fluid from within the aperture out of exits whose altitude above the ground may periodically be adjusted but which will intrinsically provide back pressure to the exiting fluid flow based on that discharge altitude.
• a reversible pump such as a progressive cavity or a peristaltic pump whose rate is adjusted to maintain adequate back pressure or by a hydrocyclone device which increases back-pressure intrinsically as flow rate increase.
• An additional way for this to occur is to discharge fluid from within the aperture out of exits whose altitude above the ground may periodically be adjusted but which will intrinsically provide back pressure to the exiting fluid flow based on that discharge altitude.
• Each of the methods just described for metering exit flow enables passage of solid
• movement to or from the aperture fluid may be transferred around the aperture by sequential compression of areas of the aperture. This is conceptually similar to squeezing a tube of toothpaste to move the toothpaste around inside the tube. Without surface fluid, movement to or from the aperture fluid may be transferred around the aperture by sequential compression of areas of the aperture. This is conceptually similar to squeezing a tube of toothpaste to move the toothpaste around inside the tube.
• the solids may move with the induced flow. If the solids have settled, the supernatant fluid may move in this way so as to ease its removal or recycling to transport more solids to the aperture.
• Removal of supernatant fluid from the aperture enables its recovery and reuse. This recovery is accomplished by direct addition to the injection pump sump. The recovery of valuable viscosifying agents such as guar gum, sodium bentonite and cellulose pulp is also accomplished in this way.
• the complete leak-off of extra fluid from the subterranean aperture will require about 1 week. Thus it is best to first measure the elevation achieved by injection at least one week after injection is ceased. The minimum elevation achieved with solids 50% of which do not pass a 5 mm square screen opening will be about twice the median 5mm size or about 10 mm.

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