Patent Publication Number: US-2010124463-A1

Title: Method for forming a solid soil base with a material comprising soil and spent lime

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The subject invention is directed toward methods for filling depressed land areas and/or building up land areas with backfill material and for making backfill material. 
     2. Description of the Related Art 
     Previously unusable land areas such as gravel pits, excavation sites, areas needing fill, and areas of soft or unstable ground can often be put to beneficial use once backfilled (filled and/or built-up) with fill material. For example, once filled and/or built-up, such land sites have been used for golf courses, public parks, camp grounds, building pads, retention berms, earth dams and the like. Fill material commonly used for filling or building-up such land sites has traditionally included sand, clay, gravel, and broken concrete or bricks. Such fill material can be expensive, and the resulting load bearing characteristics can be marginal. It&#39;s expensive!!! 
     Soil stabilization techniques that produce superior load bearing characteristics have long existed. These techniques typically involve using a hydratable form of lime intermixed with other materials to form a concrete-like base. Such hydratable forms of lime draw moisture from the surrounding soil to form a dry solid soil base on which construction may take place. Examples of such techniques are disclosed in U.S. Pat. No. 2,815,294 to Havelin and U.S. Pat. No. 4,373,958 to Jones. 
     The two hydratable forms of lime typically used include quick lime, CaO, and slaked lime, Ca(OH).sub.2. While yielding superior load bearing characteristics, both forms of lime have significant disadvantages. For example, slaked lime produces a great deal of dust while being intermixed with surrounding soil. Consequently, workers and the surrounding environment are exposed to lime dust. Even more problematic is the caustic properties associated with quick lime, which make the handling and spreading of quick lime especially difficult. Additionally discouraging is the cost of obtaining both of these hydratable forms of lime. 
     Some of the drawbacks associated with the use of hydratable limes have been mitigated by the use of specially developed spreading techniques, as shown in U.S. Pat. No. 3,793,841 to Dozsa. Also, the use of polymeric additives in conjunction with hydratable lime has been used, as shown in U.S. Pat. No. 4,134,862 to Eden. 
     The use of portland cement as a fill material is also quite common. As with the hydratable lime materials, use of portland cement also relies upon the absorption of moisture from the surrounding soil to dry out wet unstable soil and form a solid base for supporting construction. U.S. Pat. No. 4,464,200 to Duval is illustrative of the use of portland cement. 
     SUMMARY OF THE INVENTION 
     A method is provided for filling and/or building-up land areas by providing a substance comprising spent lime, providing soil, and forming a generally non-reactive composite fill material by intermixing the substance with the soil such that moisture content of the spent lime is distributed through the material. A solid soil base is then created by depositing the composite fill material. 
     Alternatively, the step of providing a substance comprising spent lime may include generating spent lime by providing a solution of water and dissolved minerals, precipitating a residue and providing softened water by adding lime to the solution, and removing the residue from the softened water. The residue may then be further processed to form spent lime of a desired consistency. 
     Alternatively, the step of further processing the residue to form spent lime may include reducing water content of the residue by storing the residue in a containment and allowing insoluble precipitates to settle-out and form a layer of spent lime. The spent lime may then be removed from the layer. 
     Alternatively, the step of further processing the residue to form spent lime may include compressing the residue sufficiently to form a spent lime cake of a desired consistency and dampness. 
     Alternatively, the step of forming a spent lime cake may include compressing the residue using one or more press devices such as a plate and frame press, a vacuum drum press, a belt press, or a filter press. 
     Alternatively, the spent lime may be analyzed for unacceptable amounts of hazardous materials. 
     Alternatively, the step of providing soil may include providing soil comprising material more coarse than the spent lime. 
     Alternatively, the step of providing soil may include providing soil that includes sand. 
     Alternatively, the step of intermixing may include dumping the wet spent lime in a mound, dumping the soil in a mound, and then intermixing the mounds. 
     Alternatively, the step of intermixing may include providing a tossed mixture by tossing spent lime and soil together using excavation machinery. 
     Alternatively, further blending and aerating of the tossed mixture may be accomplished by bulldozing. 
     Alternatively, spent lime and soil may be provided with respective moisture contents, and may be intermixed such that the resulting composite fill material has an approximate 15% moisture content. 
     Alternatively, spent lime and soil may be provided at a ratio in the range of 9:1 to 1:9. 
     Alternatively, spent lime and soil may be provided at a ratio in the range of 3:2 to 2:3. 
     Alternatively, undesirable elements may be screened-out of the intermixed substance and soil. 
     Alternatively, the substance may be intermixed with soil within a rotating drum. The drum may include holes that allow composite fill material of a desired consistency to pass through the drum wall while causing undesirable elements of the intermixed substance and soil to pass out a downstream end of the drum. 
     Alternatively, intermixing within a rotating drum may include controlling a rate of axial movement of the spent lime and soil through the drum by adjusting drum tilt. 
     Alternatively, intermixing with a rotating drum may include providing a drum comprising a helical blade fixed along and around an inner circumferential surface of the drum. The blade may be configured to propel the spent lime and soil axially through the drum in a direction toward an outlet end of the drum and to assist in blending the spent lime and soil. 
     Alternatively, intermixing with a rotating drum may include controlling a rate of drum rotation to influence such characteristics as degree of blending, moisture distribution, and degree of aeration of spent lime and soil passing through the drum. 
     Alternatively, intermixing with a rotating drum may include providing a drum comprising smaller holes at an upstream end and larger holes at a downstream end. 
     Alternatively, intermixing with a rotating drum may include providing a drum comprising no holes at an upstream end. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the subject invention will be readily appreciated as the invention become better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a flow chart summarizing the general steps of the subject method; 
         FIG. 2  is a perspective view of a settling pond showing the wet spent lime being removed therefrom; 
         FIG. 3  is a schematic front view of a press disposed on the second story of a structure in a position to drop wet spent lime cake product into the bed of a truck; 
         FIG. 4  is a perspective view showing the intermixing of the wet spent lime with soil and the subsequent placement of the composite mixture into a depressed land area; 
         FIG. 5  is a schematic front view of a blending apparatus for blending wet spent lime and soil according to the invention; 
         FIG. 6  is a schematic orthogonal view showing wet spent lime and soil being introduced into a rotating drum of the blending apparatus of  FIG. 5 ; 
         FIG. 7  is a schematic front view of an alternative drum portion of the blending apparatus of  FIG. 5 ; and 
         FIG. 8  is a schematic front view of another alternative drum portion of the blending apparatus of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As an initial overview to the subject method,  FIG. 1  has been included in the form of a flow chart showing the major steps involved. Each of the major steps shown in  FIG. 1  will be discussed in more detail subsequently. By way of introduction, however, the subject method is a method for filling and/or building-up land areas and includes the general steps of: generating or otherwise providing a substance comprising spent lime  14  of a type that will not absorb an appreciable amount of water, forming a generally non-reactive composite fill material  22  by intermixing the substance with soil  18  such that moisture content of the spent lime is distributed through the substance, and creating a solid soil base by depositing the composite fill material, e.g., by fill and/or build-up a land area with the composite fill material. 
     As indicated in  FIG. 1 , the first step of the subject method involves generating spent lime  14 . In general terms, spent lime  14  may be generated by adding lime to unsoftened water, i.e., a solution comprising water and dissolved minerals, in order to precipitate out from the unsoftened water minerals that cause water hardness. Its usefulness in precipitating out such minerals is one reason that lime, CaO, is commonly used to soften water in large scale water treatment processes. Calcium is the primary mineral contributing to water hardness but other minerals such as magnesium and iron also contribute to lesser extents. In practice, water treatment facilities acquire unsoftened water from groundwater or surface water sources. Lime is subsequently added to the unsoftened water to react with the water hardening minerals found therein and form insoluble precipitates therewith. These insoluble precipitates form a residue that may then be further processed to form spent lime  14  of suitable or desired consistency for use in composite fill material  22 . 
     One way to achieve a suitable consistency of spent lime  14  is to remove the residue from the softened water and store it in containments such as settling ponds  10  as shown in  FIG. 2 . Over time, the residue is “de-watered”, i.e., is reduced in water content, by allowing insoluble precipitates settle out and form a layer on the bottom of the pond  10 . The remaining de-watered, but damp insoluble precipitates, hereinafter referred to as spent lime  14 , are substantially comprised of calcium carbonate (at least half by weight). Unlike quick lime, CaO or slaked lime, Ca(OH).sub.2, spent lime  14 , which may be 99% non-reactive will not react appreciably or absorb an appreciable amount of water. Usually, the spent lime  14  comprises a damp mixture of approximately 90% calcium carbonate, CaCO.sub.3, with the remaining 10% comprising magnesium hydroxide, Mg(OH).sub.2, and other insoluble salts; however, the relative proportions of each constituent of the spent lime  14  vary with the unique geological and environmental surroundings the water has previously been exposed to. Again, where the residue is stored in a settling pond  10 , over time, the spent lime  14  builds up in the bottom of the settling pond  10  and may subsequently be removed and disposed therefrom. 
     Another way to process spent lime  14  to obtain a consistency and dampness suitable for use in composite fill material  22  is to remove the residue from softened water and form it into a cake  15  of spent lime using any suitable compression device  30  known in the art. Such a compression device  30  may include, for example, a plate and frame press, a vacuum drum press, a belt press; and/or a filter press. As shown in  FIG. 3 , such a compression device  30  may be supported at a sufficient height, e.g., on the second floor or story of a building  32  or other suitable structure, to allow resulting cake-form spent lime  15  to be dropped onto the bed of a truck  34  parked beneath the level of the compression device  30 . 
     As a precautionary step, samples of the spent lime  14  should be analyzed for unacceptable amounts of hazardous materials such as; silver, barium, mercury, phosphorous, zinc, copper, and depending upon the water source, possibly organic molecules including PCBs. Acceptable levels for these and other hazardous materials may be regionally determined. The State DNR (now called DEP) or other governmental agencies may be of assistance in determining acceptable levels of these and other materials. By conducting precautionary analytical testing of the spent lime, the safety of the resulting composite fill and surrounding land area can be assured. 
     The spent lime  14  used in the composite fill material  22  and in the subject method may be collected from water softening facilities by draining the water from the settling ponds, leaving behind wet spent lime  14  in the form of a slurry-like mixture consisting of roughly 60% spent lime and 40% water. The wet spent lime is typically removed from settling ponds, as shown in  FIG. 2 . More specifically, the settling pond, generally shown at  10 , is drained leaving behind only a limited amount of water  12 . Beneath the water  12 , lies a layer of wet spent lime  14 . The wet spent lime  14  is removed from the pond by the use of a back hoe  16  or like equipment. 
     Once removed from the settling pond  10 , the wet spent lime  14  is transported, preferably by truck, to the selected land site where it is intermixed with soil  18  to form a composite fill material  22 . The soil  18  used to form the composite fill material  22  may be native soil found about the land site, however, to obtain optimum results, the soil  18  should comprise a larger portion of sand or other material coarser than the spent lime  14 . The desired fill material characteristics are achieved by, among other things, void filling through an intermixing of desired particle sizes. Ideally, the soil  18  comprises bankrun sand. If the native soil does not contain a large portion of sand, i.e. the native soil is primarily clay, gravel, or silt, sand from a non-native source may be transported to the land site and may be substituted for native soil. 
     The wet spent lime  14  and soil  18  may be intermixed at a location adjacent the area to be filled. Although any one or more of many suitable techniques can be used to intermix the wet spent lime  14  and soil  18 , three particular techniques have been found to work especially well. One of those techniques is shown in  FIG. 4  and involves dumping the wet spent lime  14  in an elongated narrow mound or row. The soil  18  may likewise dumped in an elongated narrow mound or row, parallel to the wet spent lime mound located a few feet away. Subsequently, a mixing machine  20 , which may be of a type typically used for composting applications, may be used to intermix the mound of wet spent lime  14  with the mound of soil  18 . Several passes over the parallel mounds may be required to properly mix the wet spent lime  14  with the soil  18 , depending of course, upon the relative proportions of soil to spent lime being mixed. The spent lime  14  being intermixed with the soil  18  may be wet. Where the spent lime  14  is wet, the mixing operation generates little or no dust. Such moisture content of the wet spent lime  14  allows for relatively quick and easy intermixing with the soil  18  to form a dense, composite fill material  22 . 
     To provide desirable compacting characteristics, the resulting fill material  22  may preferably include roughly 15% moisture. In other words, spent lime  14  and soil  18  are provided having respective moisture contents such that their intermixing provides composite fill material  22  having an approximate 15% moisture content. The moisture content of the composite fill  22  may preferably be monitored on site by the use of nuclear density meters, or other like apparatus commonly used for measuring moisture content of soils. The remaining 85% of the composite fill material  22  may comprise soil  18  and spent lime  14 . The ratio of soil  18  to spent lime  14  in the composite fill material  22  may vary drastically depending upon the requirements for the fill material  22 , the nature of the surrounding land area, the quantity of spent lime  14  to be disposed of, etc. Depending upon the results of an evaluation of these variables, the ratio of soil  18  to spent lime  14  selected for a given application may vary anywhere from 9:1 to 1:9. Studies thus far indicate that optimum load bearing characteristics are achieved from fill consisting of roughly equal portions of soil  18  and spent lime  14 , i.e. ratios from 3:2 to 2:3 depending, of course, upon the nature or characteristics of the specific soil used. 
     Another of the preferred techniques for intermixing is to provide composite fill material  22  by simply tossing spent lime  14  and soil  18  together using excavation machinery such as the backhoe  16  shown in  FIG. 2 . The “tossed” mixture may then be further blended and aerated by bulldozing. 
     The remaining preferred technique for intermixing wet spent lime  14  and soil  18  is shown in  FIGS. 5 and 6  and involves forming composite fill material  22  by passing wet spent lime  14  and soil  18  at a desired ratio through a blending apparatus  36  configured to blend and aerate the spent lime  14  and soil  18 . The blending apparatus  36  may also be configured to screen-out undesirable elements  38  of the resulting mixture. 
     The blending apparatus  36  may include a generally cylindrical drum  40  supported for rotation on an axis  42  that is generally perpendicular or slightly angled relative to Earth gravity as best shown in  FIG. 5 . The drum  40  may include a cylindrical wall comprising an array of holes  42  in the form of perforations or openings in a grate or screen. The holes  42  may be configured and sized to allow composite fill material  22  of a desired consistency (particle size, stickiness, moisture content, chunk size, etc.) to fall through the wall of the drum rather than being passed out a downstream end of the drum. 
     As shown in  FIG. 5 , the blending apparatus  36  may further include a motorized variable-tilt mechanism  44  configured to allow an operator to control the rate of axial movement of the spent lime  14  and soil  18  through the drum  40  by adjusting drum tilt. Alternatively, or in addition, a helical blade  46  may be fixed along and around an inner circumferential surface of the drum  40  and configured to both propel the spent lime  14  and soil  18  axially through the drum in a direction toward an outlet end  48  of the drum  40 , and to assist in blending the lime  14  and soil  18  as shown in  FIG. 6 . 
     The blending apparatus  36  may further include a motorized rotational speed control  50  configured to allow an operator to control the rate of drum rotation. The rotational speed control  50  may be used to influence the degree of blending, moisture distribution, and degree of aeration of spent lime  14  and soil  18  passing through the drum  40 . Where the apparatus  36  includes a helical blade  46 , the rate of axial flow of material through the drum  40  may also be influenced by adjusting the rate of drum rotation. 
     A feed conveyor  52  may be positioned and configured to feed wet spent lime  14  and soil  18  into an upstream end  54  of the drum  40  as best shown in  FIG. 6 . An output conveyor  56  may be positioned and configured to collect and remove composite fill material  22  exiting through the wall of the drum  40  as shown in  FIG. 5 , and a de-stoning conveyor  58  may be positioned and configured to carry away from the downstream end  48  of the drum  40  stones and other objects  38  too large to pass through the holes  42  in the drum wall, and/or other elements of the composite fill material  22  of a consistency that prevents them from passing through the holes in the drum wall. 
     As spent lime  14  and soil  18  move through the drum  40  the spent lime  14  and soil  18  are blended and aerated by rotation of the drum  40  which continuously picks up and throws together the lime  14  and soil  18 . While blending, the lime  14  and soil  18  may be urged axially through the drum  40  by the helical blades  46  and/or by tilting the drum such that the upstream end  54  of the drum  40  is higher than the downstream end  48  of the drum  40  as best shown in  FIG. 5 . 
     The array of through-holes  42  may be sized to allow composite fill material  22  of a desired consistency and/or particle or chunk size to fall through and be collected and removed by the output conveyor  56 , which may, as shown in  FIG. 5 , be positioned below the drum  40  for that purpose. Alternatively, the blending apparatus  36  may include a drum  60 , as shown in  FIG. 7 , which includes smaller holes  62  at an upstream end  64  and larger holes  66  at a downstream end  68  to insure that the composite fill material  22  is sufficiently blended and aerated before passing through the wall of the drum  60 . As a further alternative, the blending apparatus  36  may include a drum  70 , as shown in  FIG. 8 , having a drum wall section  72  toward an upstream end  74  of the drum  70  including no holes at all to further insure that the composite fill material  22  is properly blended and aerated before exiting through the drum wall. Where a trommel is used as the blending apparatus, it may be any one of a number of suitable trommels such as the 621 Trommel Screener available from McCloskey International. 
     The use of such a blending apparatus  36  such as a trommel type blender more uniformly blends, aerates, and distributes the moisture content of the spent lime  14  and soil  18 , and may also screen out undesirable elements  38  of the mixture  22 , providing a more consistent, uniform and homogeneous composite fill material  22  product. The use of such a blending apparatus  36  also provides greater control of the blending and moisture content of the fill material  22 . 
     Once properly intermixed, the composite fill material  22  may be placed into the selected land area to create a solid soil base, as shown in  FIG. 4 . Typically, the selected land area  24  is a gravel pit or other depressed land area. However, the subject composite fill material  22  and method for filling may be used to build-up land areas that may or may not include depressed areas, i.e., to build mounds, berms, or hills. A front-end loader  26  or other common earth moving or excavating machinery may be used to load and carry the composite fill material  22  and deposit it at the selected location. Depending upon the final application of the filled land, it may be further necessary to compact the fill material  22  while filling. That is, the composite fill material may be rolled with heavy rollers or compressed by other suitable means intermediately between adding loads of fill material, thus creating a denser solid soil base. 
     The subject composite fill material  22  is relatively inexpensive due to the inexpensive nature of spent lime. Generally there is an over abundance of spent lime at municipal water treatment facilities; thus the only cost involved is usually that associated with collecting the spent lime from settling ponds and trucking it to the land site. The resulting solid soil base created by the subject method is relatively impermeable to water and will not easily erode away. Moreover, depending upon the mix ratio of soil  18  to spent lime  14 , the resulting solid soil base may be specifically designed to exhibit sufficient load bearing characteristics to support land uses ranging from city parks to commercial buildings. 
     This is an illustrative description of embodiments of the invention and thus uses terminology that&#39;s intended to be descriptive rather than limiting. 
     Obviously many modifications and variations of the present invention are possible in light of the above teachings. Within the scope of the appended claims, in which reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.