Method for filling land areas with a material comprising soil and spent lime

A composite fill material (22) comprising soil (18) and spent lime (14) and a method for filling depressed land areas (24) therewith. The method for filling land areas (24) includes generating spent lime (14) by adding lime to water (12) in order to precipitate out minerals causing water hardness. The generated spent lime (14) is mixed with soil (18) to form a composite fill material (22) which is subsequently utilized to fill depressed land areas (24) thus creating a solid soil base.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The subject invention is directed toward methods for filling depressed land 
areas with backfill material. 
2. Description of the Related Art 
Previously unusable land areas such as gravel pits and excavation sites can 
often be put to beneficial use once backfilled with fill material. For 
example, once filled, such land sites have been used for golf courses, 
public parks, camp grounds and the like. Fill material commonly used for 
filling such land sites has traditionally included sand, clay, gravel, and 
broken concrete or bricks. Although such fill material is relatively 
inexpensive, the resulting load bearing characteristics are often quite 
marginal. 
Soil stabilization techniques have long existed which produce superior load 
bearing characteristics. These techniques typically involve using a 
hdyratable 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 4,373,958 to Jones. 
The two hdyratable 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 hdyratable 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 hdyratable 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 AND ADVANTAGES 
The present invention is directed toward a composite fill material and 
method for filling land areas therewith. The subject method includes the 
following steps: generating spent lime which will not absorb an 
appreciable amount of water, intermixing the spent lime with soil to form 
a composite fill material, and filling a land area with the composite fill 
material to create a solid soil base. 
An advantage of using spent lime in the subject method is realised by 
substantial cost savings by reducing the cost of the fill material. 
Another advantage of using spent lime in the subject method is the 
elimination of dust problems associated with prior art backfill materials. 
Still another advantage of using spent lime in the subject method is the 
increased load bearing characteristics of the resulting fill material over 
typically used fill materials including native soil. 
Yet another advantage of using spent lime is the efficient and effective 
use of otherwise unusable spent lime.

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 filing 
land areas and includes the general steps of; generating spent lime which 
will not absorb an appreciable amount of water, intermixing the spent lime 
with soil to form a composite fill material, and filing a land area with 
the composite fill material to create a solid soil base. 
As indicated in FIG. 1, the first step of the subject method involves 
generating spent lime. In general terms, the spent lime is generated by 
adding lime to water in order to precipitate out minerals which cause 
water hardness. More specifically, lime, CaO, is commonly used in large 
scale water treatment processes to soften water by precipitating out 
minerals causing water hardness. 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 which is removed 
from the softened water and stored in nearby settling ponds. Overtime, the 
insoluble precipitates settle out and form a layer upon the bottom of the 
pond. The insoluble precipitates, hereinafter referred to as spent lime, 
are substantially comprised of calcium carbonate (at least half by 
weight). Unlike quick lime, CaO or slaked lime, Ca(OH).sub.2, spent lime 
will not react or absorb an appreciable amount of water. Usually, the 
spent lime comprises 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 vary with the unique geological and environmental 
surroundings the water has previously been exposed to. Overtime, the spent 
lime builds up in the bottom of the settling ponds and must be removed and 
disposed therefrom. 
As a precautionary step, samples of the spent lime should by 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 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 used in the composite fill material and in the subject 
method is preferably collected from water softening facilities by draining 
the water from the settling ponds, leaving behind a slurry-like mixture 
consisting of roughly 60% spent lime and 40% water, hereinafter referred 
to as wet spent lime. 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 to form a composite fill material. The soil used to 
form the composite fill may be native soil found about the land site, 
however, to obtain optimum results, the soil should comprise a large 
portion of sand. Ideally, the soil 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 are preferably intermixed at a location 
adjacent the area to be filled. Although many techniques can be used to 
intermix the wet spent lime 14 and soil, one particular technique has been 
found to work especially well. The preferred technique is shown in FIG. 3 
and involves dumping the wet spent lime 14 in a long narrow mound or row. 
The soil 18 is likewise dumped in a long narrow mound or row, parallel to 
the wet spent lime mound located a few feet away. Subsequently, a mixing 
machine 20, typically used for composting applications, is used to 
intermix the row of spent lime 14 with soil 18. Several passes over the 
parallel rows may be required to properly mix the wet spent lime 14 with 
the soil 20, depending of course, upon the relative proportions of soil to 
spent lime being mixed. It is important to note that the spent lime 14 
being intermixed with the soil 18 is wet and accordingly, generates 
substantially no dust during the mixing process. Due to the moisture 
content of the wet spent lime 14, the soil 18 intermixes therewith 
relatively quickly and easily forming a dense, composite fill material 22. 
The resulting fill material 22 preferably includes roughly 15% moisture, 
which maintains ideal compacting characteristics. The moisture content of 
the composite fill 22 is preferably monitored on site by the use of 
nuclear density meters, or other like apparatuses commonly used for 
measuring moisture content of soils. The remaining 85% of the composite 
fill material 22 comprises soil and spent lime. The ratio of soil to spent 
lime in the composite fill may vary drastically depending upon the 
requirements of the fill material, the nature of the surrounding land 
area, the quantity of spent lime to be disposed of, etc. Depending upon an 
evaluation of these variables, the ratio of soil to spent lime may vary 
anywhere from 9:1 to 1:9. Studies thus far indicate that optimum load 
bearing characteristics are achieved from fill consisting a roughly equal 
portions of soil and spent lime i.e. ratios between 3:2 to 2:3 depending 
of course upon the nature of the specific soil used. 
Once properly intermixed, the composite fill material 22 is placed into the 
selected land area to create a solid soil base, as shown in FIG. 3. 
Typically, the selected land area 24 is a gravel pit or a depressed land 
area but the subject composite fill material 22 and method for filling may 
be used to build up land areas not previously depressed i.e. to build 
mounds or hills. A front-end loader 26 or other common machinery may be 
used to load and carry the composite fill 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 22, while filling. 
That is, the composite fill material may be rolled with heavy rollers 
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 
to spent lime, 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. 
The invention has been described in an illustrative manner and it is to be 
understood that the terminology which has been used is intended to be in 
the nature of words of description rather than of limitation. 
Obviously many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore, to be 
understood that within the scope of the appended claims wherein 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.