IV. SOILS AND HOMESITES
Homesite Selection and General Practices Next Section>>
People who plan to build a house must consider various soil and landscape features. Many homes in Indiana are on sites where serious problems will occur if soil and landscape conditions are not considered. Wet basements, poor surface drainage, excessive settling, and home sewage disposal system failure are frequently encountered problems.
Builders and developers, as well as planning commissions, are becoming more conscious of how soils affect new development. Many are now routinely considering soil properties in the plan and design of individual homesites and subdivisions in communities that are expanding into rural Indiana. Many people are concerned about the competition between urban development and agricultural production for the same land. This conflict is leading toward consideration of preserving good agricultural land for crop production (see section on Prime Farmland). Urban development located in areas not well suited to intensive row crop production would lessen this conflict. Once land is used for houses, it can never again be used for growing crops.
Ideal sites for homesites have deep, well-drained, gently sloping, medium-textured soils that do not flood. Preferably, the surface soil is dark and not eroded. Nationwide, these are also desirable properties for crop production, which places the competition for “the best land” into focus. In Indiana, another set of conditions often occurs. Many of our best soils for row crop production are deep, level, poorly or somewhat poorly drained, and medium textured. These soils are excellent agricultural soils after proper drainage systems have been installed. They occur in wide areas near many of Indiana’s major cities. Thus, there is considerable pressure for their development, even though most of them are considered to have severe limitations for homesites.Soil Properties
The same soil properties used to determine agricultural practices are used to judge homesite practices. The significance of the various properties to constructing a homesite is discussed in this section.
Landforms have a direct and indirect influence on the suitability of a site for building homes. Directly, they largely determine if a site will receive water from other areas. Indirectly, landforms influence the natural drainage of a soil. Floodplains are nature’s location for storing excess floodwater. Floodwaters spread out over the floodplain and are retained there during periods of high runoff and flow. As the stream or river level drops, the water stored on the floodplain gradually returns to the stream channel by surface flow and percolation through the soil.
All too often we read reports of lives that were lost and houses that were destroyed because homes were destroyed by floodwater. Most of these houses were built on flood plains. Many of these losses could have been prevented by following the rule below which says that houses should not be built on floodplains.
Depressions on uplands and terraces usually accumulate water from upslope. This water plus the rain that falls on the depression must percolate through the soil, so soils in depressions may not be able to absorb all these waters in addition to home wastewater. If the depression receives so much run-on and sediment from surrounding areas that it has more than 20 inches of recent sediment over the original soil, it is not a suitable site for any kind of homesite. In soil evaluation, depressions with less than 20 inches of local overwash are included with flats. Many flat areas are suitable for some onsite systems, so the use of onsite systems is often marked YES for flats and depressions. In actual practice, however, onsite systems should not be installed in depressions.
|Mark all homesite practices (51-64) NO if the landform is a flood plain or a filled depression.|
The ideal slope for homesites is 2% to 6%. Flat areas are less desirable
because much grading may be required to slope the land to carry surface
water away from buildings. On slopes steeper than 6%, problems of erosion,
soil stability, and septic effluent seepage can occur. The steeper the
slope, the more serious are the problems. Soils on very steep slopes
may be physically unstable, and houses built on them may tend to slide
downhill unless proper foundation construction practices are followed.
Besides complicating construction,
these slopes would make landscaping, such as establishing grass or shrubs, much more difficult.
Houses built on slopes may receive water from upslope areas by surface flow and subsoil seepage. This water should be diverted away from the house to keep the area near the house and the basement dry.
Surface color, texture, and erosion
Surface colors and textures generally do not impose serious limitations for homesites, although dark-colored, medium, or moderately sandy surface soils with high organic matter contents would be beneficial in the establishment of grass or other landscape improvements.
The texture of a surface soil mainly affects its use for growing lawns, shrubbery, and trees around the homesite. Clayey and sandy surface textures are less desirable. Fine-textured soils remain wet and soggy for a long period after rain and become hard when dry. Sandy soils lack water and nutrient holding capacity and may require improvement with topsoil or organic matter. In some instances, builders stockpile the soil removed in construction and replace it on the surface after final grading.
Valuable surface soil has been eroded from moderately or severely eroded soils and the more clayey subsoil may be near the surface or exposed. This makes it more difficult to grow a lawn and other plantings.
Subsoil texture is a very important property in homesite evaluation. It affects the transmission rate of water through the soil (permeability) and also the swell-shrink potential of a soil, which, in turn, affects foundation performance. Soil structure also has an important effect on permeability.
Usually finer-textured soils transmit water more slowly than sandy textured ones. Therefore, water may drain so slowly through clayey and moderately clayey soils that it accumulates around the foundation and seeps into the basement. Poorly and somewhat poorly drained soils are more likely to have this problem than well-drained soils. These factors illustrate the wisdom of establishing good surface and subsurface drainage away from the house.
Relative to sandier soils, some fine-textured soils can bear less foundation weight and are more likely to shrink (occupy less space) during dry weather and swell (expand) during wet conditions. The forces involved in shrinking and swelling may be enough to cause cracking and movement of the foundation walls. The shrink-swell properties of fine-textured soils depend on the type of clay mineral present. Fortunately, extreme cases are rare in Indiana, although troublesome foundation settling and movement are common in many areas of the state.
Water flows over the surface or moves through the profile of well-drained soils fast enough that the soil is not wet for long periods of time. These soils are ideal for homesites. Any restriction of drainage, either because of impermeable subsoils or high water tables, can cause wet basements and unusable yard areas. Wet soils impose further restrictions on homesites that depend on onsite wastewater disposal, as explained later.
If bedrock occurs within the depth of excavation for basements, the builder must blast it out to excavate for a basement or otherwise adapt his foundation design. Either of these choices would greatly increase construction costs. Fragipans and dense till transmit water and sewage effluent so slowly that they limit use of onsite wastewater disposal systems. Coarse sand and gravel soil horizons also impose limits for onsite wastewater disposal systems because they transmit effluent so fast that it does not get purified in the soil.back to top
The practices described in this section should help overcome soil problems and add to homesite quality. They apply to all homesites, regardless of the kind of wastewater disposal system.
Maintain soil cover during construction
Construction on all sites, especially sloping ones, should be done with the least possible disturbance of vegetation, but this is not always possible. For example, land shaping or cuts-and-fills may be necessary for roads or surface drainage improvement. When vegetation is removed, new vegetation should be established as soon as possible to reduce erosion and offsite damage from the sediment resulting from erosion. Annual ryegrass can be used if lawns will be established within several months. If the site is to be under construction for a longer time, perennial grass or other vegetation should be seeded.
Several other practices can be used to protect building sites. Structures to stabilize slopes will help control erosion. Some erosion is inevitable, however, and the sediment produced should be kept on the building site with sediment control basins. On larger sites, runoff from hard surfaces such as streets and parking lots should be held temporarily in water retention basins and released slowly to protect downstream areas from large surges of runoff.
Soil compaction during construction will cause the homeowner problems for many years in growing grass and other plants. It may also ruin a site for onsite wastewater disposal. Some compaction is inevitable, but the area that is compacted should be kept small. In some areas, part of the lot is fenced off before construction begins and builders are not allowed into this area.
|Mark Maintain soil cover during construction YES for soils with slope greater than 2%.|
Improve surface drainage
Good surface drainage is important and frequently needed in Indiana. The gently undulating topography of central and northern Indiana has very slow surface drainage. This relatively flat area is dominated by poorly and somewhat poorly drained soils. Much of the flat topography in the southern part of the state has even slower surface drainage. Homes located on these soils need special care beyond simply grading the lot to provide water movement away from the house. Poorly drained soils are often in depressions, which form natural drainageways or frequently ponded spots.
Surface drainage water should be channeled away from the house and from wastewater soil absorption fields. If this is not done, the surface water will only make the high water table problem worse. Homesites should be carefully chosen with surface drainage in mind. Level sites on poorly drained or somewhat poorly drained soils require special attention. Sloping soils are assumed to have sufficient relief to carry surface water off the site or at least away from the buildings.
Mark Improve surface drainage YES for soils with both properties:
1. poorly or somewhat poorly drained, and
Improve surface soil
Not all surface soils have medium textures or are ideal materials in which to establish plants. Sandy surface soils are too coarse to hold water or added fertilizer. Moderately clayey or clayey surface soils are hard when dry and stay wet after rains. They are difficult materials in which to establish lawns and gardens.
For this reason, addition of organic material such as peat or dark-colored, medium-textured topsoil improves the chances of successful lawn and shrubbery plantings on these problem soils.
Some contractors follow the excellent practice of removing surface soil from the construction site and stockpiling it before excavation begins. Then after construction, at final grading, the stockpiled surface soil is returned, providing a good material for lawn establishment.
Mark Improve surface soil YES for soils that have both:
1. brownish or gray surface color, and
Locate home to fit soil restrictions
House locations must be chosen with care. Surface drainage patterns are important for homesites whether they are on sewers or onsite systems. The area for an onsite absorption field, if needed, should be given prime consideration.
Homesites on sloping soils or where bedrock is found at shallow depths require a detailed examination to find an acceptable location for the home. When a septic system is to be used on sloping sites, the absorption field distribution lines must be laid out on the contour with special design features that minimize the risk of downslope seepage of effluent. Shallow bedrock will also increase home location problems and construction costs.
Mark Locate home to fit soil restrictions YES for soils that have either:
1. slope more than 6%, or
Provide foundation drainage
The house foundation is where construction methods encounter soils and their properties. To understand why some soils are problems for homes with basements, some knowledge of foundation construction is necessary (Fig. 28). The goal is a dry basement at all times during the year with minimal settling or support problems.The practices given here are not a guarantee of this, but they point out what can be done to minimize problems.
Fig 28. Foundation construction showing floor and footing drains.
Under extended high water table conditions, foundations should be made stronger and more watertight. A high water table may cause pressure build up under a basement floor. These pressures can be great enough to crack the floor and are responsible for numerous cases of flooded basements.
Provision must be made to remove soil water from around the base of the foundation and from underneath the basement floor. Footing drains (Fig. 28) are typically plastic drain tubes laid next to the footings during foundation construction.
They remove water from outside of the basement walls and reduce water pressure on the basement walls and floor. If a gravity outlet is not available for the footing drains or sub-floor drains, a sump pump is needed to remove the water. Footing drains generally do not remove water from underneath the basement floor. To relieve the pressure caused by this water, tile is laid in the pea gravel under the basement floor. A sump pump is placed in a hole at the end of the tile lines to lift water into drainpipes or to the soil surface. Remember that good surface drainage should be combined with this practice.
Foundation drainage is a relatively inexpensive practice when done during construction but quite costly if it has to be done later. This practice can mean the difference between a usable basement and one that is wet or subject to periodic water problems.
|Mark Provide foundation drainage YES if soil drainage is poor, somewhat poor, or moderately well.|
Accommodate high clay subsoils
Soils with high clay contents cause some special construction problems for houses. Compared with coarser-textured soils in which weight is supported by friction between sand particles, clayey soils lose strength rapidly as they take up moisture. The clay particles have layers of water between them and slide easily over each other. For this reason, an increase in size (width and depth) of footings is advisable on clayey subsoils. This practice is recommended for all drainage classes, since finer-textured subsoils generally become saturated with moisture at some time during the year.
Also, many fine-textured soils expand when wet and shrink when dry. If the excavated area around basement walls is back-filled with soil material, a space between the wall and the soil will develop when the soil dries out and shrinks. Soil material might fall into this crack, and when the soil again becomes wet, it swells, and the added soil material presses into the foundation wall and may cause it to crack. The excavated area around the basement walls should be backfilled with pea gravel to minimize this swelling pressure. Homeowners should be aware of these problems when planning and building houses, and should discuss them with builders and contractors.
|Mark Accommodate high-clay subsoils YES for soils in which subsoil texture is clayey.|
Install diversion structures and drains
If a house is built on sloping land but not at the top of a hill, the lot may receive much runoff from the land above it, especially if soil permeability is slow. If there are houses and streets upslope, the runoff problem is greater because the hard surfaces of roofs and streets are completely impermeable and produce even more runoff. Diversion structures can be built to direct surface runoff away from the lot. In some soils, water moves downslope within the soil profile. This seepage can result in wet basements or cause sewage disposal systems to fail. Subsurface drain tubes (curtain drains) can be installed to intercept seepage water and divert it off the property. The bottom of the curtain drain trench must be at least two inches into the slowly permeable limiting layer (dense till, fragipan, or bedrock). These drains must be free flowing (no pumps). They usually flow downslope into a stream or large drain tile. Care should be taken, however, that the diverted water does not cause problems for downslope properties. Diversion structures and curtain drains are illustrated in Fig. 29.
Fig 29. Cross section through a surface water diversion and a curtain drain.
Mark Install diversion structures and drains YES for soils that have both:
1. slope more than 2% slope, and