Accurate Home Inspection of Atlanta
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Many atlanta subdivisions are mass graded. This means an undesirable building location(lots of steep grade are uneven lots) is transformed into individual flat or moderately sloped lots by movement of dirt. This usally includes removal of soil at hill(the cut lot),which which is them imported to other areas on site to create fill areas(the fill lot) or cut-fill areas(transitional lot).Cut lot tens to perform well since the soil is undisturbed where the hill was removed.Fill lot can compact more once the home is completed;this movement,however,is usually uniform and rarely cause distress th the home. These condition are consider when inspecting a home when built from mass graded lots. The homes soil,and foundation are in constant movement and forces fighting against one another.New homes may not give any indication of foundation issues for several years down the road.Although there are methods for inspectors to gauge that accurate standards were followed site prep,and adequate footing drains to help with hydrostatic pressure against the structures foundation.A strong foundation and proper lot drainage is the key to a stable foundation.In a perfect world every property would be built on the perfect lot,but as I know and you should as well this can not always be the chase.
A structure is expected to stand up. The force of gravity is constantly working to bring it down.A structure has to be designed to resist gravity.It must support its own weight,which is called DEADLOAD of the structure.It must also support the live load which are imposed open it,which include the people inside,the furniture,and other weight such as snow,and the materials used in the roof structure skeleton.
A structure does transfer its weight through the exterior walls,and load bearing partions to the foundation which in then transfers the weight to the soil through the footing.Not only is a structure expected to stand up, it is also expected to stand still. The structure movement is partially determined by the conditions of the soil support the structure,and proper drainage around the stucture.When the ground below the house fails,the house sinks.Soil moves. The foundation resists the pressure of the soil against the structure.Homes built on the proper site should be built strong enough to resist this natural pressure.
MOVEMENT:
The effects of settlement and movement on a home and their effects on the rest of the structure are not always obvious.While some signs are obvisous,other signs might need more in depth study to determine the cause of underlying issues.Wall cracks appear as the result of overloading or because of settlement or heaving. The location of the cracks can be a clue to what is going on to the foundation.
Is a dynamic system.Soil Moves.A house built on the bottom of a hill can have soil moving toward it over time and exerting more and more pressure against the foundation.It may be pushed from its original position.
WINDS
Plays an effective upon a structure.With heavy winds theres forces of pulling,and uplifting.Structures must be strong enough to resist these forces as well.
Different foundation problems also require different solutions. If your foundation is only suffering from minor seasonal movement, it has the equivalent of a cold and might only need watering. If your foundation has suffered from permanent settlement, you might need foundation repairs. The exact type of support you will need depends on the type of foundation that you have and on the types of soils under your home.Some methods of foundation repair are concrete press piling, steel press piling and bellbottom piers. A Bellbottom pier is where you actually drill a hole in the ground, bell it at the bottom, pour concrete down in the hole, and then uses that to lift off of.
Resistance are hydraulically pushed or driven straight down through the soil using the weight of the structure as a counter balance. The piers are pushed down until the end reaches a layer of soil hard enough to support the structure. Resistance piers are best suited for structures that need to be raised or
have very heavy load requirements.
Helical Piers are hydraulically twisted or turned into the soil much like a corkscrew. The piers contain one or more wings that pull the pier into the soil. These piers are screwed down until they reach soil that is thick enough to support the desired result. Since they are screwed in, they cannot be pushed or pulled out. They can be used to either support a structure or to keep a structure from coming away from the soil such as a retaining wall or a home on a hillside. These types of piers can also be used as pre-construction piers to prevent future foundation failure.
Mud jacking is a good low cost way to lift a foundation. Seldom does mud-jacking give results that are satisfactory for the long run. Sometimes, mud-jacking is even destructive to the structure. Most companies only result to mud-jacking as a last resort for very poor built foundations and will obtain a damage waiver prior to beginning repairs.
Pressure grouting is used in areas that geotechnical engineers have found to be sinkhole conditions. This involves the injection of a low slump grout, which mainly consists of cement, sand, water and fly ash, into the soils at or above the limestone layer.
Another foundation repair that is economical is to drill or pour concrete piers. Holes are typically drilled to a depth of 9-12 feet below the surface, and then filled with reinforcing steel and concrete. Poured concrete is topped with concrete spacers and shims.
When starting your foundation, the best thing to do is hire a structural engineering firm. They will be the first to board test the soil to recommend which foundation would the best. Once they have tested the soil, the engineer can design a specific slab for the specific soil conditions.
Compaction Grouting
Compaction grouting is a technique of injecting low slump grout under pressure to densify granular soils. This process reduces the effects of subsidence and settlement. Compaction grouting has been employed to arrest sinkhole movement, and recently for large scale site improvement where unstable soil strata
make alternative methods of stabilization unfeasible.
The process of compaction grouting consists of installation of injection pipes to the bottom of the zone being densified. The pipes are either drilled or driven into place with a sacrificial point. The pipe is withdrawn to open the end of the injection pipe. A specially designed low volume, high pressure pump is used to place the grout. As the grout expands in a homogeneous bulb, the radial force exerted compacts the surrounding soils. A relatively slow injection rate is used to prevent fracturing the soils, allowing water to dissipate and thereby reduce uplift. Injection continues until either refusal pressure is attained or heaving occurs at the surface. Grout placement continues at shallower elevations as the injection pipe is withdrawn in stages.
Downstage: Provides an advantage of additional restraint and containment of future injection, for work performed in less than 15 feet. Compaction grouting downstage involves: drilling an oversize hole to the top of the soil zone to be densified; the insertion of casing; drill through the casing and advance the
hole, approximately 3 to 6 feet, inject grout; and repeat the process once the injected grout has hardened.
Upstage: This method of grouting tends to be the fastest and most economical, and is generally accomplished in a continuous operation. Compaction grouting upstage involves: drilling a hole to the bottom of the zone to be improved; casing is placed within a few feet of the bottom of the hole; grout is injected;and the casing is raised at regular intervals and grouting is resumed until the improvement area is treated.
Compaction Grouting techniques are used for pre-construction site improvement, to arrest foundation settlements, rectify sinkhole problems.
The soils best suited to compaction grouting are fine grained with sufficient permeability to allow excess water to dissipate. The process has also been used successfully in a wide variety of soils and fills. Irregular fills or varying native soils will become more uniform with compaction grouting.An advantage of compaction grouting is the tendency to improve the weakest soils. The effective radius of the grout hole varies with the type of soil being treated.
Where large areas are being treated, the primary hole pattern is a diamond or square pattern with holes on 5 to 10 feet centers. Secondary or check holes are placed to the center of the pattern.
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