Shallow and deep foundation anchors
A couple of soil failure may occur depending on the depth of the helix; shallow and deep. Foundations expected or proven to exhibit a specific mode are usually referenced as shallow or deep foundations. Which basically points out the location of the surface and a sudden drop in load resistance to almost zero. With deep foundations, the soil fails sequentially, maintaining significant post-ultimate load resistance , and exhibits little or no surface deformation. The dividing line between shallow and deep foundations has been reported by a number of investigators to be three to eight times the foundation diameter . The five-diameter depth is the vertical distance from the surface to the top of the helix. The five-diameter rule is often simplified to 5 feet minimum. Anytime a foundation anchor is considered, a deep foundation should be exercised. Deep foundations have two key advantages over shallow foundations. (1) it provides an increased ultimate capacity, (2) failure will be incremental with no sudden decreases in load resistance after the ultimate capacity has been obtained.
Bearing capacity theory
This theory suggests that the capacity of a foundation anchor is equal to the sum of the capacities of individual helixes. The helix capacity is determined by calculating the unit bearing capacity of the soil and applying it to the individual helix areas . Friction along the central shaft is not used in determining ultimate capacity. Friction or adhesion on extension shafts may be included if the shaft is rounded and at least 2.5” in diameter.
Soil test probe
Foundations have long been dependent upon excavation, penetration and lab tests of core samples. When construction is concentrated in an area, this is still desirable, but for an overhead line or underground pipeline, which may extend for hundreds of miles, economic feasibility requires a less costly yet dependable determination of soil properties.
The portable soil test probe provides a new dimension. This instrument, portable and operable by one man, will provide reproducible numerical data related to resistance of the soil to flow under load . It may be used in soils up the uniformity of hardpan , to any depth below the surface and without the need to make an excavation or otherwise disturb the soil.
A probe consists of a head on a square shaft with a number of extensions, all of which may be coupled together. A ratchet wrench with a torque-measuring handle is used to install, remove or take readings. Corner marks at 1-foot intervals provide means to determines the depth below the surface when a reading is taken. The hub of the probe head is forced into the ground by application of torque acting on the blade of the probe. Thus the torque required to turn the probe is proportional to the resistance of the soil to penetration of the hub. When determining end bearing foundation work , the bearing strength of the soil can be calculated directly from the probe reading. Most heavy-duty probes can withstand torque to 1800 (units?). That basically means that the probe will not penetrate packed gravel, shale or rock.
Probe chart
Chart under construction
Below depth (ft) probe (ft) description
13 0 0-100 top soil
10 5 150-175 Gray clay
13 10 150-175 Gray clay some red clay
13-15 175-225 Gray clay, traces of sand
20 20 225-300 gray clay with sand, light rock-wet
| Site Map | Contact Denver Foundation Repair | About Denver Foundation Repair |