There are numerous published correlations between soil stiffness and shear strength and SPT N-values. Due to the inherent variability in SPT N (delivered energies can vary from 40% to over 90%), these correlations should be used with extreme caution. In addition, the SPT was invented for...
We use crushed stone or gravel as mud-mats in footings in clayey soils similar to your case. We normally recommend a No. 57 gradation crushed stone or gravel, and a thickness of 8 to 10 inches. If thicker layers are used, we recommend that each 12-inch thickness of stone backfill be densified...
Any soil (no matter how weak) will provide some lateral resistance to lateral loading. Whether the available capacity is sufficient to support the anticipated loads must be evaluated. The programs LPILE (single piles or shafts) and GROUP (pile or shaft groups)by ENSOFT are good and relatively...
Drilled shafts are typically used by the DOT in Florida for the support of signposts as they are very efficient in carrying lateral loads. A comprehensive design guide for drilled shafts can be obtained from the ADSC at www.adsc-iafd.com.
We use proofrolling to detect near surface zones of bad fill materials, or soft clays or clayey sands. We normally recommend use of a loaded dump truck for proofrolling. Areas where the soil ruts permanently are identified by the proofrolling operations. One can then perform shallow manual...
I generally agree with the others. The pocket penetrometer is used in the lab to estimate the unconfined compressive strength and/or cohesion of cohesive soil samples (preferably undisturbed samples). Once a profile of values is obtained, the ultimate bearing capacity of a footing or pile can...
Youy may want to consider use of flexible, lightweight, plastic pipe (such as Spirolite) in this application. The use of lightweight bedding materials (such as Solite gravel) is also suggested to reduce the net stress increase felt by the peats. Geosynthetics may also be of benefit in limiting...
If the sands are relatively clean (less than 15% fines), I would recommend that you compact the upper 12 inches of bearing soils to 95% ASTM D1557 (Modified Proctor) density. Perform density tests to confirm acceptable compaction. Dewater prior to compacting the soil, if necessary. If the...
Peaty soils can create some pretty acidic conditions--is it possible that there has been some degradation of the chalk due to acidic groundwater below the embankment?
In addition to the above comments, you might want to consider helical piers (AB Chance Co. or Atlas Systems, Inc.) or small diameter minipiles that would be installed by a specialty contractor. Both Atlas and Chance should have websites that will direct you to their residential underpinning...
Is it possible that creation of the wetland area caused a drop in the water table beneath the embankment? If so, the effective stress on the peat has increased, resulting in new load and settlement. Another posssibility is exposure of some of the peat due to a lowering of the water table...
Besides using footings, you might want to consider short, helical compression piers. A grade beam or cap would still be required. Both the AB Chance Company and Atlas Systems, Inc. make these foundation elements, and have web sites.
This is the case of many structures built in Florida. Main issues will be relatively low available bearing capacity, and constructability. Buoyancy effects should also be considered. Contractor should be aware that dewatering will be required for footing construction. Depending on required...
