Young Modulus of Rock/Sand Fill 1

[pang]

Can anyone suggest how to estimate the elastic modulus of General Fill (a mixture of cobbles, gravels and sand)?

 

[Ron]

The value you want is more likely the resilient modulus, a parameter used in pavement construction to assess strength and stability. You can estimate the resilient modulus from various stability parameters such as CBR and unconfined compressive strength. Correlations for these are given in the AASHTO Guide for the Design of Pavements (A three part design manual).

As a general rule, if completely granular and poorly graded, somewhere between 10,000 psi and 25,000 psi. If slightly cohesive or well graded, then values may go from around 25,000 psi to over 100,000 psi. To give you a "measuring stick", a good, granular pavement base material will typically be somewhere around 50,000 to 70,000 psi.

Ron

 

[KAM_imported]

If you are interested in the compression modulus of the soil for use in predicting shallow foundation settlement, the best way is to perform in-situ testing using the cone pentration test (CPT) or Marchetti dilatometer test (DMT). These methods cause less disturbance than the SPT method and are more reproducible; however, the DMT test would not be any good at this site due to the gravel, which would damage the blade. There are also correlations published in the geotechnical literature between SPT N-values and various soil types--but these are frought with uncertainty due to variability in N-values caused by inconsistent SPT procedures. Your site is complicated by the presence of gravel and cobbles in the soil--these particle sizes can result in erroneously high SPT N-values and estimated soil strength parameters due to the presence of rocks in the soil deposit--so be careful. Most good soil mechanics testbooks (Bowles, for example) provide N vs. E correlations. Depending on your budget, Schmertmann's Conical Load Test Method would allow you to back-calculate the actual elastic modulus of the upper soils at your site based on measured deflections of a conical temporary fill mound. Whatever you do, be conservative.