LLC

With our long-lost-cone (LLC), you can now
determine and log soil grain size, soil consistency,
and equivalent SPT N-values, to 8 meter depths,
using our hand-carried, low headroom apparatus.

This long-lost-cone (LLC) differs from our normal cone by having a 4 inch long mantle, rather than
a 1.5 inch long mantle, and by being engaged onto the sounding rods so that the cone is turned as a torque wrench that has been inserted into the anvil is turned. It's called the long lost cone because of its mantle length, not because of its age, We believe in losing a cone at completion of each test because the cones' no-clearance extraction is both uneconomically time-consuming and too stressful to the sounding rods.

You drive the LLC by a manually or electric cathead raised conventional, 35 pound, 15 inch drop, hammer through an end rod that locks onto the LLC with respect to torque, but slips away from it with respect to extraction. Polymer slurry, filling the annulus between the cone's path and the rods, prevents soil to rod friction.

Blows per 10 cm penetration are noted as usual. Every 10 to 30 cm, driving is halted and the socket and hex key of a torque wrench are inserted into the anvil cap bolt through the vent hole in the top of the hammer. The developed mantle adhesion torque is then measured and recorded for that depth.

That measured adhesion, along with the blows per 10 cm, allow determination of the soils' grain size, because for any relative density or consistency; granular soils have less adhesion than silts, silts have less adhesion than clays, and clays have less adhesion than organics.

However, logging of grain size, consistency, and SPT N-values from an LLC is complicated by, as well as made possible by, the longer cone mantle. Calculated dynamic cone resistances presume that the entire dynamic force reaction is provided by the bearing resistance of the soil. With the LLC, part of the resistance to penetration comes from the adhesion of the longer mantle, which is greater for clays than for sands. Our logging software recognizes the adhesion's effect on calculated dynamic cone resistances, and adjusts the logged dynamic cone resistances appropriately.

For those familiar with the logging of soil grain sizes by static fricton cone, where a sleeve's vertical friction is measured every 20 cm and used to identify soil grain sizes, this dynamic, long-lost-cone's use is analogous. When using the static friction cone,soil grain sizes are estimated with the help of a Schmertmann Chart having Friction Ratio as the abscissa and Cone Bearing as the ordinate. The Wildcat dynamic cone LLC logging software uses a similar chart to estimate and log soil grain sizes from LLC driving and torque records.

In 1991 we tested a large number of sites to correlate our dynamic cone resistances with SPT N-values. Since that time, hundreds of firms have used those correlations, and verified the validity of our correlations. With the LLC we have again correlated Dynamic Cone Resistances to SPT N-values, and we again use our software to log equivalent SPT N-values.

Look at the enclosed Log in LLC Log. It is an LLC test of a local site having SPT samples and visual classifications, and it fully logs grain sizes, consistencies or relative densities, and SPT N-values.