Ciao agi,
purtroppo non ho il libro di Bruschi e non conosco la formula che tu citi; ma posso forse aiutarti indirettamente confermandoti che nella terza edizione di "Piling engineering" Fleming et al. (2009) sono riportate le stesse indicazioni citate da Bruschi ma non la formula della prima edizione. Poi introduce nuove interessanti formulazioni legate all'utilizzo del penetrometro statico MA solo sui pali infissi che non mi sembra essere il tuo caso.
come vedi
"...while for piles bored with continuous-flight auger, values of 0.9 (for sandy soils) down to 0.6 (for silts and silty sands) are taken."
Interessante è anche
"In general, the roughness of the hole will ensure that the full soil friction is mobilized at the pile edge. However, potential loosening of the soil during the installation process maybe allowed for by taking the friction angle between phi' e phicv"
Proseguendo come ricapitolazione
"For continuous-flight auger piles, experience indicates that a value of K=0.9 is appropriate in sands and gravels. Rather lower values, as low as 0.5 to 0.6, have been found with silts and silty sands, possibly due to entraining material from the sides of the pile into the spoil during augering, thus reducing the horizontal stresses in the ground. Close control is needed during construction in order to monitor the amount of material removed and the rates of concrete delivery and auger extraction as the pile is formed"
Era meglio se ti scannerizzavo la pagina direttamente....
Un saluto
