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Subsidence Inve�,tigation Quiros-Martine�z Residence-Zephyrhills,Florida SDII Project Number•3023547 ------- Push (Hand).Penetrometer Measurements The hand perietrometer measures the force required to thrust a probe into the soil. The hand penetrometer has been in use for many years, and experience has shown that there is a strong correlation be;tween penetrometer readings and the bearing strength of the soil. The farce required to advance the penetrometer is measured in mass per unit area. There is no st�indard method for the hand penetrometer. Standard Penietration Testing The Standard Penetration Test (SPT) is the most widely used method for testing the strength (bearing capac;ity) of a soil. SPT is a standard method that involves driving a split spoon sampler into the soil b;y dropping a 140 lb. hammer 30 inches onto an anvil connected to the drill siring. The number of hammer blows required to drive the spoon in 6-inch inerements is counted(these are termed blo w counts). For an 18-inch spoon, there are three blow count measurements, which are recorded as n�/n2/n3 (i.e., 3/4/15). The blow count for the first 6 inches (nl} is considered a seating blo� count and is not considered a meaningful measurement. The seating blows set the spoon and caL�se the spoon to pass through any materials that have fallen into the hole or that have been disturbed by drilling. The second and third blow counts (n2 and n3) are summed (N = nz + n3) to pr�,,duce the N value. N is measured in blows per foot of penetration. If a 24-inch spoon is used, the second and third coLmts are used to calculate N. The fourth 6-inch interval is for added info�-mation and sample recovery;the count is not part of the N determination. The split spoc�n is a hollow cylinder 2 inches in outside diameter and 1.5 inches inside. The spoon is split iin half along its length (18 or 24 inches) so that the soil can be recovered after the spoon is retrie�ved. The spoon is broken open, and the soil can be easily extracted from the spoon for characteriz��tion. It is possible t�;� conduct SPT continuously above the water table if the soils do not cave into the borehole and if ASTM methods are properly followed. Unless there is a risk of encountering buried utilitie�; or caving is probable, SPT measurements are usually taken continuously to a depth of 10 fe„t. If encountering a utility is a concern, the first few feet of the borehole may be hand augered. If caving is a problem, the SPT method utilizes drilling mud (a clay-water suspension) to stabilize the walls of the borehole. Typically, at 10 feet depth or when the water table is encouritered,caving is a concern and mud rotary baring begins. Rotary wash t�oring utilizes a rotating drill bit to cut through the soil. Drilling mud is flushed down the cent:;r of the drill pipe and bit (drill string), and it rises back to the drilling tub at the land surface �,here it is recirculated into the drill string. The mud cools the bit, stabilizes the borehoie wall,r, and flushes cuttings out of the hole. The ASTM method calls for drilling by rotary wash m��thods for 3.5 feet, then using the split spoon to determine blow counts and collect soil samples fitir the next 1.5 feet. Therefore, once mud rotary drilling is necessary, one N value is collected pez 5-foot interval.