{"id":48,"date":"2026-08-27T18:19:09","date_gmt":"2026-08-27T18:19:09","guid":{"rendered":"https:\/\/tmgmfg.com\/blog\/?p=48"},"modified":"2026-08-27T18:19:09","modified_gmt":"2026-08-27T18:19:09","slug":"how-to-perform-spt-testing-field-procedure-guide","status":"publish","type":"post","link":"https:\/\/tmgmfg.com\/blog\/how-to-perform-spt-testing-field-procedure-guide\/","title":{"rendered":"How to Perform SPT Testing: A Complete Field Procedure Guide"},"content":{"rendered":"\n

SPT testing drives a 2-inch split-spoon sampler 18 inches into the bottom of a borehole using a 140-pound hammer falling 30 inches. Mark the rod every 6 inches, count blows for each increment, and add the second and third counts. That sum is the N-value. The first 6 inches is seating and is never counted.<\/strong><\/p>\n\n\n\n

That is the whole test, and almost every part of it can be done wrong without anyone noticing. The N-value on a boring log looks like a measurement. It is really the output of a procedure — rod marking, hammer release, sampler condition, how you reached depth — and the procedure is where the error lives. A crew that seats the spoon in slough, or lets the rope drag on the cathead, hands the engineer a number that is 30 percent off and looks completely normal on the log.<\/p>\n\n\n\n

TMG Manufacturing builds the rigs that run this test and also manufactures the deep foundation products engineers design from<\/em> those N-values — the hammers, tripods, split spoons and baskets, and the helical piles<\/a> sized off the resulting log. We have no interest in making SPT sound more precise than it is.<\/p>\n\n\n\n\n\n

What the Standard Penetration Test Actually Measures<\/h2>\n\n\n\n

The SPT measures the resistance of soil to being displaced by a driven, thick-walled tube. It is a disturbance test, not a strength test: no stress-strain curve, no undrained shear strength, no friction angle directly. Those come from correlations, and every correlation carries the scatter of the field procedure inside it.<\/p>\n\n\n\n

Governing standard: ASTM D1586\/D1586M-18e1<\/strong>, active as of August 2026, with a revision work item (WK99626) open in subcommittee D18.02. The energy input is a 140 lb hammer<\/strong> falling 30 in.<\/strong> The current edition lists 750 mm as the separate hard-metric drop value; older editions and the ISO family use 760 mm, which is why you see both numbers in the wild.<\/p>\n\n\n\n

\"SPT
Figure 1. The 18-inch drive, the three 6-inch increments, and why the seating increment is discarded.<\/em><\/figcaption><\/figure>\n\n\n\n

Anatomy of a Split-Spoon Sampler<\/h2>\n\n\n\n