ETL 1110-1-138 Standard Penetration Test

DEPARTMENT OF THE ARMY U.S. Army Corps of Engineers CEEC-EG Washington, DC 20314-1000 ETL 1110-1-138 Technical Letter No. 1110-1-138 31 March 1988 Engineering and Design STANDARD PENETRATION TEST Distribution Restriction Statement Approved for public release; distribution is unlimited. CEEC-EG Engineer Technical Letter liiO-i-138 DEPARTMENT OF THE ARMY ETL 1110-1-138 u s. Army (Jorps Engineers Washington, D.C, 20314-iOOC~ 31 March 1988 Engineering and Design STANDARD PENETRATION TEST i, Purpose, This letter furnishes l.nformation and guidance on the conduct of the Standard Penetration Test (SPT), when Its penetration values are used in soil liquefaction evaluations. 2. APP llcabllity. This letter is applicable to all HQUSACE/OCE elements and field operating act.ivlties (FOA) having mlllt,ary construction and cIv1l works design responsibility, 3. References, See Enclosure i. Throughout this letter numbers in brackets refer to the numbered items in Enclosure i, 4. Background. In 1958, the American Society for Testing and Materials (ASTM) first adopted the “Standard Method for Penetration Test and Spilt-Barrel Sampling of Soils, ASTM Di586 (SPT)”. The SPT has been used routinely in subsurface exploration and SO1l design, with many engineering relationships between SPT N values and other SOI1 design parameters (such as relative density, angle of internal friction, shear strength, bearing capacity, and SO1l liquefaction potential) having been developed, However, In spite of the seemingly detailed “standard” method speclfled in ASTM D 1586-84 [i], there still exists many factors (see Enclosure 2 for factors affecting the SPT results [4] ) which lead to a wide variation In SPT results for a given S0114 This variation, t>r the low degree of repeatability, has caused difficulties in interpreting SPT results and using historical data with confidence. Recent research, especially In the dynamics of the SPT and the field energy measurement of the SPT hammers, have greatly advanced tlie knowledge of the SPT and as a result, the varlatlon of the test can be mlnlmlzed, ETL lllo- I-138 31 Mar 66 5. Dlscusslon. a. The theoretical SPT energy, E*, suppl led by a 140 lb hammer, falling freely 30 inches, 1s 4200 Ln-lb. From field measurements [8], the available energy, El, that actually reaches the sampler for doing the work of penetration can vary from 30Z tc} 85X of E*. The average El for the safety hammer and the donut hammer are 6iZ (ranging from 40Z to 78X), and 45Z (ranging from 30Z to 76%) of E*, respectively [5], I+.has also been shown [8] that SPT N values vary lnVerSelY with El. Therefore, the N values for a given soil can vary by a factor of about three due to variations In Ei. Ei depends on such factors as the mechanism of the drill rig, the fall height of the hammer, the efficiency of energy transfer at the impact from hammer to anvil, and to the drill rod, the length and type of drill rod, the number of turns of the rope around the cathead, the age of the rope, and the operator. If El 1s measured, the effect of such factors on the SPT can be eliminated or mlnlmized. b. ASTM D 4633-86, “Standard Test Method for Stress Wave Energy Measurement for Dynamic Penetrometer Testing Systems” [2], speclfles the requirements and the use of energy measurement equipment to measure El. The theoretical background of the two formulas and their related correction factors utilized BY ASTM D 4633-86 can be found In references [3], [8], and [10]. With the loss of energy traveling through the rod being considered negligible for rod lengths less than 100 feet [8], and after applylng the correction factors, the energy measured by a load cell located at least ten rod diameters length below the anvil (the hammer Impact point) should produce El, c,. To date, there have been only eight units of the SPT energy measurement equipment called SPT energy calibrators or s~mply calibrators [3], built in accordance with ASTM D 4633-86. One of the units 1s owned by the National Bureau of Standards (NBS) and the remainder are owned by private firms. Presently, Dr, George Goble at the University of Colorado is developing a new version of the SPT energy measurement equipment using the well known pile driving analyzer. The SPT energy calibrator [3], made by Binary Instruments Inc. , consists of a strain gage load cell and an Instrument box (essentially an analog computer). The load cell, which 1s located at least ten rod diameters length below the anvil transmits the stress wave (force-time history) by a cable to the instrument box that performs the Integration of the force-time history according to the two fOrmUlaS of ASTM D 4533-86 within the t.lme duration (At) of the first compressive wave tc~ obtain energy El. The SPT calibrator [5] does not always produce a 2 ETL 1110-1-138 31 Mar 88 rellable result due to damage of electronic circuits in the load cell, which causes the calibrator to prematurely cut off the recording of the downward travellng compressive wave resultlng In a reduced El. Also, a compressive wave returning (sometimes even without a hard driving condltlon) from the sampler results in an increased El. However, these two problems can be detected by checking the time duration of the first compressive wave, At, which should be theoretically equal to 2L’/C, where L’ = length of drill rod from load cell to the tlp of the sampler, and C = 16,800 ft/sec (the stress wave veloclty of the steel drill rod). Any results showing excessive deviation from the value At = 2L’/C should not be used, d. The sampler without liners (1,e, liavlng 1.5“ inside diameter) would obtain a lower N value of about 10% to 30Z than that of a sampler with llners (i,e. having 1-3{8” lnslde diameter). Schmertmann [7] concluded that removing the liners from a SPT sampler designed for llners improved recovery and removal, but It produced a significant reduction in N and tended to make the SPT more dependent on the sampler end bearing resistance, Seed [9] showed that the percent reduction was about 10X for looser sand and 25Z to 30Z for denser sand, Drillers in the United States often do not use such llners, while the routine practice of drillers in Japan uses a sampler having an inside diameter of 1-3/8” throughout its length. 6, Action to be Taken, The equipment and procedures used for the standard penetration test should be in general conformance with ASTM D 1586-84, The additional specifications below, with the exception of the method of recording penetration in gravelly materials, are Intended to improve the repeatability of the results, and provide results that are comparable to the bulK of the historical data, which are the emplrlcal basis for evaluating liquefaction potential and other important engineering properties by the SPT. It must be emphasized that special care and attention to detail are needed to obtain results of the quallty and reliability needed in seismic stability studies, All relevant details of the procedure should be clearly shown on the driller’s log. a, Drive Weight Asse~&. To produce results that are comparable to the historical data, the ideal drive assembly should consistently deliver sixty percent of the theoretical free fall energy to the rods [9], Safety hammers using a rope and cathead with two turns of the rope around the cathead produce an average of approximately sixty percent of the theoretical energy, 3 ETL lliO-1-138 31 Mar 88 but the results can vary depending on the operator and other factors as mentioned In paragraph 5a. Automatic hammers that permit nearly a free fall can produce more consistent results with proper setup and adjustments, but generally deliver more energy to the rods. The best results can be obtained by using an automatic hammer with a known energy output, When the data 1s analyzed, the results can be corrected to the standard sixty percent ener~y with the following relationship. Where ERl = El/E* IS measured energy ratio for the drill rlg and hammer system used, Nm q blowcounts measured with El, and N6~ = blowcounts corrected to 60Z energy ratio, Improvements to the hammer or changes in the operating procedure can change the results in an unknown way, and should be avoided unless the hammer WI1l be recalibrated. For SO1l liquefaction analyses, the energy El of the drill rlg and the hammer to be used for the project should be measured with a SF’T energy calibrator. Llml+.ed and changing sources for SF’T energy callbrat.icln are avallatle, :and fI-1*3 F~.3Ashould contact. HG1.ISACE, CEEC:-EG when SUCI-Jcallbratlclll lr needed for equipment operated by the Corps of KnRlneeP:;, or’ specified f~>r use by contractors, b. ~iJd. Type NW rods should genel’.ally he used and +.h.etype —. of rods should be recorded. Because t-he correction to the blowcount 1s required for short rod lengths [3], [8], [10], the length of rod should also be recorded for each drive where the rod length is less than 45 feet, The current practice [91 for correcting the reduced Ei for short rod lengths is by multiplying the measured N values, made wlthln the hole depth of less than 10 feet, by a factor of 0. 75. Alternately, the measured N values can be divided by the K2 values llsted in ASTM ~)4633-86 tcl obtain the corrected N values. The threaded couplings in the rods should be snug. Generally, grease should be used to ald in breaking the rods, but string or other energy absorbing materials should not be used In the ,Iolnts. c. Sampler. A sampler with a st..raight.inner wall having an inside diameter of 1-3/8 inches should be used. If the SamIJlel’ has provisions for a liner, It should be used with a llner In place. This practice would be comparable to the condlt.lon under which the bulk of the historical data was obtained. d. Blowcoun+. Rate. The blOWCOUnt rate should generally be 20 to 40 blows per minute, If lt is necessary to use a slower rate (see paragraph 61) that fact should be carefully noted in the log. 4 ETL 1110-1-138 31 Mar ~.5 e. Drllllng Mud. A bentonlte base drilllng mud sh~ulfi be used to support the hole and to prevent heave of the bo~.t.ornl~f the hole. The mud column must also be above the level needed to balance artesian pressures that may be encountered, Care stlould be taken ‘to insure that a safe mud level 1s maintained while the sample 1s being withdrawn. f! Hole Diameter, To provide lateral support. for the drill rod +-he hole should be Kep+. to a diameter of five Inches maximum. Where casing IS used, it should be of four Inch lnslde (ilamet.er and the casing should be kept- as far as possible away from the test Interval. e, ~ the Hole. To mlnimlze disturbance, the hole should be cleaned out to a depth of about one foot below the previous drive. This permits one test In each 2-1/2 foot. interval. The method of rotary drilllng with side discharge bits and drilling mud should be used to advance the hole with special precautions required so that the material below the bottom of the hole 1s not disturbed, Tricone roller bit’s have been used su~cessfully, Fishtail or drag bits should have baffles that divert the flow of the drilllng fluld upwards. h, Samples. Generally, It. w1ll be necessary to perfOrm a sieve analysls on each sample and possibly a hydrometer analysls and!or determine Atterberg limlts. Therefore, as much of the sample should be saved as feasible, after the contaminated material at the top of t-he sample tube 1s discarded. More than one jar sample may be required to be saved In some cases. 1. Gravelly Sands. In granular SOIIS con+.alnlng occasional pieces of gravel, the method of recording should be modl.fle~?., The mocllfled procedure 1s to measure and record, to the nearest 1/4 inch, the cumulative penetration after each blow. However, lf the penetration per blow 1s less than about 1/2 inch the measurement may be made after every other blow or less frequently, so long as at least one measurement IS rel;orcl.edfor each Inch of penetration. For each measurement, ref:erd the cumulative number of blows and the cumulative penetra+.lon. The “ results should be presented on a plot of cumulative penetratlc,n versus cumulative blowcount. Using the slope of this curve, an estimate can frequently be made of what the blowcount would have been without the influence of gravel. ETL iliO-I-138 3i Mar 88 7, Implement a%lon, This letter will have routine appllcatl~n as defined In paragraph 6c, ER lliO-345 -iOO. FOR THE COMMANDER: 2 Encls as GERBERT H. KENNON / Chief, Englneerlng Dlvl.slon Directorate of Eng~neerlng and ConstructIon 6 ETL 1110-1-138 References 31 N!ar88 1. American Society for Testing and Materials (ASTM), “Standard Method for Penetration Test and Split-Barrel Sampling of Soils,” Designation D 1586-84, ASTM, 1987 Annual Book of Standards, Section 4, Volume 04.08. 2. American Society for Testing and Materials (ASTM), “Standard Test Method for Stress Wave Energy Measurement for Dynamic Penetrometer Testing Systems,” Designation D 4633- 86, ASTM, 1987 Annual book of Standards, section 4, Volume 04.08. 3. Hall, J.R. (1982), “Drill Rod Energy as a Basis for Correlation of SPT Data,” Proceedings of the Second European Symposium on Penetration Testing, Amsterdam, A.A. Balkema, Rotterdam, Volume 1, PP. 57-60. 4. Kovacs, W.D., Salomone, L.A., and Yokel, F.Y. (1981), “Energy Measurement in the Standard Penetration Test,” Building Science Series 135, U.S. Government Printing Office, Washington, D.C. 5. Kovacs, W.D., Salomone, L.A., and Yokel, F.Y. (1983), “Comparison of Energy Measurements in the Standard Penetration Test Using the Cathead and Rope Method,” Final Report, prepare for the U.S. Nuclear Regulatory Commission, NuREG/cR-3545 . 6. Kovacs, W.D. and Salomone, L.A., (1984), “Field Evaluation of SPT Energy, Equipment, and Methods in Japan Compared With the SPT in the United States,” NBSIR 84-2910, U.S. Government Printing Office, Washington, D.C. 7. Schmertmann, J.H. (1979), “Statics of SPT,” Journal of the Geotechnical Engineering Division, ASCE, Vol. 105, No. GT5. 8. Schmertmann, J.H., and Palacios, A. (1979), “Energy Dynamics of SPT,” Journal of the Geotechnical Engineering Division, ASCE, Vol. 105, No. GT8. 9* Seed, H.B., Tokimatsu, K., Harder, L.F., and Chung, R.M. (19850), “Influence of SPT Procedures in Soil Liquefaction Resistance Evaluations,” Journal of the Geotechnical Engineering Division, ASCE, Vol. 111, No. 12. 10. Yokel, F.Y. (1982), “Energy Transfer in Standard Penetration Test,” Journal of the Geotechnical Engineering Division, ASCE, Vol. 108, No. GT9. Enclosure 1 ETL 1110-1-138 31 Mar 88 Factors Affecti~ the Usults of the SPT After Fletcher, 1965,~rcusonlt e2. 1977,lnd S~rcnoo, 1917 r 1 I I 1 T.-t Det*ll I Estimted ?ercemt \ I Cffectoa N-vslue ~ by Uhich Guse I \ I -n Chtoge N ~I \ I 1 Inedcquate cleaaln80f disturbed *terfa2.t in the borehole I I Tailure touintaio mlfficient I hydrostatic beed in the borehole / Variations frm the lrect 762 m (30 in) drop I I kY18thof drill rods <30 (lo ft) : 10 to 16m (30t086ft) I >30= (loOft) I Any laterference with free fall : cusiw2 to3 turaa) ~ UafnX defomd SQ1* spoon 1 I Excesalve driving of somple spoon before the blow count ! i ?allure of drf22er tocqletely -&a#e I the tentioa of the rope I I Drivfn& 889pleopoonabove tbe bottmof I the -sins ! Uoe ofuire 22ne r8ther ttimb rope I C&re2uenes8 In recordi~ blow count ! ~ Xtuoffic3ent lmbrimtfon of tbeabve Le*rstieof borehole ~ Pmtretioo fsteml I Wto12do-t~dH6 to 18i0 I I -12 ~ozt~wreu$sb~jsfi I I US* of drlXXi~mucl-r*ueusiog In I Decrm8e8 hcrea8ea Zither Increases Increases Increeses Decrea8es lncreeaes Increases Increeaes Zither &creases DecrU8e* nem8*s hcruses Xnt-ses tieee Utber k~ee Enclosure 2