1.1 本试验方法描述了通常称为标准贯入试验（SPT）的程序，该程序用于在140 lb[63.5 kg]的锤子下落30 in的情况下驱动分体桶取样器。[750 mm]以获得用于识别目的的土壤样品，并测量土壤对标准2英寸渗透的阻力。直径为[50 mm]的取样器。SPT“ N “数值是在1.5 ft[0.45 m]驱动间隔的0.5至1.5 ft[0.15至0.45 m]深度间隔内驱动采样器所需的锤击次数。 1.2 试验方法 D4633 通常需要测量给定落锤系统的钻杆能量，并使用测量的钻杆能量， N 可以将值校正到标准能级。实践 D6066 使用测试方法 D1586 和 D4633 并对锤击、锤击能量和钻探方法提出了额外要求，以确定用于液化评估的松散砂的能量修正贯入阻力。 1.3 实践 D3550/D3550M 是一种类似的程序，使用由锤子系统驱动的更大直径分体桶取样器，可以允许不同的锤子质量。实践中的贯入阻力值 D3550/D3550M 不符合本标准。 1.4 测试结果和识别信息用于地下勘探，有着广泛的应用，如岩土、地质、地质环境或地质水文勘探。当地质水文调查需要详细的岩性时，使用连续采样方法( D6282/D6282M , D6151/D6151M , D6914/D6914M )建议在增量SPT时 N 设计目的不需要值（参见 4.1.1 ). 1.5 除非另有规定，否则贯入阻力测试通常在5英尺[1.5米]的深度间隔或在钻井过程中观察到材料发生重大变化时进行。 1.6 本试验方法仅限于在非岩化土壤和最大粒径约小于1的土壤中使用- 取样器直径的一半。 1.7 本试验方法涉及使用旋转钻井设备（指南 D5783 实践 D6151/D6151M ). 其他钻孔和取样程序（指南 D6286 和 D6169/D6169M )是可用的，可能更合适。未考虑无钻孔的手动或浅层采样。应按照惯例记录地下调查 D5434 . 样品应按照惯例进行保存和运输 D4220/D4220M 使用B组。土壤样本应按照惯例通过组名和符号进行识别 D2488 . 1.8 所有观察值和计算值应符合实践中确定的有效数字和舍入准则 D6026 ，除非被本试验方法取代。 1.8.1 用于规定如何在标准中收集/记录和计算数据的程序被视为行业标准。此外，它们代表了通常应保留的有效数字。 使用的程序不考虑材料变化、获取数据的目的、特殊目的研究或用户目标的任何考虑因素；通常的做法是增加或减少报告数据的有效位数，以与这些考虑因素相称。考虑工程数据分析方法中使用的有效数字超出了这些测试方法的范围。 1.9 单位- 以英寸-磅或国际单位制（括号内）表示的数值应单独视为标准值。每个系统中规定的值可能不是精确的等效值；因此，每个系统应相互独立使用。将两个系统的值合并可能会导致不符合标准。以英寸磅以外的单位报告试验结果不应视为不符合本惯例。本文所示的SI等效单位通常符合现有国际标准。 1.10 渗透阻力测量通常涉及安全规划、管理和文件。本试验方法并非旨在解决勘探和现场安全的所有方面。 1.11 测试的执行通常涉及使用钻机；因此，适用安全标准（例如OSHA法规、， 2. NDA钻井安全指南， 3. 必须遵守钻井安全手册和其他适用的当地机构法规）。 1.12 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.13 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 4.1 该测试是全球最常用的地下勘探钻井测试。SPT有许多国际和国家标准，这些标准大体上符合本标准。 6. 该测试提供了用于识别目的的样本，并提供了可用于岩土工程设计目的的贯入阻力测量。许多当地和广泛发布的与击数相关的国际相关性，或 N -土壤的工程特性值可用于岩土工程目的。 4.1.1 对于环境或水文地质勘探，SPT增量采样不是首选的土壤采样方法，除非SPT N -设计需要值。连续采样方法，如直接推动土壤采样（指南 D6282/D6282M )，或使用空心杆螺旋钻连续取芯（实践 D6151/D6151M )或声波钻（练习 D6914/D6914M )提供岩性的最佳连续记录。可以使用SPT取样器进行连续采样，但与其他方法相比速度较慢，并且 N 数值可能不可靠（请参阅 4.6.1 ). 通过使用地球物理等筛选测试和圆锥贯入仪等直接推动剖面测试（测试方法），可以减少详细岩性的采样 D5778 )、动态圆锥贯入仪或电阻率探头。 4.2 标准贯入试验 N 值受测试设计和执行中允许的许多变量的影响（参见 附录X1 ). SPT测试中的能量传输研究始于20世纪70年代，研究表明，不同的落锤系统为深度采样器提供不同的能量。有许多不同的液压锤设计，因此根据测试方法获得所用液压锤系统的能量传递比（ETR）非常重要 D4633 . 各种液压锤系统的ETR在最大势能（PE）的45%到95%之间变化。 自 N -值与传递的能量成反比，从而 N 来自不同系统的数值远未达到标准。现在通常的做法是纠正 N 能量水平达到总能量（PE）的60%，或 N 60 本文和实践中提出的价值观 D6066 . 本标准不要求报告ETR或 N 60 但强烈建议注意并报告（如有）。如果已知锤子/砧座/杆系统的ETR，则校准后锤子PE仍可能变化，因此必须监测锤子跌落高度/速率，以确认一致的性能。报告任何出现的锤击高度不符合要求的30英寸值。试验期间[750 mm]。对于液压锤系统，使用以前的ETR数据并不能确保其在当前项目中也能执行相同的操作。如果未获得现场ETR，请确保检查液压锤跌落高度/速率，以确保液压锤的操作与之前检查时相同。 4.2.1 其他机械变量和钻孔误差也会对 N 价值如中所述 X1.4 . 钻孔方法可能对测试产生重大影响（参见 4.5 ). 虽然标准贯入试验锤系统是标准化的，了解ETR，但钻探方法不是标准化的，可以使用多种钻探方法。 4.3 SPT适用于各种土壤。土壤术语 N -数值参考 附录X2 对于粘土（粘性土）的稠度和砂（无粘性土）的相对密度，由Terzaghi和Peck提出，并在岩土工程实践中常用。在密度较大的土壤中，可以使用多种钻探方法轻松进行SPT钻探，但在较软和较松的土壤中存在一些困难。本试验方法仅限于非岩化或非胶结土壤以及最大粒径约为取样器直径一半或更小的土壤。大颗粒导致更高的锤击数，并可能使数据不适用于与更细土壤的经验相关性。 例如，洁净砂的室内试验表明，粗砂的锤击数高于中细砂（参见 X1.6 ). 在砾石含量低于20%的砾石土壤中，液化调查可能需要记录每次锤击的贯入度，以尝试将结果推断为击砂次数（见 X1.7 ). 含有砾石、鹅卵石或巨砾的土壤沉积物通常会导致贯入受阻、设备损坏和不可靠 N 砾石堵塞采样器时的值。 4.3.1 沙地- 标准贯入试验广泛用于测定渗透过程中排水干净砂的工程特性。获取干净沙子的“完整”土壤样本进行实验室测试既困难又昂贵（见薄壁管，实践 D1587/D1587M )因此，工程师使用砂土中的渗透结果来预测工程特性( 附录X1 ). 附录X2 和 X1.6 提供了砂的一些估计特性。潜水面以下松散砂中的SPT存在问题，因为它们在钻井过程中不稳定。 实践 D6066 提供了松散砂中SPT的受限钻探方法，以评估地震液化潜力。实践 D6066 该方法依靠泥浆旋转钻井、套管推进器和充液空心螺杆螺旋钻。 4.3.2 粘土- SPT易于在中硬稠度和更高稠度的粘土中使用各种钻探方法进行。SPT在软至极软粘土中不可靠，因为粘土在测试开始前仅在杆的静态重量或杆和锤的重量下屈服或“失败”。自动液压锤总成的重量更重，这一问题更加突出（参见 X1.3.1.4 )但是可以通过设计为浮动在铁砧上的自动锤来缓解（参见 5.4.2.1 ). 可能存在如此大的变化 N 软粘土的SPT值是公认的粘土不排水抗剪强度的较差预测值。建议使用更合适的方法评估软粘土，如CPT（试验方法 D5778 )，叶片剪切（试验方法 D2573/D2573M )和/或薄壁管取样（实践 D1587/D1587M )和实验室测试。 4.4 落锤系统- SPT可以使用多种锤击系统进行。典型液压锤系统按使用顺序如下所示: (1) 液压自动链凸轮/机械把手释放锤 (2) 机械式炸面圈锤 (3) 绳索和猫头操作的安全锤 (4) 绳索和猫头操作的油炸圈饼锤 4.4.1 为了在试验过程中获得一致的能量，首选自动和跳闸锤。自动链式凸轮锤也是最安全的，因为锤子是封闭的，操作员可以远离设备。如果使用绳索和猫头方法，封闭式安全锤比圆环锤更安全，因为冲击砧是封闭的。有关液压锤系统的更多信息，请咨询 X1.3 . 4.5 钻孔方法- SPT使用的主要钻井方法是裸眼旋转钻井（指南 D5783 )和空心螺杆钻（实践 D6151/D6151M ). 比较这些方法及其对SPT的影响的研究有限 N 值（参见 X1.5.1.1 ). 4.5.1 研究表明，对于大多数地下水位以下的土壤，裸眼膨润土旋转钻井是最可靠的方法。空心杆螺旋钻存在饱和松散砂问题，因为它们必须充满流体。研究还表明，如果将套管打入测试深度段附近，使用水作为钻井液的打入套管会对标准贯入试验产生不利影响。使用套管并允许流体不平衡也会对地下水位以下的砂造成扰动。充液旋转套管推进器（指南 D6286 )在实践中，作为松散砂的允许钻探方法 D6066 . 4.5.2 SPT与其他钻井方法一起使用，包括反循环、声波钻井和直接推进法。有一些问题没有被研究记录下来，直接推动（指南 D6282/D6282M )，声波钻孔（实践 D6914/D6914M )和使用重型套管锤的反循环方法（指南 D6286 )极端动态荷载和振动可能会干扰一些土壤，如砂和软粘土，使其超过固定区间。负责调查的专业人员应在这些条件下评估SPT，如果怀疑钻井干扰，则 N 可以对照第节中的其他钻孔方法检查值 4.5 或者在套管前后部署替代钻井方法。 4.5.3 SPT也使用实心螺旋钻在地下水位以上的浅层进行（实践 D1452/D1452M )，但在地下水位以下，钻孔可能会发生坍塌砂。已在稳定材料中钻至100英尺或更深处的实心阀杆钻孔。 4.5.4 SPT很少在电缆工具或空气旋转钻井中进行。 4.6 规划、执行和布局- 当使用SPT钻孔时，通常要求其他配套钻孔或测试孔位于SPT钻孔附近或周围。 一般来说，在100英尺[30米]的深度内，表面钻孔不应小于10英尺[3米]。最小值将接近5英尺[2米]，但在此间距下，如果存在显著的垂直偏差，则可能会遇到钻孔。 4.6.1 测试深度增量- 测试间隔和位置通常由项目工程师或地质学家规定。典型做法是在均质地层中以5英尺[1.5米]或更少的间隔进行测试。如果在基质中遇到不同的土壤类型，则在发现变化后立即进行测试。建议在两次测试之间，以至少1 ft[0.25 m]的最小清理间隔清理钻孔，该清理间隔超过先前测试深度的终止点，以确保测试隔离，并检查下一次测试的钻孔条件。因此，标准贯入试验典型实践的最近间距为2.5 ft[0.75 m]。用户可以根据钻孔条件和设计数据需求（如硬土或薄层）调整测试间隔之间的清理。 连续SPT的实践 N -不建议确定值，但可以在测试前仔细清理。测试之间必须清理钻孔（参见 6.5 ). 在连续间距下，没有额外的清洗深度， N 数值可能会受到之前样本驱动干扰的不利影响，尤其是在较软的土壤中，但影响尚不清楚。一些实践者喜欢将采样器超速行驶0.5英尺[0.15米]，以获得总行驶间隔为2.0[0.6米]的额外土壤样本。如果 N -该值仍然是驱动间隔的0.5到1.0 ft[0.15到0.3 m]间隔的总和，并且在测试之间进行合理的清洗。 4.7 本试验方法根据实践提供了a类和B类土壤样本 D4220/D4220M 适用于土壤识别和分类（实践 D2487 和 D2488 )，含水量（试验方法 D2216 )和比重试验（试验方法 D854 ). 土壤可以进行一些高级实验室测试。小直径、厚壁、驱动取样器将无法获得适用于高级实验室测试的样品，例如用于核心强度或压缩性的样品。参考指南 D6169/D6169M 对于提供实验室级完整样品的取样器。 注1: 本实践产生的数据和解释的可靠性取决于执行该实践的人员的能力以及所用设备和设施的适用性。符合实践标准的机构 D3740 通常认为能够进行合格测试。本规程的使用者应注意遵守规程 D3740 不能保证可靠的测试。可靠的测试取决于几个因素和实践 D3740 提供了一种评估其中一些因素的方法。 实践 D3740 是为从事土壤和岩石测试、检验或两者兼有的机构开发的。 因此，它并不完全适用于执行该现场测试的机构。该测试方法的用户应认识到实践框架 D3740 适用于评估执行本试验方法的机构的质量。目前，没有已知的合格国家机构对执行该试验方法的机构进行检查。

1.1 This test method describes the procedure, generally known as the Standard Penetration Test (SPT), for driving a split-barrel sampler with a 140 lb [63.5 kg] hammer dropped 30 in. [750 mm] to obtain a soil sample for identification purposes, and measure the resistance of the soil to penetration of the standard 2 in. [50 mm] diameter sampler. The SPT “ N ” value is the number of hammer blows required to drive the sampler over the depth interval of 0.5 to 1.5 ft [0.15 to 0.45 m] of a 1.5 ft [0.45 m] drive interval. 1.2 Test Method D4633 is generally necessary to measure the drill rod energy of a given drop hammer system and using the measured drill rod energy, N values can be corrected to a standard energy level. Practice D6066 uses Test Methods D1586 and D4633 and has additional requirements for hammers, hammer energy, and drilling methods to determine energy corrected penetration resistance of loose sands for liquefaction evaluation. 1.3 Practice D3550/D3550M is a similar procedure using a larger diameter split barrel sampler driven with a hammer system that may allow for a different hammer mass. The penetration resistance values from Practice D3550/D3550M do not comply with this standard. 1.4 Test results and identification information are used in subsurface exploration for a wide range of applications such as geotechnical, geologic, geoenvironmental, or geohydrological explorations. When detailed lithology is required for geohydrological investigations, use of continuous sampling methods ( D6282/D6282M , D6151/D6151M , D6914/D6914M ) are recommended when the incremental SPT N value is not needed for design purposes (see 4.1.1 ). 1.5 Penetration resistance testing is typically performed at 5 ft [1.5 m] depth intervals or when a significant change of materials is observed during drilling, unless otherwise specified. 1.6 This test method is limited to use in nonlithified soils and soils whose maximum particle size is approximately less than one-half of the sampler diameter. 1.7 This test method involves use of rotary drilling equipment (Guide D5783 , Practice D6151/D6151M ). Other drilling and sampling procedures (Guides D6286 and D6169/D6169M ) are available and may be more appropriate. Considerations for hand driving or shallow sampling without boreholes are not addressed. Subsurface investigations should be recorded in accordance with Practice D5434 . Samples should be preserved and transported in accordance with Practice D4220/D4220M using Group B. Soil samples should be identified by group name and symbol in accordance with Practice D2488 . 1.8 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026 , unless superseded by this test method. 1.8.1 The procedures used to specify how data are collected/recorded and calculated in the standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of these test methods to consider significant digits used in analysis methods for engineering data. 1.9 Units— The values stated in either inch-pound or SI units [presented in brackets] are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. Reporting of test results in units other than inch-pound shall not be regarded as nonconformance with this practice. SI equivalent units shown herein are in general conformance with existing international standards. 1.10 Penetration resistance measurements often will involve safety planning, administration, and documentation. This test method does not purport to address all aspects of exploration and site safety. 1.11 Performance of the test usually involves use of a drill rig; therefore, safety requirements as outlined in applicable safety standards (for example, OSHA regulations, 2 NDA Drilling Safety Guide, 3 drilling safety manuals, and other applicable local agency regulations) must be observed. 1.12 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.13 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 4.1 This test is the most frequently used subsurface exploration drilling test performed worldwide. Numerous international and national standards are available for the SPT which are in general conformance with this standard. 6 The test provides samples for identification purposes and provides a measure of penetration resistance which can be used for geotechnical design purposes. Many local and widely published international correlations which relate blow count, or N -value, to the engineering properties of soils are available for geotechnical engineering purposes. 4.1.1 Incremental SPT sampling is not a preferred method of soil sampling for environmental or geohydrological exploration unless the SPT N -value is needed for design purposes. Continuous sampling methods such as Direct Push Soil Sampling (Guide D6282/D6282M ), or continuous coring using Hollow-Stem Augers (Practice D6151/D6151M ) or Sonic Drills (Practice D6914/D6914M ) provide the best continuous record of lithology. Continuous sampling can be performed with SPT samplers, but it is slow compared to other methods, and N values may unreliable (see 4.6.1 ). Sampling for detailed lithology can be reduced by using screening tests such as geophysics and Direct Push profiling tests such as Cone Penetrometers (Test Method D5778 ), Dynamic Cone Penetrometer, or electrical resistivity probe. 4.2 SPT N values are affected by many variables allowed in the design and execution of the test (see Appendix X1 ). Investigations of energy transmission in SPT testing began in the 1970’s and showed that differing drop hammer systems provide different energies to the sampler at depth. There are so many different hammer designs that it is important to obtain the energy transfer ratio (ETR) for the hammer system being used according to Test Method D4633 . ETR of various hammer systems has shown to vary between 45 to 95 % of maximum Potential Energy (PE). Since the N -value is inversely proportional to the energy delivered, resulting N values from different systems are far from standard. It is now common practice to correct N values to an energy level of 60 % of total (PE), or N 60 values as presented here and in Practice D6066 . In this standard it is not required to report ETR or N 60 but strongly advised to be noted and reported if available. If ETR of the hammer/anvil/rod system is known, the hammer PE can still vary after calibration, thus it is essential that hammer drop heights/rates be monitored to confirm consistent performance. Report any occurrence of hammer drop heights that do not meet the required value of 30 in. [750 mm] during testing. Using previous ETR data for a hammer system does not assure that it will perform the same on the current project. If onsite ETR is not obtained, be sure to check hammer drop height/rates to assure the hammer is operating the same as when previously checked. 4.2.1 Other mechanical variables and drilling errors can also adversely affect the N value as discussed in X1.4 . Drilling methods can have a major effect on testing (see 4.5 ). While the SPT hammer system is standardized knowing ETR, drilling methods are not, and a variety of drilling methods can be used. 4.3 SPT is applicable to a wide range of soils. For nomenclature on soil in terms of N -value refer to Appendix X2 for consistency of clays (cohesive soils) and relative density of sands (cohesionless soils) as proposed by Terzaghi and Peck and used commonly in geotechnical practice. SPT drilling can be performed easily using a variety of drilling methods in denser soils but has some difficulty in softer and looser soils. This test method is limited to non-lithified or un-cemented soils and soils whose maximum particle size is approximately one-half of the sampler diameter or smaller. Large particles result in higher blow counts and may make the data unsuitable for empirical correlations with finer soils. For example, chamber tests on clean sands have shown coarse sands have higher blow counts than medium fine sands (see X1.6 ). In gravelly soils, with less than 20 % gravel, liquefaction investigations may require recording of penetration per blow in an attempt to extrapolate the results to sand blow counts (see X1.7 ). Soil deposits containing gravels, cobbles, or boulders typically result in penetration refusal, damage to the equipment, and unreliable N values if gravel plugs the sampler. 4.3.1 Sands— SPT is widely used to determine the engineering properties of drained clean sands during penetration. Obtaining “intact” soil samples of clean sands for laboratory testing is difficult and expensive (see thin walled tube, Practice D1587/D1587M ), so engineers use penetration results in sands for predicting engineering properties ( Appendix X1 ). Appendix X2 and X1.6 provides some estimated properties of sands. There are problems with SPT in loose sands below the water table since they are unstable during drilling. Practice D6066 provides restricted drilling methods for SPT in loose sands for evaluating earthquake liquefaction potential. Practice D6066 method relies on mud rotary drilling, casing advancers, and fluid filled hollow-stem augers. 4.3.2 Clays— SPT is easy to perform in clays of medium to stiff consistency and higher using a variety of drilling methods. SPT is unreliable in soft to very soft clays because the clay, yields or “fails” under the static weight of the rods alone, or weight of rods and hammer before the test is started. This problem is accentuated by the heavier weights of automatic hammer assemblies (see X1.3.1.4 ) but can be alleviated with automatic hammers which are designed to float over the anvil (see 5.4.2.1 ). There is such a large variation in possible N values in soft clays it is well accepted that SPT is a poor predictor of the undrained shear strength of clay. It is recommended to evaluate soft clays with more appropriate methods such as CPT (Test Method D5778 ), vane shear (Test Method D2573/D2573M ), and/or Thin-Wall Tube sampling (Practice D1587/D1587M ) and laboratory testing. 4.4 Hammer Drop System— SPT can be performed with a wide variety of hammer drop systems. Typical hammer systems are listed below in order of preference of use: (1) Hydraulic automatic chain cam/mechanical grip-release hammers (2) Mechanical trip donut hammers (3) Rope and cathead operated safety hammers (4) Rope and cathead operated donut hammers 4.4.1 Automatic and trip hammers are preferred for consistent energy during the test. Automatic chain cam hammers are also the safest because the hammer is enclosed, and the operators can stand away from the equipment. If the rope and cathead method is used, the enclosed safety hammer is safer than donut hammer because the impact anvil is enclosed. For more information on hammer systems, consult X1.3 . 4.5 Drilling Methods— The predominant drilling methods used for SPT are open hole fluid rotary drilling (Guide D5783 ) and hollow-stem auger drilling (Practice D6151/D6151M ). Limited research has been done comparing these methods and their effects on SPT N values (see X1.5.1.1 ). 4.5.1 Research shows that open hole bentonite fluid rotary drilling is the most reliable method for most soils below the water table. Hollow-stem augers had problems with saturated loose sands since they must be kept full of fluid. The research also showed that driven casing using water as the drilling fluid, can adversely influence the SPT if the casing is driven close to the test depth interval. Use of casing combined with allowing a fluid imbalance also causes disturbances in sands below the water table. Fluid filled rotary casing advancers (Guide D6286 ) are included as an allowable drilling method for loose sands in Practice D6066 . 4.5.2 SPT is used with other drilling methods including reverse circulation, sonic drilling, and direct push methods practices. There are concerns, undocumented by research, with direct push (Guide D6282/D6282M ), sonic drilling (Practice D6914/D6914M ), and reverse circulation methods using heavy casing drive hammers (Guide D6286 ), that the extreme dynamic loading and vibrations could disturb some soils such as sands and soft clays past the seating interval. The professional responsible for the investigation should evaluate SPT under these conditions and if drilling disturbance is suspected, then N values can be checked against other drilling methods in section 4.5 or deploy the alternate drilling method through and ahead of the casings. 4.5.3 SPT is also performed at shallow depths above the groundwater table using solid stem flight augers (Practice D1452/D1452M ), but below the water table borings may be subject to caving sands. Solid stem borings have been drilled to depths of 100 ft or more in stable material. 4.5.4 SPT is rarely performed in cable tool or air rotary drilling. 4.6 Planning, Execution, and Layout— When SPT borings are used, often there are requirements for other companion borings or test holes to be located near or around the SPT boring. In general, borings should be no closer than 10 ft [3 m] at the surface for depths of up to 100 ft [30 m]. A minimum would be as close as 5 ft [2 m], but at this spacing, boreholes may meet if there is significant vertical deviation. 4.6.1 Test Depth Increments— Test intervals and locations are normally stipulated by the project engineer or geologist. Typical practice is to test at 5 ft [1.5 m] intervals or less in homogeneous strata. If a different soil type in the substratum is encountered, then a test is conducted as soon as the change is noted. It is recommended to clean out the borehole a minimum cleanout interval of at least 1 ft [0.25 m] past the termination point of the previous test depth between tests to assure test isolation and to check drill hole condition for the next test. Therefore, the closest spacing for typical practice of SPT is 2.5 ft [0.75 m]. The cleanout between test intervals can be adjusted by the user depending on borehole conditions and design data needs such as hard soils or thin strata. The practice of performing continuous SPT for N -value determination is not recommended but can be done with careful cleanout before testing. The borehole must be cleaned out between tests (see 6.5 ). At continuous spacing, with no additional cleanout depth, N values may be adversely affected by disturbance of previous sample driving especially in softer soils but the effect his not known. Some practitioners like to overdrive the sampler an additional 0.5 ft [0.15 m] to gain additional soil sample for a total drive interval of 2.0 [ 0.6 m]. This is acceptable if the N -value remains the sum of the 0.5 to 1.0 ft [0.15 to 0.3 m] intervals of the drive interval and reasonable cleanout is performed between tests. 4.7 This test method provides a Class A and B soil samples according to Practice D4220/D4220M which is suitable for soil identification and classification (Practices D2487 and D2488 ), water content (Test Methods D2216 ), and specific gravity tests (Test Methods D854 ). The soil can be reconstituted for some advanced laboratory tests. The small-diameter, thick wall, drive sampler will not obtain a sample suitable for advanced laboratory tests such as those used for strength or compressibility from the core. Consult Guide D6169/D6169M for samplers that provide laboratory grade intact samples. Note 1: The reliability of data and interpretations generated by this practice is dependent on the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 generally are considered capable of competent testing. Users of this practice are cautioned that compliance with Practice D3740 does not assure reliable testing. Reliable testing depends on several factors and Practice D3740 provides a means of evaluating some of these factors. Practice D3740 was developed for agencies engaged in the testing, inspection, or both, of soils and rock. As such, it is not totally applicable to agencies performing this field test. Users of this test method should recognize that the framework of Practice D3740 is appropriate for evaluating the quality of an agency performing this test method. Currently, there is no known qualifying national authority that inspects agencies that perform this test method.