Standard penetration tests (SPTs) have been used to estimate strength parameters of soils and weak rocks when it is difficult to obtain high-quality samples for laboratory shear testing. SPTs require 45 cm (18 in.) of split-spoon sampler penetration to determine the blowcounts per 0.3 m (1 ft), which is difficult to impossible to obtain in weak rock, that is, intermediate geomaterials. As a result, a modified SPT is presented here for sampler penetrations less than 45 cm (18 in.) in weak rocks. This new procedure is termed the modified standard penetration test (MSPT) and uses the penetration rate, not the sum of penetration blowcounts per 0.3 m, to estimate the unconfined compressive strength for the design of drilled shafts in weak fine-grained rocks. The penetration rate is the inverse of the linear slope of the penetration depth versus blowcount relationship. With this new test and interpretation procedure, 45 cm (18 in.) of sampler penetration is no longer required to estimate the unconfined compressive strength of weak rocks. An empirical correlation between MSPT penetration rate and laboratory-measured unconfined compressive strength is presented here for weak Illinois shale. This correlation could be used to estimate the unconfined compressive strength for the design of drilled shafts in weak rocks.

当难以获得用于实验室剪切测试的高质量样品时，标准渗透测试 (SPT) 已被用于估计土壤和软弱岩石的强度参数。SPT 需要 45 厘米（18 英寸）的分流勺采样器穿透来确定每 0.3 米（1 英尺）的打击次数，这在弱岩中很难获得，即中间地质材料。因此，此处介绍了一种改进的 SPT，适用于弱岩中小于 45 厘米（18 英寸）的采样器穿透。这种新程序被称为修改后的标准穿透测试 (MSPT)，它使用穿透率，而不是每 0.3 m 穿透击数的总和，来估计弱细粒岩石中钻孔轴设计的无侧限抗压强度。穿透率是穿透深度与打击次数关系的线性斜率的倒数。有了这个新的测试和解释程序，就不再需要 45 厘米（18 英寸）的采样器穿透来估计弱岩石的无侧限抗压强度。对于弱的伊利诺伊州页岩，MSPT 渗透率和实验室测量的无侧限抗压强度之间的经验相关性在这里给出。这种相关性可用于估算弱岩中钻孔竖井设计的无侧限抗压强度。对于弱伊利诺伊州页岩，MSPT 渗透率与实验室测量的无侧限抗压强度之间的经验相关性在这里给出。这种相关性可用于估算弱岩中钻孔竖井设计的无侧限抗压强度。对于弱伊利诺伊州页岩，MSPT 渗透率与实验室测量的无侧限抗压强度之间的经验相关性在这里给出。这种相关性可用于估算弱岩中钻孔竖井设计的无侧限抗压强度。