同位素密度静力触探仪（ND-CPT）是一种把同位素密度仪并入到静力触探仪的探头中，同时测量锥尖阻力、侧壁摩阻力、孔隙水压力和密度的新型原位测试仪器。根据ND-CPT测量的密度为 射线源和检测器之间回转椭球体内土体的平均密度 的原理，首先建立了可以计算回转椭球体内土体的平均密度 的后向散射模型和平均值模型，然后调查了ND-CPT贯入各种非均质地层时的测量密度 剖面与实际密度 剖面的区别，结果表明在地层分界处附近的测量密度 与实际密度 有较大差别，最后对ND-CPT在实际工程中测量的有明海底泥的测量密度 剖面进行了理解，得到了海底泥的实际密度 剖面。研究结果可为利用ND-CPT准确划分地层提供依据。

Nuclear density cone penetrometer(ND-CPT), incorporating the nuclear density probe into the probe of piezocone penetrometer, is a newly developed in-situ testing device that can simultaneously measure cone resistance, sleeve friction, pore water pressure and density. According to the principle that ND-CPT measures the average wet density of the soil within a spheroid volume around the central point of the source and the detector, the backscatter and average value models which can calculate the average density of soil within a spheroid volume are firstly proposed. Then, assuming ND-CPT is penetrated into various heterogeneous strata, the differences between the average density profiles and the actual density profiles are investigated; and the results show that the measured values are considerably different from the actual values near the boundaries of strata. Finally, the measured profiles of seabed sediments in Ariake Sea, Japan, are interpreted and the actual profiles are deduced. The research results can provide the basis for accurate soil classification using ND-CPT.