Soil/rock interface detection is an essential and critical task in geological site investigation for underground and tunnel projects. The required accuracy is within a few meters both vertically and horizontally. The required resolution poses big challenges to geophysical surveys to be applied in near-surface engineering works. This paper presents a new approach of non-invasive geophysical survey, namely autocorrelation. It is originally derived from seismic interferometry cross-correlation, which can convert a physical geophone to a virtual source. To the extreme is autocorrelation. It turns a single geophone into a self-source receiver. With this concept, the proposed approach includes two methods aiming to reduce the reliance on reference boreholes. A field testing carried out in Singapore is presented to demonstrate the concept and results step by step. The case study also demonstrates that the proposed method can fine-tune the autocorrelograms to achieve the required resolution both laterally and vertically. A by-product of realistic average $V_p$ of the soil layers above soil/rock interface can be estimated reasonably by the proposed method. Two more case studies are followed to illustrate the proposed methods can produce reasonable 2D and 3D soil/rock interface profiles. Due to the self-source feature, this approach is convenient to implement on site. The proposed approach can be an attractive option for geotechnical and geological site investigation especially for delineating the soil/rock interface topography.

土壤/岩石界面检测是地下和隧道项目地质现场调查中必不可少的关键任务。所需的垂直和水平精度都在几米之内。所需的分辨率对在近地表工程中应用的地球物理测量提出了巨大挑战。本文提出了一种新的无创地球物理测量方法，即自相关。它最初源自地震干涉测量互相关，可以将物理地震检波器转换为虚拟源。极端的是自相关。它将单个地震检波器变成自源接收器。有了这个概念，建议的方法包括两种旨在减少对参考钻孔的依赖的方法。介绍了在新加坡进行的现场测试，以逐步展示概念和结果。案例研究还表明，所提出的方法可以对自相关图进行微调，以在横向和纵向上达到所需的分辨率。现实平均值的副产品${伏}_{磷}$土/岩石界面以上土层的数量可以通过所提出的方法进行合理估计。另外两个案例研究说明了所提出的方法可以产生合理的 2D 和 3D 土壤/岩石界面剖面。由于具有自源特性，这种方式便于现场实施。所提出的方法对于岩土和地质现场调查来说是一个有吸引力的选择，尤其是在描绘土壤/岩石界面地形方面。