Geological and hydrogeological conditions in karst areas are complicated from the viewpoint of engineering. The construction of underground structures in these areas is often disturbed by the gushing of karst water, which may delay the construction schedule, result in economic losses, and even cause heavy casualties. In this paper, an innovative method of multichannel transient Rayleigh wave detecting is proposed by introducing the concept of arrival time difference phase between channels (TDP). Overcoming the restriction of the space-sampling law, the proposed method can extract the phase velocities of different frequency components from only two channels of transient Rayleigh wave recorded on two adjacent detecting points. This feature greatly improves the work efficiency and lateral resolution of transient Rayleigh wave detecting. The improved multichannel transient Rayleigh wave detecting method is applied to the detection of karst caves and fractures in rock mass of the foundation pit of Yan’an Road Station of Guiyang Metro. The imaging of the detecting results clearly reveals the distribution of karst water inflow channels, which provided significant guidance for water plugging and enabled good control over karst water gushing in the foundation pit.

Theoretical analysis shows that there are several values of the phase velocity to a certain frequency of Rayleigh wave on the surface of a layered medium model, which is called the multiple mode property of Rayleigh wave. The multiple mode property of surface wave results in the complication of measured dispersion curves, especially when a soft interlayer exists in strata. This brings more difficulties to the explanation of the dispersion curves measured on this kind of site. In order to facilitate engineering application, a new method, improved equivalent homogenous half‐space method, is put forward to compute the theoretical dispersion curve of a layered medium model based on the equivalent homogenous half‐space theory. This new method does not need to deal with the multiple value problem of the phase velocity, and the phase velocity resulting from this method can reflect the synthetic effect of all modes of Rayleigh waves. The inverse fitting program is compiled based on the improved equivalent homogenous half‐space method, which has gotten a very good effect in an engineering application.