Increase of Velocity (Vs) (%) (Figure 3)
The same velocity (Vs) difference sections previously displayed are now calibrated in velocity with respect to the original velocity values. The calibrated
values are presented here in percent (%).
In the section comparing velocity increase 4 days after grouting (top), only small amount of velocity (Vs) increase (e.g., ≤ 35%) is observed at the
deepest depths (e.g., ≥ 15 m) near the horizontal center (e.g., 27 m ≤ X ≤ 40 m). However, the amount of increase drastically rises and its spatial
dimension significantly extends laterally 2 months after grouting (bottom). It is also observed the shallow depths (e.g., 5-7 m) achieved a noticeable
velocity (Vs) increase of about 20%.
Again, the depth can be over-estimated (by, for example, 20%).
Evaluation of Grouting (Before and After)
Data Acquisition Geometry
This application shows results of MASW surveys conducted over the same surface distance (about 50-m long)
three times; before, 4 days after, and 2-month after the grouting was applied (site photo in Figure 1). Results
show the most significant increase of subsurface shear-wave velocity (Vs) occurs at depths (> 12 m) where an
excessive amount of grouting mortar was injected during the field operation.
Velocity (Vs) Cross Sections (Figure 2)
Each data set was processed by following the normal MASW data analysis sequence to produce one 2-D
velocity (Vs) cross section per data set. Location of grouting holes is indicated on the cross section before
During the process to extract dispersion curves, lateral smoothing was applied to filter out such effects as
much as possible that may not be related to the grouting effects (for example, transient ambient noise,
small-scale velocity variations, subjective picking in dispersion curves, etc.). In consequence, detailed velocity
(Vs) variations are not visible and only general trends of vertical and horizontal variations are observed in all
three cross sections.
Considering the possibility of depth over-estimation during the inversion process, actual depth can be smaller
by, for example, 20%.
Figure 1. Grouting site photo.
(Below) Figure 3. Difference (%) of velocities (Vs's) between two post-grouting stages (4 days
and 2 months after) and one pre-grouting (before) stage.