5:15 PM - 6:45 PM
[HTT18-P04] Measurement of S-wave velocity distribution in road embankment by geophysical exploration
Keywords:surface wave survey, microtremor array survey, S-wave tomography survey
1. Necessity of measuring S-wave velocity distribution in road embankment by geophysical exploration
Damage to earth structures caused by earthquakes and heavy rains has continued to occur in recent years. The earthquake resistance of road embankments is greatly affected by the shear modulus of the embankment. Discrete information such as borings can be spatially interpolated by geophysical explorations with spatially continuous information. It prepares geotechnical investigations to keep sufficient productivity. This study introduces geophysical exploration methods which are effective for measuring S-wave velocity distribution inside shallow ground such as road embankment.
2. Method of measuring S-wave velocity in the ground by geophysical explorations
Various geophysical exploration methods have been developed to obtain S-wave velocity distribution. This study introduces three methods which are highly practical for civil engineering: surface wave survey, linear microtremor array survey, and S-wave tomography survey.
2.1 Surface wave survey
Surface wave survey can investigate the S-wave velocity distribution inside the ground up to a depth of about 10 m using the vibration of sledgehammer. Since the vibration of sledgehammer can be the signal source for survey, it is highly applicable to survey works on sloping terrain. In addition, surface wave has lower attenuation than P- and S-waves, so that the surface wave has strong resistant to traffic vibrations and allows the survey along major roads.
2.2 Linear microtremor array survey
Linear microtremor array survey is selected when the depth of exploration by surface wave survey is insufficient. There are only a limited areas with flat plane around the infrastructure such as road embankments and levees. Therefore, it is practical to conduct exploration using a linear arrangement.
2.3 S-wave tomography survey
Surface wave and linear microtomography array surveys cannot be used to survey cross sections of embankments and levees that have undulating ground surfaces. If it is desired to acquire S-wave velocities inside the ground where the ground surface is not flat, S-wave tomography survey can be used. An example of the analysis of S-wave tomography is shown in the Figure.
3. Summary
We have introduced a method of measuring S-wave velocity in the ground by geophysical explorations, which can be used to determine the distribution of ground strength used for evaluating earthquake resistance of road embankments. It is recommended that the surface wave survey is planned for basic measurement to acquire S-wave velocity distribution in the ground. The linear microtremor array survey is planned to measure deeper areas and the S-wave tomography survey is planned to measure the lower part of the road where excavation is difficult.
Damage to earth structures caused by earthquakes and heavy rains has continued to occur in recent years. The earthquake resistance of road embankments is greatly affected by the shear modulus of the embankment. Discrete information such as borings can be spatially interpolated by geophysical explorations with spatially continuous information. It prepares geotechnical investigations to keep sufficient productivity. This study introduces geophysical exploration methods which are effective for measuring S-wave velocity distribution inside shallow ground such as road embankment.
2. Method of measuring S-wave velocity in the ground by geophysical explorations
Various geophysical exploration methods have been developed to obtain S-wave velocity distribution. This study introduces three methods which are highly practical for civil engineering: surface wave survey, linear microtremor array survey, and S-wave tomography survey.
2.1 Surface wave survey
Surface wave survey can investigate the S-wave velocity distribution inside the ground up to a depth of about 10 m using the vibration of sledgehammer. Since the vibration of sledgehammer can be the signal source for survey, it is highly applicable to survey works on sloping terrain. In addition, surface wave has lower attenuation than P- and S-waves, so that the surface wave has strong resistant to traffic vibrations and allows the survey along major roads.
2.2 Linear microtremor array survey
Linear microtremor array survey is selected when the depth of exploration by surface wave survey is insufficient. There are only a limited areas with flat plane around the infrastructure such as road embankments and levees. Therefore, it is practical to conduct exploration using a linear arrangement.
2.3 S-wave tomography survey
Surface wave and linear microtomography array surveys cannot be used to survey cross sections of embankments and levees that have undulating ground surfaces. If it is desired to acquire S-wave velocities inside the ground where the ground surface is not flat, S-wave tomography survey can be used. An example of the analysis of S-wave tomography is shown in the Figure.
3. Summary
We have introduced a method of measuring S-wave velocity in the ground by geophysical explorations, which can be used to determine the distribution of ground strength used for evaluating earthquake resistance of road embankments. It is recommended that the surface wave survey is planned for basic measurement to acquire S-wave velocity distribution in the ground. The linear microtremor array survey is planned to measure deeper areas and the S-wave tomography survey is planned to measure the lower part of the road where excavation is difficult.