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Seismograph Comparison StudySeismograph Comparison Study

Project: Supergraph II Comparison Study at the BART Transbay Tub During Underwater Pier Blasting for Caltrans
Date: January 29, 2016

Background

This Seismograph Comparison Study summarizes a side-by-side study of three different seismograph systems used to record vibrations measured on a subway tunnel wall during this underwater blast of a bridge pier. Monitoring of background train and the blast vibrations in the BART Transbay tube between San Francisco and Oakland California, took place on November 14, 2015. The Transbay tube is a reinforced concrete submerged tunnel under the San Francisco Bay that is buried in engineered fill within the Bay mud. The tube carries BART commuter trains on two tracks oriented eastbound and westbound.

Seismograph Comparison Study
DRAFT REPORT

Background

This report summarizes a side‐by‐side study of three different seismograph systems used to record vibrations measured on a subway tunnel wall during an underwater blast of a bridge pier. Monitoring of background train and the blast vibrations in the BART Transbay Tube between San Francisco and Oakland, CA, took place on November 14, 2015. The Transbay Tube is a reinforced concrete submerged tunnel under the San Francisco Bay that is buried in engineered fill within the Bay mud. The Tube carries BART commuter trains on two tracks oriented eastbound and westbound.

Figure 1 shows a plan view of the instrumentation location relative to the blast of Pier E3 approximately 3000 ft away. Table 1 provides a summary of operating parameters for each instrument. The comparative study was conducted to determine relative peak amplitudes of motions and frequencies as a function of sample rate and geophone low‐end resolution. Seismographs included a Nomis Supergraph II set to record at 16,384 Hz, a White MiniSeis III set at 4096 Hz, and two MiniSeis II, set at 2048 Hz. The MiniSeis II units employed geophones of two different low‐end resolutions. A PCB Piezotronics accelerometer, model 356A34, was mounted on the tunnel wall to obtain direct acceleration that was of interest to the BART engineers. A SoMat eDAQ‐Lite data acquisition system was used to capture acceleration time histories at a sample rate of 100,000 Hz.

For the full report, click here.