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Home My WebLink AboutSDP 2022-0003; FPC RESIDENTIAL - SB 330; NOISE VIBRATION ANALYSIS; 2022-09-20 HELIX Environmental Planning, Inc. 7578 El Cajon Boulevard La Mesa, CA 91942 619.462.1515 tel 619.462.0552 fax www.helixepi.com September 20, 2022 00321.00026.0001 Ryley Webb H.G. Fenton Company 7577 Mission Valley Road San Diego, CA 92108 rwebb@hgfenton.com | 619.400.1034 Subject: FPC Residential Complex Train Vibration Measurements Dear Mr. Webb: At your request, HELIX Environmental Planning, Inc. (HELIX) has prepared this report, which analyzes potential vibration impacts associated with the proposed FPC Residential Complex Project (project). Groundborne noise impacts were previously analyzed in a separate letter. The project site, located northeast of the intersection of Ponto Road and Ponto Drive in the City of Carlsbad, is adjacent the North County Transit District (NCTD) railroad tracks and may be affected by train pass-by vibration. Vibration measurements were taken at the proposed project location. Vibration levels at the site are not anticipated to exceed Federal Transit Administration (FTA) screening levels; therefore, future residential uses would not be subject to excessive vibration. SITE VIBRATION MEASUREMENTS Multiple vibration measurements were taken for both northbound and southbound passenger train pass-bys on the afternoon of Wednesday September 14, 2022. An accelerometer was mounted on a heavy steel plate with spikes placed in the ground at approximately 120 feet from the centerline of the tracks. This location is within the expected outdoor use area for the project and adjacent to the railroad right-of-way closest to the future residential foundations. The following equipment was used to measure train vibration levels at the project site: • SAMURI 4-channel Data Acquisition System (manufactured by Messtechnik GmbH with the Sinus software) • PCB J353B33 accelerometer • PCB 394C06 vibration calibrator Letter to Ryley Webb Page 2 of 3 September 20, 2022 VIBRATION TERMINOLOGY AND DESCRIPTORS Vibration is measured in feet (ft) or inches (in). Acceleration is measured by comparing acceleration to that of the Earth’s gravity, and this unit is “G.” These units of acceleration or velocity are relative to time in seconds (sec) and are noted as in/sec2 for acceleration and in/sec for velocity. Displacement is not relative to time and is only shown as inches. Vibration effects can be described by its peak and root mean square (RMS) amplitudes. Building damage is often discussed in terms of peak velocity, or peak particle velocity (PPV). The PPV is defined as the maximum instantaneous positive or negative peak of the vibration signal. PPV is related to the stresses that are experienced by buildings and is often used in monitoring of blasting vibration or to discuss construction vibration impacts. The RMS amplitude is useful for assessing human annoyance. Because the net average of a vibration signal is zero, the RMS amplitude is used to describe the “smoothed” vibration amplitude. The RMS of a signal is the average of the squared amplitude of the signal. The RMS amplitude is always less than the PPV and is always positive. The RMS average is typically calculated over a one-second period. Although it is not universally accepted, decibel notation is commonly used for vibration. Decibel notation serves to compress the range of numbers required to describe vibration. Vibration velocity level in decibels is defined as: LV=20 × LOG10(V/V𝑟𝑟𝑟𝑟𝑟𝑟), where “Lv” is the velocity level in decibels, “V” is the RMS velocity amplitude, and “V𝑟𝑟𝑟𝑟𝑟𝑟” is the reference velocity amplitude. The reference must be specified whenever a quantity is expressed in terms of decibels. All railroad vibration levels in this report are referenced to 1 × 10-6 in/sec with the notation VdB. FTA VIBRATION CRITERIA The FTA has established guidelines for the evaluation of transit noise and vibration for trains that operate at speeds less than 90 miles per hour. The guidelines are set forth in the Transit Noise and Vibration Impact Assessment Manual, last updated in September 2018. These guidelines establish impact criteria for rail noise and vibration, define sensitive receivers, and provide methodology for assessing impacts. These guidelines are appropriate to use for the existing rail operations associated with the railroad tracks adjacent to the project site. The project falls within the FTA’s Category 2 guidelines, which include residences and buildings where people sleep (hotels, hospitals, and dormitories). The criteria for acceptable ground-borne vibration levels are expressed in VdB. The project is subject to the general vibration assessment criteria, which are based on vibration-sensitive land use categories. Table 1, Ground-Borne Vibration Impact Criteria for General Assessment, presents the FTA’s ground-borne vibration impact criteria that apply to the project. Letter to Ryley Webb Page 3 of 3 September 20, 2022 Table 1 GROUND-BORNE VIBRATION IMPACT CRITERIA FOR GENERAL ASSESSMENT Land Use Category Ground-Borne Vibration Impact Levels (VdB re 1 micro-in/sec) Frequent Events1 Occasional Events2 Infrequent Events3 Category 2: Residences and buildings where people normally sleep 72 VdB 75 VdB 80 VdB Source: FTA 2018 1 Frequent Events is defined as more than 70 vibration events of the same source per day. Most rapid transit projects fall into this category. 2 Occasional Events is defined as between 30 and 70 vibration events of the same source per day. Most commuter trunk lines have this many operations. 3 Infrequent Events is defined as fewer than 30 vibration events of the same kind per day. This category includes most commuter rail branch lines. in/sec = inch per second; mPa = micropascals; VdB = vibration decibels VIBRATION ANALYSIS The measured vibration levels for a single northbound and southbound train pass-by are presented in Attachment A, Train Vibration Measurements. The graphic presents the maximum values for each frequency spectra up to 100-Hz and the summed vibration level for all frequencies from 1 to 100-Hz, as compared to the FTA criteria of 72 VdB. The northbound pass-by summed to 57.86 VdB and the southbound pass-by summed to 62.54 VdB. Train pass-bys in both directions were below the FTA specified level of 72 VdB for frequent events. The southbound track had a clearly audible discontinuity in the track (there is a siding switch at this location), yielding an audible thump when each wheel struck it. This produced an associated higher vibration level throughout much of the lower frequency spectra. However, even with the wheel thump, vibration levels were below the FTA criteria. CONCLUSION Based on the pass-by measurements taken at the project site, vibration levels from pass-bys in either direction would not exceed the applicable FTA criteria. Therefore, residential land uses would not be subject to excessive vibration due to their proximity to the tracks. Regards, Charles Terry Principal Specialist, Noise, Acoustics & Vibration Attachments: Attachment A: Train Vibration Measurements Attachment A Train Vibration Measurements 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 Vd B Frequency North Bound Pass-By VdB Sum FTA Max Criteria 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 Vd B Frequency South Bound Pass-By VdB Sum FTA Max Criteria