ارزیابی تأثیر محتوای فرکانسی بارهای لرزه‌ای به‌منظور شناسایی ناهنجاری‌های زیرسطحی با استفاده از امواج رایلی و طولی

نوع مقاله : علمی - پژوهشی

نویسندگان

1 استادیار گروه عمران و محیط‌زیست، دانشگاه صنعتی شیراز، شیراز، ایران

2 دانشجوی دکتری ژئوتکنیک، گروه عمران و محیط زیست، دانشگاه صنعتی شیراز، شیراز، ایران

چکیده

آگاهی از خصوصیات زیرسطحی همواره مورد توجه مهندسان بوده است به‌خصوص زمانی که احتمال وجود مخاطرات ناشی از ناهنجاری‌های زیرسطحی همچون فروچاله یا حفره مدنظر باشد. شناسایی موقعیت این ناهنجاری‌ها در اعماق بیشتر به خاطر کاهش وضوح و دقت داده‌های برداشت‌شده هنوز موضوعی چالش‌برانگیز و نیازمند مطالعات بیشتر می‌باشد. در این مقاله با استفاده از روش اجزا محدود، تأثیر انواع بارهای لرزه‌ای به‌منظور شناسایی حفرات زیرسطحی مورد ارزیابی واقع‌شده است بارهای لرزه‌ای شامل ضربه چکش، ضربه سینوسی، ضربه کوتاه و بار ریکر با فرکانس های حداکثر 100، 50 و 20 هرتز می باشند. به علاوه اینکه با روش‌های فیلتر کردن و جداسازی امواج در فضای میدان موج، توانایی امواج طولی و رایلی جهت شناسایی حفرات در اعماق 2، 6، 10 و 20 مورد مقایسه قرارگرفته است. نتایج حاصله نشان دادند که محتوای فرکانسی و فرکانس غالب بار ارتعاشی، تأثیر قابل‌توجهی بر وضوح تصاویر و عمق نفوذ دارند. به‌عنوان‌مثال، بارهای لرزه‌ای ریکر100 هرتز، ضربه چکش و ضربه کوتاه با محتوای فرکانسی بالا برای شناسایی حفرات در عمق 2 متر دارای وضوح خوب، عمق 6 متر دارای وضوح متوسط، عمق 10 متر دارای وضوح ضعیف‌تر می‌باشند و برای حفره در عمق 20 متر امواج رایلی برگشتی به‌سختی قابل‌مشاهده بوده ولی در مقابل امواج طولی دارای وضوح و دقت بهتری هستند؛ حال‌آنکه بار لرزه‌ای با محتوای فرکانسی پایین همچون بار ریکر 20 هرتز نتایج مناسب‌تری از وضعیت امواج طولی و رایلی بازگشتی از حفره در اعماق بیشتر را فراهم نموده است. به‌طورکلی می‌توان این‌گونه اظهار داشت که استفاده ترکیبی از امواج طولی رایلی و طولی و اعمال بار لرزه‌ای متناسب با عمق شناسایی حفره منجر به نتایج قابل قبولی می گردد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Effect of frequency content of seismic source load on Rayleigh and P waves in soil media with cavity

نویسندگان [English]

  • Hossein Rahnema 1
  • Sohrab Mirassi 2
1 Assistant Professor, Department of Civil and Environmental Engineering, Shiraz University of Technology, Shiraz, Iran
2 Ph.D. Candidate, Department of Civil and Environmental Engineering, Shiraz University of Technology, Shiraz, Iran
چکیده [English]

Subsurface characterization has always been an interesting issue in Geotechnical and geological engineering, especially when there is a potential risk of subsurface anomalies such as cavities and sinkholes. Due to the low resolution and accuracy of seismic recorded data at higher depths, anomalies identification has become more difficult. In this paper, the effect of various types of seismic source loads such as hammer impact, short-time impact, sinusoidal source and Ricker wavelet with a peak frequency of 100, 50 and 20 Hz is evaluated to identify the subsurface cavities by using the Finite Element Method in Abaqus 6.14 software. In addition, The ability of R and P waves are compared after the filtering the waves to detect cavities at different depths of 2, 6, 10 and 20 m. The results show that the frequency content and peak frequency of source load have a significant effect on the penetration depth and wave field resolution. Furthermore, filtering methods and separating R and P waves could be more helpful to identify the shallow and high depths cavities. Also, Ricker seismic source with a central frequency of 100 Hz, hammer impact and short-time impact indicate suitable results for cavities located at depths of 2, 6 and 10 meters. Whereas, it is difficult to identify the backscattered R waves from the cavity at the depth of 20 meters. However, low-frequency seismic load, such as 20 Hz Ricker source load, provides backscattered R and P waves from the cavity at the depth of 20 m. In general, the acceptable results can be obtained by using a combination of P and R waves and applying seismic load proportional to the depth of identification.

کلیدواژه‌ها [English]

  • Cavity
  • Seismic Source load
  • Frequency content
  • Rayleigh wave
  • P-waves
  • Wave field
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