Assessment of Small Strain Dynamic Soil Properties of Railway site Agartala, India by Bender Element Tests

Abstract

Small strain dynamic properties of soil is the primary input parameter in seismic ground response analysis studies. This study examines the small strain shear modulus (Gs or Gmax) and damping ratio (ξ) using bender element tests on subsoil samples along with evaluation of liquefaction potential (Sandy soil) collected from a railway construction site at Agartala, India. The objective of this study is to develop a database and empirical relationship on dynamic properties of soil Agartala which may help to carry out site specific seismic hazard studies of Agartala city. In present study, both undisturbed and disturbed soil samples were collected from twelve boreholes near the study area which is mainly of soft marshy ground with localized deposits of peat layer. Similar type of soil is often found in various parts of Agartala basin and other regions of India. Experimental results indicate that Vs, Gmax and ξ vary within a wide range depending upon the type of soil and a closed form empirical equation are proposed to calculate Gmax for different types of soil which would be applicable for evaluating dynamic properties for similar nature soil available across various sites of India.

Shear Wave Velocity Measurements in Tropical Peat Using In-house Device

“…When these factors vary on peat samples prepared, results obtained for 𝑉 𝑠 will contribute to great errors. Hence, it was anticipated from the beginning that results measured can be very much different from the theoretical data mentioned in Table (3). Table (8) and (9) shows the results of peat samples using the in-house BET device.…”

“…When referring to Table (10), it is known that the data errors in percentage was calculated by comparing the theoretical data in Table (3). The shear wave velocity is greater when it comes to coarser soil samples, meanwhile a drastic drop was observed in both the shear wave velocity and small shear strain modulus of hemic and fibric peat.…”

“…Only samples which have been air dried for several weeks before testing was conducted is used as a reference value. Table (3) shows the reference densities for various samples from different authors. [10], [11] Kaolin clay 1.61 258.00 150.00 [13], [14] Silty loam 1.35 150.00 70.00 [9], [15], [16], [17] Hemic peat 0.24 54.00 0.70 [9], [15], [16], [17] Fibric peat 0.17 Figure (2) shows the complete setup for the proposed in-house device in performing bender element test.…”

“…With different frequencies shown in Table ( 4) established, time taken for shear waves to travel across the sample is also recorded. Using Formula ( 1) and ( 2), the shear wave velocity and small strain shear modulus of Ottawa sand was calculated in reference values in Table (3). Based on the results in Table (4) and values in Table (3), the Ottawa sand shows similar trend of shear wave velocity and small strain shear modulus values as the ratio of travel length to wavelength increases with frequency.…”

“…Hence, dynamic soil parameters such as the shear wave velocity 𝑉 𝑠 and the small strain shear modulus 𝐺 0 plays a vital role in understanding the behavior of peat. For example, in several earthquake related geotechnical engineering applications such as ground response analysis, soil-structure interaction analysis, liquefaction potential evaluation, and to design structures in earthquake prone areas require these parameters [3].…”