Designing and Evaluation of Low-Cost Dynamic Triaxial Apparatus
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TECHNICAL NOTE
Designing and Evaluation of Low-Cost Dynamic Triaxial Apparatus Afshin Shafigh1
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Mohammad Siroos Pakbaz1
Received: 3 June 2020 / Accepted: 27 August 2020 Ó Indian Geotechnical Society 2020
Abstract Dynamic triaxial test is one of the most common geotechnical laboratory tests to measure the dynamic properties of soils. Therefore, dynamic triaxial devices have been developed to increase the accuracy of measuring dynamic soil parameters as well as to automate the test steps. However, this matter requires complex design and modern instruments that can considerably increase the cost of construction. In this paper, a dynamic triaxial test apparatus was made with an emphasis on cost reduction by using inexpensive and available devices. In this regard, an open-loop control system has been used instead of a conventional closed-loop control system. However, there are two limitations for using this system as follows: (a) the tests can be conducted only in strain-controlled conditions and (b) dynamic loading must be applied at the frequency range of 0.5 Hz or less. The frequency of 0.5 Hz is recommended in relevant standards. To evaluate the performance of the apparatus, two tests were performed according to the conditions of a test conducted by a standard apparatus, and the results were compared together. The tests were performed in consolidated–undrained conditions on saturated sand specimens at 0.5 Hz loading frequency for a peak axial strain of 0.2% and 0.7%. The results showed the apparatus can be used to conduct the dynamic triaxial tests if these limitations are considered. Keywords Dynamic triaxial test Dynamic loading Open-loop control system Strain-controlled criteria
& Afshin Shafigh [email protected] 1
Department of Civil Engineering, Faculty of Civil Engineering and Architecture, Shahid Chamran University of Ahvaz, Ahvaz, Iran
Introduction The dynamic triaxial test is one of the most versatile and widely performed geotechnical laboratory tests, allowing dynamic properties of soil such as damping ratio, dynamic shear modulus and liquefaction resistance to be determined for use in geotechnical research. To date, advanced dynamic triaxial testing systems are capable of providing fully automatic static and dynamic triaxial testing. Additionally, new capabilities have been considered in some triaxial devices. Some of these are as follows: measuring local radial strains of specimen [1], determination of elastic wave velocities during infiltration tests on unsaturated soils through [2], permeability measurement of unsaturated soils [3] and determination of granular soils rheological properties analysis [4]. Dev et al. [5] proposed a procedure to estimate the critical state parameters in the triaxial test because isotropic compression tests are usually not conducted. Generally, standard dynamic triaxial devices are designed based on a closed-loop control system (Fig. 1). In this system, the response or the actual result is continuously compared with the desired result, and the control
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