The Development Of The Measuring Instrument For Dynamic Deformation Modulus And Its Application In Engineering

The compacting quality of railway subgrade is an important requisite to ensure the railway's stability and smoothness as well as its high-speed and safe operation. The standards, methods and equipment for measuring and controlling the compacting quality are critical elements to guarantee the compacting quality of subgrade.The traditional methods to control compacting quality use density parameters such as standard compacting factor K and relative density Dr. Since 1970s, many countries started utilizing strength and deformation parameters for subgrade compacting quality control. Examples include the CBR standard in the US, the static deformation modulus E_v2 standard in Germany, France, Austria, Sweden and other countries, and the ground factor K₃₀ standard in Japan. China started using Japan's K₃₀ standard firstly in constructing Datong-Qinghuangdao Heavy Railway and later in constructing new trunk lines and quasi-highspeed railways. However, the parameters mentioned above are obtained by static test and cannot reflect the real impact of the dynamic stress caused by high-speed trains. To solve this problem, in 1990s, German scientists developed the measuring instrument for dynamic deformation modulus, and employed a new standard for controlling subgrade compacting quality—Evd standard, whose foremost characteristic is being able to reflect the real impact of dynamic stress caused by trains running at a high speed.To meet the demand of Chinese infrastructure development, in 1996, the author formed a team and began to develop the China-made instrument for dynamic deformation modulus on the basis of absorbing the advanced technologies from foreign countries. After several years' efforts, the DBM Dynamic Deformation Modulus Measuring Instrument was successfully developed and corresponding technical standards were created. The main technical specifications of this instrument are:1 Applicable situations: All types of subgrade soil and subgrade bed filling materials that meet requirement of the current standards; the effect depth range of the test: 400～500mm; the scope of measurable materials: 10MPa≤E_vd≤125MPa.2 Weight of the falling hammer: 10 kg; the maximum impacting force: 7.07kN.3 The range of measurable dent: 0.2～2.00mm.4 Testing speed: 3～5 min/point.5 Automatic gathering and treatment of the test data.6 The total weight of the equipment: 35 kg. The instrument has been successfully used in the quality control of subgrade construction in Qinghuangdao-Shenyang Passenger Special Line and Xinchang Railay. It was patented in 2000, and passed the formal appraisal by the Chinese Ministry of Railways. The instrument was also awarded the first-class Sci-Tech Progress Prize by China Railway Construction Corporation, and the third-class Sci-Tech Progress Prize by the Ministry of Railways. "Technology for testing bearing capacity of filling soil by dynamic plate load" was chosen as the "Ministry-level Technology" of the Ministry of Railways. "Evd dynamic plate load test" was adopted by "Soil engineering test standard for railway engineering" (TB10102—2004). "E_vd compacting standard using dynamic deformation modulus" was adopted in "Temporary regulations for the design of Beijng-Shanghai high speed railway" (Tiejianshe [2004] No. 157) and "Temporary checking-and-accepting standards for subgrade construction quality of Beijng-Shanghai high speed railway" as the compacting standard of mandatory tests for the surface layer of subgrade and transition sect.This paper describes in detail the working principle and technical standards of DBM dynamic modulus instrument. In addition, the author established the relationship between K₃₀ and E_vd for coarse-grained soil, fine-grained soil, crushed stone and graded crushed stone, on the basis of 800 in-situ and laboratory tests and fitting analysis of all the test data, which indicates that there is a good correlation between the two parameters.