# Innovative Quality Assessment of Pavement Subgrades Using the Glegg Impact Soil Tester
## 2 Infrastructure Used to Identify Interest Correlations  
This article describes the results of the author's research on the implementation of the CIST device in a system approach for pavement subgrade quality assessment. Dr [PERSON] developed the concept of the CIST device [10] in the late 1960s while lecturing at the University of Western Australia in Nedlands (Perth). The University of Western Australia established a marketing division in 1976 to promote the device and make research results available for the quality control of earth construction. In honor of Dr [PERSON], the CIST output parameter was named the Clegg Impact Value (CIV). In 1993, Dr. [PERSON] founded the company bearing his name. The aim was to provide a worldwide information service supporting research and development cooperation in the quality control of earth structures through CIST [11]. Since 2005, the authors considered the possibility of using CIST type WS 32830 (Figure 1) for quality control of fine-grained soils and bulk materials [12].  
Figure 1: Device CIST-Type 31820 and homomorphic clay pavement subgrade models.  
This device measures the compaction of soils indirectly using the CBR value. The value is evaluated based on the rate of deceleration of a falling 4.5 kg weight moving in a vertical guide roller. After being released from a certain height, the weight falls in the roller and hits the surface of the foundation slab. The rate of deceleration is determined by the force dependent on the compaction of the material at the point of compaction. The device provides practically immediate results for the rate of compaction of the soils under consideration. This eliminates the major disadvantages of other methods of compaction quality control (determination of bulk density, static load tests, and geodetic control methods). The operation of the device is simple, and the handling of the device is physically easy due to its weight.  
All measurements with the CIST device were carried out strictly according to the instructions for the use of the CIST device type WS 32830 (Figure 1). The CIV measurement was always recorded after the fourth fall of the hammer when the fifth measurement met the required deviation.  
As part of the research activities, measurements were carried out primarily on the following models:  
* Homomorphic clay subgrade models (Figure 1);
* Isomorphic pavement model built within the Scientific Research Workplace of the Faculty of Civil Engineering of the University of Zilina (Figure 2);
* Experimental field for research on unbonded pavement structures (Figure 3).  
The next device was a lightweight dynamic plate LDD 100 representing a falling weight deflectometer (FWD) with a light weight (Figure 4).  
According to the Slovak technical standard STN 73 6192, the basic formula for calculating the modulus of dynamic deformation \(E_{\text{rd}}\) is as follows:  
\[E_{\text{rd}}=\frac{\pi}{2}\cdot\left(1-v^{2}\right)\cdot\frac{a\cdot\sigma}{ y_{m1}}=\frac{\pi\cdot d\cdot\sigma}{4\cdot y_{m1}}\cdot\left(1-v^{2}\right) \tag{1}\]  
The variables in Formula (1) are as follows: \(a\) radius of the loading plate [m], \(d\) diameter of the loading plate [m], \(\sigma\) contact stress [MPa], \(y_{m1}\) amplitude of deflection at the center of the loading plate [m], and \(\
u\) Poisson's ratio [-].  
Figure 2: Construction of the Scientific Research Workplace of the Faculty of Civil Engineering at the University of Zilina and measurements of the quality of the clay subgrade.