## 5 Summary and Conclusions  
This paper presents the results of bender elements (BEs) tests on anthropogenic soil--Recycled Concrete Aggregate (RCA), and its modified version--a mixture with rubber grains. In this study, dynamic properties of these two artificial materials in terms of shear wave velocity (\(V_{S}\)) are presented. The main observations from this study are as follows:  
1. Shear wave velocity of modified anthropogenic soil is influenced by the rubber content. Concerning the amount of rubber content used, 15% by RCA volume, all three compositions exhibit lower \(V_{S}\) values than pure RCA specimens, up to 40%. This can be explained by insignificant contribution of soft rubber particles on shear wave velocity of mixture solid skeleton. Normal soil (0% rubber) is stiffer, due to greater values of \(V_{S}\) and thus higher shear modulus. The addition of rubber makes the material softer. Another advantage of using rubber grains is less susceptibility to the near field effect. Additionally, regarding the tested mixtures, the results are more scattered, without any consistency. This can be due to the properties and behavior of rubber itself. Rubber grains may be differently arranged in the specimen during the test set on the same specimen. 2. The results of this research present the behavior of mixtures of materials with non-optimized compositions. In order to better examine the effect of rubber inclusion on dynamic properties of modified anthropogenic soil, different combination of soil and rubber chips should be tested. Such research would be helpful in determining the eventual limit in the rubber amount that does not make any significant changes in the dynamic properties of such mixtures. 3. The results of shear wave velocity of pure RCA specimens and RCA-rubber compositions that were obtained by means of peak-to-peak_1 and peak-to-peak_2 techniques are in a good agreement. The average difference between the velocities from both methods does not exceed 0.5%. It is appropriate to make the wave's propagation analysis during BEs test and after it. 4. Application of different interpretation methods of BEs tests in this study suggests rejection of zero crossing method, due to rather overestimated \(V_{S}\) values, up to a maximum of 33% for pure RCA specimens and 76% for RCA-rubber compositions. The minimum value of \(V_{S}\), in the most analyzed cases, is received from cross correlation method. These values are lower than the average \(V_{S}\) values in the range of 1% to 40%. On the other hand, the higher shear wave velocities are obtained from the frequency domain technique, especially for modified RCA specimens. These values are higher than the average \(V_{S}\) values in the range of 2% to 32%. Figure 15: Percentage distribution of \(V_{S}\) values between two different materials: pure RCA and RCA with rubber chips for \(p^{\prime}=180\) kPa. 5. The time domain methods (e.g., peak-to-peak) provide results that are more consistent. The spread of the results for peak-to-peak method is from 5.5 (pure RCA specimens) to 70 (modified RCA specimens) times lower than for frequency domain, which is considered to be the second method with the greatest spread of the results after zero crossing. This can indicate that for BEs testing in anthropogenic soil the time domain methods are more reliable. 6. The small values of standard error, maximum 1.3 m/s for pure anthropogenic material and 4.4 m/s for its modified version using frequency domain method, may prove the accuracy in the choice of methods for analyzing of the test results. A similar conclusion can be drawn by analyzing how much of the average value of \(V_{S}\) represents standard error. For pure RCA specimens, standard errors are from 0.2% to 0.4% of the average value of \(V_{S}\), and for RCA with rubber chips, from 0.4% to 3.3%. 7. By means of uncertainty analysis, the precision and reliability of performed laboratory tests can be confirmed. In the most cases, relative uncertainty is in the range of 0.1% to 10%, what is most correct.