# Experimental Study on Dynamic Response Characteristics of RPC and RC Micro Piles in SAJBs
## 2 Experimental Program  
### Specimen Design and Fabrication  
As noted previously, it is known that the micro piles are the vertical supporting piles below approach slabs in SAJB for practical engineering. The maximum size of the structure for micro pile in real-life is about 0.1-0.3 m in diameter and 2-5 m in length. In this experiment, two micro piles were designed and fabricated according the Chinese code for Building Pile Foundations in terms of the similar principle of pile diameters 'D.' They were labeled as RPC and RC, respectively. The shaking table tests on the dynamic response of full-scale micro pile-soil interaction were carried out in this work. Therefore, the pile model is the same as the practical situation, its geometrical scale is 1:1, and the stress level ratio is 1 [31]. The RPC and RC specimens are 2.20 m in long, and 100 mm in diameter. The RPC micro pile model is a new type of pile made by new concrete materials, which is composed of steel fiber, fly ash, and other materials by mixing. Furthermore, steel fiber of 2% concrete content (mass fraction) in diameter of 8 mm was mixed into the mix design of the RPC micro pile, which enhanced significantly the strength, stiffness, and toughness of the RCP pile without coarse aggregate. In this case, the water binder ratio of 0.18, the silica tune with 0.3 of concrete, and fine sand with 1.2 times (mass fraction) of concrete were employed as the mixtures. In addition, the mechanical parameters of its test cube as compressive strength of 141.6 MPa, Poisson ratio of 0.25, and an elastic modulus of \(4.41\times 10^{4}\) MPa were measured after 28 days. Meanwhile, the designed strength grade of the RC micro pile was C40. It serves as a comparative specimen of the RPC micro pile. Therefore, the material properties and other parameters of RPC and RC model piles are also summarized in Table 1. The transverse reinforcement of two micro piles was 6 mm in diameter and its spacing was 200 mm, and 6\(\Phi\)10 mm in diameter rebars were selected as the longitudinal reinforcement bars. The reinforcement ratio of each micro pile was 6%, which meets the minimum reinforcement ratio of 0.65% of the Chinese code. The process of fabrication and reinforcing bars of micro piles are shown in Figure 2a,b, respectively. The PVC pipe with 100 mm in diameter was used as the mold of micro piles before the construction of model piles.  
The inertia mass block was embedded at the pile head to replace the approach slab in SAJB supported by micro-piles [32]. Assuming the actual dimensions with the length of 3 m and the thickness of 0.2 m for each unit width of the approach slab, and this approach slab was supported by three micro piles in a row at the end of the abutment. Meanwhile, the supporting influence of soil lower the slab on the approach slab, which was neglected, and the weight of the concrete was calculated as 2.2 ton/m\({}^{3}\). As a result, the inertia mass at the top of each micro-pile was 220 kg, and the mass block was made by welding the counterweight iron brick, as shown in Figure 3a. In addition, it is convenient that the fixed connection of mass block and pile head, as well as a hole with a diameter of 60 mm was reserved in the center of the mass block, and the steel tube was welded on the pile head along the axis direction of the pile. Therefore, the mass block was embedded on the outer wall of the steel tube along the length direction of the steel tube, and the mass block was fixed by welding to the steel tube.