Issue 41

S. Zhao et alii, Frattura ed Integrità Strutturale, 41 (2017) 412-423; DOI: 10.3221/IGF-ESIS.41.53 419 piles DN=200mm, and the length of the piles is 600 mm. The test piles adopt the concrete C30, the six main bars adopt the first-class steel bar whose diameter is φ8, the stirrup is made of Wire No.8@200mm, the thickness of the protective layer of the concrete is 50 mm, the diameter of the heat-transfer tubes pre-embedded in the piles is DN=30mm , and the single U-shaped plastic pipes. The material ratio of the concrete piles in each group is shown in Tab. 6, Fig. 12 refers to the hydraulic pressure testing machine, and Fig. 13 shows the preparation before the pile's static pressure. No. Combination Steel fiber(g) Graphite (g) Copper slag(g) Fine aggregate (kg) Coarse Aggregate (kg) Cementitious materials(kg) Water (kg) 1 First group 0 0 0 16.02 27.06 11.58 5.34 2 Second group 0 0 0 16.02 27.06 11.58 5.34 3 Third group 1117.8 25.2 787.2 15.21 27.06 11.58 5.34 Table 6: Material ratios of the test piles. Test results and the analysis The ultimate strength in of the three groups should be recorded respectively separately as collected in Tab. 7 when the foundation pile load is put on the upper part of the pile until the pile body is damaged, and Fig. 14 shows the damage situation of the foundation pile. Category No. Group 1 Group 2 Group 3 Strength of the test pieces(KN) 1 375 311 382 2 361 300 396 3 345 285 373 Table 7: Ultimate strength of the test piles (kN). (a) (b) (c) (d) Figure 14: Damage situation of the pile body: (a) The end face of the pile with non-steel- fiber embedded pipes; (b) Non-steel- fiber pile without embedded pipes; (c) End face of the reinforced pile with steel fiber embedded pipes; (d) Reinforced pile body with steel fiber embedded pipes. Fig. 14 shows the situation when the load is put on the upper part of the piles until the piles are damaged. The pile in Diagram a is a pile for burying the heat transfer tubes in the reinforced concrete piles. As can be seen from the damage, there are irregular cracks on the surrounding heat transfer tubes which are to be embedded, indicating that when the vertical load is carried out on the pile, the bearing capacity of the pile is affected due to by the irregular damage caused by reasons for the addition of the heat transfer tubes. The pile in Diagram b is the reinforced concrete pile under normal perfusion. The pile body is damaged due to the vertical load on it. Under the action of After the hydraulic pressure testing machine has been applied, cracks appear on the upper part of the concrete pile, and the concrete in the middle part of the pile breaks off, indicating that under the action of the vertical load force, the degree of the damage of to the pile is also serious. The piles in Diagrams c and Diagram d are the steel fiber- reinforced concrete piles with single U-shaped heat transfer tubes. It can be seen from Diagram c that although there are cracks on the top face of the pile, yet less but not as