## 3 Test Results and Discussion
### Effect of Inclination Angle on Pile Bearing Characteristics  
In Figure 6b,c, for the model piles with a 2% and 4% inclination, the settlements of the pile tops were significantly smaller than those of the equal-section inclined piles when the variable-section diameters were 17 mm and 15 mm, respectively. For the model pile with an 8% inclination, the settlement of the pile top is smaller than that of the equal-section inclined pile only when the diameter of the variable section is 17 mm. When the inclination of the variable-section inclined pile is 2%, the vertical ultimate bearing capacity of the single pile of the equal-section inclined pile is 150 N, and the vertical ultimate bearing capacity of the single pile of the variable-section inclined pile with variable-section diameters of 17 mm, 15 mm, and 13 mm are 190 N, 160 N, and 130 N, respectively. In terms of the vertical ultimate bearing capacity of the single pile, when the length of the variable section is certain, and the ratio of the variable-section piles with variable-section diameters is 20/17, the vertical ultimate bearing capacity of the pile is the highest. And, when the length of the variable section is 1/4 of the pile length and the radial dimension of the variable section is 75% of the complete pile diameter, the load carrying capacity of the pile can be increased by as much as 26%. When the inclination of the variable cross-section inclined pile is 4%, the vertical ultimate bearing capacity of the single pile of the equal cross-section inclined pile is 160 N, and the vertical ultimate bearing capacity of the single pile of the variable cross-section inclined pile with diameters of 17 mm, 15 mm, and 13 mm are 200 N, 150 N, and 140 N, respectively. in terms of the vertical ultimate bearing capacity of the single pile, when the length of the variable cross-section is certain, and the ratio of the variable cross-section of the pile is 20/17, the vertical ultimate bearing capacity of the pile is the highest. When the variable-section length is 1/4 of the pile length and the radial dimension of the variable section is 75% of the complete pile diameter, the load carrying capacity of the pile can be increased by as much as 37%. This indicates that, when the pile body has a variable cross-section and the inclination angle is suitable, the soil at the lower part of the pile body at the variable cross-section is compacted to a greater extent because of the existence of the variable cross-section and the inclination angle in the pile foundation during the bearing process. The lateral frictional resistance of the pile body is improved, and the soil at the lower part of the variable section of the pile body shares more pressure from the top of the pile, so the pressure of the soil at the pile end is reduced, thus reducing the settlement of the pile end. The slope of the curve for the 4% inclination 15 mm variable-section pile is smaller than that of the 2% inclination 15 mm variable-section inclined pile in the figure, mainly because of the different resistance produced by the inclination of the pile body. In Figure 6d, when the inclination is 8%, the vertical ultimate load capacity of the single pile for equal-section inclined piles is 97 N. The ultimate load pattern of variable-section inclined piles with different vari-diameter ratios is slightly different from that of variable-section straight piles. The vertical ultimate load capacity of the variable-section inclined piles with diameters of 17 mm, 15 mm, and 13 mm are 100 N, 80 N, and 70 N, respectively. In terms of the vertical ultimate load capacity of the single pile, when the length of the variable section is certain, and the variable-section piles have a ratio of 20/17, the pile has the highest vertical ultimate load capacity, but the increase in the capacity of the friction piles is not obvious.