竖向-水平组合荷载下桩筏受力特性的试验研究

Experimental Study on the Mechanical Characteristics of Piled Rafts Under Vertical-Horizontal Combined Loads

为研究竖向-水平组合荷载作用下桩筏基础的受力特性,开展了室内模型试验,考虑桩长、桩数、竖向荷载及桩间距对桩筏基础承载性能的影响,并分析了桩身弯矩、剪力及桩侧土压力的变化规律。试验结果表明:桩筏基础的水平承载力随着竖向荷载、桩数、桩长、桩间距的增大而增大,水平位移相应减小;桩身最大弯矩位于0.3倍桩长处,且前桩桩身最大弯矩较大,约为后桩的1.14倍;桩身弯矩及剪力均随着竖向荷载的增大而减小,桩身最大弯矩随着桩间距的增大而减小,但桩顶及桩端弯矩几乎保持不变;增大桩间距可以调整最大负剪力位置,桩顶剪力随桩间距的增大而减小,而桩端剪力值则随桩间距增大而增大;增大桩间距可以带动更大范围的桩间土,桩身内力分布规律保持相同且变化值较小;桩筏基础受组合荷载作用下的破坏模式符合刚性桩破坏规律,桩身水平极限承载力主要由桩侧土体的抗压强度控制。

To study mechanical characteristics of piled raft under vertical-horizontal combined loads, several indoor model tests were conducted, considering the influence of length to diameter ratios, pile numbers, vertical loads and pile spacing, and the changes of the bending moment and shear forces in pile shafts and earth pressure on piles were analyzed. The test results showed that: The horizontal bearing capacity of piled rafts increased with the increase of vertical loads, pile numbers, length and spacing of piles, on the contrary, the horizontal displacement of piled rafts decreased with their increase. The maximum bending moment was located at 0.3 times length of piles below the earth’s surface, and the maximum bending moment in the front piles was larger than that in the rear, which was about 1.14 times bending moment in the rear piles. The bending moment and shear forces decreased with the increase of vertical loads, and the maximum bending moment of piles increased with the decrease of pile spacing but the bending moment at tops and tips of piles almost kept stable. The location of the maximum negative shear forces could be controlled by adjusting the pile spacing, and the shear forces at the tops of piles decreased with the increase of pile spacing but the shear forces at the tips changed conversely. To increase the pile spacing could mobilize a wider range soil between piles, however the internal forces in piles almost kept steady. The failure mode of piled raftes conformed to the failure laws of rigid piles under the combined loads. The ultimate horizontal bearing capacity of piles was mainly controlled by the compressive strength of soil around piles.