土体三轴加卸荷对桩基影响模型试验系统研制与应用

DEVELOPMENT AND APPLICATION OF SIMULATION SYSTEM FOR MODEL PILES IMPACTED BY SOIL TRIAXIAL LOADING AND UNLOADING

为模拟土体三轴加卸荷对桩基侧摩阻力产生的影响,研制土体三轴加卸荷对桩基影响模拟试验系统。该系统包括4个子系统:三轴加卸荷系统、模型桩组、量测系统及数据自动采集系统。该系统可通过气压加载法在大直径土样顶面及侧向以较高荷载进行加卸荷,模拟不同土性、不同桩端约束条件下土体沉降或回弹对模型桩产生的影响,并通过试验验证其有效性和可靠性。试验表明:系统智能化程度高,可实现大荷载长期稳压,量测系统灵敏度高稳定性好;桩端自由悬空条件下,随土样竖向及侧向施加气压荷载增加,最大正负侧摩阻力增大,中性点发生在(0.5～0.6)L(其中,L为桩身长度)区域。卸荷初期土体回弹变形不大,但桩受拉力发展很快至较大值。系统可用于模拟土体不同路径加卸荷对工程桩的影响。

A simulation system is developed to investigate the changes in skin friction of piles due to the triaxial loading and unloading of soil. The system consists of four subsystems： triaxial loading and unloading system, model piles, measuring system and automatic data acquisition system. The system can get higher pressure with the help of pneumatic loading method; so that the impact of soil compression and rebound on model piles under different soil properties and end restraint conditions is simulated. The validity of the apparatus is verified by elementary tests. The test results show that the system with high intelligence can achieve long-term constant load. The maximum value of positive and negative skin friction for the bottom free piles increased with the increase of applied triaxial load. The neutral point lies in the region from 0.5L to 0.6L. At the beginning period of unloading small rebound deformation of the soil happened; but the tension of the pile caused by the rebound has developed rapidly to a larger value. The system can be used to simulate the effect of the soil loading and unloading on piles under different strss paths.