中文摘要：

为探究海上桩基础在长期水平动循环荷载作用下桩周土体中应力分布规律,选取典型的中细砂作为试验土体,开展砂土中单桩水平动荷载作用下的模型试验,获得不同幅值和频率的长期循环荷载作用下桩周土体应力循环弱化的变化规律。试验结果表明：桩周土的弱化主要集中在前1万次循环,随后便逐渐趋于稳定。相同幅值的循环力,频率越高,土中应力越大,但加载频率与土中应力弱化率没有明显的相关性;相同频率,循环动荷载的幅值越大,土中应力越大,但土体中应力弱化率越大;在达到稳定状态时,土体中应力弱化率达到20%~40%。水平方向上,土中应力的弱化趋势集中在1.5倍的桩径范围,在1倍的桩径范围内弱化明显;竖向土体中应力弱化集中在地表下1/2桩长范围,在1/3桩长范围内弱化明显。

英文摘要：

To explore the stress distribution law of offshore pile foundation under long-term horizontal cyclic loading,a series of indoor model tests using medium sand were conducted. The circulation weakening law of the resistance for the soil around pile was obtained under the action of long-term cyclic at amplitude of loads and frequencies.Experiment results showed that soil weakening mainly occurred in the first 10 000 cycles and gradually stabilized.When under the same load amplitude,the greater the frequency,the greater stress was,and weakening ratio of stress had no direct relationship with frequencies. When under the same frequency,the greater the load,the greater the weakening ratio of stress was. After getting stable,the stress around the pile weakened about 20% to 40%. In horizontal direction,the weakening of stress mainly occurred in the zone of 1. 5 times pile＇s diameter around the pile,obviously within the zone of 1. 0 times pile＇s diameter. In vertical direction,the weakening of stress mainly occurred within the zone of half pile＇s length beneath the ground surface,obviously within the zone of 1/3 pile＇s length.