防波堤椭圆形桶式基础结构的贯入受力特性实验研究

Penetration resistance and wall friction of ellipse lower bucket of breakwater into soft ground in centrifuge

某工程拟在深水软土地基上修筑防波堤,为了尽量减少地基处理充分利用天然地基,创新性设计出一种轻型薄壁的预制防波堤结构,其挡浪部分为直立薄壁圆筒,基础部分则为倒扣的薄壁椭圆形桶,并且椭圆形下桶为外壁和内隔板分成9个格室,防波堤结构浮运至指定位置后,拟采用负压工法施工安装就位。这种新型防波堤结构为国内外首次提出,其下沉施工设计尚无规范可循,为此开展了土工离心模型试验,在模型加速过程中模拟了椭圆形下桶基础在淤泥层中的自重下沉,之后利用新研发了一种大行程作动加载装置给椭圆形下桶施加下推力,让其继续向下贯入直至穿越整个淤泥层,以模拟负压工法的贯入下沉。试验测量了下桶贯入下沉过程中的推力与贯入位移,还尝试测量了桶壁和内隔板断面的压应变,由此分析了下桶基础的下沉总阻力、桶壁摩擦力以及截面压应变随贯入位移的变化。结果发现,这些曲线均出现了转折点,根据转折点对应的下沉总阻力确定了椭圆形下桶基础贯入过程所遭遇的临界下沉总阻力值,据此估算了负压工法中所需施加的压力差。

An innovatively prefabricated breakwater is proposed with an ellipse thin-walled bucket as its foundation for a new offshore breakwater project, where a thick weak ground is prevailing, so that the underwater ground improvement for the construction of the traditional breakwater can be avoided to save cost. Each unit of the breakwater consists of two large-diameter cylinders as its upper wave barriers and one large-size ellipse suction bucket with 9 partitioned chambers as its lower foundation. The large bucket is fully embedded in natural soft ground after installation. Integrated into the preliminary design study of this breakwater project, one geotechnical centrifuge model test is carried out to investigate the penetration resistance and skin friction of the large bucket into a layer of thick muddy clay. A driving actuator of large travel is developed to simulate the sinking action force, which is produced in prototype by means of vacuum in bucket chambers. The model bucket is first sunk into the muddy clay layer under its self-weight during the elevation of centrifugal acceleration to the appointed value and then penetrated through the layer and rested upon a silty clay layer by means of the driving actuator. It is found that a turning point occurs on the relationship curve of total resistance with penetration displacement, indicating the contacting of the soil within chambers with their inner ceiling. Accordingly, the value of resistance at the turning point is specified as the critical resistance of penetration, which governs how much vacuum value will be utilized in its sinking process by means of vacuum method. The friction profile with penetration depth is also analyzed of outside wall and inner partition boards of lower bucket.