基于探头能量测试的动力触探锤击数修正方法研究

    BLOW COUNTS CORRECTION METHOD OF DYNAMIC PENETRATION TEST BASED ON CONE TIP ENERGY TESTING

    • 摘要: 动力触探是一种可用于评价土层均匀性、密实度等的原位测试技术,不同国家与地区的落锤系统并不一致,动力触探锤击数受土层摩擦阻力、能量损耗等影响较大,需修正后才能进一步应用。本文在成都平原卵石地层开展重型、超重型动力触探平行试验,探索不同落锤系统、能量传递等对锤击数的影响。重型与超重型动力触探的有效传递能量之比为0.39,而超重型与重型动力触探的锤击数之比为0.4,表明有效传递能量与锤击数呈现良好的比例关系,为采用能量对动力触探锤击数进行修正提供试验依据。由于重型动力触探的落锤能量较小,受较大直径砾石或卵石的影响,动探曲线易出现锤击数突然增大后迅速恢复正常趋势;而在同一卵石地层试验点,超重型动力触探锤击数随深度的变化显示出较高的一致性与可靠性。研发可测定动力触探探头处能量的装置,探索侧壁摩擦力、能量损耗等对锤击数的影响,超重型动力触探探头处的能量传递系数从地表处的62.5%降低至10 m处的55%。探头能量传递系数是一个能够反映落锤系统、试验工艺、摩擦阻力、能量损耗等对锤击数影响的综合测试指标,给出基于探头能量测试的修正方法,为动力触探锤击数的修正提供了新的思路。

       

      Abstract: Dynamic penetration test(DPT)is an in-situ testing technique used to evaluate the uniformity and density of soil layers. The drop hammer systems vary across different countries and regions, and the blow counts of DPT is significantly affected by factors such as soil layer friction resistance and energy loss, requiring corrections before further application. This paper conducts parallel experiments with heavy and super-heavy dynamic penetration tests at gravelly soils sites in the Chengdu Plain to explore the impact of different drop hammer systems and energy transfer on the number of blow counts. The ratio of effective transferred energy between heavy and super-heavy DPT is 0.39, and the ratio of the number of blow counts between super-heavy and heavy DPT is 0.4, showing a good proportional relationship. This provides experimental evidence for correcting the DPT number of blow counts using transferred energy. The drop hammer energy of heavy DPT is smaller, and due to the influence of larger diameter gravel or cobblestones, the DPT curve tends to show a rapid increase in the number of blow counts followed by a quick return to the normal trend; in the same gravelly soils site, the number of blow counts in super-heavy DPT changes consistently with depth, showing higher repeatability and reliability. Developing devices that can measure the transferred energy at the cone tip of DPT rod and exploring the effects of sidewall friction force and energy loss on the number of blow counts, the energy transfer coefficient at the cone tip of super-heavy DPT decreases from 62.5% at the ground surface to 55% at 10 m depth. The energy transfer coefficient at the cone tip is a comprehensive test indicator that reflects the impact of the drop hammer system, test process, friction resistance, and energy loss, providing a new approach based on cone tip energy measurement for correcting the number of blow counts.

       

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