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Título

THE EFFECT OF AN ECCENTRIC BLOW IN THE HIGH STRAIN DYNAMIC PILE TEST

Resumo

The High Strain Dynamic Pile Test (HSDPT) has been used on piles to detect damage along the shaft and to determine the pile capacity. The Beta Method is commonly used to identify the magnitude of the pile damage. A broken pile may not support a low-energy blow applied to the pile top (Murakami et at, 2020). Moreover, good dynamic-collected data is fundamental for a reliable diagnosis of the piles, particularly for detecting pile damage (Murakami et al., 2022a, 2022b). This paper presents a case study in which poor data quality indicated false damage on 30 cm-square precast concrete piles. The project site is in Cubatão, SP, Brazil, and the piles were driven by a 5-ton hydraulic hammer up to 32m depth. The soil profile indicated a thick soft clay layer up to 28m depth, followed by a sandy layer up to 38m depth. The 5-ton hydraulic hammer applied four blows with a drop height of 40cm, and the Beta values were between 52% and 90%, indicating severe pile damage (broken pile). The RMX (maximum static resistance) was between 107 and 132 tons. However, the set per blow was zero, and the force signals demonstrated an eccentric blow, indicating that this bending on the pile may have resulted in this “false pile damage.” The collected signals indicated that velocity signal increased sharply relative to the force before the 2L/c time on the blow number 6. This fact would indicate that a damage on the pile had weakened the pile (Goble et al., 1977). Further, the pile-driving machine’s hammer had been appropriately adjusted on blow number 7 with no indication of negative values at the beginning of the strike on sensor F3. The Beta values were conservative, with a value of 71. However, the CAPWAP demonstrated slight damage on the piles. In addition, with a blow of 60 cm, the RMX was 192 tons. This paper shows that the pile testing engineer may evaluate if the collected data has good quality. If not, an investigation must be done to identify the cause of the bad-quality data. Otherwise, the outcome of the HSDPT will not be reliable, and may indicate a false pile damage on the pile shaft as observed by Murakami et al. (2020, 2022).

Palavras-chave

High Strain Dynamic Pile Test (HSDPT), Beta Method, False Pile Damage, Data Quality, Precast Concrete Piles

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