自由约束条件下分层地基中PHC能源桩热力响应原型试验研究

Prototype experimental investigation on the thermo-mechanical behaviors of free constrained full-scale PHC energy piles in multi-layer strata

现场PHC能源桩在分层地基中的热力学响应研究相对较少。通过现场原型试验,对位于分层土地基中PHC能源桩热学响应及力学特性进行试验研究,并结合桩周土孔压静力触探试验(CPTU)与钻孔取样试验分析能源桩的热–力学响应特征。结果表明:桩身温度总体分布较均匀,平均上升20.0℃,桩两端与高热导率土层处温度较低,分层地基的换热能力不均对桩温增长量产生显著影响;桩身内产生压应力,其中最大桩身应力为4.70 MPa,桩底应力为3.77 MPa;中性点在16.3 m深左右,位于靠近桩下端2/3桩长处,且位置不变;对比其他现场试验发现,桩身附加应力大小与桩侧土强度、成桩工艺与桩型有关;桩上部出现负摩阻力,下部产生正摩阻力,其中负摩阻绝对值较大,其原因可能是由于两端桩–土相对位移大小不同。最后,依试验结果提出一种简化的桩–土相对位移与桩身应力分布形式。

Investigations on the thermo-mechanical behaviors of precast high strength concrete(PHC) pipe piles,especially surrounded by multi-layer strata,are relatively few. Based on in-situ prototype tests,piezocone penetration tests and drill sampling method,the thermal and mechanical responses of a full-scale PHC energy pile in layered soil were analyzed. The results show that the temperature of piles distributes relatively uniform with an average increase of 20.0 ℃. The temperature of the pile near the ends or high conductive soil layers is lower,indicating obvious influence of inhomogeneous heat transfer ability of layered soils on the temperature of the pile. The compressive stress is generated in the pile body. The maximum stress is 4.70 MPa p and the stress at the bottom of the pile is 3.77 MPa. The neutral point locates at 16.3 m depth which is about 2/3 of the pile length,and the position keeps stable during the test. Compared with other field tests,it was found that the additional stress of the pile body is related to the strength of the surrounding soil and the pile type. The negative shaft friction develops in the upper part of the pile and positive shaft friction occurs in the lower part. The negative shaft friction is larger than the positive,which may be due to the difference between the pile-soil relative displacements of both ends of the pile. According to the results,a simplified distribution of pile-soil relative displacement and pile body stress was proposed.