In tunnelling using tunnel boring machine (TBM), the surrounding rocks are typically supported by precast lining segments, pea-gravel backfilling and grouting. The compactness of the backfill layer is critical for ensuring the safety of the tunnel construction. However, poor fluidity of cement generally leads to uneven grouting effects, resulting in lower density in certain areas of the backfill layer. In contrast, enzyme-induced carbonate precipitation (EICP) is an environmentally friendly and sustainable technique which has superior mobility and diffusivity compared to cement. To investigate the reinforcement effects of EICP technique on backfill layer, a series of bio-cemented sand column tests and model tests were conducted in this study. The optimal working range of pea gravel and sand for effective bio-cementation were determined by comparing the permeability, unconfined compressive strength (UCS), calcium carbonate content (CCC), and wave velocity of bio-cemented sand columns. The effects and homogeneity of reinforcement based on model tests were assessed by point load tests, wave velocity measurements, and calcium carbonate content evaluations. The model tests with different grouting hole layout density were conducted to obtain the optimal hole placement scheme. The column test results demonstrated that the optimal working range of pea gravel to sand ratio for effective bio-cementation is 1.25–1.5. As the number of grouting cycles increases, the point load strength, wave velocity, CCC and UCS of the specimens increase while the permeability of the specimens decreases. The point load strength of bio-cemented specimens could reach up to 16.53 MPa, while the permeability was reduced by three orders of magnitude compared with that of untreated specimens. The EICP has been demonstrated to be an effective technique capable of improving the compactness and strength of the backfill layer, with aggregates effectively cemented by calcium carbonate generated. The model test results demonstrated that the full-coverage arrangement hole scheme achieves uniform cementation, while the space arrangement hole scheme produces concentrated CaCO3 near grouting holes. Furthermore, a new and improved grouting scheme is proposed based on the model test results. The data obtained in this study offer valuable references for the reinforcement of the backfill layer in TBM tunnelling using the EICP technology.

中文翻译：

---

基于模型试验的 EICP 技术对 TBM 隧道衬砌后加固回填层的可行性分析


在使用隧道掘进机 （TBM） 进行隧道掘进时，围岩通常由预制衬砌段、豌豆砾石回填和灌浆支撑。回填层的紧凑性对于确保隧道施工的安全性至关重要。然而，水泥流动性差通常会导致灌浆效果不均匀，导致回填层某些区域的密度较低。相比之下，酶诱导碳酸盐沉淀 （EICP） 是一种环保且可持续的技术，与水泥相比具有优异的流动性和扩散性。为研究 EICP 技术对充填层的加固效果，本研究开展了一系列生物胶结砂柱试验和模型试验。通过比较生物胶结砂柱的渗透性、无侧限抗压强度 （UCS）、碳酸钙含量 （CCC） 和波速，确定豌豆砾石和沙子有效生物胶结的最佳工作范围。通过点载荷测试、波速测量和碳酸钙含量评估评估基于模型测试的加固效果和均匀性。通过对不同注浆孔布局密度的模型进行试验，得到最优的孔位布置方案。柱子测试结果表明，豌豆砾石与沙子比的最佳工作范围是 1.25-1.5随着注浆循环次数的增加，试件的点载荷强度、波速、CCC 和 UCS 增加，而试件的渗透性降低。生物胶结试件的点载荷强度可达 16.53 MPa，而渗透率与未处理试件相比降低了 3 个数量级。 EICP 已被证明是一种有效的技术，能够提高回填层的致密性和强度，产生的碳酸钙可以有效地胶结骨料。模型试验结果表明，全覆盖布置孔方案实现了均匀的胶结，而空间布置孔方案在注浆孔附近产生浓 CaCO3。此外，在模型试验结果的基础上，提出了一种新的和改进的注浆方案。本研究获得的数据为使用 EICP 技术加固 TBM 隧道掘进中的回填层提供了有价值的参考。