堤脚区土体扰动对海堤稳定性影响数值研究

Numerical study on influence of soil disturbance close to seawall foot on stability of seawall

水泥搅拌桩是常用的软基处理方式,能够改善其力学性质,使其满足工程要求。但水泥搅拌桩施工过程将对结构性软土造成扰动,因此软基处理初期由于水泥土胶结作用尚未形成,土体强度甚至低于原状土。本文基于某临海滩涂围垦区地下隧道建设过程中海堤堆填及堤脚附近软基处理,开展了一系列三维有限元数值分析。首先在不考虑施工不确定性条件下,将整体简化模型与考虑实体水泥搅拌桩模型进行对比,对其合理性进行评价。计算结果表明,海堤安全系数随扰动度增大而减小,按照规范要求需控制扰动度不大于60%,并且针对本研究问题,整体简化模型稳定性评价结果与后者接近,不同扰动度下两模型计算得到的安全系数最大误差不超过2%。在此基础上,针对实际工程中出现的部分节段堤顶沉陷或海堤侧向变形较大现象,取两个典型加固断面进行堤下地基处理范围土体参数反算。基于反算结果验证按实际工程施加堤脚反压后,海堤稳定性满足要求,同时也进行了堤脚附近软基处理对加固断面海堤稳定性影响评估。结果表明,对于外侧堤脚抛石镇压作用显著的断面,其潜在破坏模式在不同扰动度下均为向内滑动;对于外侧堤脚抛石体体积较小,而内侧堤脚砂袋镇压作用范围较大的断面,其潜在破坏模式随扰动度的增大由向外滑动转变为向内滑动。结合以上计算结果,实际工程中堤脚附近软基处理过程应注意控制施工速率,降低土体扰动度。

Deep cement mixing method(DCM) is a common method dealing with soft foundation. It improves the mechanical properties of soft soil to meet engineering requirements. However, the construction process of DCM will cause disturbance to the structural soft soil. Therefore, when the cement-soil cementation is in the initial stage of soft foundation treatment, the strength of treated soil is lower than that of undisturbed soil. Hence, this article is based on the seawall filling and soft foundation treatment close to the seawall foot during the construction of an underground tunnel in a reclamation area. First, a series of 3-D numerical analyses were carried out. The simplified model and the model considering the solid cement piles were compared without considering the construction uncertainty to evaluate the rationality of the simplified model. The calculation results indicate that the safety factor of the seawall decreases with the increase of disturbance.According to the code, the disturbance degree should be controlled to less than 60%. In addition, in response to the case in this article, the stability analysis result of the simplified model is close to the model considers the solid cement piles. The maximum error of the safety factor calculated by the two models with different disturbances is less than 2%. On this basis,in view of the subsidence or the excessive lateral displacement of the seawall in engineering practice, two typical reinforced cross-sections are chosen to back analyse the parameters of the soil in the foundation treatment range under the seawall. It is verified that the stability of the seawall meets the requirements after applying the overload at the seawall foot according to the real condition. The influence of foundation treatment close to the foot of the seawall on the seawall stability of these two reinforced cross-sections is also considered. The calculation results demonstrate that for cross-sections with significant overload applied at the outer foot of the seawall, the potential failure modes with different disturbances slide inwardly. However, while the volume of the stones at the outer foot is small and the sandbag at the inner foot has a larger suppression effect, the potential failure mode of the seawall changes from sliding outwardly to sliding inwardly as the disturbance increases. In the construction process, attention should be paid to controlling the construction velocity and deducing soil disturbance during the foundation treatment close to the foot of the seawall.