多向加芯搅拌桩是一种新兴的软土地基处理技术，当前应用不多，实际经验稍显不足，需要结合工程实践，对其关键技术展开深入研究。本文以河北省唐山市丰南钢厂项目软土地基处理工程为例，在介绍软土地基处理方案比选、多向加芯搅拌桩工程设计与施工工艺的基础上，通过物理检测，评价了其工程质量，利用ANSYS有限元进行数值模拟，评价了其关键技术参数选取的合理性，并提出了可能进一步优化的技术方案。 丰南钢厂项目区分布有典型的软土地基，具有高含水量、孔隙比大、压缩性高、灵敏度高、物理力学性质差等特点。多向加芯搅拌桩通过刚性内芯桩承担荷载，柔性外桩提供侧摩阻力，承载力高于柔性桩，成本低于刚性桩，在较小沉降时能提供足够高的承载力，又能充分发挥预应力管桩的强度。丰南钢厂项目选择多向加芯搅拌桩作为软土地基的加固方案，在技术和经济等方面均具有明显的合理性和优越性。 通过对多向加芯搅拌桩在竖向荷载下的工作性状进行数值模拟发现：在正常荷载情况下，桩侧侧摩阻力分担总荷载的90%以上；增加内外芯长度比，可以有效减小多向加芯搅拌桩的桩顶沉降量，最优内外芯长度比应为0.75；多向加芯搅拌桩的桩顶沉降量可通过增加芯桩面积比来减少，多向加芯搅拌桩的最优截面含芯率应为0.25；水泥掺入量宜为22%左右，为提高水泥土强度，可适当增大下部桩身掺灰量。 群桩破坏模式由群桩的极限承载力决定，分为群桩侧阻破坏和群桩端阻破坏；影响多向加芯搅拌桩群桩效应的主要因素是承台和桩距。承台会限制群桩基础上部土的相对位移，影响桩身荷载的传递规律，从而使桩身上部的侧摩阻力值发挥不完善，桩侧摩阻力的最大值不同于单桩出现在桩身上部，而是出现在桩体的中下部。群桩基础中，在不考虑桩长因素影响的前提下，随着桩数的增加、桩距的减小，其桩侧摩阻力值发挥越小。当内外芯桩长比0.75，含芯率0.25，桩间距3m时，承载效果最佳，经济效益最好。

A new soft soil foundation treatment technology multidirectional mixing cored pile is not widely applied and lack of practical experience. To develop in-depth research for it’s key technologies needs to combine with engineering applications.Taking the soft soil foundation treatment project of Fengnan Steel Factory(located in Tangshan City,Hebei Province) as an example, this article evaluates the project’s quality by physical testing, appraising its key technical parameters and putting forward a technical proposal for further optimization through ANSYS finite element numerical simulation on the basis of introducing the comparison and selection of soft soil foundation treatment schemes, the design and construction technology of multi-directional mixing cored piles. Fengnan Steel Factory are distributed typical soft soil foundation with characteristics of high water content, void ratio, compression, sensitivity but poor physical properties etc.multi-directional mixing cored pile can not only provide with enough bearing capacity,but fully play a role in strength of prestressed pipe pile.Fengnan Steel Factory project chooses Multi-directional mixing cored pile as reinforcement scheme of soft soil foundation, which has obvious rationality and superiority in terms of technology and economy. Through the numerical simulation of multi-directional mixing cored pile under working vertical load, it is found that in normal load, the lateral friction of pile can share more than 90% of the total load,increasing the ratio of inner and outer core length which can effectively reduce the settlement on the top of multi-directional mixing cored pile, the optimal ratio of inner and outer core length should be 0.75; the settlement on the top of multi-directional mixing cored pile can be decreased by increasing the ratio of inner and outer core length. As the ratio decreased, the optimum cross-section core content of multi-directional mixing cored pile should be 0.25, and for the cement content,it should be about 22%. To improve the strength of cement-soil, the ash content of lower pile body can be increased appropriately.The results shows that the failure mode of pile group is determined by the pile’s ultimate bearing capacity, which is divided into side resistance failure and end resistance failure of pile group. The main factors which influence group effect of multi-directional mixing cored pile are pile cap and pile spacing. Pile cap restricts the relative displacement of soil on pile group foundation and influence the pile body’s load transferring rule, resulting the imperfect lateral resistance value on pile body. The lateral resistance on pile body maximum value is different from the single pile on the top of the pile, but appears in the middle and lower part of pile body.In pile group foundation, without considering the influence of pile length, as the increase of piles and decrease of pile space, the pile side resistance will be smaller and smaller. When the length ratio of inner and outer core piles is 0.75, the core ratio is 0.25, and the space of piles is 3m, the load bearing and economy effect is perfect.