属于高压喷射搅拌工法中一种之喷射灌浆工法(以下简称「JG工法」)，于地层结构复杂之地质条件下，因地质软硬差异造成有效桩径不同，故对于设计或施工管理值标准之采用为一尚待检讨之课题。即针对该等JG工法之技术性问题，根据大范围开挖改良体内部之施工案例所获得之观察结果提出报告。由改良体内部之观察结果可知，若无流木等障碍物之存在，先行灌浆形成之改良体各水平断面大致呈圆形，且后行灌浆形成之改良体与先行灌浆改良体之间呈密合状态。此外亦针对将改良体整体性列入考虑之强度，提出新的评价方法。

The jet grouting method is commonly used for ground improvement. However, little is known about its actual improvement structure in the ground. The extent of improvement, such as the size of effective grout diameter and the degree of overlapping is still in question, especially for complicated ground conditions such as ground with different soil strata. This paper presents the actual findings of the condition of improved ground by jet grouting method, from a tunneling site. It was observed that preceding grout column had a near circular shape, and that they interlocked with the adjacent grout columns, hence meeting the ground improvement requirements. In the evaluation of ground improvement by jet grouting, the compressive strength test is generally employed by means of the boring core specimen, which can be obtained as a test cylinder. However, the ground improvement without such improve condition is estimated to be able to support a certain extent of load. The purpose of this study is to establish the evaluating criterion of condition of jet grouting, and to propose the evaluation method for ground improvement.