The invention discloses a flat hole grouting 
subgrade reinforcement method and structure without damaging the 
road surface. The steps are: A. determining the hole position of the grouting hole; B. drilling a horizontal or oblique grouting hole;  The main direction is orthogonal; C, the grouting holes are drilled alternately; D, the inward grouting is drilled from the periphery of the roadbed 
lesion; E, the grouting flower tube is installed; F, the front end of the grouting holes arranged in a three-dimensional staggered way through the cross section of the roadbed  Install the seamless grouting outer 
pipe; G. Inject 
cement slurry evenly, and the grouting pressure is determined by the test and the area; H. During the grouting process, observe the settlement, inclination, deformation and displacement of the 
subgrade pavement, structures and surrounding buildings.  The grouting hole is formed by horizontal or oblique dry drilling of the 
subgrade slope in the diseased area, and the grouting flower 
pipe and the seamless grouting outer 
pipe are installed, and the grouting flower pipe and the seamless grouting outer pipe are connected by joints and screws.  The method is easy to operate and the operation is simple and convenient.  It does not damage the pavement structure, significantly improves the 
bearing capacity and stability of the subgrade structure in the diseased area, and the reinforcement effect is remarkable.