Geotechnical knowledge mapping is very important throughout the pre and post civil engineering construction particularly close to or within the geohazard space. belowground ground instability reflects problem of engineering investigation task particularly to work out the attainable belowground ground instability for rehabilitation, maintenance and observation functions. This study applied a seismal refraction method to analyze a geotechnical knowledge for preliminary geotechnical and engineering geology assessment because of belowground ground instability. the tactic used a thought of seismal waves generated by one among many types of energy sources and detected by arrays of sensitive devices known as geophones. the data was processed by Optim computer code for generating belowground velocity distribution (primary velocity, vp) and interpretation with supported by existing borehole information. The result obtained three main velocity layers and attainable belowground ground instability zone. the primary layers with velocity 330 – five hundred m/s consists of top soil/residual soil, the second layer with velocity of 700 – 1800 m/s and depth zero – vi m, consists of weatherworn zone with a attainable mixtures of soil, boulders and rock fractured, and the third layer with velocity > two300 m/s and depth 2 – 25 m is bedrock. The thickness and dimension of belowground ground instability zone varies inside the survey line from 5 – 25 m and fifty seven – 75 m severally with a primary velocity of 700 – 1700 m/s. The seismal refraction survey produces a decent similarity results compared to the borehole information in term of stratigraphy and geomaterials features. This study proven that the seismal refraction method was a decent geophysical technique to be integrated in geotechnical mapping assessment since its covers an oversized space which extends the borehole results. the employment of seismal refraction method can increase the effectiveness of geotechnical knowledge in term of price and time since it can determine the belowground information in two dimensional (2-D) profiles apace by using fewer workers compared to the geotechnical and engineering geology standard mapping techniques. moreover, this geophysical method used a surface techniques that may minimised the positioning damageability throughout the activity which might profit the setting and appropriate for our sustainable development.