An optical probe and method for analysing a soil located in an underground area are provided. The optical probe includes a probe head insertable into the underground area, the probe head including a transparent wall defining a hollow chamber within the probe head; a light source mounted in the hollow chamber, configured to generate an illumination beam towards the soil, the illumination beam passing through the transparent wall to irradiate the soil, thereby producing a resulting light emanating from the soil, a portion of the resulting light returning towards the probe head and being guided in the transparent wall by total internal reflection along the optical path; a detector configured to receive the portion of the resulting light and outputting an output signal representative of characteristic(s) of the soil; and an optical element guiding the portion of the resulting light from the transparent wall to the detector.