AASHTO R 40:10(2018) Standard Practice for Measuring Pavement Profile Using a Rod and Level.
4.1. Longitudinal profile measurements are used during construction to assess the smoothness of new pavement. Elevation profiles, when converted to roughness measurements, are also gathered for estimating the performance of in-service pavements, and can then be utilized in a pavement management system.
5.1. The rod and level used in routine surveying and road construction generally will not have the resolution needed for pavement profile measurements. For pavement profile measurements, precision leveling instruments are required. The instrument used for profile measurement shall satisfy the resolution criteria noted in ASTM E1364. Table 1.
5.2. The rod used shall be equipped with a bubble level so that it can be held vertical accurately. A suitable base shall be selected for the rod in order to reduce the sensitivity to small variations in rod placement. For smooth-textured pavements, any type of base is suitable. For textured surfaces, a circular pad with a diameter of at least 2.0 cm (0.8 in.) is recommended. As only relative elevations are required for computing roughness indices, no correction is required for attaching a pad to the bottom of the rod.
Note I It is recommended that an invar rod be used to minimize the effects of temperature changes. This is particularly important for Class 1 surveys on smooth roads, for which the resolution requirements given in ASTM E1364, Table I are more stringent.
6.1. Maintenance—Use shockproof packaging when transporting the instrument. Clean the instrument after completing a profile measurement. Before cleaning the lenses, blow the dust of’f the lenses. Clean the lenses using a soft cloth. Do not touch the lenses with the fingers. If the instrument becomes wet in the field, dry it completely before packing. Inspect the tripod regularly to ensure that the connections are not loose.
6.2. Adjustment—The user manual for the level shall be consulted on how to perform adjustments of the instrument. Different makes and models of levels will require different adjustments to be performed. The following are some common adjustments that are required in levels in order to obtain accurate measurements. The user manual for the level shall be consulted to determine whether the following adjustments are needed for the level being used and, if so. how to perfonn the specific adjustment.
6.2.1. Make Axis of Level Bubble Perpendicular to Vertical Axis—After setting up the level, center the bubble. Move the telescope 180 degrees about the vertical axis. If the bubble moves, the instrument needs adjustment.
6.2.2. Adjust Horizontal crosshairs—T his adjustment will ensure that the horizontal crosshairs are truly horizontal when the instrument is leveled.AASHTO R 40 pdf download.