Abstract: A modular cast concrete element of this invention, capable of being assembled with other, similar elements into a tubular underground installation (e.g., sewer duct, tunnel liner) has a well opening to each of its axially-facing end surfaces wherein a rod is received that is insertable in a like well in an axially adjacent element to guide one of the elements to a predetermined position relative to the other and lock it in that position. In each well is a securement member having an annular radially outer marginal portion confined in a circumferential radially inwardly opening groove in the well and having resilient radially inwardly projecting teeth. The teeth have radially inner edges on a circle of smaller diameter than the rod and are flexible axially to enable the rod to be easily inserted into the securement member but to engage it under convergent bias for holding it against withdrawal from the well.

Abstract: A solar powered lighting system including a light emitting unit electrically connected to a rechargeable power storage unit, a solar powered recharger connected to that power storage unit, means to prevent discharge of that power storage unit through the solar powered recharger, means to prevent overcharging of the power storage unit, means to prevent discharging the power storage unit below a predetermined level and means to automatically connect the disconnect the light emitting unit from the power storage unit wherein the voltage output of the solar powered recharger and the power storage unit is matched to the voltage required by the light emitting unit.