Abstract: Arms extending laterally from an upwardly moving weight, such as a rebounding seismic gas exploder, terminate in guide assemblies adapted to engage a plurality of parallel semi-rigid, resilient ropes connected between the top and the bottom of a supporting frame so that the weight must follow their path. Each guide assembly contacts its respective rope at several vertically spaced positions so as to distribute side loads along the rope resulting from eccentric exploder movement. The construction prevents the exploder from tilting sufficiently to catch or lock on the one or more ropes, thus avoiding pendulum movement of the exploder and abrasion of the ropes.

Abstract: In a longwall mining system, a work face extends between parallel sets of multiple head- and tailgate entries, adjacent entries of each set being separated by rows of chain pillars. Lengths of a headgate entry immediately adjacent the longwall panel and the pillar breakthroughs to the next headgate entry are progressively pump packed in advance of the longwall face with a coherent thixotropic roof supporting material. As the longwall face is mined, a bidirectional shearing machine cuts through the roof supporting material and the chain pillars, which are then removed in a continuous operation.

Abstract: A gas exploder for injecting seismic signals into the earth is provided with a high speed hydraulic catching apparatus which allows the exploder to rebound essentially unrestrained after it is fired at the surface and replaces it on the ground in one second or less without generating a significant false signal. The exploder falls freely from its maximum rebound height to within a few inches of the ground and is then lowered slowly to its starting position. Means are provided for automatically adjusting the position of the exploder after each shot so that it rests on the earth ready for the next firing even though compaction of the earth has taken place.

Abstract: A method and machine for constructing ice roads upon snow-covered regions. The machine gathers snow from the region upon which the road is to be built, heats the gathered snow until it is partially melted and becomes slush, and then spreads the slush to form the road. In one embodiment, the surface upon which the slush is deposited is pre-heated to enhance the road base.

Abstract: A method for measuring the thermal conductivity of well casing in situ. The instrument consists of a probe several feet in length lowered into a well and decentralized so that it maintains contact with the casing wall. Two temperature sensors situated adjacent opposite ends of the probe are thermally insulated from an electrically heated intervening portion of the probe body. The probe is moved from one depth to another at a constant predetermined velocity, and the sensors continuously measure the temperature of the casing wall before and after passage of the heated probe portion thereover. The effective thermal conductivity of the casing is directly proportional to the flux applied by the heater and inversely proportional to the temperature change as the heater passes a point along the casing.

Abstract: A method and apparatus for recording the position of a sensor to reduce turbulence errors in airborne magnetic surveying includes, in one embodiment a camera mounted on a gyrostabilized platform to maintain it at a constant downward orientation from a bird towed from an airplane. The bird, in addition to the platform and camera, carries a magnetometer sensor which measures the magnetic field at the bird at a predetermined rate. The camera is actuated at the times the magnetic field is measured, whereby the position of the magnetometer can be precisely located for each measurement taken. In another embodiment, two birds towed from an airplane each carries a magnetometer sensor. The two birds are towed at different altitudes, one above the other, and a camera is carried by the bird at the higher altitude to photograph the bird at the lower altitude and the earth to precisely record the relative locations of the birds with respect to each other and the earth when the magnetic measurements are made.

Abstract: A pulse of ultrasonic acoustic energy applied to an earth formation by means of a well logging tool initiates a first compressional formation pulse followed by a secondary pulse of lower amplitude and velocity traveling exclusively in the formation fluid. These two pulses are located, identified and quantized with cross-correlation techniques to give a direct indication of formation permeability, to identify accurately the nature of the formation fluid, and to provide a more accurate determination of formation porosity.

Abstract: An apparatus for generating seismic waves includes an elongated closed tube with a piston in its internal cavity. The piston is carried by a piston rod which extends through the top of the tube, and includes a fuel inlet and exhaust channel. The piston also carries a second tube to define a combustion chamber therein, and a fuel conducting tube extending along the length of the piston rod and beyond the piston to approximately medially within the second tube. When a combustion fuel is introduced to within the combustion chamber and ignited, a force is applied to the piston in one direction and an opposite force is applied to the tube moving the tube with respect to the piston a distance approximately three times the diameter of the piston.

Abstract: A gas exploder consisting of a rigid cylindrical lower member and a rigid upper member telescoping therein to form a chamber in which a gas explosion can take place is supported beneath the surface of the water from a float by means of low resilience ropes connected to the bottom of the lower member so as to substantially limit its allowable downward movement. The upper member includes a piston downwardly biased within the lower member by an air spring and a hollow pedestal connected to the piston and extending freely through the float above the surface of the water to accommodate fuel, compressed air and exhaust conduits communicating with the interior of the housing. The energy of an explosion in the combustion chamber is expended primarily through rapid upward movement of the piston, which compresses the air spring and then lifts the lower member. Implosion of the resultant cavitation bubble adjacent the bottom surface of the lower member generates a pressure pulse of large peak amplitude.

Abstract: An apparatus and method for controlling the travel of a vehicle mounted seismic gas exploder adapted to deliver a downwardly directed pulse to the earth and thereafter be driven in an upward direction by the resultant reaction force. The exploder is flexibly coupled by means of a rope and pulley arrangement to the piston rod of a hydraulic cylinder. Compressed coil spring means aligned with the cylinder are released when the exploder jumps upward and apply a force to extend the piston rod and in so doing cause the rope to be retracted with gradually diminishing force. The exploder may be held at the upper limit of its travel, and its subsequent descent is utilized to recompress the spring means.

Abstract: A seismic gas exploder is coupled to the movable piston of a hydraulic catching system so that the piston is constrained to move with the exploder as it rebounds upward from a shot and then falls back to earth. The weight of the gas exploder is applied through the piston to increase the pressure of the hydraulic fluid in the system when the exploder is moving in a downward direction. A two-position diaphragm actuated pressure switch monitors the fluid pressure, the position of the switch contacts being effective to control an exploder firing circuit or provide other indication of the exploder's position.