To analyze the working equipment of a rotary bucket excavatDr, it is necessary to determine the components of the total resultant of horizontally and verticaliy directed forces induced in ~ae roar by digging. The components are determined by the value and direction of the resultant. The resulting direction of the resultant depends in turn on the spatial orientation of the rotor and the direction of rotation of the arm In plan during working of the face.A previous communication [1] showed that when the rotor is Inclined in the horizontal or vertical plane (or both), its spatial orientation changes with the slope of the arm and may be expressed by two equations: f cos'..

The efficient operation of a rotor in cohesive ground requires buckers capable of rapid discharge.Experimental investigatiom [1] have shown that the shape of the bucket, in perticular its oross-sectional profile, is governed by rbe properties of the rock being worked. The literature contains recommendations on the best bucket lxofiles for various types of ground. The most soundly-based of these are found in [2]. which takes the coefficient of internal friction as the soil characteristic. The calcular.ion considers the upper position of the bucket on the rotor, and to obtain the shape of the bucket makes use of the arch equation of Prof. M. M. Protod'yakonov, from which it derives a formula for the shape, allowing only for the weight of the soil in the bucker and neglecting the centrifugal force. However, this solution is open to several objections: in the first place, in compiling the equations the position of the bucket on the rotor should be considered; in the second place, no justification is given for neglecting the cen~ifugal force, which is fundamental in preventing the load from falling out of the bucket.To determine the czoss-sectional shape of the bucket we must comider it in a position where, as it turns about the rotor axis, the soil can theoretically begin to faLl out. At this moment, die cross-sectional shape of the bucket should not prevent the soil including the parr furthest from the unloading hatch, from falling out. For our calculation we take the most general case when the buket is filled: with cohesive soiL In this case, on the basis of experiments on rotor excavators [1], we can assume that he sol1 wiLl be discharged from the bucket in layers. However, if this starting-point is to be soundly based we need a more carefttl qnalRative study of discharge of cohesive soil from the bucker. For this purpose at the UkrNHProekt we have built a laboratory test rig of the upright shovel type, in which we can fill the bucket with soil at a face and then discharge it.The test rig consists of a lower frame which moves along the face, an upper rotatable frame with hand winch and pointer, an arm, and a bucket with a capacity of q = 0.04 ms.This article gives the resulrs of experiments with this rig under laboratory conditions. The process of discharging soil from the bucket (Fig. 1) was studied with the bucket in a stationary position at an angle ~ to the arm, which was set horizontally. The bucket had a deliberately non-optimum (rectangular) crosssectional shape, its cutting edge being formed by three solid knives 1, 2, and 3. The bucket has a sliding wall 4

In [1] we showed that to determine the constructive-kinematic parameters of a chamberless bucket-wheel (rotor) it is necessary to know the properties of the soil characterizing its state in the bucket at the beginning of the load discharge process. These properties are the bulk density (unit weight) yp, the tensile cohesion o t, the coefficient of internal friction g, and the shear cohesion c.A feature of the soil in the bucket is its disturbed structure and its state of stress due to internal forces only. When the bucket approaches the discharge sector the medium breaks up by successive separation of layers [2]. Owing to the small mass of the soil in the bucket breakup occurs at small normal pressures (o -< 0.1daN/emz) on the surfaces of limiting equilibrium. For the most typical soils worked by bucket-wheel excavators [3], the literature either contains no data on these properties of the disturbed structure (Or) or contains limited data applying only to high normal pressures (g, c). The reason is that in research on soil properties such data were needed for undisturbed soils only under normal pressures o > 1.0 daN/cm2. Therefore, to find the optimum rotor characteristics from the viewpoint of load discharge, we needed (together with the available data from [3]) experiments to find the values of the properties in question. We studied mainly the properties of the most typical cohesive soils worked with bucket-wheel excavators. The present article is devoted to the method and main results of our investigation of the cohesion a t .To measure the tensile cohesion of sand-clay soils in the natural and loosened states, at the UkrNIIProekt Institute we have developed a device different from those at present in use for similar purposes [4]. With this instrument the cohesion of the soil is determined by the following procedure. The two halves of the dismountable mold are tightly pressed together and the clamps closed. The instrument is placed on a prepared area of the test soft, in a vertical position, and pressed into the soil until the mold is filled. Then the instrument with the filled mold is pulled out of the soft and excess material cut off. The soil specimen in the mold is pulled apart with the instrument in a horizontal position on a plate after removal of the clamps. For this purpose, by turning a screw a thrust is set up between the blades of an adapter which is fixed to the indicator of the measurement attachment. The indicator together with its spring is calibrated under compressive force.The tensile cohesion is given bywhere Pl is the thrust, equal to the difference between the reading of the measuring device at the moment of rupture and the reading obtained from the intrinsic resistance, in newtons, h is the distance from the axis joining the adapter blades to the point of application of the thrust, in centimeters, r is the distance from the axis joining the adapter blades to the cutting edge of the mold, in centimeters, b is the width of the specimen at the point of rupture, in centimeters, and h is the d...