EXPERIENCE OF STEEL PILE DRIVING BY PNEUMATIC HAMMERS IN UNDERGROUND CONSTRUCTION BY THE CUT-AND-COVER METHOD

The timeliness of application of pneumatic hammers in the deep bore tunneling in underground construction is justified. The penetration resistance forces in steel pipe driving in soil are determined. The analysis of long-term operation of adjustable capacity pneumatic hammers shows the conformity of the blow energy and the driven pipe diameter. The relationship between the unit blow energy and the open-ended pipe diameter is proposed. The main pneumatic hammer parameter to govern the machine performance is substantiated. The standard pneumatic hammers of adjustable capacity are characterized. The cases of vertical pipe driving at construction sites in Russia are described. The technological capability of construction of retention wall in soil using rolled steel, namely, I-beams, U-sections, piling bars, etc. is illustrated. The production tooling arrangements to ensure secure mounting of the hammer on the axial element driven in soil are described.

EXPERIMENTAL VALIDATION OF PARAMETERS OF HEAVY GRAVITY PNEUMATIC HAMMERS FOR CASING PIPE RAMMING IN SOIL

Vertical penetration of steel pipes with a diameter of 530-1420 mm and to 100-150 m long in soil requires high blow energy (10-100 kJ). Design of the percussion machines using the available pneumatic hammers is constrained due to the high flow rate of an energy source required. It is of the current concern to design an air-driven percussive tool capable to ensure high blow energy at low flow rate of compressed air. This study describes the testing data of a breadboard model of a new gravity pneumatic hammer. The operating mode of the model hammer is studied, and the blow energies, blow frequencies and compressed air flow rates are evaluated as functions of air pressure in the main line. The tests proved stability of cycling operation of the model tool at the high blow energy and low flow rate of the energy source at the main line pressure of 0.36-0.77 MPa. Using the dynamic similarity criteria, the standard sizes of heavy pneumatic hammers are developed, their blow energy and air flow rate are determined, and the efficiency is evaluated.

LUBRICANT TEMPERATURE INFLUENCE UPON PULSE HYDROPNEUMATIC DRIVE OPERATION

A pulse hydropneumatic drive can make a percussive effect up to 15,000 J. A head carrying out a pulse effect (a blow) on an object is cocked in an operation position by liquid. At the same time occurs a compression of a working body (gas) in a gas accumulator. The pulse influence occurs because of head acceleration at the expense of a working body in a pneumatic accumulator. The operation of a pulse hydropneumatic drive depends on a number of parameters: viscosity and temperature of operating fluid, pressure of pneumatic accumulator initial charge and others. In the course of work oil becomes warm because of a high rate of travel in control equipment of a pulse drive in hydromains that results in changes in blow energy. A simulator describing stages and acceleration of the head of a pulse hydro-pneumatic drive. As a result of a numerical experiment carried out in the en-vironments of Mathcad and Matlab there are obtained dependences of blow energy upon working liquid tem-perature. To investigate the influence of different parameters of a pulse hydro-pneumatic drive upon its operation was designed and carried out a test bench which allows changing different parameters of a drive in a wide range. The experimental dependences of blow energy upon temperature of a working body and the dependences of blow energy upon working liquid viscosity are obtained. A comparative analysis of theoretical and experimental results which has given good convergence is carried out. The conclusions obtained: the operation of a pulse hydro-pneumatic drive is effected greatly both by the viscosity of a working body, and its temperature; the best values of head energy correspond to the mean viscosity of working liquid; to obtain a constant of blow energy it is necessary to use working liquids with stable viscosity at high tempera-tures: it is expedient that different additives should be used in working liquid to reduce a constant of friction and wear-resistance increase.

Passive car safety system updating at head-on collision with lorry

At emergency brake application before collision a car clearance decreases considerably, a car front side comes lower and actually does not participate in blow energy absorption. A car “dives under” a lorry and al-most all blow energy falls to the roof and windshield posts which do not figure on the perception of such a load that often results in fatal consequences. To reduce weight of consequences after such a collision there was developed a design for a passive car safety. The device consists of a ring pneumatic cylinder which is situated round a front shock strut next the upper bearing of a shock absorber and connected with a squib. It is intended for lifting and car body fixation along the height before a collision with a lorry. There are two such devices installed in a motor car, with one for each front wheel. It is not difficult to make this device there is no need in essential changes in the car design. It can be installed in any car with front posts of the type «macferson». The offered device is integrated in the general system of a car passive safety and at unavoidable head collision with a lorry is activated by means of a squib explosion. Key words: life-saving device, car, head-on collision, lorry.