PRESSURE RE-ORIENTATION NEAR SLITS IN THE FOUNDATION SOIL AS A CONSEQUENCE OF AN ARCHING EFFECT

DRUCKUMLAGERUNG NEBEN SCHLITZEN IM BAUGRUND ALS FOLGE EINER GEWOELBEWIRKUNG

THE CONSTRUCTION METHOD OF PREPARING EXCAVATION WALLS AS SLIT WALLS IS PARTICULARLY ECONOMIC WHERE THE REINFORCED CONCRETE WALL, BUILT SECTIONALLY IN THE GROUND, CAN ASSUME A FUNCTION NOT ONLY IN THE CONSTRUCTIONAL BUT ALSO IN THE FINAL STATE. IN THIS WAY, IT HAS BEEN SHOWN THAT SLITS ARE MADE ONLY SECTIONALLY IN LENGTHS OF 2 TO 6 METRES SINCE OTHERWISE FOUNDATION LOADS ORIGINATING FROM NEIGHBOURING BUILDINGS MAY CAUSE THE HOLLOW SPACE TO COLLAPSE. IT HAD TO BE ASSUMED THAT THE STABILITY OF A SLIT DUE TO A 3-DIMENSIONAL SOIL PRESSURE REARRANGEMENT IN THE GROUND IS BROUGHT ABOUT AS A KIND OF ARCHED BRACING OR BY A REDISTRIBUTION OF THE FORCES WITHIN THE STRUCTURE ENDANGERED BY THE SLIT. WITH THE FINANCIAL BACKING OF THE FEDERAL MINISTRY FOR REGIONAL PLANNING AND URBAN DEVELOPMENT 1971 - 73, THE INSTITUTE FOR FOUNDATION ENGINEERING AND SOIL MECHANICS OF STUTTGART UNIVERSITY, TESTS WERE CARRIED OUT WHICH SHOULD CONTRIBUTE TO THE CLARIFICATION OF THE MECHANICAL ARCHING EFFECT. IN ALL, 7 PRELIMINARY AND 27 MAIN TESTS WERE CARRIED OUT IN A MODEL WITH DIMENSIONS 5 X 2.40 X 2.0 METRES. A GRAVEL SAND WAS USED AS A TEST BASE: INSTEAD OF A CLAY SUSPENSION, WATER WAS USED FOR MAKING THE SLIT WHICH WAS MADE LEAKPROOF BY USING FOIL. THE SOIL PRESSURE REARRANGEMENT NEAR THE SLIT DUE TO A WEAK LINE LOAD WAS THEN MEASURED BY MEANS OF PIEZO ELECTRIC GAUGES WHEREBY THE CONSOLIDATION DENSITY, THE SLIT LENGTH (1 = 40,65 AND 90 CM) AND THE LOAD DISTANCE FROM THE SLIT (A = 15-75 CM) WERE VARIED. EVALUATION OF THE TESTS PERMITS OF THE FOLLOWING CONCLUSIONS: 1) IF THE DISTANCE OF THE LOAD FROM THE SLIT WAS SMALL NO ARCHING EFFECT COULD BE MEASURED. 2) IF THE DISTANCE OF THE LOAD FROM THE SLIT WAS ONE TO TWO TIMES THE LENGTH OF THE SLIT, INCREASED DISPLACEMENT OF THE FORCES IN THE SOIL TAKES PLACE. 3) WITH GREATER DISTANCES OF THE LOAD FROM THE SLIT NO SIGNIFICANT EFFECT OF THE SLIT ON THE LOAD BEHAVIOUR OF THE LOAD LINE COULD BE DETECTED.