Displacement auger piles with compacted base

299A 9O5359 Displacemem auger piles with compacted base Massarsch, K R; Tancre, E; Brieke, W Proe 1st International Geoteeluu'cal Seminar on Deep Foundations on Bored and Auger Piles, Ghent, 7-10 Jane 1988 P333-342. Publ Rotterdam: A A Balkema, 1988 An improved displacement auger pile is described. The auger has a large diameter hollow stem, which reduces the risk of soil decompression and allows emplacement of support before the auger is withdrawn. The pile base may be compacted and enlarged similarly to a conventional Franki pile. Load tests demonstrate the superiority of the VB pile over conventional auger-cast piles. Results consistent with the load tests were obtained using de Beer's analysis. 905360 Foundations on drilled and grouted mini piles - a case history (In Japanese) Soliman, N; Munfakh, G Proc 1st International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, Ghent, 7-10 June 1988 P363-369. Publ Rotterdam: A A Balkema, 1988 Floor slabs which were subject to subsidence for over 60 years have been stabilised by drilled and grouted minipiles. Two design approaches were used: one was based on displacement pile formulae, the other on ground anchor formulae. Ten static tests evaluated effects of different construction and loading procedures and the presence or absence of pile caps or casings. Acceptance was based on maximum allowable displacement. Best predictive formulae, and construction and economics are discussed. 9O5361 Effective stresses on the shafts of bored and cast-in-situ piles in clays Anderson, W F Proc 1st International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, Ghent, 7-10 June 1988 P387-394. Publ Rotterdam: A A Balkema, 1988 Instrumented model tests were carried out in the laboratory to examine stress changes which occur after bored pile construction. Piles were tested to failure after various periods after casting, using a maintained load technique. Results indicate that pre-construction earth pressures are restored in the soil mass after a period of some weeks. Comparison with ring shear test data shows that unit shaft adhesion may be determined by assuming only residual shearing resistance will be mobilised on the pile shaft.

Dams and embankments See also: 905052. 905065, 905071, 905075

9O5363 Postfallnre analysis: Tramping Lake causeway, Saskatchewan, Canada Labossiere, J L; Sauer, E K; Christiansen, E A Can Geotech J I"26, N4, Not" 1989. P687-704 A fill embankment for a traffic causeway across the saline Tramping Lake failed during construction in 1982. Attempts to complete the project were unsuccessful because of the continuously active failure. Failure was controlled by sedimentary structures and Artesian water conditions, and occurred when excess pore pressures developed during loading. The shear zone is in a soft near-normally consolidated sandy silt, 22m thick. Back analysis indicates effective friction angle is sensitive to variation in pore pressure ratio. 905364 Geomechonical calculation models for dam abutments in jointed rock (In German) Poisel, R Felsbau V8, N1, April 1990, P17-23 The importance of using both continuum and discontinuum models for study of jointed rocks is illustrated. Three dimensional finite element analysis of a dam abutment with individual rocks separated from the mass by gap-friction elements indicates how influence of block deformation and rotation can affect overall stability. Special reference is made to the Malpasset dam. 9O5365 Finite element analysis of pcogressive failure of Carsington embankment Potts, D M; Dounias, G T; Vaughan, P R Geoteclmiqne V40, N1, March 1990, P79-101 Progressive failure of brittle soils occurs when they are loaded non-uniformly, with average shear stress below peak strength. This cannot be analysed by conventional limit equilibrium methods. The failure of the Carsington embankment is examined. Limit equilibrium analysis gave a safety factor around !.2. Finite element analysis using a strain softening soil model and pre-failure data from records reproduces observed behaviour and collapse, indicating the probability of progressive failure. Sensitivity of results to assumptions made is low, suggesting the procedure used is of adequate accuracy for engineering purposes.

9O5362 Axial cyclic loaded piles Koreck, H W; Sehwarz, P Proc 1st International Geotecimical Seminar on Deep Foundations on Bored and Auger Piles, Ghent, 7-10 Jane 1988 P395-399. Publ Rotterdam: A A Balkema, 1988

905366 Design and construction of geecell foundation mattresses supporting embankments over soft ground Bush, D I; Jenner, C G; Bassett, R H Geotext Geomem V9, N1, 1990, P83-98

Five 130mm diameter, 5m length continuous flight auger-cast piles were constructed in a test pit in sand. Two were tested statically (tension and compression), two under alternate loads, and the remaining pile under cyclic compression. Under alternate loads, skin friction can decrease significantly, and failure occurs suddenly and depends on load amplitude and number of cycles. Under cyclic compression, the pile penetrated into the sand slowly and at a constant rate.

Construction of embankments over weak, relatively thin foundation soils poses problems. A recent technique using a geocell foundation mattress to contain and confine the granular layer at the base of the embankment is presented. Concepts of the method and development of bearing capacity from slip line fields are described. Case histories demonstrate the effectiveness in reducing overall and differential settlements and costs for construction of embankments on soft ground.

© 1990 Pergamon Press plc. Reproduction not permitted