Drilled Pier Foundations Research Articles

Heaving-Bedrock Hazards, Mitigation, and Land-Use Policy: Front Range Piedmont, Colorado

Abstract Heaving bedrock is a geological hazard that is related to expansive soils, but it is more complex in terms of its uplift morphologies, deformation mechanisms, and regional distribution. It is common along Colorado’s Front Range piedmont where steeply dipping sedimentary bedrock containing zones of expansive claystone is encountered near to the ground surface. It occurs in the Pierre Shale and other Upper Cretaceous formations. The heave features associated with heaving bedrock are distinctly linear and are caused by differential swelling and/or rebound movements within the bedrock. Heaving bedrock has caused exceptional damage to houses, roads, and utilities along the Front Range piedmont since suburban-type development began in the early 1970s. Much of this damage may be attributed to the longstanding tendency to assume that the bedrock may be treated, for site-exploration and design purposes, as an expansive soil having essentially uniform properties. This approach ignores the strong heterogeneity that is often present in the bedrock. In particular, drill-hole exploration surveys and drilled pier foundations, which are generally appropriate for expansive soil hazards, have proven to be inappropriate for recognizing and mitigating heaving-bedrock hazards. This article presents a summary of heaving bedrock as a distinct geological hazard and describes the technological and policy advances that have been made in recent years to promote understanding and effectively mitigate the problem. The Colorado Geological Survey has played a key role in these advances by introducing the term “heaving bedrock” to differentiate the problem from expansive soils; leading stakeholder field trips and conferences; investigating the physical characteristics, mechanics, causes, and distribution of heaving bedrock; publishing the investigation results; assisting county governments in creating new land-use regulations; and reviewing site investigation reports for actual subdivision projects. From this experience, we conclude that a state geological survey must be active in numerous arenas—scientific, practical, and political—to assist effectively in addressing potential hazards that impact the general public.

Design of Tie Bars for Large Drilled Pier Foundations

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Drilled pier foundation practice for highrise buildings in Montreal, Canada : Ladanyi, B; Bensoussan, A; Castonguay, J; Tommasel, A M Proc Ninth Danube-European Conference on Soil Mechanics and Foundation Engineering, Budapest, 2–5 October 1990P239–246. Publ Budapest: Akademiai Kiado, 1990

Drilled pier foundation practice for highrise buildings in Montreal, Canada : Ladanyi, B; Bensoussan, A; Castonguay, J; Tommasel, A M Proc Ninth Danube-European Conference on Soil Mechanics and Foundation Engineering, Budapest, 2–5 October 1990P239–246. Publ Budapest: Akademiai Kiado, 1990

Limitations of Residential Structures on Expansive Soils

Failures due to expansive soils tie with hurricanes for second place among America's most destructive hazards in terms of economic loss to buildings. This paper discusses the limitations of conventional design, construction, and repair of residential structures. Two specific case studies are presented. The first addresses excessive movement and damage at several posttensioned slab‐on‐ground condominium buildings. The second discusses severe vertical and horizontal deformation of a tract home supported by a drilled pier foundation system. Remedial recommendations for each case study are discussed along with lessons learned from each. Damages and movement that initially indicate upward movement may actually be caused by settlement even in an area of extremely expansive soils. The unique situation of each type of residence often requires the decision of which path to take during repair; that is, one of providing additional flexibility or rigidity. This type of decision‐making process should also be considere...

Long-term settlement of model rock-socketed piers

Very little information is available concerning the long-term settlement behaviour of drilled pier foundations socketed into rock. This paper summarizes the results of laboratory investigations of the long-term settlement (creep) behaviour of model socketed pier foundations. The testing program included seven model piers constructed with different materials and different load-support conditions. The primary models were two small-diameter concrete piers constructed in soft shale. For all models tested the results indicated similarly shaped time–displacement curves, having two distinct regions. The initial portion of the curves represents a region of primary creep and the remaining portion represents a zone of secondary creep having a much lower rate of displacement. A comparison of short-term (1 day, which is a normal maximum duration of a full-scale load test) and long-term (200 days) settlements for the model piers showed an 84–245% increase in settlements. In addition, some information concerning load transfer with time in the model piers and available data from loading tests on large-scale socketed piers are included. Key words: socketed pier foundations, long-term settlement, creep model tests, soft rock.

Load–displacement behaviour of socketed piers—Hamilton General Hospital

Monitoring the settlement behaviour of full-scale drilled pier foundation that are in service is seldom possible. This report describes the instrumentation and monitoring program for three of the drilled pier foundations socketed into weak shale used for the Hamilton General Hospital addition, and presents and summarizes the data collected over a period of almost 2 years.The three socketed piers were constructed so that each had different load support conditions. Pier P5 was conventional, and supported loads through shaft resistance in the soil and rock and end bearing in the rock. Pier K3 was similar except shaft resistance in the soil was eliminated by installing a sonotube casing in the upper portion of the shaft. Pier P3, which also had a sonotube casing, was constructed with a void apparatus at the base to eliminate end bearing resistance so that support was achieved only through shaft resistance in the rock socket.Instrumentation included multiple-point rod extensometers, with remote readout, to measure vertical displacements at the top of the pier, top of the rock, and bottom of the socket. Load cells, reinforcing bar load cells, and concrete embedment strain gauges were also installed in an attempt to determine load distribution in the pier foundations.Under approximately full dead loading, less than 3 mm (1/8 in.) settlement has been observed. The settlement and bottom load cell data suggest that very little of the applied loading (less than 5%) has been transferred to the base of the socket. Key words: rock-socketed piers, settlement, load transfer, weak shale, instrumentation, monitoring, full-scale foundations.

A Review of: “Construction of drilled pier Foundations” D. M. Greer and W. S. Gardner John Wiley & Sons Ltd, Chichester, UK, 1986, 240 pp, £38.50

(1987). A Review of: “Construction of drilled pier Foundations” D. M. Greer and W. S. Gardner John Wiley & Sons Ltd, Chichester, UK, 1986, 240 pp, £38.50. Civil Engineering Systems: Vol. 4, No. 3, pp. 164-164.

Instrumentation for load transfer in socketed pier foundations : Horvath, R G Trans Res RecN1004, 1985, P34–46

An investigation of methods to improve the performance of drilled pier foundations socketed into soft rock was made on full-scale test piers. Instrumentation of the test piers enabled load transfer behavior of the piers to be studied. Flatjack (FREYSSI) load cells were used to measure applied loads and the end-bearing component of pier load support. Vibrating wire concrete embedment strain gauges (Geonor) were used to determine axial and radial stresses at the middepth of the test section. Thus, load distribution along the length of the pier socket could be determined. The description, calibration, and installation of the instruments are briefly summarized. The satisfactory performance and reliability of the instruments are supported by the test data that, in general, were in good agreement with predictions from elastic solutions. Comparison of the results of several piers having different support conditions, and displacement measurements using telltale systems, also support the reliability of these instruments. The versatility of a flatjack load cell to perform three different functions: (a) passive load cell, (b) active (applied) load cell, and (c) void, at the base of one test pier subjected to multiple loading cycles, is also briefly discussed.

Multiple loading method for field testing drilled piers

A multiple loading testing method is suggested, which permits testing a single drilled pier foundation under three different conditions of load support. The pier may be tested under conditions of combined shaft and end-bearing resistance, end-bearing resistance only, and shaft resistance only. The advantages of this multiple loading test method include observation of the load-transfer and displacement behaviours of the pier under these three different support conditions and verification of the values obtained for the components of load support, i.e., shaft and end-bearing resistance, all from a single test pier.A special base load cell capable of performing a different function during each cycle of loading is required. A suitable load cell, consisting of a series of Freyssi flatjacks, and the method of operation are described.A multiple loading test procedure was used successfully as part of a field investigation program on full-scale pier sockets in weak shale. Data on the load-displacement behaviour of the pier tested using the multiple loading method are reported. Information concerning piers tested using conventional single loading methods are provided for comparison.The multiple loading test results were in good agreement with results obtained from conventional testing methods. Thus the multiple loading test method provides an economical means of obtaining a large amount of design information for drilled pier foundation systems, using a single test pier. Key words: field load test, multiple loading, drilled piers and caissons, shaft resistance, end-bearing resistance, combined shaft and end-bearing resistances, base load cell, shale.

Design of Laterally Loaded Drilled Piers

This paper presents the results of an applied research study directed at improving the state-of-practice, and resulting foundation economy, in the design of laterally loaded drilled pier foundations subjected to high ground-line moments or high ground-line shears. A theoretical four-spring, subgrade modulus model was developed in this study and was subsequently modified using the results of 14 full-scale load tests. The resultant semi-empirical nonlinear model formed the basis for the development of a design/analysis computer program (PADLL) for drilled pier foundations embedded in multi-layered subsurface profiles. The predicted behavior of two test piers, using both state-of-practice techniques and PADLL, are compared with measured behavior. Potential cost savings associated with piers designed using the semi-empirical model are discussed.

Results of tests to determine shaft resistance of rock-socketed drilled piers : Horvath, R G; Kenney, T C; Trow, W A Proc International Conference on Structural Foundations on Rock, Sydney, 7–9 May 1980, P349–361. Publ Rotterdam: A A Balkema, 1980

Three case histories have been presented to provide useful information concerning full- scale load tests to determine the shaft resistance of rock- socketed drilled pier foundations. A relationship between shaft resistance and material strength has been indicated. The tentative correlation suggested may be used for preliminary foundation design provided good engineering judgement is exercised. Actual design values of shaft resistance should be verified by suitable field testing. The effect of roughness on shaft resistance mobilized, which is greatly influenced by construction methods, has been discussed. The relatively small values of shaft resistance as compared to the strength of the controlling material indicates that significant improvements in shaft resistance can be achieved. The suggested means of accomplishing this is to increase the roughness of the wall of the socket so that load is supported directly by the two materials in contact rather than by adhesion of the two materials at their interface. Increasing the load supported by end- bearing resistance at small relative pier displacements would also improve the load- displacement behaviour of socketed piers. A research program to study these methods is presently in progress at the university of toronto.