Search Documents

By Andrew Budek

Reinforced concrete piles are used to carry foundation loads through considerable depths of soil to provide superstructure stability under gravity loads and lateral forces. The creation of cast-in-place (or cast-in-drilled-hole, i.e., CIDH) piles begins with the auger-drilling of a hole of the appropriate depth, into which a cage of reinforcing steel is placed (the cage length is generally equal to the depth of the hole, a construction joint being used to connect the in-ground pile with the superstructure). The pile is then finished by casting with concrete, and the superstructure then appended. The superstructure may either be a column (denoting the structure a pile-column), a column and cap beam, or a footing. Typical pile-column configurations are shown in Fig. 1 (a CIDH pile used in a footing would be similar in overall configuration to Fig. 1(b), with H=0). CIDH piles are well-suited for alluvial soil profiles with a deep water table; such conditions generally allow the auguring of a clean and regular hole.

Jan 1, 2007

By Jesús E. Gómez

A recent bridge underpinning project provided a unique opportunity to obtain information on the load-deflection response of 260 hollow-core bar micropiles. All production micropiles were proof-tested to a maximum load of 125 percent of the design load. In addition, four verification tests were performed on sacrificial micropiles to at least two and a half times the design loads. This paper presents the results of the verification and proof tests performed for this project, and provides recommended values for design of hollow core bar micropiles in soils similar to those encountered. This work shows that hollow core bar micropiles provide a significant unit bond capacity in both granular and fine soils, which may be greater than that typically expected in pressure-grouted (Type B) micropiles. The hollow core bar system allows faster installation rates in the soil types encountered than other traditional micropile techniques, and can be installed with relatively simple quality control procedures.

Jan 1, 2007

By Khamis Y. Haramy

Quality assurance and quality control of drilled shafts has become a concern due to difficulties in accurately locating construction anomalies and determining load bearing capacity of defected drilled shafts. Various non-destructive evaluation techniques have been developed to estimate the integrity of the concrete in drilled shafts. While these techniques have been widely accepted, variables and unknowns can affect the measurement results. Results are typically difficult to interpret, leading to unnecessary construction delays and possible litigation over shaft integrity. In addition, influences of surrounding ground materials, stress states under different load conditions, and crack and residual stress development during concrete curing further complicate determination of shaft performance. This paper focuses on the evaluation of load bearing capacity of defected drilled shafts under various conditions by numerical analysis and modeling.

Jan 1, 2007

By Monique Nykamp

"INTRODUCTIONTerminal 46 is located just south of downtown Seattle, and is one of the Port of Seattle’s busiest container terminals. The Terminal 46 Redevelopment Project was undertaken to replace the existing 15-m-wide (50 ft) cranes along the apron with 30-m-wide (100 ft) cranes, which can unload larger, post- Panamax ships. The project included upgrading the existing waterside crane rail with new piles and constructing a new land-side rail behind the sheetpile bulkhead. The new piles had to be installed adjacent to the existing apron without causing damage, which was a signifi cant geotechnical challenge due to the soft soil conditions at the site. An instrumentation program performed during the test pile program evaluated this challenge and allowed for the development of specifi c production pile installation procedures that had the least possible effect on construction costs and schedule. SITE HISTORYThe site lies along the west side of Elliott Bay, north of the mouth of the Duwamish Waterway. Prior to development, this area was part of the tide fl ats where the Duwamish River drained into Elliott Bay. Prior to 1970, there were several existing timber piers and structures in the area. In the 1970s, the Port of Seattle constructed a 900-m-long (3,000 ft), 30- m-wide (100 ft) apron to support fi ve, 15-m-wide (50 ft) container cranes. The contained backland area was then fi lled with dredged spoils (sand and silt with organics) and the upper 5 to 20 m (16 to 65 ft) backfi lled with sand and gravel.The existing apron was constructed using 0.4 m (16 in) octagonal prestressed concrete piles to support the precast concrete deck and crane rails. The pile-supported bents were spaced at 6.1 m (20 ft), center-to-center, along the longitudinal direction. Pile lengths typically varied from about 20 to 40 m (65 to 130 ft) with 15 to 26 m penetration below mudline (50 to 85 ft penetration). The slope below the apron was constructed at about 1.75 horizontal to 1 vertical to allow for suffi cient water depth for cargo ships. In most areas, a riprap buttress was placed at the toe of the slope. A typical cross section of the apron is shown on Figure 2.Several stability, settlement and pile driving issues arose during the original construction of T-46 (Pita, 1983). Reportedly, movement of the submarine slope occurred during pile driving, resulting in settlement behind the bulkhead. Pile driving reportedly caused settlement of adjacent piles. In addition, some piles were “running” (dropping quickly under one hammer blow) during installation."

Jan 1, 2007

By Emad Farouz, Roger Failmezger

"The proposed reconstruction of I-75 downtown consists of widening an approximately 2.46 Km section of IR-75 through the northern section of downtown Dayton, OH, USA. Bridge B-13 is a 9-span continuos prestressed concrete I-beam, 319.0-meter (1,048-foot) long bridge with a stub abutment on MSE walls for the rear abutment, and a stub abutment with spill-through slopes for the forward abutment. The piers in the river were located parallel to the Great Miami River, and are full-height reinforced concrete walls. PRESSUREMETER TEST PROCEDUREThe driller advanced either casing or augers approximately 1 meter above the pressuremeter test. Steel casing was used to advance borings performed in the river, and augers were used for borings on land. Mud rotary drilling with a large diameter roller bit was used to remove all of the gravel and cobble fragments inside the casing or augers.At the pressuremeter test elevation the driller used a 63.5-mm (2.5-inch) carbide button bi-cone bit, using a rotation rate of about 60 rpm, a mud fl ow rate of about 10 gallons per minute (40 liters per minute), and an advance rate of 6 to 10 minutes per meter (2 to 3 minutes per foot). To minimize vibrations, advance rates were slower where excessive cobbles were encountered. The 63.5-mm (2.5-inch) O.D. slotted casing pressuremeter was lowered to the test elevation, often requiring either pushing or hammering into the test zone. We believe that the test zone was not perfectly straight, or that gravel or cobble fragments jutted into the test zone and had to be displaced to advance the pressuremeter into the test zone. The slotted casing prevented membrane damage during insertion. A photograph of the slotted casing being lowered into the borehole is shown below.The pressuremeter was calibrated for system compressibility and membrane resistance. At full expansion of 800 cm3, the membrane resistance of the slotted casing was about 2.5 bars.Strain-controlled tests were performed using a Texam control unit with a monocell probe. Volume increments of 20 cm3 were injected into the probe and corresponding pressures were measured. Near the end of the elastic portion of the test, an unload-reload cycle was done. A creep test was performed for 10 minutes at the next volume increment. The test continued until either 800 cm3 were injected or the membrane burst."

Jan 1, 2007

By Artak D. Mirzoyan

Pile foundations near the edge of a slope are often required to resist lateral loads. This is particularly important for piles at abutments of bridges. However, very few full-scale tests are available that compare the effect on lateral resistance of piles installed in sloping ground to piles installed in horizontal ground. To investigate the effect of a slope on lateral pile resistance, three full-scale lateral load tests were performed on an instrumented steel pipe pile. For the first test, the pile was laterally loaded in horizontal ground; in the second test, the pile was at the crest of a 30º downward slope; and for the third test, the pile was located three pile diameters from the crest of a 30º slope. The soil around the pile consisted of well-graded clean sand (concrete sand) and was compacted to 95% of the modified Proctor maximum unit weight in all three tests. Lab and in-situ direct shear tests indicated that the friction angle of the sand was approximately 39 degrees. The pile was instrumented with strain gauges so that the bending moment versus depth profile could be determined. Pile head load, deflection and rotation were also measured. Based on the load versus deflection curves, the presence of the slope resulted in a decrease in lateral resistance of about 20% for the pile at the crest of the slope and 8% for the pile at 3D from the crest of the slope relative to the pile in horizontal ground. The presence of the slope also resulted in an increase in the maximum moment of 29% and 20% for the piles at the slope crest and at 3 pile diameters from slope crest, respectively. Analyses using LPILE with the measured friction angle significantly underestimated the lateral resistance for the horizontal soil profile. After calibrating the model with the response of the pile in horizontal sand, analyses including the slope still underestimated lateral resistance by about 20%.

Jan 1, 2007

By Monique Nykamp

"INTRODUCTIONTerminal 46 is located just south of downtown Seattle, and is one of the Port of Seattle’s busiest container terminals. The Terminal 46 Redevelopment Project was undertaken to replace the existing 15-m-wide (50 ft) cranes along the apron with 30-m-wide (100 ft) cranes, which can unload larger, post- Panamax ships. The project included upgrading the existing waterside crane rail with new piles and constructing a new land-side rail behind the sheetpile bulkhead. The new piles had to be installed adjacent to the existing apron without causing damage, which was a signifi cant geotechnical challenge due to the soft soil conditions at the site. An instrumentation program performed during the test pile program evaluated this challenge and allowed for the development of specifi c production pile installation procedures that had the least possible effect on construction costs and schedule.SITE HISTORYThe site lies along the west side of Elliott Bay, north of the mouth of the Duwamish Waterway. Prior to development, this area was part of the tide fl ats where the Duwamish River drained into Elliott Bay. Prior to 1970, there were several existing timber piers and structures in the area. In the 1970s, the Port of Seattle constructed a 900-m-long (3,000 ft), 30- m-wide (100 ft) apron to support fi ve, 15-m-wide (50 ft) container cranes. The contained backland area was then fi lled with dredged spoils (sand and silt with organics) and the upper 5 to 20 m (16 to 65 ft) backfi lled with sand and gravel.The existing apron was constructed using 0.4 m (16 in) octagonal prestressed concrete piles to support the precast concrete deck and crane rails. The pile-supported bents were spaced at 6.1 m (20 ft), center-to-center, along the longitudinal direction. Pile lengths typically varied from about 20 to 40 m (65 to 130 ft) with 15 to 26 m penetration below mudline (50 to 85 ft penetration). The slope below the apron was constructed at about 1.75 horizontal to 1 vertical to allow for suffi cient water depth for cargo ships. In most areas, a riprap buttress was placed at the toe of the slope. A typical cross section of the apron is shown on Figure 2.Several stability, settlement and pile driving issues arose during the original construction of T-46 (Pita, 1983). Reportedly, movement of the submarine slope occurred during pile driving, resulting in settlement behind the bulkhead. Pile driving reportedly caused settlement of adjacent piles. In addition, some piles were “running” (dropping quickly under one hammer blow) during installation."

Jan 1, 2007

By Terrence R. Udland, Russell D. Call

"Honored with a DFI 2006 Special Recognition Award, the Four Bears Bridge was constructed across Lake Sakakawea and opened to traffi c in September 2005. The very large lake size and severe winter conditions required an effi cient foundation design capable of resisting extreme ice loading and able to be effi ciently constructed in waters up to 90' deep (27.4m).DESIGNING FOR EFFICIENCYLocated in a remote area of North Dakota, the Four Bears Bridge replacement was a major undertaking for the North Dakota Department of Transportation, with dual goals of providing a new structure that would endure a severe environment, while enhancing the natural beauty of the area. Competing bids would achieve the best price for the owner, challenging the design team to creatively solve the engineering challenges unique to the site. Foundations for North Dakota’s new Four Bears Bridge had to accommodate water level fl uctuations of up to 40 feet (12m), along with extreme ice loading and be effi cient in order to be the low cost solution at the time of bidding. All three major criteria were achieved through the use of an effi cient ‘fl oating’ lost precast concrete cofferdam founded on steel pipe piles, which allowed the contractor to achieve the project schedule. The result is an award-winning bridge that is contextually sensitive to the environment. The bridge aesthetics pay tribute to the Three Affi liated Tribes, the Mandan, Arikara and Hidatsa, who reside on the Fort Berthold Indian Reservation, adjacent to the bridge site.The original Four Bears Bridge was located over the Missouri River near Elbowoods, the native grounds of the Three Affi liated Tribes. Construction of the Garrison Dam in the early 1950’s created Lake Sakakawea, a fl ood control project on the Missouri River, and resulted in the area being fl ooded. The bridge, along with many tribal members, was relocated to a site near New Town. The bridge provides the primary crossing of Lake Sakakawea and is a critically important transportation element for the residents of the Fort Berthold Indian Reservation. The relocated bridge had become functionally obsolete and not replacing it would require a detour of 170 miles (274km). The North Dakota Department of Transportation determined that it should be replaced. In order to achieve the most effective solution, the North Dakota Department of Transportation selected a design team responsible for the creation of competing steel and concrete designs that were competitively bid. The design team was led by Kadrmas Lee & Jackson, with FIGG responsible for the concrete bridge design, while Lichtenstein Consulting and Kadrmas Lee & Jackson completed the alternate steel bridge design."

Jan 1, 2007

By Aly M. Mohammad

Croton Point Avenue Bridge carries Croton Avenue over Metro-North main tracks at Harmon Rail Yard in Westchester County, New York. The new bridge is 1100 foot long and 36 foot wide nine span structure with three spans continuous units. The spans are steel multi-stringers, composite with concrete deck. The piers are solid wall piers and the foundations are spread footings. During the design of the bridge foundations it was determined that the relatively loose to medium dense sand layer is susceptible to liquefaction under a design earthquake with a seismic coefficient of 0.15g. Several foundation options were considered for the new bridge including both shallow and deep foundations. It was determined that the most cost effective alternative is to use spread footing foundations supported on densified soils. Vibratory probes were utilized to densify the loose to medium dense sand layer and reduce the risk of liquefaction. Densification test sections were performed to determine the optimum spacing for the vibro probes. The test sections included performing piezocone tests before and after the densification to compare the increase in relative density of the sand. In addition, ground surface settlement due to the vibro probes was measured and correlated to the increase of soil relative density. The paper will present the results of the ground improvement method utilized and correlate the spacing of the vibro probes and the increase in relative density and the results of the piezocone tests performed before and after the densification. It was found that the vibro probes are not as effective as thought at shallow depth below the ground surface. It is believed that the results and finding presented in this paper will benefit both the design and construction industries by providing a relatively cost effective means to improve the soils

Jan 1, 2007

By Gokhan Inci

Stability problems with dam spillways on existing landslides and appropriate mitigation measures to remedy them are ongoing concerns for geotechnical engineers. The first successful application of drilled piers as stabilizing structures under the spillway was at the Trinity Dam in Sicily, Italy. ?Underpinning? was considered as an alternative to spillway relocation during the Alpaslan 2 embankment dam design in eastern Turkey. Based on the available literature the first application of drilled piers to stabilize a spillway chute in the U.S. was at the Ralston Dam in Colorado. Ralston Dam, which is a 175-foot-high zoned fill dam located 15 miles northwest of downtown Denver, was built in the late 1930s. The concrete spillway for the dam was built on the Pierre Shale Formation in the left abutment. Since reservoir operations began, mass movements have occurred downstream of the chute area. These movements have required periodic spillway maintenance. After the occurrence of recent movements and because of high piezometeric levels, URS was contracted by Denver Water to develop a more permanent solution by the installation and monitoring of additional instrumentation, analysis of slope stabilizing measures, design, repair, and reconstruction of the distressed section of the spillway chute. With state of the art modifications that include: 1) a stabilizing berm with a toe trench that improves the global stability; 2) seepage prevention and control measures that prevent the infiltration of water; and 3) the structural support of the replaced chute section with drilled piers and reinforced concrete the probability of future displacements or other problems have been reduced for the Ralston Dam Spillway.

Jan 1, 2007

By Khamis Y. Haramy

Curing temperature, density, and moisture significantly affect the velocity measured in the crosshole sonic logging, the rate of strength gain, and the final strength of concrete in drilled shafts and, thereby, affect their structure capacities. Non-destructive field measurements can enhance the QA/QC program by measuring temperature, density, moisture, and sonic velocity of curing concrete during the construction and curing of drilled shafts. The curing environment can greatly affect the concrete strength, and requires close attention during construction. This article shares the experience with the NDE technology used in the QA/QC program in the drilled shaft construction. To understand the mechanism by which a drilled shaft cures under field conditions, two newly constructed drilled shafts were monitored for up to seven days, immediately following concrete placement using the following geophysical logging methods: a) temperature logging; b) crosshole sonic logging; c) gamma-gamma density logging; and d) neutron-moisture logging. One additional drilled shaft was also monitored to a shorter duration. Temperatures were monitored using the sensor in access tubes and/or thermocouples embedded at the center of a drilled shaft and near its reinforcing cage. For a small shaft under 1m diameter, curing temperatures appeared to peak at 41° ? 68° C at different depths at around 24-hour curing time and decreased to and stabilized at around 23° ? 35° C in 6 days. The shaft curing rate varied with depth, shaft diameter, surrounding geo-material types, and the depth of ground water. CSL logging was performed in one shaft from top to bottom from six access tubes and limited monitoring in another shaft. The velocity increased with curing time till 4 to 7 days, and, at a specific time, the velocity appeared to be inversely correlated to curing temperatures. The gamma-gamma density log (GDL) results from 5 different depths were obtained at a source-detector separation of 355 mm. The average density was found to increase with curing time, but decrease slightly in 3 to 5 days. At a given time the GDL density curves seemed to correlate with the neutron monitoring logging (NML) moisture curve. The NML moisture was monitored from 1st to 6th day after concrete placement. The moisture was highest when surrounded by bedrock, then clay, and sand due to different hydration rates.

Jan 1, 2007

By Bernard H. Hertlein

The introduction of LRFD methods for structural design has been a gradual process by AASHTO, ACI, AISC, ASCE, and the FHWA, which has largely been ignored by the deep foundations industry. In 2007, however, the industry has been obliged to embrace LRFD for any deep foundations on projects involving federal funds. The authors are concerned that the risks caused by the need for, and the difficulty of providing, reliable quality assurance, will result in unnecessarily high safety factors that will defeat part of the purpose of LRFD. A primary attraction of LRFD for owners and engineers alike is that it promises more efficient design, and therefore cost reductions. Unfortunately, a key element of LRFD philosophy is often overlooked - that the applied safety factors can be rationally reduced, often allowing less material to be used, thus saving costs, but only if all the risk factors involved are identified and closely controlled. This means that both the quality of the materials and the quality of the construction work must be adequately monitored, and held to an acceptable standard. In the case of deep foundations, the soil in which the foundation is constructed is also a critical component that must be taken into account in the assessment of risk factors.

Jan 1, 2007

By Issa S. Oweis

Two Towers are currently under construction in Central Moscow in the Russian Federation. Building A is a 96 story tower and Building B is a 65 story tower. The columns in both structures bear on a thick concrete mat that is supported on drilled shafts, 1.5 m in diameter. The shafts derive their capacity from weak limestone with layers of marl. Assigned allowable shaft loads were initially based on rock strengths that were later verified by load tests using the Osterberg Cell. One of the load tests was carried to near failure which allowed refining socket friction values that were later used in the design of Building A. All shafts were advanced using an auger and concrete placed in the dry. Grout tubes were placed with the reinforcing cage which allowed grouting of the limestone in contact with the shaft. Load sharing between the shafts and the mat was approximated using published methods as well as site specific finite element analysis. This paper covers the methodology of design, analysis of the Osterberg results to derive non-linear stiffness of the rock and differences between finite element analyses and results by approximate methods.

Jan 1, 2007

By Bin Zhang

Drilled shafts are a popular type of foundation for transportation applications. They feature the advantages of providing high bearing capacity and generating low construction noise. Advancements in construction technology make it possible to construct drilled shaft with large diameters. In some transportation projects, the full structural loads are carried by a single large diameter drilled shaft; therefore accurately determining the bearing capacity of drilled shafts has important practical and safety implications. The increase of drilled shaft diameter combined with the structure properties of the surrounding soil play in an important role in their bearing capacity. The conventional methods for bearing capacity determination, which mostly come from experience with small diameter drilled shafts, may not work satisfactorily. This paper studies the influence of diameter on the bearing capacity of laterally loaded drilled shafts. Numerical simulations are conducted to investigate the effects of pile diameter on the lateral bearing capacity, especially the influence of shaft diameter and its structural contributions.

Jan 1, 2007

By James C. Scott

Compression and tension load testing were performed on bored concrete piles installed to depths of 18 to 34 meters below excavation levels for a large mixed-use development in Kuala Lumpur, Malaysia. The 900 mm diameter piles were installed in weathered graphitic schist bedrock. Load testing confirmed the side shear and end bearing capacities of the piles. The work formed part of the investigations for the 56,000 m2 site which includes a 79-story office tower, hotel tower, apartment tower, retail complex, and plaza area underlain by 4 to 6 basement levels. The paper provides the results of the site investigations, pile-load testing procedures, pile-load settlement behavior, and shaft load distribution.

Jan 1, 2007

By Richard Short

Shallow rainfall-induced landslides in residual and colluvial hillslopes and steep embankments are a common occurrence in many settings [1, 2, 3]. While occasionally posing a threat to property and life-safety, they more often present an ongoing maintenance problem and can lead to the initiation of larger failures. Typically, these slides consist of 2 to 4-foot thick translational movements of silty and clayey soils down slope through the reduction of strength from increases in pore water pressures. Direct surficial infiltration and indirect groundwater seepage are the normative triggers for failure. In the residential community of Blackhawk, California, located east of the San Francisco Bay, these types of landslides are a common occurrence (Figure 1). However, shallow landslides have also been a repetitive and constant problem along many state highways where steep embankments have been constructed in close proximity to busy thoroughfares. Given the real threat to property values in residential and commercial settings and the constant maintenance problem posed to lifeline structures such as utilities, roadways, and pipelines, new methods to deal with these landslides are needed.

Jan 1, 2007

By Kyle Kershaw

Micropiles are routinely used in the United States for foundation support and stabilization of slopes. In recent years, several retaining walls have been constructed using micropiles in an A-frame type configuration to support temporary and permanent excavations at sites with limited access and limited right-of-way. Typical A-frame micropile walls consist of a row of vertical micropiles at the face of the wall and a row of battered micropiles extending into the soil or rock to be retained. The two rows are then tied together with a pile cap such that the front pile acts primarily in bending and the back pile acts primarily in tension. Because of tight right-of-way constraints at a residential site in Aspen, Colorado, it was not possible to construct the wall using conventional shoring systems or micropiles in the typical A-frame configuration. Rather, the wall was designed such that the row of battered piles was installed at the wall face and the row of vertical piles was installed adjacent to the property line behind the wall. As a result of the reverse configuration of the A-frame wall, FLAC, a two-dimensional, finite difference software program, was used to model the soil-structure interaction. The final wall design consisted of both temporary and permanent retaining wall sections with maximum heights of 26 feet. Inclinometers were installed in several piles to monitor the behavior of the retaining walls during and after excavation. This paper presents an overview of the design method, a discussion of construction techniques, and a comparison between the FLAC model and the measured behavior of the wall in the field.

Jan 1, 2007

By Lawrence F. Johnsen

Six case histories are presented in which tall, slender high rises are supported on high capacity minicaissons. The recent development of a high strength rebar cage has resulted in compressive loads of up to 3400 kips on 24 inch diameter minicaissons. Provisions in the pending NYC building code will allow borehole video inspection in lieu of load testing. The ?new? technology results from the marriage of several well established methods: rotary duplex well drilling, high capacity micropiles and high capacity reinforced concrete building columns.

Jan 1, 2007

By Ke Yang

Drilled shafts are widely used as foundation system for sound walls to resist lateral loads. The design method based on the ultimate lateral capacity, such as Broms method, is often used for sound wall foundation design. Allowable Stress Design (ASD) is currently used for deep foundation design. However, by October 2007, all states Department of Transportations are required to use the Load Resistance Factor Design (LRFD) approach for the design of foundation in highway projects. There is a need to develop a calibrated resistance factor in LRFD lateral design of drilled shafts supporting sound barrier walls. This paper provides resistance factors for design of laterally loaded drilled shafts supporting sound walls using Broms method based on the study using reliability based method and fitting to ASD method. Additionally, the resistance factors for static lateral load tests are recommended. Furthermore, a methodology to update the resistance factors using Bayesian approach by incorporating the on-site full-scale lateral load test results is presented. To illustrate the Bayesian update methodology, two lateral load tests in Colorado were employed to develop the updated resistance factors.

Jan 1, 2007

By Terence P. Holman

Instrumented load testing of high capacity micropiles, followed by detailed analysis and numerical modeling, provided an opportunity for real foundation performance to be incorporated into the design of a complex urban high-rise structure. This paper discusses a design-based load testing program and subsequent analysis for micropiles incorporated into a piled raft foundation beneath a portion of a high-rise residential structure in Brooklyn, New York. Preliminary numerical analysis, performed using the commercial finite element package PLAXIS 3D Foundation, indicated that soil stiffening and transferring heavy core loads to greater depths was required to minimize the total and differential settlements. High capacity micropiles were modeled below the tower core mat to create a piled raft effect, reducing the settlements to acceptable levels. Final design of the foundation and micropiles, and final numerical analysis of the proposed foundation system required an instrumented load testing program to provide the Owner and design team with a level of comfort. The instrumented load test provided data on the evolution of load transfer, including the mobilization of significant tip resistance, frequently ignored in design, and micropile axial stiffness. Final numerical analysis of the foundation system involved refining the PLAXIS model based on the micropile behavior and load transfer mechanism observed during the load test program. The authors believe that the combination of design-based load testing and numerical analysis in this project yielded a more refined foundation system with realistic expectations of performance.

Jan 1, 2007