GeoSupport 2004: Drilled Shafts, Micropiling, Deep Mixing, Remedial Methods, and Specialty Foundation Systems

Most major structures in the Charleston, SC area of the U.S. are supported on deep foundations bearing in the Cooper Marl. The fine grained Cooper Marl, which typically classifies as highly plastic clay, has a calcium carbonate content of 60 to 80 percent. Unlike some other calcareous soils, the Cooper Marl is generally an effective foundation material for both driven and drilled foundations. In general, the performance of driven and drilled foundations is comparable but the marl's cementation does cause some differences. The relatively open structure collapses upon shearing which causes large excess pore pressures. As a result, the capacity of a driven pile is highly time dependent and increases as the excess pore pressures dissipate. Vibratory installation, which generates a large number of shear reversals, is particularly damaging to the soil structure and negatively impacts the performance of foundations installed in this manner. Drilled foundations often use a vibratory installed steel casing as a construction aid and performance data consistently indicate that the cased zone of the shaft within marl, even when the casing was extracted during concrete placement, experiences a reduction in side resistance as compared to an uncased excavation.

With apologies to author Robert Pirsig (Zen and the Art of Motorcycle Maintenance, 1974), this paper pursues the concept of quality with respect to construction of drilled shaft foundations. With the evolution of more sophisticated techniques for integrity testing and load testing, it is possible now to better observe the end result of our construction activities and make judgments about the effectiveness of techniques and materials at achieving quality. This paper describes some aspects of construction techniques and materials that can lead to defects or less than optimal performance for drilled shaft foundations. Examples are cited of some of the more common problems encountered in drilled shaft construction in order that lessons can be learned from these problems. The case is made for designers and contractors to emphasize constructability in designs, workability in construction materials, and individual responsibility toward quality on the jobsite.

Four representative types of drilled foundations (drilled shafts, augered cast-in-place piles, pressure-injected footings, and micropiles) are examined from the standpoint of axial capacity evaluation, generalized behavior, and normalized load-displacement response. As shown, the capacities can be computed rationally, taking into account the particular characteristics of each foundation type, and the results agree well with the interpreted failure load from field load tests. The interpreted failure load also is linked consistently and simply to the elastic limit and the conventional slope tangent methods for interpreting compression and uplift load test results. The displacements also exhibit consistent patterns of behavior in compression and uplift, at both the interpreted failure load and elastic limit. These results will be useful for better understanding axial foundation behavior over a range of drilled foundation types.

Construction contracts in the USA frequently contain a clause on "Value Engineering" — an interesting and curious clause — allowing contractor-initiated design changes. Misleading is the interpretation of value engineering to imply cost savings shared with the owner, and its implementation, just before or during actual construction, is problematic. It is not surprising that such a clause would simply be ignored because it involves changes in design, often major changes in very short time; and change is feared, and moreover, vehemently resisted by all parties, owner, designer, and contractor. The problem may lie in the divergence and separation of the two entities, designer/engineer and builder/contractor, assigned to the "one" engineering project. Their priorities and incentives are very different. The engineer spends years, even decades, in design and prepares contract documents often without a deep-seated understanding of construction methods, including geotechnical construction. Even worse, given the tremendous computational advancements, the designer submits plans that are inexcusably exaggerated code-based design with excessive safety factors. The contractor on the other hand, often builds, without appreciation of design principles or regard for design engineers. Owner budget and schedule constraints (not commensurate with his demands) and the ever-increasing litigious climate have exacerbated the situation. Adverse and hostile relationship between the various groups is often the norm resulting in extended disputes and claims, not to mention the excessive costs these entail. Redesign to apply a new technology or optimization of an inferior design just before construction becomes unthinkable. Major design changes were nevertheless successfully implemented in record speed on several very large projects in the metropolitan New York area. Four case histories spanning from 1998 to 2002 are presented.

Construction of a transmission line for a new power plant presented the opportunity to utilize a relatively new construction technique involving blasting for drilled shafts. Drilled shafts are often used as foundations for transmission line pole foundations, where they are commonly constructed by auger and rock coring techniques. However, rock coring, especially for large diameter shafts in hard metamorphic and igneous rock, is slow and expensive. This paper describes how a contractor utilized blasting techniques to assist the construction of drilled shafts for transmission line pole foundations. Controlled blasting techniques generally improved the production rate of drilled shaft excavation in hard schist and quartzite rock, without adverse impacts. However, the resulting rock sockets tended to be irregular in shape and a few had significant amounts of overbreak. Recommendations are provided for improved controlled blasting techniques for drilled shafts.

The Bandra Worli Sea Link Project (BWSL) includes a 500 m long cable stayed bridge with two 250 m cable supported main spans on either side of a single central tower with a height of 158 m. Foundations for the project consist of 676 drilled shafts, 72 with a diameter of 2 m and 604 with a diameter of 1.5 m. Working loads on the shafts range from 3.3 MN to 25 MN. The shafts were constructed using a reverse circulation drilling unit and ranged from 4 m to 34 m in length. Rock encountered at the site included highly weathered, fractured and oxidized volcanic material with RQD's of less than 25 percent and unconfined compressive strengths of 1 MPa to massive intact material with unconfined compressive strengths in excess of 100 MPa.

In an effort to reduce the required rock socket lengths for a new bridge over the Susquehanna River near Harrisburg, Pennsylvania, full scale Osterberg Cell load tests were performed on two rock sockets in strata of the Gettysburg Formation. Within each socket, two different zones of interest were identified. One of the objectives of the testing was to compare the side resistance obtained from the load tests with that obtained using empirical methods found in AASHTO and Pennsylvania Department of Transportation publications. Based on the results of this testing, ultimate side resistance exceeded empirical calculations in three of the four zones (977, 757, and 1,006 kPa (20, 16, and 21 ksf) observed versus 407, 304, and 359 kPa (8, 6, and 7 ksf) predicted). For one zone, side resistance was approximately 40% of predicted values (192 kPa (4 ksf) observed versus 497 kPa (10 ksf) predicted), apparently due to construction difficulties.

Dynamic loading tests take advantage of the high impact load that a relatively small mass can generate by falling from a preselected height. For driven piles, where the readily available driving hammer itself is the loading apparatus, this test method is particularly convenient. The uniform geometry and material properties of driven piles makes pile load and motion measurements and their interpretation relatively easy. For drilled shafts, however, the testing effort is somewhat more involved because a ram with a weight equal to 1 to 2% of the test load must be available and dropped from heights of 1 to 3 m by using a crane. Additionally, potentially irregular shape and non-uniform material properties of cast-in-place pile tops make accurate force measurements more challenging. This paper further describes how the dynamic testing procedure has been simplified and made more accurate by the APPLE (Advanced Pile Proof Loader/Evaluator) method, which combines the force measuring device with the loading system. In effect, the pile top force is calculated from the product of measured deceleration and mass of the drop weight; motion is also measured at the pile top. The paper describes two tests, conducted on different field sites, and presents correlations that further verily the soundness of this approach.

Results of ten lateral load tests conducted on micropiles are presented. The micropiles were 15.2 m long and reinforced with a centered high-strength threaded bar along the entire length. Bending stiffness and capacity in the upper 9 m of the micropile were increased by including a 244 mm-OD casing with a 13.8 mm thick wall. Lateral load behavior measured during the load tests were compared with behavior predicted using conventional p-y methods originally developed for laterally loaded piles. Predicted and measured displacements usually agreed within 10 percent. Most of the lateral load tests were terminated when lateral displacements exceeded the displacement capacity of the jacks; however, two of the ten micropiles experienced excessive displacement at relatively small lateral load. Excavating beside these two micropiles revealed that excessive rotation occurred at the threaded connection in the casing about 2 meters below the ground surface. The threaded connections in these two micropiles experienced excessive rotation at one-fourth of the first-yield moment as determined from structural tests on an intact casing.

The use of inclined micropiles as reinforcement to prevent soil liquefaction in level ground has been investigated experimentally. Deposits of loose (D_r = 0.2 to 0.4), dry sand were prepared inside a large (2.0 m deep by 1.8 m long by 0.8 m wide) laminated box and subjected to shaking of different intensities on a one-dimensional shake table. For low intensity shaking (up to 0.12 g) the cyclic shear strains were modest (up to 0.11 percent) and there was a modest settlement (0.31 percent). For higher intensity shaking, (0.16 g) there was a significant transformation in response with much greater cyclic shear strain (0.65 percent) and settlement (3.1 percent). Other deposits were reinforced by use of Titan 26-14 self-drilling micropiles installed at 30 degrees inclination. Reinforcement by one inclined micropile was found to have little effect on response to shaking but installation of two diagonally opposed, inclined micropiles was found to reduce cyclic shear strain by half and settlement to one fifth that of similar unreinforced deposits.

Results from a series of small diameter vertical drilled and compacted grout micropiles that were installed and load tested to failure in axial tension are presented. Tests were performed in the clay crust at the National Geotechnical Experimentation Site at the University of Massachusetts. Micropiles with a diameter of 76 mm and length of 3.05 m were tested. The micropiles were constructed by incrementally applying dynamic compaction energy from the SPT hammer of a conventional drill rig to the concrete grout as the hole was filled. The results of the tension tests showed that in comparison with a micropile constructed using gravity free-fall placement of the concrete, the pullout capacity of the micropiles was significantly increased when compaction energy was used. This increase is primarily due to the increase in lateral stress produced by the compaction.

Due to the small diameters, Pin Piles, generically known as micropiles, are often considered to have little to no lateral capacity. This paper focuses on lateral load performance and design of Pin Piles. The intent is to demonstrate that micropiles and micropile groups can be designed to support lateral loads and provide options and considerations for lateral load design. The results of lateral load tests are compared to the predictions using various available methods. Design considerations of combined stresses, options for increasing lateral resistance, and analysis for battered piles are then discussed.

Micropiles are small diameter piles often used for support of foundations in difficult conditions. They are one of the more efficient deep foundation systems available in the industry. They can tolerate very large loads for their size, especially when socketed in rock. This paper presents three case histories on micropiles; all piles were socketed into weathered rock or bedrock. The micropiles were installed as foundations for a power plant, a retail shopping mall, and an industrial building. The case histories present information on the subsurface conditions, foundation selection, and micropile construction in schist, gneiss, and karstic limestone. The case histories also present information on pile drilling issues particularly that, from a production perspective, the success of any micropile application is a function of the tools and equipment that are used to drill the piles in an efficient, reasonable time. Pile load test data along with other pertinent information is also presented and discussed. The results illustrate that micropiles can be successfully utilized for virtually all kinds of ground conditions and that they are highly flexible to modification at anytime during construction in response to changing ground conditions.

Significant uncertainty remains in predicting the stabilizing forces that can be developed in slender reinforcing members used for slope stabilization. This uncertainty arises from the high number of potential failure modes as well as from uncertainties present in predicting the resistance contributed by the individual failure modes themselves. The aim of this research has been to identify the most significant sources of uncertainty in the design of slender reinforcement through parametric analyses so that the uncertainty can be addressed by modifications to current design and construction practice, and future research. Results of the parametric analyses showed that the degree of improvement in the factor of safety of a reinforced slope depends on a combination of the design parameters evaluated. The parameters with greater influence on the factor of safety for a given soil condition were slope inclination, method for predicting limiting soil resistance, and capacity of reinforcement used. While the uncertainty in limiting resistance for weak reinforcing members is greatly reduced due to the controlling effect of the structural failure mode, significant uncertainty still exists in predicting the limiting resistance on strong reinforcing members.

Modern methods for designing drilled shafts, ACIP piles and similar foundations in soft rock require knowledge of the compressive strength and modulus of the rock. However, jointing at many sites prohibits the recovery of samples of sufficient length and integrity to test rock cores in either unconfined or triaxial compression. Since rational design procedures usually require values of compressive strength, surrogate methods must be employed to estimate the compressive strength of the rock. The surrogate methods considered here are the splitting tension test, the point load index test and the TxDOT dynamic penetrometer test (in which a 76-mm-diameter solid steel cone is driven into rock at the bottom of a borehole in much the same way as a split spoon is driven during the performance of a standard penetration test in cohesionless soil). Soft rock formations typical of those for which such substitutions might be used are the upper Cretaceous formations of North Central Texas, including the Eagle Ford (clay shale) and Austin (limestone) formations. Correlations of the results of the tests listed above with compression strengths of soft rock cores from these formations are provided in the paper. The correlations are formation-dependent, most likely through the degree of cementation present in the geomaterial. The strongest and apparently most reliable correlation was between compressive strength and the TxDOT cone penetration test, although separate correlations were observed in limestone and in clay shale. A clear correlation, but with considerable variance, was found between point load index strength and compressive strength in clay shale. No clear correlations between either point load index or splitting tension strength and compressive strength appeared in the limestone.

Increasingly, Cast-In-Place (CIP) pile foundations are being used in place of traditional driven pile foundations to support settlement sensitive structures. The advantages of CIP pile foundations include quick installation, flexibility to adjust pile length for varying subsurface conditions, and reduced noise and vibration. There are inherent uncertainties in all CIP systems and thus detailed testing and production monitoring programs may be appropriate to verify the integrity of each individual CIP pile. This paper presents the design considerations, load testing program, production monitoring, and integrity testing of Drilled Soil Displacement Piles (DSDP) installed for a gas-fired power plant in Bartow, Florida. Efficient planning of the load testing and integrity testing programs resulted in the foundation construction being completed ahead of schedule while verifying the piles met the design requirements.

It has traditionally been assumed that when cast-in-situ piles, such as drilled shafts or ACIP piles, are constructed, the residual stresses after curing are zero. When conducting load tests on instrumented cast-in-situ piles, therefore, the readings in the strain gauges at the beginning of the load test are assumed to represent an unstressed condition. The implementation of ACIP piles in a bridge foundation in the Texas DOT system recently has allowed for the measurement of residual loads in several ACIP piles during curing. These loads were found to be relatively small, but not insignificant, and appear to have been related to site-specific soil profile characteristics.

There are many types of deep foundations currently being used in the San Francisco Bay Area, one of the most common being driven precast, prestressed concrete (PC/PS) piles. PC/PS piles are frequently selected for use due to of ease of installation, availability, and relatively low cost. Disadvantages of using PC/PS piles are noise, vibrations, front-end delays due to indicator pile programs, and reduced flexibility. An acceptable alternative to driven PC/PS piles was selected for construction of foundations for the heavy housing and administrative buildings at the San Francisco County Jail No. 3 replacement project in San Bruno, California. The pile type selected, the Auger Pressure Grouted Displacement (APGD) pile, was chosen to reduce noise, vibrations, installation time, and cost, and to allow for greater flexibility of installed pile lengths. This paper presents a case history of the use of APGD piles that were substituted for driven PC/PS concrete piles for the subject project. Standard and quick loading pile load tests were performed to confirm adherence with the design criteria originally used for the driven PC/PS concrete piles. The APGD piles were found to increase shear strength around the piles similarly to driven displacement piles. In addition, this paper presents the methodology used in monitoring APGD pile installation.

Analytical and empirical design methods are available to determine side shear and tip resistances of large diameter drilled shafts in cohesionless soils. The replacement of Cranston Viaduct in Rhode Island provided a good opportunity to test these design methods and compare it with a full-scale load test in the field. The foundation support for the replacement Viaduct consists of nine-foot (2.75m) diameter drilled shafts. As required by the Federal Highway Administration design guidelines, nine-foot (2.75m) diameter trial shaft was drilled at the site to establish the proper construction procedures and to verify design assumptions. The construction of the trial shaft and the production shafts for the southbound of the viaduct has already been completed. The paper will present a description of the unique design and construction methods adopted for the foundations. In addition, the paper will present the results of the Osterberg load test performed on the nine-foot diameter trial shaft and will compare side shear resistance and end bearing values obtained from the test to the values computed during design. The design equations for drilled shafts in cohesionless soils, adopted by the Federal Highway Administration and AASHTO, proved to provide a good design tool in this project and compared very well with actual field measurements.

The paper describes the foundation design and construction history of a 19-story residential high rise on deep foundations on the south side of downtown Chicago, including: 1) a value engineering foundation design innovation; 2) the changes in anticipated conditions actually encountered during construction; 3) the additional subsurface exploration and special testing and new engineering analyses performed to better predict ultimate foundation performance; and 4) the foundation design modification required to make the predicted foundation performance acceptable. The paper also presents the actual measured foundation performances, compares prediction with performance and offers possible explanations where there are significant differences.

The existing control tower at King County International Airport in Seattle, Washington, was severely damaged during the Nisqually Earthquake, February 28, 2001. As a result of the damage, the control tower was immediately closed and the existing timetable for a seismic retrofit of the control tower was expedited. The existing tower and associated support structures were founded on timber piles of unknown lengths (probably extending to depths between 25 and 35 feet); subsurface explorations indicated liquefiable soils to a depth of approximately 35 feet. The foundation retrofit included compaction grouting to densify the loose, liquefiable sands beneath the existing structures and the installation of drilled shafts adjacent to the tower to support the new structural steel bracing which was added to increase the resistance of the tower to overturning during the design earthquake. With the air traffic control operations being performed in a temporary facility, the urgency of performing the retrofit led the Federal Aviation Administration to negotiate a contract directly with the general contractor. This paper addresses the method of contract delivery, compaction grouting methods and results for liquefaction mitigation, and the construction of drilled shafts adjacent to an existing structure.

This case history illustrates how a successful "Value Engineering" redesign with slurry-drilled shafts and an O-Cell test saved considerable costs and expedited early completion of a large bridge project for the Nebraska Department of Roads (NDOR). The paper first describes the original project and its geologic setting. It then relates the inception, development and verification of the redesign concept and its implementation via NDOR's "Value Engineering Proposal" (VEP) standard specification provisions. The comparative advantages of drilled shafts versus driven piles relative to the site geology, some benefits of using polymer drilling slurry and the practicality of foundation verification with an O-Cell test and cross-hole sonic logging (CSL) are discussed. The lack of redundancy in drilled shafts and the increased importance of having an experienced contractor using appropriate equipment and procedures under an effective quality control program are also emphasized. The paper concludes with a discussion of the overall impact of the VEP redesign on the project cost and schedule, as well as on NDOR's subsequent bridge design and construction practices.

A new 84 inch water pipeline project for Tampa Bay Water included a tunnel section under the Alafia River in Riverview, FL. Access shafts were required on each side of the river for the pressure-balanced tunnel boring machine. Since the 70 ft. deep access shafts extended roughly 25 ft. into the confined Floridan Aquifer (Tampa Limestone) under an artesian head, control of groundwater flows was a serious concern. Two circular cofferdams (one 40 ft. and one 24 ft. ID) were designed and built for these access shafts. Alternating, overlapping hard/soft secant piles (36 inch diameter) were utilized to act as a lateral cutoff wall. Circular concrete compression ring waters were constructed to support the secant piles at five (5) levels. In order to maintain bottom stability and to control bottom water inflows, a pressure relief well system was installed at each cofferdam. The smaller cofferdam was instrumented with an inclinometer in one of the secant piles to monitor lateral deflections. In addition, vibrating wire strain gages were installed in the concrete ring waters to measure compressive strains and the resulting stresses during the excavation process.

The T-REX Project is a $1.67 billion project in the Denver Metropolitan area that consists of approximately 19 miles of a new Light Rail Transit (LRT) line, and improvements to approximately 17 miles of two interstate highways. Several miles of new retaining walls were required to provide for widened roadways and new light rail track. Because the right-of-way was restricted, tied-back walls were often infeasible, and so cantilever caisson walls with heights of over 30 feet and diameters up to 4 feet were employed. The caisson walls represented a considerable expense to the design-build team, and significant studies were performed to optimize the design. Foundation conditions along most of the alignment consisted primarily of stiff clays and relatively weak claystone, often with moderate to high swell potential. A study of design methods available for walls in these materials indicates that uncertainties exist in selecting the appropriate long-term loading, soil strength, and even the method of analysis for design of long-term soldier pile walls. This paper describes the evaluation of the uncertainty and selection of a design approach for the project.

Excavation for a building in Washington, D.C. required support systems to limit the deformation of several adjacent structures. One adjacent structure would have been difficult to underpin conventionally because column footings are located approximately 13 feet behind the face of the excavation. A geo-support system consisting of tangent piles and two rows of tieback anchors was presented as an alternative to direct underpinning. In order to predict potential ground movements adjacent to the 27-foot deep excavation, tangent piles were analyzed as beam-columns subjected to lateral earth pressures, footing surcharge loads, and anchor loads. Deformations of the adjacent building were monitored during construction for comparison with the predictions. In addition, the drilled shafts of the tangent pile wall were used as a permanent foundation for the new building columns. This paper describes the design, analysis, construction and performance of the anchored tangent pile wall. This case history demonstrates the effectiveness of using this configuration of drilled shafts to limit ground movements in deep excavations close to existing structures.

The use of vertical or near-vertical buried structural members to stabilize slope failures is an established and effective approach to landslide correction and can be economical in urban areas constrained by property limits, access restrictions, and high land costs. Traditional designs for such slope stabilization methods have relied on assumed active and passive pressures mobilized by the failing soil mass. Increasingly, sites are being developed in soils of marginal slope stability where some form of stability enhancement is required to achieve a minimum safety factor against deep-seated failure. In such pre-failure situations, a different set of design criteria is required because the ground movements necessary to mobilize active and passive pressures might exceed structural tolerances and even result in strains that might initiate soil failure. A practical method is presented for the design of drilled shaft cutoff walls used to enhance slope stability in marginally stable soils. The method specifically addresses the pre-failure condition and applies limiting deflection criteria to structural members to preclude soil failure. The use of commercially available slope stability and soil-structure interaction programs is adopted. Emphasis is placed on practical application by the experienced practitioner.

A cantilever wall located along the tailrace channel of the Hodenpyl Hydroelectric Dam was undergoing significant lateral displacement. An unsuccessful repair attempt was carried out in 1996 using conventional strand tiebacks. Remediation of the movements was accomplished in 2002 by installing additional tiebacks through the wall. The tieback system selected for this project was Single Bore Multiple Anchors (SBMA), bonded into high-plasticity clays behind the potential slip surface. The SBMA system provided the desired tieback capacities in the clay with a reduced potential for long-term creep. This was the first application of post-grouted SBMA technology in the United States. The limited monitoring data collected after remediation suggests that the SBMA system has performed remarkably well. To expedite remediation of the wall, the design had to be completed in phases and adjusted according to the monitoring data obtained until the start of construction. This paper presents a description of the investigation and analyses performed for design of the remediation. It also describes briefly the SBMA system and the results obtained as interpreted from the wall monitoring performed up to this date. A companion paper by Bruce et al. describes in more detail the SBMA design and construction details for this project.

Despite the installation of a row of anchors in 1996, the right downstream retaining wall of Hodenpyl Dam, MI, continued to move inward and downstream. The remediation design called for installation of additional anchors. However, there were concerns about creep-induced relaxation of the anchor load over time given the existence of high-plasticity clays at the site. The solution was the installation of post grouted multi-anchors along the base of the retaining wall (Single Bore Multiple Anchors — SBMAs). SBMAs utilize several "unit" anchors within the same borehole, each with its own short efficient bond length positioned at staggered intervals along the bond zone. This staggered arrangement allows each unit load component to be transferred to the soil in a controlled manner over a discrete length of the borehole, thereby producing a very efficient load transfer mechanism. A larger factor of safety against creep is therefore attainable using SBMAs as compared to that provided by conventional tendons. One sacrificial anchor and 13 production anchors were installed. An innovative testing setup and program were developed to allow extended creep testing of the sacrificial anchor followed by load testing to 2.8 times the design load without anchor failure. This paper describes the design and construction of the SBMAs, the load testing setup, and results of extended creep load testing.

Special applications of permanent anchors and micro piles are used mainly for foundations and to secure construction, but also can be used for a variety of additional geotechnical applications. The following are three noteworthy case histories. In tension piles for harbor construction with a service load of 270 Kips and a length of 86 feet, the firm was able to improve the load transfer into the soil by increasing the diameter of the pile in the upper part by high-pressure injection up to a depth of 40 feet. Through the use of the post-tensioning permanent anchor system with a service load of 142 Kip and a length of 86 feet, the company was able to provide protection of the permanent anchors against aggressive concrete-attacking groundwater. In underpinning historical buildings in Berlin with micro piles with a service load of 194 Kip and a length of 105 feet, the firm was able to fabricate and install piles within cramped cellars, apply special constructive measures for connecting the piles and provide for corrosion protection within the aggressive organic soil. All details of the construction are described. As a basis for reliable, controlled performance, details regarding the quality control program are also discussed.

In 1978, Idaho Transportation Department (ITD) designed and constructed the first U.S. "true" MSE bridge abutment over the Union Pacific Railroad (UPRR) tracks in Soda Springs. This project was one of the six original FHWA Demonstration Projects introducing reinforced earth technology to the U.S. transportation industry. In the summer of 2002, approximately six of the precast concrete facing panels "popped out" in a localized area of one of the MSE earth retaining walls supporting the bridge approaches. It was determined that the galvanized steel soil reinforcing strips had corroded at the panel connection to a point where the lateral earth pressures exceeded the connection's remaining capacity. Concerned, ITD and UPRR officials immediately prepared the contract documents for the repair of approximately 3,700 m² of MSE walls and bridge abutments. The scope of work in the ITD contract documents included installing horizontal drilled and grouted crosstie ground anchors in the approach walls, anchored soldier piles at the abutments and a reinforced shotcrete facing structurally attached to the existing MSE facing panels. The crosstie anchors connected the "back-to-back" MSE approach walls located approximately 25 m from panel to panel. Challenges included traffic control and rail traffic sequencing, winter construction, monitoring the condition of the existing structures, drilling ground anchors (from panel to panel) horizontally through a compacted fill with thousands of steel soil reinforcing elements and installing the soldier pile and rock anchor elements from the existing bridge deck.

A series of static one-way lateral load tests was performed on prototype-scale drilled shafts installed in a stiff surficial clay crust to investigate the effect of ground water on lateral load behavior. Tests were conducted under different ground water conditions at the National Geotechnical Experimentation Site at the University of Massachusetts, Amherst. The load-displacement results of the tests are presented herein. The results of the tests show that the load-displacement behavior was significantly influenced by the ground water regime at the time of testing. The ultimate lateral load capacity, defined as the load at a displacement of 10% of the shaft diameter, and the initial stiffness increased as the water table dropped. A drop in the ground water table from 0.4 m to 2.3 m below ground surface increased the ultimate lateral load from 30 kN to 95 kN. The paper presents a summary of the testing and illustrates the influence that ground water can have on field tests.

Development on land underlain by limestone formations that exhibit karst conditions can present unique engineering and construction challenges. These challenges often include concerns regarding questionable subgrade for foundation support and economical methods for foundation construction. Over the past decade, many structures have been constructed in the Central Texas area over limestone formations exhibiting karst features such as voids and solution cavities, as well as soil seams and layers. The most common geologic formation to exhibit such properties in Central Texas is the Edwards Group limestone. Significant foundation design challenges may be encountered for structures constructed over such formations, particularly larger structures with significant column loads. Many such structures often require a pilot hole program for evaluation of the bearing stratum below each foundation unit. Through multiple projects in the Central Texas area, the authors have compiled experience with three major categories of pilot hole programs, including 1) the use of geotechnical drilling rigs, 2) air percussion drilling equipment, and 3) drilling pilot holes during construction with pier drilling equipment. This paper discusses the benefits and drawbacks of utilizing each of these three different pilot hole methods, and presents several case histories.

The procedures used for a successful Class "A" prediction are documented for the lateral load-displacement response of four drilled shafts (d = 0.914 m and L = 11 m) constructed in Piedmont residual sandy silts at the National Geotechnical Experimentation Site (NGES) near Opelika, Alabama. The approach was based on the results of flat plate dilatometer tests (DMT) to evaluate the lateral soil resistance (p_u = p₀) for determining the static capacity (H_u) and equivalent soil modulus (E_s = E_D) to represent stiffness within the context of elastic continuum solutions. A more generalized Class "C" approach is discussed using an approximate closed-form expression and data obtained from seismic dilatometer tests (SDMT), since the shear wave velocity provides a fundamental initial stiffness of the ground in terms of the small-strain shear modulus (G_max).

The axial-load-displacement-capacity response of drilled shaft foundations can be analyzed efficiently using the results of seismic piezocone tests (SCPTu) which provide four independent readings in the ground: cone tip stress (q_t), sleeve friction (f_s), penetration porewater pressure (u_b), and downhole shear wave velocity (V_s). The penetration data are used in a direct CPT method to assess side resistance and end-bearing capacity components, while the shear wave provides the initial stiffness for an elastic continuum analysis of vertical displacements and axial load transfer distributions. Results from instrumented drilled shaft load tests conducted at the national geotechnical experimentation sites at College Station, Texas and Opelika, Alabama are utilized to illustrate the methodology.

Results from Texas Cone Penetration Tests are employed for assessing the bearing capacity of drilled shafts in relatively soft sedimentary rocks. The test involves driving a solid, nominally 76-mm diameter cone tip into the rock at the bottom of a borehole and recording the number of blows associated with the measured penetration. While the test is common in Texas and Oklahoma, it has many shortcomings due to the dynamic nature of the test and the small penetrations that can occur. Alternatively, the Pressuremeter Test can be employed in test holes within the shale to assess the stress-strain behavior and bearing capacity. While not without limitations, the Pressuremeter Test seems inherently better for assessing bearing capacity of shale, mainly because it involves carefully controlled quasi-static loading of a substantial portion of the formation to failure, resulting in well defined stress-strain behavior. This paper presents results of Texas Cone Penetration and Pressuremeter Tests conducted primarily in Permian age shale and sandstone at nine sites in central Oklahoma. Correlations between results of the two tests and comparisons of predicted end-bearing capacities for drilled shafts are presented and discussed.

The usual process for obtaining subsurface soil and rock information is to obtain bids for soil borings on a cost per foot basis and awarding the contract to the lowest bidder. Thus, there is no incentive to do good quality work and there is every incentive to somehow get a hole down as quickly as possible without regard to obtaining the best soil, rock, water levels and collateral information. As a result, perched water tables and important soil layers and other important information are often missed. In general the equipment, techniques, and procedures for obtaining better quality samples and other subsurface information has long been available, but there is no incentive on the part of the drilling contractor to make use of them. Many new techniques for geophysical prospecting have been developed but the geotechnical engineer seldom uses them except for large or special projects. The geotechnical engineer often fails to use his knowledge of geology in laying out an exploratory program and interpreting the borings and soil test results.

In the past five years, over 25 structures in the states of California, Oregon, and Washington, have been supported by Rammed Aggregate Piers constructed in granular soils. The piers are installed by drilling 60 to 90 cm diameter holes and ramming thin lifts of highway base course stone within the drilled cavities. The elements are used to support conventional shallow footings. The system is unique and innovative because it incorporates features associated with the design and construction of shallow and deep foundation systems. Accordingly, the design procedures include concepts derived from conventional shallow foundation design, historical stone column soil improvement system design, and cast-in-drilled-hole concrete shaft design. Unlike design values for drilled deep foundation systems, which are well-documented in the literature, parameter values for rammed aggregate piers are established from the results of modulus tests conducted at each project site. This paper presents results of 19 rammed aggregate pier modulus tests performed at sites underlain by granular soils. Test results are correlated to matrix soil characteristics and length of the piers. This paper is of particular significance because it presents a database of in-situ modulus values used in the design of a cost-effective and increasingly popular drilled foundation system.

The use of Vibro-Concrete Columns (VCC) to improve soft ground is growing in popularity in various parts of the world due to its cost effectiveness and proven performance. A case history involving the first use of VCC by a US Department of Transportation to support an approach embankment is presented. The project involves the installation of VCC supporting 10 m high back-to-back mechanically stabilized earth walls underlain by a geotextile-reinforced sand platform. The design concept of the embankment supporting system is outlined. Static load tests results performed on two VCC are also presented and the acceptance criteria are discussed. The performance of the embankment supporting system is assessed based on monitoring data obtained from various instruments installed during construction including settlement platforms, probe extensometers, inclinometers, piezometers and strain gages attached to the sand platform geotextile reinforcing elements. Finally, recommendations are presented regarding the design aspects of the VCC and the geotextile-reinforced sand platform.

There are a lot of ground improvement techniques that have been developed. One of them is the aggregate pier foundation system. The response of an aggregate pier foundation system during seismic loading was investigated. Comprehensive numerical modeling using FLAC were performed. The research was divided into three parts: 1) ground acceleration, 2) excess pore water pressure ratio, and 3) shear stress distribution in the soil matrix generated during seismic loading. Two earthquake time histories scaled to different maximum acceleration (pga) were used in the numerical modeling: the 1989 Loma Prieta earthquake (pga = 0.45g) and the 1988 Saguenay earthquake (pga = 0.05g). The results of the simulation showed that: 1) the aggregate pier amplifies the peak horizontal acceleration on the ground surface (a_max), 2) the aggregate pier reduces the liquefaction potential up to depth where it is installed, 3) pore pressures are generally lower for soils reinforced with aggregate pier than unreinforced soils, except when the applied shear stresses exceed the cyclic shear resistance of the aggregate materials, and 4) the maximum shear stresses in soil are much smaller for reinforced soils than unreinforced soils.

Full scale compression and uplift load tests were conducted on 3 Rammed Aggregate Piers in the upper surficial clay fill at the NGES located at the University of Massachusetts — Amherst. The tests were conducted to evaluate the performance of this intermediate foundation system in a fine-grained soil. The field investigation also included measurements of vertical and lateral soil deformation to evaluate the active zone of soil resistance. The results show viable uplift and bearing capacity application for the foundation system in fine grained soils.

A stone column test program was conducted for ground improvement below an earth embankment project in western Washington. Stone columns were initially designed to mitigate soil liquefaction, improve shear strength, and reduce subgrade settlements to provide a stable foundation for the embankment. The test program includes four test areas of stone columns installed with varying control parameters such as diameter, spacing, and area replacement ratio. Each test area consists of 32 to 41 vibro-replacement stone columns. Stone columns were installed through the post-glacial, loose to medium dense, silty sand and soft to medium stiff silt and embedded into glacially overridden, dense, silty sand and stiff to hard, sandy silt. Standard Penetration Tests (SPT) and Cone Penetration Tests (CPT) were used as verification tests in each of the four test areas before and after the installation of stone columns. Results indicated densification of the matrix in soil zones containing less than approximately 15 percent fines and little to no improvement in soil zones containing over approximately 15 percent fines. In some deeper zones where native soils were over-consolidated by glacial actions, disturbance in the stiff to hard silt actually caused a decrease in penetration resistance.

The slurry wall technique has undergone an evolution from its invention to its today's status. In the early stages slurry walls were built with cable grab, later on with much stronger hydraulic grab and last but not least with the use of the cutter technique. The cutter allows thick walls with high verticality to extreme depths through hard soil and rock formations. With the rising demand of the construction of watertight diaphragm walls different joint systems have been developed. In addition to the rapid development of excavation systems it was necessary to improve slurry treatment and desanding plants, especially in conjunction with high performance trench cutters.

The Walter F. George dam was built in 1962 on the Chattahoochee River by the Corps of Engineers and it soon developed seepage problems. Two partial cut-offs were built in the past to attempt to remedy the situation, but the problems continued, jeopardizing the safety of the structure as well as reducing its power generating potential. In 2001 the Mobile district of the Corps advertised a design-build contract for the construction of a 200 feet deep cut-off in front of the concrete structure of the dam starting from 90 feet of water, cutting through a concrete lock structure, a submerged retaining wall and extending on both sides on the earthen embankments. The winning proposal of the joint venture of Treviicos and Rodio anticipated the use of a secant pile wall in the portion to be built in front of the structure, working from barges with a reverse circulation drilling rig, and a conventional slurry wall built with a hydromill rig for the portion out of the water.

Deep underground basements that are integrated into urban development projects early in the overall project design offer many inherent improvements to the overall quality and value of the project and its surrounding community. Diaphragm walls combine into a single foundation unit the functions of temporary shoring, permanent basement walls, hydraulic cutoff, and vertical support elements/shear walls, and, because of this combination, have proven to be an economical alternative in many circumstances. This paper examines the evolution of deep underground basement construction, identifies considerations associated with diaphragm wall construction, and provides several case history examples to illustrate the resolution of key issues.

A comprehensive study on the effectiveness of two different toe-grouting methods, known as tube-â-manchette and drill-and-grout, commonly applied for deep-seated bored piles in Bangkok is presented in this paper. Mobilized unit end bearing of bored piles constructed by two toe-grouting methods are compared. The problems encountered in practical application of different methods for large diameter deep seated bored piles are highlighted. Despite considerable extra cost, various construction problems encountered and risks involved in successful execution of grouting, drill-and-grout method does not offer particular advantage over tube-â-manchette method as far as pile capacity improvement is concerned.

Three 6-ft (1.83-m) diameter, 120-ft (36.6-m) long test drilled shafts were constructed and load tested to evaluate the effects of using bentonite and polymer slurry on full-scale drilled shaft load carrying capacity. Ground conditions at the Miami, Florida site consisted of alternating layers of soft sedimentary rock and sand. Load tests were performed using embedded multi-level Osterberg-type loading jacks (O-cells) where maximum equivalent top loads of as much as 12,200 kips (54.3 kN) were applied. This paper presents the test drilled shaft construction procedures, and the load test procedures and results. Shaft drilling procedures, equipment, and bottom cleaning methods; slurry mixing and testing procedures; and construction time are also presented. Conclusions are drawn regarding the effects of construction methods and drilling slurries on observed side shear and end bearing load transfer.

The paper presents the results of an Osterberg load test program performed for the Paksey Bridge over the Padma (Ganges) River in western Bangladesh. The test program included the installation and testing of two 1.5-m diameter bored piles to depths of 65 m and 91 m. The paper discusses the design of the high capacity bored piles for a site susceptible to deep scour. The paper also discusses the installation of the test piles, and the application of base-grouting to improve end bearing resistance. Finally, the paper documents and evaluates the results of Osterberg load tests at the two test piles, including a comparison of pile capacity prior to and following base grouting.

This paper describes the load distribution and settlement of reinforced drilled shafts subjected to axial loads. The emphasis was on quantifying the reinforcing effects of rockbolts placed from the shafts to surrounding weathered rock based on a numerical analysis and 1/8 scale load tests performed on instrumented piles. The piles with and without rockbolts were instrumented with strain gages, load cell and tell tale, and load tests were performed on four piles: tension and compression. The results of the four load tests are presented in terms of top load-top movement curves. In addition numerical analyses are performed for the major influencing parameters on the behavior of reinforced drilled shafts such as the number of rockbolts, the positions on the shaft, reinforcement level, and the inclination angle at which the rockbolts are placed. As a result, the parametric study is highlighted. It was found that as the number of reinforcing levels increases, the incremental effect of reinforcement tends to increase, whereas the reinforcing effect on relative positions is negligible. In addition there is a reinforcing effect as the inclination angle increases up to 30 degrees.

Numerical analyses are presented for the response of a 2 m diameter drilled shaft with flagpole configuration subjected to lateral loading. The analyses were conducted using three software programs: LPILE (subgrade reaction model), SWM (strain wedge model), and ABAQUS (3-D finite element model). The analyses consider nonlinear behavior of the reinforced concrete shaft, contact-slip-gap at the soil-shaft interface, and elastic-plastic properties of the soil. Numerical results are compared with measurements from a full-scale field test for the shaft and include lateral displacement at the top of the shaft, subgrade reaction (p-y) curves at three depths, and distributions of bending moment and shear force along the shaft.

This paper focuses on investigating potential bending or torsional failure modes in axially loaded pile groups caused by defective piles and on investigating the effect of short piles on the response of vertically loaded bored pile groups socketed into rocks. A hypothetical group of six bored piles, 2.0 m in diameter and 25.5 m in length, was analyzed and six cases with different numbers and configurations of short piles in the pile group were considered using a three-dimensional pile foundation analysis program FB-Pier. It is found that the number and configuration of short piles have a significant effect on behavior of the pile group. The presence of short piles forces "intact" piles to carry larger loads. An important aspect of the group response is that the presence of short piles can result in induced lateral deflections of the pile group and additional bending moments in piles even under "concentric" axial loads at the pile cap. The lateral deflections and bending moments can cause lateral failures of the pile group in terms of both ultimate limits and serviceability limits. For the axially loaded cases analyzed, the torques developed in the piles are much smaller than the bending moments; a torsional failure mechanism is therefore not likely to occur.

The performance of drilled shafts is known to be controlled by the type and quality of the construction methods. A comparison between different methods or different contractors is typically not available under the prevailing bidding and testing procedures. Six drilled shafts 0.70 m in diameter and 25.0 m long were installed and tested to structural failure at a site in Haifa, Israel. Three of the shafts were constructed using the Continuous Flight Auger (CFA) construction method and three of the drilled shafts were constructed using bentonite slurry. Site and shafts details are provided. The drop weight testing system is reviewed. Test results comparing the load carrying capacity of the shafts, load distribution and structural outlines are presented and discussed. While the bentonite slurry construction resulted in a more uniform constructed foundation capable of carrying higher load, the explanation to the variation at the given site conditions may be a result of the contractor's quality rather than advantages of one technology over another.

Highway construction projects in the mountains typically present access challenges and slope stability risks during construction. Long narrow working corridors restrict activities complicating construction staging and lengthening schedules. On a recent Colorado Department of Transportation (CDOT) project near Aspen, Colorado, a micropile shoring system was built in-lieu of temporary tieback walls to improve on-site workability. The micropile shoring system consisted of approximately 7,400 square meters of retained face along 1,600 linear meters of wall with a maximum-shored height of 7.5 meters and an average height of 4.5 meters. Micropile shoring design methodologies are presented and compared to field measurements of wall performance collected from inclinometers and strain gauges.

The case history involves a major retrofit of the D. E. Karn power plant at the Consumers Energy's Karn/Weadock Generating Facility near Bay City, Michigan to meet current environmental requirements. The retrofit required the installation of heavily loaded columns above and between existing equipment, overhead piping, underground utilities and various structures without disruption to the operation of the plant. High capacity micropiles were proposed as the most practical alternative to meet the project budget and schedule requirements. Micropiles with a single high-strength steel bar and permanent upper steel casing (Type A) were installed in groups and extended into competent sandstone. An instrumented load test of a micropile was performed to determine the stress distribution in the rock socket and verify the design requirements. A total of 112 micropiles were installed in time for the steel erection to keep the project on schedule.

Micropiles are being used today for a variety of applications. As the size and complexity of today's superstructures increase, difficult subsurface conditions in karstic dolomite preclude the use of traditional deep foundation systems. A report is presented on the redesign of the proposed deep foundations and installation of the micropile systems for two different projects. The similarities and differences of the two projects with regard to geology, design, load transfer, and installation are summarized.

Micropiles and permanent anchors are important elements in geotechnical engineering. To use them successfully under difficult site and soil conditions it is necessary to improve the normal systems in due compliance with project specific specialist measures. Necessary improvements for difficult site and soil conditions are explained by three case histories. The first shows the production of micropiles und permanent anchors in tidal-zone and the improvement of the load bearing zone to guarantee the load bearing capacity through a wharf foundation. In the second example it is described how to protect permanent anchors against lime-attacking carbon dioxide in the groundwater in rock. The concept for the post-foundation under organic soil conditions of the Berlin State Library "Unter den Linden" is the third case history.

Micropiles have been used effectively in many applications of ground improvement to increase the bearing capacity and reduce the settlements particularly in strengthening the existing foundations. Frictional resistance between the surface of the pile and soil and the associated group/network effects of micropiles are considered as the possible mechanism for improvement. This paper deals with a case study in which micropiles of 100 mm diameter and 4 m long have been used to improve the bearing capacity of foundation soil and in the rehabilitation of the total building foundation system. The micropiles were inserted around the individual footings at inclination of 70° with the horizontal. The actual design for retrofitting was based on the assumption that the vertical component of the frictional force between the soil and the micropile resists the additional load coming from the structure over and above the bearing capacity. The technique was successful and the structure did not show any signs of distress later. Detailed finite element analysis conducted validated the suggested treatment. The paper describes the case study, the method of treatment adopted in the field and the results of numerical analysis.

In 1994, USAID provided funding to the Sisters of Mercy of the Americas for construction of a three-story expansion to the St. Joseph's Mercy Hospital in Georgetown, Guyana, South America. Subsurface conditions consist of approximately 16.5 m of very soft to soft marine clay overlying stiff to very stiff clays. The foundation system employed was a soil-supported, monolithically-cast, reinforced concrete mat foundation with down-turned beams arranged in a grid pattern below the mat. Damaging building settlement occurred within the first few years after completion of construction. In 1997, investigations were conducted to identify the cause of the on-going building settlement, and a remedial foundation design was subsequently developed. Foundation underpinning was performed in 2000, and consisted of installation of 102 grouted mini-piles (approximately 15 cm in diameter; 21 to 29 m long) drilled through the foundation mat and upper soft clay into the underlying very stiff/hard clay stratum. This is the first use of drilled, grouted mini-pile foundations in Guyana. Load transfer to the mini-pile foundations was achieved by constructing 28 reinforced concrete pile caps at existing column locations. The paper will describe: a) the nature of the building settlement problem, b) the basis for and details of the remedial foundation design, c) the unique aspects of mini-pile installation adopted by the Contractor, d) results of pile load tests, e) and post-construction settlement monitoring results.

Urban development in West Conshohocken, near Philadelphia, has been occurring at a fast pace over the past 10 years. The 300 Four Falls office complex was to be constructed in one of the few remaining undeveloped sites, near the original 100 Four Falls office building from the early 1980s. The site conditions were a major issue in the development. With an odd-shaped narrow lot, a creek across the site, and existing grade changes of nearly 18.3 m (60 ft), fitting a 26,942 m² (290,000 sf) building represented a major challenge. Exploration revealed further difficulties, including cuts of over 12.2 m (40 ft) into hard rock on one side of the site, and very-soft soil materials to depths of over 24.4 m (80 ft) on the other. Solutions included a combined foundations system consisting of spread footings on rock, micropiles, and 890 kN (100 ton) driven H-piles. To accommodate the deep excavations around three sides of the site and extensive filling on the fourth side, various earth support structures were built. These consisted of soldier piles and tiebacks, soil nails, rock bolts, and Mechanically Stabilized Earth (MSE) walls. This project was truly a study m geotechnical engineering challenges and solutions that met the needs of a difficult site. This paper describes the most relevant geotechnical aspects of the project, and the application of different geo-construction techniques to meet the demands of the site.

Typically, temporary shoring support systems are not required to provide for design level earthquake occurrences consistent with the building or structure being constructed inside the excavation. This paper evaluates the seismic response of the deepest soil nailed walled constructed in the U.S. at the time of construction, for a Mw 6.8 earthquake in the Puget Sound Region in Washington State. In addition, an extended life analysis was required when the project was stopped in the middle of an economic downturn. The construction was stopped at a depth of 86.5 feet with the basement slab in place and no lateral support from the eight levels of planned reinforced concrete parking slabs. Project start up is not expected for 2 to 4 years; therefore, the life of the temporary soil nails had to be evaluated for their ability to support the cut for the interim time period. The construction design life was initially set for one year.

This paper describes the design, construction, and performance of a soil nail wall system used by the Pima County Department of Transportation (PCDOT) to stabilize and retain two steeply sloping bluffs up to 18 meters high as part of a major road widening and realignment project along River Road, a major arterial roadway in Tucson, Arizona. The use of a soil nail wall system precluded the need to relocate major components of the Altamira Apartments, a luxury apartment complex situated atop the bluff west of an access road (Campaña Drive) leading from River Road to the apartment complex. The impacted components included a large swimming pool, a clubhouse, and a two-story apartment building, all located close to the crest of the slope. Because of the high property values in the area, replacement costs of these components were prohibitive. In addition, the artificial sculpted-rock architectural facing appealed to a citizen's advisory group because of its aesthetics.

Soil nailing can be used with a wide variety of facades to meet architectural and structural needs of the design team and owner. Soil nailing generally consists of small diameter, reinforced steel elements, grouted in approximately 4 to 6 inch diameter sub horizontal boreholes. A reinforced shotcrete façade is generally applied for surficial stability. A rough gun finish is usually satisfactory for temporary support. For permanent walls, it may be desirable to smooth or sculpt the shotcrete façade, form a concrete wall directly against the shotcrete, or build a separate wall structurally connected to the soil nail wall. Exploring the wide variety of facades that can be used with soil nail walls can create many job opportunities for the design team and contractor.

Drilled shafts socketed into bedrock are a common foundation type for support of large and/or important structures in downtown Philadelphia. The bedrock beneath the city is the Wissahickon Formation, a mica schist bedrock encountered with various degrees of weathering. The interface between soil and rock is known to be transitional, varying significantly with depth, and is usually difficult to identify. Based on an extensive geotechnical investigation program, the properties of mica schist rock in the city of Philadelphia area are summarized. The side resistance values in the rock socket measured from O-cell test results for a recent project in the city of Philadelphia are presented. The side resistance values are then compared with measured rock properties, such as, the unconfined compressive strength, RQD, and elastic modulus.

Osterberg-cell or O-cell tests are an effective method for load testing drilled shaft foundations, and can identify the relative contributions of side resistance and end bearing. A series of O-cell tests was conducted for several production shafts socketed into mica schist in downtown Philadelphia. The bearing material is the Wissahickon Formation, which is a mica schist bedrock typically encountered with various degrees of weathering. This paper describes a finite element model developed to simulate the drilled shaft rock socket subject to axial loadings. The material parameters used in the analyses were calibrated based on the O-cell test data during the "bottom up" loading and supported by results from shaft instrumentation. The calibrated model is used to investigate the load distribution in the weathered rock socket and the contribution of end bearing, both when loaded from the bottom during the load test and under the service loading from the top.

A procedure that uses the structural damping concept for estimating the capacity of a pile based on the Statnamic pile load test results is proposed in this study. Although the interpreting procedure is similar to that of the commonly used UPM, however, displacement related soil damping is used instead of the velocity dependent damping. Hence, soil resistance is determined directly from the measured load-displacement curve. Three case studies are presented in this paper to study the validity and applicability of the present method. Comparison of predicted results with available test or analytical data shows that the proposed method accurately models the tested pile behavior.

This paper demonstrates the application of the strain wedge (SW) model to assess the response of laterally loaded isolated long piles, drilled shafts and pile groups in layered soil (sand and/or clay) and rock deposits. The basic goal of this paper is to illustrate the capabilities of the SW model versus other procedures and approaches. The SW model has been validated and verified through several comparison studies with model- and fall-scale lateral load tests. Several factors and features related to the problem of a laterally loaded isolated pile and pile group are covered by the SW model. For example, the nonlinear behavior of both soil and pile material, soil-pile interaction (i.e. the assessment of the p-y curves rather than the adoption of empirical ones), the potential of soil to liquefy, the interaction among neighboring piles in a pile group and the pile cap contribution are considered in SW model analysis. The SW model analyzes the response of laterally loaded piles based on pile properties (pile stiffness, cross-sectional shape, pile-head conditions, etc.) as well as soil properties. The SW model has the capability of assessing the response of a laterally 1 loaded pile group in layered soil based on more realistic assumptions of pile interaction as compared to techniques and procedures currently employed or proposed.

Results are presented of a field testing program for a full-scale, large diameter cast-in-drilled-hole (CIDH) shaft/column under large displacement cyclic lateral loading. The test shaft was extensively instrumented to enable high-precision section curvature measurements in addition to measurements of contact pressure at the soil-shaft interface around the shaft perimeter. Among the principal objectives of the testing was to characterize the soil-shaft interaction across a wide displacement range in order to gain insight into the adequacy of existing design guidelines (which are based principally on the testing of small diameter piles) for the large diameter shafts commonly used to support highway bridges. The component stresses of resistance and the effects of nonlinear soil resistance to relative displacements between the soil and shaft are presented.

A wide range of in situ techniques has been developed in the last two decades in Europe and Asia to assess the quality of deep mixed soil columns. These methods use either conventional or specially designed tools to penetrate into the hard columns (such as pushing, pulling, rotary, driven, or displacement methods); or use geophysical concepts (such as seismic, resistivity, and echo-pulse methods). The main objective of this paper is to present the results of an international survey conducted for the quality assessment of deep mixed columns. The objectives were (a) to identify the most commonly accepted field methods of quality assessment practiced in different parts of the world, and (b) to understand the operational problems occurred when the method was applied for deep mixing projects. The respondents of the survey had diverse backgrounds, which included engineers, academicians, researchers, and contractors. The summary of the international survey provided valuable insights for the selection of in situ techniques for the quality assessment of deep mixing projects.

This paper describes how electrical resistivity (ER) and time-domain reflectometry (TDR) were used to determine the electromagnetic (EM) properties, electrical resistivity (ρ) and apparent dielectric constant (K_a), of soil-cement mixtures. Laboratory tests simulating cement-mixed soil were performed on large-size specimens (286-mm diameter and 305-mm height) of different soil, cement, and water proportions at regular time intervals up to 56-days. Soil, cement, and water have measurably different EM properties, and as cement consumes water during hydration and bond formation continues during hardening the EM properties change over time. Water content and unconfined compressive strength (UCS) were also measured at 7-, 14-, 28-, and 56-days. For soil-cement samples K_a decreased and ρ increased with time. ρ was found to be directly related to strength gain. Increasing cement content increased strength but decreased electrical resistivity.

Construction of embankments on soft ground poses a challenge to the design engineer to address settlement and stability concerns. For this reason a wide range of technologies has been developed for support of embankment foundations on soft ground, including deep soil mixing. One barrier for implementation of these technologies is lack of engineering guides for feasibility study, preliminary evaluation, simplified analysis and design tools, quality assessment and monitoring of the constructed facility. This paper aims to presents several initiatives for developing engineering guides to address these deficiencies when deep mixing and geosynthetics is used for support of embankments. The initiatives include, synthesizing the-state-of-the practice in the US and overseas, developing design charts for geosynthetically reinforced embankments on deep mixed columns, evaluating in situ methods for quality assessment, and developing a simplified tool to handle uncertainties associated with interpretation of strength and stiffness of soil cement using reliability theory. This effort is expected to provide practitioners with engineering tools, advance the state of current practice, and enhance the user's confidence in applying deep mixing and geosynthetics system for embankment support.

The paper reports the results of a parametric study undertaken to investigate the influence of deep mixing (DM) of soil columns on the porewater pressure response in the vicinity of the treatment. The study utilized a two-dimensional effective stress program, TARA-2M. The predictive capability of TARA-2M was initially verified by using a well-documented centrifuge database generated as a part of the NSF funded study VELACS. The porewater pressure responses have been provided for two levels of excitation (a_max = 0.2g and 0.4g) and for two DM column spacing distances. Computed results show the extent of the influence of the treated columns in reducing the excess porewater pressures. The results are presented in normalized form such that the estimates of porewater pressures at interior locations can be made, if porewater pressure response is known in the free-field.

The process of jet grouting has become a worldwide system of ground treatment. Specialized equipment vendors abound, each focusing on a niche of the jet grouting market. Specialty contractors build their experience using certain equipment and procedures so that they may be better apt to understand the risks that they assume. This paper will compare the jet grouting systems available today, and bracket the parameters most often utilized. A discussion on the advantages and disadvantages of each system will be presented as well as how they may influence performance for a variety of applications. This evaluation should offer a guide for a better understanding of this often misunderstood technology.

The paper deals with the main features and the results of a field trial related to a jet grouting treatment in very soft peaty soil; for this soil the technical literature offers few reference examples in terms of operative parameters and treatment effectiveness: actual average diameter, compressive strength and deformability parameters of the treated soil. The trial field was instrumented to monitor the induced vertical and horizontal displacement, the excess pore pressure values and the dissipation velocities. The actual column diameters were evaluated by means of direct measurements of the top of the columns and by means of a cross holes technique. The test was carried out by Rodio S.p.A., one of the largest foundation contractor in Italy.

Located at the westerly end of Dana Point Harbor, the Ocean Institute annually educates over 78,000 children through "immersion" expeditions into the wonders of the marine environment. A long awaited expansion of the facilities was begun in early 2001, to create the Ocean Education Center. This new waterfront campus is a 3,066 m² working marine research station, intended to maximize student participation in the learning process. Remedial grading for construction of the campus expansion involved removal and recompaction of old fill soils, immediately inland of the adjacent seawall and revetment. Excavation procedures included a shoring wall for protection of the seawall during soil removals. A sudden breach in the shoring system during a high-tide event flooded the construction excavation with over 10,000 m³ of seawater. Local erosion during this event resulted in subsidence of the revetment and a voided condition in the vicinity of the breach, leaving an approximately 8-m section of the seawall foundation unsupported. Consequently, repair of the breach was essential for construction to proceed. The repair process involved application of four discrete grouting techniques. Macroscopic voids were filled with a bentonite/cement slurry grout in the immediate vicinity of the shoring wall. Limited-mobility displacement grouting was used to compensate for local soil loss and to supplement inbound support of the revetment. Gravel was then packed beneath the seawall behind a bulkhead, and permeated with a Type-III cement grout. Smaller voids beneath the seawall were grouted with a fly ash/cement mix. The water was then successfully pumped from the excavation, and construction of the campus was able to resume. The Institute's Ocean Education Center opened in October 2002.

The paper focuses on the role of jet grouting on tunnel support, although the influence of supplementary techniques is also considered. For this purpose, experience gained from two well documented case histories is presented. Reported observations and experimental data have been selected in order to help in the identification of proper design limit states. Jet grouting has proven to be quite effective, allowing tunnelling in very difficult conditions, but some failures have also been recorded. Failure mechanisms can be classified according to three different modes: excavation face failure, canopy tip failure, provisional lining failure. With regard to the control of settlements, jet grouting has proven to be very effective but some ground uplift can be temporarily induced by soil treatment.

The project involves the construction of a natural tunnel under Via Gramsci to connect the new high capacity railway line between Bologna and Florence with the Florence Railway Station located in the city centre. The ground involved belongs to the geological Formation of the Bacino di Firenze, consisting of silty sands and sandy silts with a varying content of clay and with lithic elements varying in size from the millimetric to centimetric. It is below the water table. Located between two stretches of artificial tunnel and diaphragms consisting of columns of ground reinforced by jet-grouting, the tunnel is approximately 50 m. in length and has an overburden of just 5 m. Excavation is performed according to "ADECO-RS" principles which consists of reinforcement of the face-core using fibreglass structural elements injected with expansive mortars and improvement of the ground around the tunnel using horizontal jet-grouting technology. A field test was carried out to fine tune the operating parameters of the ground improvement works. The results obtained are shown in the paper.

Grouting at the bottom of a pile may considerably increase the bearing capacity, reduce settlement, and improve the property of pile-soil working together, hence its wide application in recent years in China. This paper, based on a specific case of construction, explains the mechanism of how grouting improves the bearing capacity, the technical parameters of grouting, quality guarantee measures and common problems in grouting. It is proved through test piles that grouting technology is not only effective, but also economical and simple, therefore it is a worthwhile technology to consider.

When embankments are constructed over soft foundations, deep-seated slope stability often becomes one of the controlling factors in design. Deep mixing methods have been commonly used as an alternative to solve the deep-seated slope stability problem. Bishop's modified method is a commonly adopted approach for analyzing the slope stability of embankments on deep mixed foundations. Bishop's modified method assumed slopes fail along a circular slip surface and the soils along this slip surface provide shear resistance. However, experimental studies have showed that deep mixed columns under a combination of vertical and horizontal forces could fail due to shearing or bending. The possible failure modes depend on the combination of the forces, the strengths of soft soils and deep mixed columns, dimensions and arrangements of deep mixed columns. A numerical method was used in this study to evaluate the factors of safety varying with the strengths of deep mixed columns and their arrangements with three rows of columns having two different thickness. The numerical analysis indicated that the critical slip surface of the deep-seated slope failure was not circular when the deep mixed columns were used. The factors of safety obtained using the numerical method were compared with those using Bishop's modified method and Spencer's three-part wedge method. The comparisons indicated that Bishop's modified method yielded significantly higher factors of safety than the numerical method, especially when the deep mixed columns had higher strengths. The Spencer's three-part wedge method yielded lower factors of safety than the numerical method.

A design-build foundation system consisting of 6 and 8 ft. diameter soilcrete columns was constructed to support spread footings for a five level parking garage in Allentown, Pennsylvania. The soil mixing method was selected over stone columns/aggregate piers because it provided a more rigid foundation system, and would not create vertical drainage paths in the potentially karst terrain. The load on the supported footings varied between 200 and 2,200 kips. The design was subject to settlement criteria of 1.25 in. total movement and 0.75 in. differential movement. The soilcrete columns were installed through medium and stiff clay, bearing on dense sand or weathered limestone rock. A total of 120 columns were constructed below the parking structure foundations. Three soilcrete columns were core drilled using a 2 in. diameter barrel, with each achieving over 95% recovery. Twenty-eight day unconfined compressive strengths of the cores and wet-grab samples averaged 900 psi.

Deep mixing techniques for mass ground improvement are now widely accepted and are used most commonly for bearing capacity enhancement, liquefaction mitigation, and for slope stabilization. The employment of secant soil-cement columns, alternately with and without a steel profile inserted, is also well-known in the industry, the Central Artery & Tunnel Project ("Big Dig") in Boston being the most notable example of such an application here in the United States. However, the use of individual soil-cement columns for load-bearing purposes while less common is no less adaptable, either with steel reinforcement or without, and this paper will describe the particular merits of the patented Geo-Jet system of deep mixing for such an application including consideration of design issues, testing and installation. Case histories of vertically loaded soil-cement columns using the patented Geo-Jet system, including projects such as San Francisco International Airport, and the Millbrae BART Station and other projects in the Bay Area, will also be described.

A wide range of deep foundation systems has recently been developed for construction of embankments on soft soils. Controlled Modulus Columns (CMC) is one technique of ground modification, originally developed in France, for support of light structures such as highway and railway embankments. This paper presents the case history of a column supported embankment project in which 2193 CMC columns were installed up to a depth of 12.5 m to minimize settlement of an embankment. Main challenges were soft ground condition of the site, and the need for an accelerated construction technology for timely delivery of the project. Evaluation of various alternatives, design considerations, construction related issues and monitoring system are discussed in detail.

A residential foundation repair project is described. Poor construction of the original foundation, consisting of slab on grade and perimeter grade beams, resulted in damage in the form of settlement, cracking, misalignment of doors, and plumbing leaks. The initial remediation plan involved construction of underpinning piers. Pier installation beneath perimeter grade beams was accomplished, however it was discovered that interior slabs that were designed to be 6-inches thick were in fact only 2-inches thick and not properly reinforced. A 2-stage repair was used consisting of grout injection to increase the effective slab thickness followed by mudjacking to establish the original slab elevations. This process was highly successful and suggests an approach for addressing similar residential foundation repairs.

This paper presents the results of numerical analyses carried out with a program exclusively developed for simulating piled raft foundations. It was developed by Zhang and it extends the use of the finite layer method to the analysis of a general loading system applied to piled raft foundations. It allows the establishment of a coupled relationship between displacements, rotations, and external loads and it furnishes displacements, moments, shears and forces within the analyzed system. The paper explores the applicability of this program by using it to simulate the behavior of experimental field loading tests carried out at the University of Brasília (UnB) experimental site. At this site, Cunha and Sales carried out several vertical loading tests on a small scale isolated raft and piles, group of piles, and piled rafts. Zhang's program was adopted to back analyze this series of experimental results, furnishing preliminary geotechnical parameters for use in future designs with this or similar soils. The analyses also highlighted the fact that it is possible to numerically simulate the complex behavior of such mixed foundation systems founded on "non classical" materials such as the Brasília porous clay.

Increasing the bearing capacity of soils has been an important issue thousands of years ago till the time being. In 1960s the French Road Research Laboratory conducted an extensive study to evaluate the benefits of using reinforced soil as a construction technique. Nowadays, it is still an aim to increase the soil bearing capacity either through adding inclusions or through reinforcing sheets. The study aims to demonstrate the effects of embedment ratio and the length ratio of the reinforcing element on the bearing capacity of sand. About fifty plate-loading tests were conducted on steel square model footing of side dimension (B) equal to 100 mm. The effect of relative density of sand, the embedment ratio, and the length ratio of the reinforcing material were studied. It was revealed that the soil reinforcement might successfully increase the bearing capacity. Also it was found that the improvement in the bearing capacity of sand of lower relative density is more pronounced compared with higher relative density sand. The bearing capacity ratio (BCR) was found to be inversely proportional to the relative density of the sand. The most efficient length ratio (L/B) of the soil reinforcement was found to be 3.00, and the optimum embedment ratio (d/B) was found to be 0.30. Finally, the reinforced sand exhibited a failure mode that resembles typical punching-shear failure.

A survey was performed at two universities to gather information on undergraduate's perceptions of the geo-industry. The surveys were administered to students in a required soil mechanics course and in geotechnical elective courses at The University of Texas at Austin and Villanova University. These two universities — a large, public institution and a small, private institution — provided an interesting range of responses. Example questions include: What do you think geotechnical engineers do?; What is appealing about a career in the geo-industry?; and What is the highest degree you intend to seek?. Demographic information, such as the gender and GPA of the respondent, was also collected to provide a context for the survey data. Academics can use the results of the survey to improve their geotechnical course materials, and practitioners will find the results useful when recruiting students for summer internships and permanent employment after graduation.