Report of Preliminary Foundation Evaluation and Geotechnical

Report of Preliminary Foundation Evaluation and Geotechnical Review St. Croix River Bridge

Stillwater, MN

for

Minnesota DOT

by

Dan A. Brown, P.E., Ph.D. Dan Brown and Associates

Sequatchie, Tennessee

Feb. 27, 2007

St. Croix Bridge, MN Dan Brown and Associates 1

Report of Preliminary Foundation Evaluation and Geotechnical Review St. Croix River Bridge, Stillwater, MN

Introduction This report includes a review of the Mn/DOT preliminary subsurface investigation and geotechnical engineering design for the bridge foundations on the proposed St. Croix River Bridge near Stillwater, MN. The writer visited the site and DOT offices during October, 2005 and examined cores from the drilling program, which was underway at that time. The review includes all geotechnical information available to date, as well as reports from previous studies and load test information from nearby areas at the location of a prior (abandoned) alignment for the bridge. Conceptual structural design information and very preliminary foundation loads have been provided by Mr. Mirek Olmer of T.Y. Lin. The proposed bridge will be an unusual and visually striking structure known as an “extradosed” structure. Extradosed bridges have relatively short towers above the bridge with cables extending from the tower to the bridge surface, as shown in the conceptual images of one such proposed structure for the St. Croix bridge in Figure 1. The seven towers supporting the bridge will each include either two or three legs supported on a common foundation.

Figure 1 St. Croix Bridge Concepts

Foundation Concepts The generalized soil conditions across the site are illustrated on Figure 2. The rock formation which will comprise the bearing stratum is over 100 feet deep across much of the site and is overlain by a deep layer of very soft organic clay. The foundation is planned to consist of a group of drilled shaft foundations that will be drilled into a weak rock bearing stratum over 100 feet below the water surface. The schematic diagram shown on Figure 3 illustrates a 2 by 7 group of 8ft diameter shafts. The 44 ft by 160 ft pilecap connecting the towers and the drilled shafts will be constructed so that the top of the cap is around 15 feet below the water surface and thus will extend into the muck. The rock is generally composed of a weakly cemented sandstone. Preliminary indications suggest that the shafts will derive most of their axial capacity through side shear in the rock.


Figure 2 Generalized Subsurface Profile

Figure 3 Schematic Diagram of an Individual Pier Foundation

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Plan View of a Single Pier

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Detailed structural design has not be completed, but foundation loads based on the very preliminary structural design are expected to be dominated by vertical dead loads. Maximum service loads at the top of the cap are around 80,000 kips. Overturning moments on the cap may be on the order of 100,000 ft-kips, combined with shears of 2000 kips or so. For a group of 10 to 14 drilled shafts and including some additional load for the weight of the cap, individual drilled shaft axial loads are on the order of 6,000 to 10,000 kips per shaft and individual shaft lateral loads are around 150 to 200 kips per shaft. Geotechnical Conditions and Available Test Data The bearing formation for most of the shafts will consist of weakly cemented sandstones of the Franconia Formation. These rocks tend to be glauconitic and thinly bedded with layers of siltstone, mudstone, or shale. The cores sometimes appear to be very friable and easily broken after exposure, with some portions quickly breaking down to a sand-like material. Compression tests from cores have been recently completed on the current alignment (old borings from previous alignments are not included) and are summarized as a function of elevation on Figure 4. Note that the data from the borings at piers 6 and 7 are shown with a separate symbol, as these data are almost all above elevation 575 and are at higher elevations within the Franconia Formation than those cores for the piers in deeper water.

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Figure 4 Compression Tests on Rock Cores from All Current Borings


Strength data from the cores below elevation 575 (all of which are from the borings in areas of greater depth to rock at piers 2-5) show a noticeable trend of increasing strength with depth as illustrated in Figure 5.

y = -20.538Ln(x) + 679.31R2 = 0.6264

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Figure 5 Compression Tests on Rock Cores Below Elev. 575

These data suggest that the strength of the rock generally increases with depth, perhaps due to increasing in-situ confinement, reduced weathering with depth, or some combination of factors. Many of the cores were so severely weathered that the RQD was 0 and no strength tests could be performed. Glauconite is an iron rich variety of clay that can act as an intergranular cement in otherwise siliceous sandstone. Diaz et al (2002) found that glauconite tends to reduce the ultrasonic velocity (and thus, elastic modulus) of sandstones. Overlying the sandstone was a deep deposit of very soft organic silt below the mudline at elevation 650 feet and extending to the top of a sand formation at about elevation 590 to 605 in the deeper water at piers 2 through 4. The top of rock at these locations was around elevation 565. The organic silt is a cohesive material with high water contents and low undrained shear strengths of less than 200 psf (often less than 100 psf). The sand overlying the rock is likely decomposed sandstone, with standard penetration resistances often in excess of 50 b/f in the lower zones below elevation 590 and 20 or less at higher elevations. A typical profile for preliminary design is as illustrated on Figure 6.


Figure 6 Idealized Profile Near Piers 2 - 4

Additional subsurface information is available from a load testing program reported in 1996 by O’Neill and Majano (1996). This load test program included axial and lateral O-cell tests at a nearby location at a time when the bridge alignment differed from the current plan. The tests are in similar geologic conditions, but not at the current location of the bridge. The results of these tests provide some very useful information, but suffer from some limitations. A summary of some of the key points is outlined below.

• Based on the test results, maximum unit side shear resistance values for piers in areas of deeper rock in the river were recommended to be taken at 6.6 ksf within the upper 30 feet of the sandstone and 9 ksf at depths greater than 30 feet below the top of the sandstone.

• Maximum unit end bearing resistance values were suggested as 15.4 ksf at a depth 20 feet below the top of sandstone and 19.2 ksf at a depth 30 feet or more below the top of sandstone, provided that the base of the shaft can be cleaned and no weak zones are found within a zone at least 2 shaft diameters below the base of the shaft.

• The tests were performed at an “on-shore” location at which the bearing formation had a substantial thickness of overburden rock layers, similar to the conditions noted above for piers 6 and 7 but not representative of piers 2 through 5. The authors went to considerable effort to model the effects of overburden stresses in order to reliably project behavior at conditions more nearly representative of the deep water piers, but of course such analyses are subject to uncertainties in the assumptions about scaling the behavior of the rock formation to differing conditions.

v. soft organic silt

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• The tests were performed on a prototype 4 foot diameter socket, and thus scaling effects must be estimated to extrapolate prototype test results to production size foundations.

• The construction suffered from some delays during construction (15 to 17 days) and probable contamination of the base with sediment. As such, the base resistance measurements were meager and may not reliably indicate the performance of larger production shafts constructed under more favorable conditions.

• The shafts were drilled with a rock auger using plain water as a drilling fluid. It is likely that drilling with bentonite slurry or with tools such as core barrels or casing that could produce a smoother borehole could result in lower unit side shear values.

• Examination of the results of the lateral O-cell load tests on split sockets suggest that the extended period during which the shaft excavation was open may have contributed to opening of fractures within the rock so that the initial modulus of the rock was lower than might have been the case for a shorter period.

Preliminary Analyses of Foundation Performance Using the values of side shear and end bearing suggested above as an indication of the geotechnical ultimate limit, a typical foundation design might be as follows:

• Foundation for a single pier comprised of a 2 by 7 group of 8 foot diameter shafts

• Foundation subject to service loads of 112,000 kips +/- 140,000 kip-feet overturning equals approximately 8,400 kips per shaft maximum compression and a required ultimate resistance of 12,000 kips per shaft (Resistance Factor = 0.7).

• Axial resistance of 12,000 kips would require: o End bearing (>30’ below top of rock):

50 sq. ft area x 19 ksf = 950 kips o Side Shear:

Dense sand stratum between elev. 590 to 563 • Estimate avg side shear at 1.5 ksf • π (8) (27) sq. ft. x 1.5 ksf = 1,018 kips

2’ to 30’ below top of socket (elev. 563 to 535) • π (8) (28) sq. ft. x 6.6 ksf = 4,645 kips

30’ to 55’ below top of socket (elev. 535 to 510) • π (8) (25) sq. ft. x 9 ksf = 5,655 kips

o Total = 12,268 kips Thus, a hypothetical foundation for this condition would require shafts to extend 55 feet below the top of the sandstone, or to about elevation 510 feet, or 165 feet below the waterline elevation. The end bearing contributes less than 8% of the resistance, and the side shear in the rock socket contributes 84%.


• Foundation subject to lateral loads of 2000 kips equals approximately 160

kips per shaft maximum (allowing for some group effects). • Analyses of lateral response have been performed for a range of possible

soil and rock strength properties, for 8 foot diameter shafts constrained at the top by a rigid cap. Deflection and bending moment profiles are presented in Figure 7. The deflection profile shows 2 lines, the lesser values representing that of a shaft with a ¾ inch thick permanent steel casing installed to the top of rock and the higher deflection representing that of an uncased shaft. These computations include nonlinear bending stiffness for a shaft with approximately 1% reinforcement (48 #11 bars). The soils used for the results presented in Figure 7 include an undrained shear strength for the organic silt of 20 psf at the top, increasing to 140 psf at elevation 590.

Figure 7 Lateral Load Response, 8 ft. Dia. Shaft, 160 kip Shear

The analyses performed demonstrate the following points:

• An 8 foot diameter shaft is likely to represent a reasonable design for lateral loads of this magnitude

• The lateral deflections at the foundation level are mostly controlled by the shaft stiffness in flexure (which is strongly related to diameter) and the great depth to firm soil. The strength of the organic soils has a significant influence on response, but the strength of this soil is unlikely to be much different from the low values used in this analysis.

• The lateral response for these piers in the center of the bridge is not greatly affected by the lateral strength or stiffness of the rock. The

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stiffness of the sand layer above the rock has more influence than the rock itself, but the most significant factor is the depth to the top of this stratum.

• The use of a permanent steel liner for the shafts has significant benefit in terms of strength and stiffness of the shaft. Even if not considered for strength, the liner enhances the stiffness and reduces lateral deflections.

• The length of the socket into the rock will be controlled by axial rather than lateral considerations.

Foundation Alternatives Evaluation of alternative deep foundation sizes and types are discussed in this section, including the use of tip grouting to enhance capacity. Overview of Tip Grouting and Potential Use for St. Croix Bridge Because of the relatively low end bearing values obtained from the previous load test program and the presence of strong granular materials at the anticipated shaft base, tip grouting could be considered as a strong candidate for improving foundation performance at this site. Tip grouting involves the use of pressure grouting at the base of the shaft through a system of tubes incorporated into the rebar cage. Other than the small amount of plumbing used for the grouting operation, the construction of the shaft proceeds as normal. At any time after the concrete has been placed and has set, a grouting crew pressure grouts the base of the shaft using a neat cement grout to pressures of up to 1000 psi. Sometimes a base plate is used to aid in distribution of the grout across the base of the shaft, or the grouting can be performed through a series of tubes crossing the base (tube-a-manchette). A schematic diagram of the base grouting concept is provided on Figure 8. The use of tip grouting is beneficial in providing capacity enhancement as well as a proof test for each shaft. In granular soils such as the decomposed Franconia Sandstone, the increased confining pressure associated with the tip grouting can considerably increase the soil resistance of the bearing materials. The grout pressure also compensates for any stress relief resulting from the drilling operations as well as any loose residual material at the base of the shaft which may have been incompletely removed or knocked into the hole during placement of the rebar cage (as likely happened during the previous test pile program). Tip grouting will more reliably account for the contribution of the end bearing component of capacity, and the grouting process will pre-compress the shaft and allow the end bearing component to be developed at smaller displacements. Tip grouting of every shaft provides a direct measure of the axial resistance of each shaft. In much the same way as a bi-directional load test, the application of grout pressure across the base of the shaft mobilizes base resistance acting against the side shear. In fact, one of the limitations of the use of tip grouting is


the fact that the shaft must have adequate side resistance to counteract the base pressure or else the shaft is pushed upward. Because each shaft is “proof tested” using the tip grout pressure, a resistance factor of 0.7 provides a high degree of reliability with respect to axial load capacity. For quality assurance, a select few production shafts may be constructed as grout test shafts, with these shafts instrumented and monitored during the tip grouting for strain at the tip, top of shaft movement, and grout pressure and grout volume. All post grouted shafts are typically monitored for top of shaft movement, grout pressure and grout volume.

Figure 8 Schematic of Tip Grouting Concept

There are a couple of reasons why this project could benefit from the use of tip grouting:

(1) Shaft Size and Length: Because of the large loads on individual shafts at this site, the shaft diameters and lengths will be significant. Reductions in shaft lengths from will reduce construction risk and provide economy.

(2) Quality Assurance: The project owner should derive value from the enhanced quality assurance and reliability provided by the grouting of each shaft.

(3) Reliability and Reduced Risk from Bottom Cleaning: Because of the significant length and wet hole construction needed to complete these shafts, extensive measures to achieve bottom cleaning and inspection are time consuming and difficult. Tip grouting can compensate for imperfect


bottom cleaning and minimize risk during construction from questionable conditions at the shaft toe.

(4) Increased Design End Bearing: Because of questions regarding construction cleaning, displacements required to mobilize end bearing, etc., it is very common for designers to be justifiably conservative in assessing base resistance for design. The use of base grouting will allow greater end bearing to be utilized while simultaneously providing verification of end bearing in the field and pre-loading of the base resistance so that the end bearing is mobilized at small movements and therefore useable for design.

For the 8 ft diameter shafts considered earlier, it is anticipated that tip grouting could quite easily achieve a base pressure of 600 psi, or about 85 ksf. Using this value in lieu of the 19 ksf value cited previously would result in an ultimate end bearing of 4250 kips instead of the 950 kips used previously. This 3300 kip increase in effective maximum end bearing could result in a reduction in length of: 3300 kips / [(π)(8)(9ksf)] = 14.5 ft thus resulting in a shaft tip elevation of 524 instead of the 510 elevation computed previously. Besides the quality assurance issues, savings in length on shafts that are already quite long can be very cost effective from a constructability standpoint. The contractor’s drilling equipment need not reach as deeply and the reduced weight of the rebar cage can sometimes make a difference in the size of crane needed. Alternate Foundation Sizes and Types An evaluation of a foundation composed of larger numbers of smaller diameter shafts suggests that smaller diameter shafts might be more efficient in terms of axial load and might be somewhat more easy to construct. However, lateral loads (proportionally smaller than for the 8 foot shafts above, due to the greater numbers of shafts) would produce significantly larger deflections since the stiffness in flexure is roughly proportional to the 4th power of diameter. The depth to firm material is a major consideration for lateral loads. Likewise, driven pile foundations would suffer from a similar limitation due to lateral loads and the great depth to firm material. Groups of driven piles including some inclined or “battered” piles could be considered to increase lateral stiffness, but these are not likely to be very efficient for the magnitude of the loads for this bridge. Foundations could be constructed using fewer numbers of larger diameter shafts. This approach might be necessary if final design lateral loads prove significantly larger than those anticipated at this preliminary stage. It is also worth noting that the use of tip-grouted shafts can be more attractive for larger diameter shaft


since the end bearing of the larger area is used more efficiently. As an alternate to the 2 by 7 group of 8 foot diameter shafts discussed earlier, calculations suggest that a 10 foot diameter shaft with permanent casing would support almost double the lateral load supported by an 8 foot diameter shaft with similar deflections. For the preliminary loads described previously, the 2 by 7 group of 8 foot diameter shafts could be replaced by a 2 by 4 group of 10 foot diameter shafts if tip grouting were used and the shafts extended to the 510 elevation for the deeper water shafts.

Figure 9 Schematic Diagram of Foundation Using 10ft Diameter Shafts The larger diameter shafts can also be arranged to provide a smaller footprint for the foundation, as indicated in the sketch of Figure 9. At a center to center spacing of 30 feet (3 diameters) between shafts, this pile cap might be on the order of 50 ft by 110 ft compared to the 44 ft by 160 ft cap dimensions referenced previously for the 8 ft diameter shaft design. Including a 15 foot thick cap and base grouting for either case, the total volume of concrete for each design works out to be as indicated below. Note that permanent casing has been assumed, with a casing size 6 inches larger than the shaft diameter.

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Plan View of a Single Pier

Profile


• 2 by 7 by 8 ft group, tip at elev. 524: 3600 cu. yds. • 44’ x 160’ x 15’ cap: 3900 cu. yds. • Total for group with 8 ft shafts: 7500 cu. yds. • Steel casing, ¾ inch wall: 973,000 pounds

• 2 by 4 by 10 ft group, tip at elev. 510: 3500 cu. yds. • 50’ x 110’ x 15’ cap: 3100 cu. yds. • Total for group with 10 ft shafts: 6600 cu. yds. • Steel casing, 1 inch wall: 872,000 pounds

On the basis of quantities, it would seem that the use of 10 ft diameter shafts might be more efficient. However, economics may not favor larger shafts if the construction of these foundations drives potential contractors to utilize significantly larger equipment for drilling and lifting. Drilled Shaft Construction Issues Other than the normal difficulties associated with constructing large diameter drilled shaft foundations over water, there are several constructability issues specific to this project and geology.

• The experience with the earlier field test at a nearby location suggests that the contractor could have difficulty maintaining the stability of the hole, particularly in the sands above the Franconia sandstone.

• A permanent casing through the organic soils is strongly recommended. Besides the benefit in lateral stiffness for the structural response of the shaft to lateral loading, this permanent casing will avoid construction problems relating to squeezing of the very soft organic clays and minimize the risk of soil inclusions within the shaft due to this soft soil.

• The use of a bentonite drilling slurry might adversely affect the side shear resistance in the sandstone, and is best avoided. The authors of the previous load test study advised against the use of bentonite slurry in this formation, a recommendation with which the writer concurs.

• The use of slurry can be avoided if casing can be installed through the overlying sand formations to the top of the sandstone. It is likely that the sandstone can be drilled using only water. However, the installation of casing through this overlying sand in advance of drilling could be very difficult using conventional vibro-hammer driven steel pipe because of the high relative density (as indicated by the standard penetration test resistance values).

• Bentonite slurry could be used inside the permanent casing to advance through the sand, at which point a temporary casing could be installed through the slurry to the top of the sandstone and the bentonite inside replaced with water. This system is somewhat complicated by the use of two casings. During concrete placement operations there will be the potential for bentonite to be trapped in the concrete during removal of the


temporary casing, and it is imperative that the concrete mix be designed with sufficient retarding admixture so that workability is maintained until removal of the temporary casing (e.g., Brown, 2004). Any delays could result in the loss of the temporary casing inside the permanent liner. A schematic of this approach is illustrated on Figure 10.

Figure 10 Schematic Diagram of Temporary inside Permanent Casing

• An oscillator-installed or rotator-installed temporary segmental casing might be the most effective means of ensuring that casing can be installed through the sand to the top of the sandstone in advance of the hole. Thus, there would only be water in the hole, not bentonite, and an oversized, bentonite-filled hole would not be present through the sand overlying the sandstone. Figure 11 provides an example of casing installed using the Leffer rotator system from the recent Benetia-Martinez bridge project in California (photo courtesy of Malcolm Drilling). An example of the cutting shoe used at the base of the segmental casing is shown in Figure 12 (photo by author, taken at Bauer Machinenworks in Germany). This type of system is expensive to mobilize and set up on the job, but provides a very reliable and effective means of installing a cased hole without drilling slurry.

Organic Clay

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Figure 11 Segmental Casing Installed Using Rotator System

Figure 12 Segmental Casing Cutting Shoe


• To drill through through the overlying sand using water alone without casing or drilling slurry would be risky from the standpoint of hole sidewall stability. This approach might be possible, if casing were elevated to achieve significant head of water inside the borehole (in excess of the water head within the sand). To drill through this sand using only water in an uncased borehole, the casing would likely need to be elevated to a height of around 20 feet or more above the level of the St. Croix River, and the water level inside the casing would need constant maintenance to ensure that the excess head inside the hole was not compromised. The viability of this approach depends on the permeability of the sand. If sidewall sloughing were to occur, the casing could be undermined and movement of the casing could ensue.

Figure 13 Top Drive Reverse Circulation Drilling System

• In the author’s opinion, the use of an uncased hole without slurry through

the sand overlying the Franconia sandstone is likely only to be attractive for a contractor using a reverse circulation (RC) drilling system, as shown on Figure 13. This system works much like a tunnel boring machine acting in the vertical direction, and removes the excavated material through a circulating water system inside the drill pipe. The RC drilling system operates as a top-drive system mounted atop the casing. The drilling fluid enters the top of the casing via a return line, and the fluid with

Cutter head


cuttings exits the top of the drill string through a swivel head and then through a conductor pipe to the spoil barge. This system has been used on a few large bridge projects, including a couple in California, the Central Artery Project in Boston, and a bridge on I-95 in Georgia that was founded on 8 foot diameter shafts terminating in a dense sand layer about 180 feet deep. The photo in Figure 13 was taken by the author at the Walter F. George Dam in Alabama, where the contractor was installing a cutoff wall using a Wirth RC drilling system. The rig is mounted atop the casing in the background, while a cutter head is shown on the deck in the foreground. The Wirth system is normally used with a head of at least 30 feet above the surrounding water.

• Conventional drilling with polymer slurry might be effectively used to advance the hole for the entire distance below the permanent casing without resorting to temporary casing above the sandstone. Polymer drilling slurries can have difficulties in removal of fine grained sands and silts from the fluid column prior to concrete placement. However, the polymer itself is not likely to have any adverse effect on the load transfer through side shear in either the sand or the sandstone, and the addition of polymer to the water will prevent fluid loss from the hole and promote sidewall stability. The photos in Figure 14 are from the Cape Fear Bridge in Wilmington, NC where polymer slurry was used to drill several hundred shafts into a dense silty sand (the Pee Dee Formation).

Figure 14 Polymer Drilling in Dense Silty Sands


Comparative load tests performed at the Cape Fear site demonstrated that the shaft installed using polymer drilling fluid had substantially greater capacity than an identical shaft installed using bentonite (Brown, et al, 2002). Recommendations for Additional Field Testing A site specific design-phase field testing program is recommended to address foundation related design and construction issues. Specifically, an additional field test program should:

1. Include an axial load test shaft at a location similar to piers 2 through 5 where the Franconia sandstone does not have a significant overburden. The side shearing resistance in this sandstone is the most important factor affected the design of the foundations.

2. Evaluate the ability to install shafts through the sand overlying the Franconia sandstone and into the Franconia, preferably using polymer drilling fluid. Construction of production shafts can have a significant effect on the subsequent performance.

3. Evaluate the axial resistance in side shear and end bearing for shafts with a tip elevation of around 510 ft. Tip grouting is recommended for the base of the shaft. In order to evaluate the effectiveness and relative benefit of tip grouting, it might be prudent to install two prototype shafts, one with and one without tip grouting.

4. Prototype test shafts should be at least 6 feet in diameter. 5. The lateral response of the shafts is most significantly affected by the

lateral response of the deep organic clay stratum. After completion of the axial load testing, test shafts should be subjected to lateral loading at the top to better evaluate the lateral response of this soil to a large diameter shaft. The cost for lateral testing after completion of axial test should be very modest, and could easily be accomplished using the lateral statnamic device. The existing lateral O-cell data from the previous tests in the sandstone should be sufficient for design, as the foundations will not be particularly sensitive to the stiffness of this formation and the length of the shafts will be controlled by axial loading.

The benefits to the project of a design-phase testing program are that uncertainties related to construction and design values can be minimized and thus substantial cost savings may be realized. Cost savings are derived not only from improved designs, but from elimination of contingencies to project bidders and possible avoidance of future claims due to unanticipated conditions. Additional testing could be postponed until the beginning of construction, but by then the contractor has already mobilized equipment based on an assumed method of construction and changes are not so easily made.


Summary This report has provided an examination of the foundation design and construction issue relevant to the proposed St. Croix River Bridge.

• The foundations are likely to include groups of 8 to 14 drilled shafts, 8 to 10 ft diameter, and socketed around 50 feet into the Franconia Sandstone Formation.

• The most significant factors affecting the design are the magnitude of the side shear and end bearing in this relatively weakly cemented sandstone. The sandstone is highly variable in its strength characteristics, apparently due to weathering and the presence of glauconite or other fine grained materials, but generally appears to increase in strength with depth.

• The performance of drilled shafts founded into this sandstone can be significantly affected by construction, particularly the use of drilling slurry.

• Construction of the shafts through the overlying dense sands and into the sandstone may involve the use of casing and/or polymer drilling fluids (which are not considered to be adverse to side shear in the sandstone).

• Permanent casing through the soft organic soils is recommended both as a construction expedient and as a means of structurally enhancing the strength and stiffness of the drilled shafts in flexure.

• A design-phase load test program is recommended to address issues relating to both design parameters and construction methods.

References Brown, D.A., 2004. “Zen and the Art of Drilled Shaft Construction: The Pursuit of Quality” Invited keynote lecture and paper, Geotechnical Special Publication No. 124, ASCE, pp. 19-33. Geo-Institute International Conference on Drilled Foundations, Orlando. Brown, D. A., Muchard, M., and Khouri, B., 2002. “The Effect of Drilling Fluid on Axial Capacity, Cape Fear River, NC,” Proc. of the Deep Foundations Inst. 27th Annual Meeting, San Diego. Diaz, E., M. Prasad, M. Gutierrez, J. Dvorkin (2002). “Effect of Glauconite on the Elastic Properties, Porosity, and Permeability of Reservoirs Rocks,” AAPG Annual Meeting, Houston, TX O’Neill, M. and R. Majano, (1996). “Analysis of Axial and Lateral Drilled Shaft Socket Load Tests and Axial Pile Load Tests for Foundation for T. H. 36 Bridge over the St. Croix River, Stillwater, Minnesota,” report to the Minnesota Dept. of Transportation, 37 pages.

Documents

Report of Preliminary Foundation Evaluation and Geotechnical