Subsurface_Exploration.pdf

Projects\Deliverables\J017065.09 CAR2015 Museum R1.docm

SUBSURFACE EXPLORATION

CITY ARCH RIVER 2015

JEFFERSON NATIONAL EXPANSION MEMORIAL

ST. LOUIS, MISSOURI

Prepared for:

CITY ARCH RIVER 2015 FOUNDATION

St. Louis, Missouri

Prepared by:

GEOTECHNOLOGY, INC.

St. Louis, Missouri

Geotechnology, Inc. Project No. J017065.09

April 26, 2013

J017065.09

CITY ARCH RIVER 2015

TABLE OF CONTENTS

Page

I. EXECUTIVE SUMMARY

II. PROJECT DATA

Authorization Purpose and Scope of Services Project Description Site Description Previous Explorations

III. FIELD EXPLORATION

Geotechnical Exploration Shear-Wave Velocity Survey Soil Nutrient Borings Surveying

IV. SUBSURFACE CONDITIONS

Geology Stratigraphy Groundwater

V. DESIGN RECOMMENDATIONS

Temporary Excavations Site Grading Seismicity Foundations on Rock Shallow Foundations Floor Slabs Soil Lateral Load Subsurface Drainage Slopes

VI. RECOMMENDED ADDITIONAL SERVICES

VII. LIMITATIONS OF REPORT

TABLE OF CONTENTS

-Continued-

ILLUSTRATIONS

Plate Site Location and Topography Plan of Site and Boring Locations Minimum Apparent Lateral Earth Pressure Diagram for Braced Retention Systems Below-Grade Wall Schematic Drainage Detail

APPENDICES

Appendix Important Information About Your Geotechnical Engineering Report ........................... A Logs of Geotechnical Borings ............................................................................................ B Boring Log: Terms and Symbols Rock Core Descriptions Rock Core Photographs ...................................................................................................... C Logs and Photographs of Soil Nutrient Borings ................................................................ D Soil Nutrient and Groundwater Nutrient Analytical Results ............................................ E Grain Size Distributions ...................................................................................................... F

SECTION I - EXECUTIVE SUMMARY

The executive summary is provided solely for the purposes of overview, and a number of details are omitted, any one of which could be crucial to the proper application of this report.

Any party who relies on this report must read the full report.

The project includes design and construction of a museum expansion with a new entrance on the west facing the city, new ramps to the museum on the east from the Arch, ramps down to Leonor K. Sullivan Boulevard, and assorted regrading of the Arch grounds, lakes including retaining walls, and Luther Ely Smith Square.

The stratigraphy consists generally of cohesive soil fill with gravel, brick, concrete, and limestone rubble, underlain by silty clay and silt soils with clay and fine-grained sand layers, underlain in turn by limestone bedrock. The fill extends to approximate depths below ground surface of 6 to 32 feet. The depth to rock varies from approximately 20 to 49 feet. Groundwater was observed in three borings at approximate depths of 18 to 47 feet.

Recommendations for temporary slopes and shoring are provided to support excavations as deep as 25 feet for the proposed museum expansion.

Bedrock occurs at relatively shallow depths in the east and south portions of the museum. Hard rock excavation should be anticipated during excavation for the proposed museum expansion. Line drilling and splitting or chipping with a hydraulic hoe-ram could be required to remove competent limestone.

The field and laboratory data indicate that the existing fill is uncontrolled and includes layers of rubble. The fill should therefore be entirely removed and replaced with compacted, well-graded crushed rock below the proposed museum expansion and any other buildings. The fill should also be partially removed and replaced below pavements, low retaining walls, and other lightly-loaded structures.

The proposed museum expansion can be supported on drilled piers bearing in competent limestone bedrock. Spread footings bearing on rock can be used in the eastern part of the structure where the rock is relatively shallow and the main

CAR 2015 Foundation J017065.09 level of the museum is at El 424.5. Recommendations for design and construction of foundations bearing on rock are provided herein.

Retaining walls and miscellaneous, lightly loaded structures can be supported on strip and spread footings proportioned for net allowable bearing pressures of 1,500 and 2,000 pounds per square foot, respectively, provided the footings bear on stiff, natural soil or remediated fill.

Seismic parameters are provided in accordance with the International Building

Code, 2009 Edition and City of St. Louis Ordinance 68788. A multi-channel analysis of surface waves (MASW) geophysical shear-wave velocity survey conducted in the area of the proposed museum expansion determined the soil profile to be Seismic Site Class C, Very Dense Soil and Soft Rock Profile.

Nutrient analyses were performed on 47 soil and two groundwater samples from the Arch grounds. Grain size distributions were also performed on the soil samples.

SECTION II - PROJECT DATA

AUTHORIZATION

The services documented in this report are provided in general accordance with the terms, conditions, and scope of services described in Geotechnology’s authorized, revised Proposal No. P017065.09 dated December 13, 2012.

PURPOSE AND SCOPE OF SERVICES

The purpose of our services was to develop recommendations for geotechnical aspects of the design and construction of the project as defined in the Scope of Services of the referenced proposal. Briefly, our services consisted of site reconnaissance, drilling 30 geotechnical borings, three temporary piezometers, seventeen soil nutrient borings, geotechnical laboratory testing, soil and groundwater nutrient testing, engineering analyses, and preparation of this report. Important information prepared by The Association of Engineering Firms Practicing in the Geosciences (ASFE) for studies of this type is presented in Appendix A for your review.

PROJECT DESCRIPTION

The City Arch River 2015 project includes redevelopment of the Jefferson National Expansion Memorial (JNEM), namely the Arch grounds and Luther Ely Smith Square to the west. The goal of the redevelopment is to connect the Arch grounds with the City of St. Louis by making inviting entrances that are unobstructed by the surrounding highways and by building new attractions to draw people into the area. The project includes the following elements:

New entrance and underground structure connecting to the existing museum, Ramps down to Leonor K. Sullivan Boulevard, Ramps down to the museum from the Arch, Miscellaneous retaining walls, Underground water storage tanks in Luther Ely Smith Square, Soil and groundwater nutrient quality parameters for the Arch grounds.

The museum expansion will include three levels: an entry level at El 447.51, mezzanine at El 437, and the main level at El 424.5.

SITE DESCRIPTION

The site boundaries and general topography of the area from the U.S.G.S. map of the vicinity are shown on Plate 1. The Gateway Arch is situated on a bluff about 30 feet above the Mississippi River. East of the Arch, the terrain drops steeply to the river landing; the slope is covered by the Grand Staircase in front of the Arch, grass lawn north and south of the staircase, and concrete flood walls at the north and south ends of the park. West of the Arch, the ground slopes downward towards a north-south-trending valley that includes Memorial Drive. The area west of the Arch includes two lakes/reflecting pools, one north and one south of the Arch. A parking garage and maintenance building are located at the north and south ends of the park, respectively.

The Arch grounds consist mostly of lawns with trees planted along several walkways, particularly those north and south of the Arch legs. The Terminal Railroad passes through a tunnel under the grand staircase and slope east of the Arch. Luther Ely Smith Square is covered with concrete walks with intervening lawn areas.

PREVIOUS EXPLORATIONS

Geotechnology recently completed geotechnical explorations for the Park Over-the-Highway2 and Walnut Street Bridge3 projects adjacent to the Arch grounds.

Geotechnology also conducted a geotechnical exploration for the Arch Grand Staircase4.

1 Elevations used herein are in units of feet and referenced to mean sea level (msl) datum.

2 Subsurface Exploration, Park over the Highway, St. Louis, Missouri, prepared for Crawford, Murphy & Tilly, Inc., Geotechnology, Inc., Report No. J019943.01 dated January 9, 2013.

3 Subsurface Exploration, Walnut Street Bridge Replacement over I-70, St. Louis, Missouri, prepared for Crawford, Murphy & Tilly, Geotechnology, Inc., Report No. J019943.01 dated January 9, 2013.

4 Subsurface Exploration, Proposed Gateway Arch Grand Staircase, Jefferson National Expansion Memorial, St. Louis, Missouri, prepared for HNTB Corporation, Geotechnology, Inc., Report No. 0663401.2111 dated August 30, 2002.

Additional sources of subsurface data are listed in the Geotechnical Desk Study5 prepared by Geotechnology for CAR 2015 Foundation.

SECTION III - FIELD EXPLORATION

GEOTECHNICAL EXPLORATION

Borings. Twenty-six (26) geotechnical borings, designated as Borings 1.1a through 1.6a, 3.1a through 3.12a, and 5.1a through 5.8a, were drilled at approximately the locations shown on Plate 2. The borings were drilled using a track-mounted CME 55 rotary drill rig equipped with hollow stem augers. Borings 3.1a through 3.8a were drilled to auger or split-spoon sampler refusal at depths of 20 to 49 feet. Four of these borings were advanced 5.5 to 10 feet into bedrock using NQ rock coring techniques. The remaining borings were terminated at pre-determined depths of 20 to 30 feet. However, auger refusal in rubble fill occurred at depths of 5 and 9.5 feet in Borings 1.3a and 5.5a, respectively. Hard drilling through the fill also occurred in several other borings. Standard Penetration Tests (SPT's) were performed using an automatic hammer. Split-spoon and relatively undisturbed Shelby tube samples were obtained at the depths indicated on the boring logs presented in Appendix B. Descriptions of the rock cores are provided on the boring logs. An explanation of the terms and symbols used on the boring logs and rock core descriptions are also provided in Appendix B. Photographs of the rock cores are presented in Appendix C.

Four geotechnical borings, designated as Borings 7.1a through 7.4a, were drilled using a hand auger to refusal at depths of 1.5 to 2.5 feet. Grab samples and shear vane tests were performed at the approximate depths indicated on the boring logs presented in Appendix B.

A geologist from Geotechnology provided technical direction during field exploration, observed drilling and sampling, assisted in obtaining samples, and prepared descriptive logs of the material encountered. The boring logs represent conditions observed at the time of exploration, and have been edited to incorporate results of the laboratory tests.

Unless noted on the boring logs, the lines designating the changes between various strata represent approximate boundaries. The transition between materials could be gradual or could occur between recovered samples. The stratification given on the boring logs, or described herein, is for use by Geotechnology in its analyses and should not be used as the basis of design or construction cost estimates without realizing that there can be variation from that shown or described.

5 Geotechnical Desk Study, The City+The Arch+The River 2015, Jefferson National Expansion Memorial, St. Louis, Missouri, prepared for The CAR Foundation by Geotechnology, Inc., Report No. J017065.01 dated February 16, 2011.

The boring logs and related information depict subsurface conditions only at the specific locations and times where sampling was conducted. The passage of time could result in changes in conditions, interpreted to exist, at or between the locations where sampling was conducted.

Laboratory Testing. Laboratory testing was performed on the soil samples to estimate pertinent engineering and index properties. Moisture contents were determined for cohesive soil samples, and Atterberg limits tests were accomplished on selected samples. Unconfined compression tests were performed on select Shelby tube samples. Results of the laboratory tests are presented on the boring logs.

SHEAR-WAVE VELOCITY SURVEY

Multi-channel analysis of surface waves (MASW) is a surface geophysical shear-wave velocity survey method used to calculate the average shear-wave velocity profile to a depth of approximately 100 feet (Vs100). This information can be used to assign a Seismic Site Class per Section 1613 of the 2009 International Building Code (IBC 2009). MASW is performed by recording and analyzing seismic surface waves (predominantly fundamental-mode Rayleigh waves) propagating horizontally along the ground surface. The dispersion of the propagating waves is measured directly from an impact source to an array of closely spaced geophones. A one-dimensional shear-wave velocity model is generated from the surface wave phase velocities for each impact source location.

On March 8, 2013, Geotechnology conducted the MASW survey at the location of the proposed museum expansion. The survey line location is presented on Plate 2. The MASW survey line was approximately 115 feet in length and consisted of 24 geophones spaced 5 feet apart in the north-south direction. A sledgehammer was used to generate the surface wave energy during the survey.

The MASW data were processed and modeled using Surfseis MASW software (Kansas

Geological Survey). Geotechnology calculated the seismic site class below the following reference elevations: the existing ground surface (El 465); the western entry-level portion of the proposed museum (El 447.5); and the eastern portion or main level of the museum (El 424.5).

Based on the processed MASW data, the following average shear-wave velocities were calculate for the upper 100 feet of the referenced elevations:

Reference Location Reference

Elevation (ft msl) Shear-Wave

Velocity (ft/sec) Seismic

Site Class Existing

Ground Surface 465 1,392 C

Western, Entry-Level Floor of the Museum

447.5 1,561 C

Eastern, Main Level Floor of the Museum

424.5 2,259 C

SOIL NUTRIENT BORINGS

Geoprobe sampling with standard geoprobe acetate liners (24- and 48-inch long by 1.625-inch diameter) were performed to depths 6 feet or refusal at 11 locations. Six additional locations were sampled using a hand auger. Boring logs and photographs of the recovered soil samples are presented in Appendix D.

Soil samples for nutrient analysis were collected in each boring at typical depths of 0 to

6 inches, 6 to 12 inches, and 12 to 24 inches and analyzed by Midwest Testing Laboratories for nitrate-nitrite, potassium, calcium, magnesium, total nitrogen, ammonium nitrogen, total phosphorus, and sodium. Analytical results are presented in Appendix E. Geotechnology performed a washed sieve analysis on each sample; grain size distributions are presented in Appendix F.

SURVEYING

The geotechnical and soil nutrient boring locations were surveyed and staked in the field by the project surveyor, EDSI, who determined ground surface elevations. Some borings were offset from the staked location to avoid tree limbs or below-grade obstructions and utilities.

Locations and elevations of these borings are therefore approximate.

SECTION IV - SUBSURFACE CONDITIONS

GEOLOGY

Bedrock at the site is comprised of the St. Louis Limestone and Salem Formation of the Meramecian Series of the Mississippian System. The St. Louis Limestone is grayish-white to gray, micritic to fine-grained, thick bedded to massive limestone containing blue and bluish-gray shale seams and chert. The Salem Formation is bluish-gray to white, argillaceous, oolitic limestone. The St. Louis Limestone grades gradually into the underlying Salem Formation. The bedrock in the St. Louis area dips slightly to the east-northeast, influenced by the Ozark Dome to the southwest and the Illinois Basin to the east.

STRATIGRAPHY

The stratigraphy consists generally of cohesive soil fill with gravel, brick, concrete, and limestone rubble, underlain by silty clay and silt soils with clay and fine-grained sand layers, underlain in turn by limestone bedrock. The fill extends to approximate depths of 6 to 13 feet in borings drilled at the Luther Ely Smith Square and 14 to 32 feet within the footprint of the proposed museum expansion. The depth to rock, based on auger refusal depths and recovered samples, varies from approximately 20 to 49 feet.

Fill. Existing fill is comprised of silty clay and clay with variable amounts of sand, gravel, cinders, brick, concrete, and limestone rubble. The fill is low plasticity based on Atterberg limits test results. Dry unit weight determinations of 105 to 112 pounds per cubic foot (pcf) were measured from Shelby tube samples of the fill.

Silty Clay and Silt Soils. The underlying silty clay and silt soils are generally very soft to medium stiff in consistency and have low plasticity based on Atterberg limits test results. The soils have shear strengths of 840 to 1,300 pounds per square foot (psf) based on unconfined and UU compressive strength tests. Dry unit weight determinations of 94 to 102 pcf were measured from Shelby tube samples of the soils.

Sand Layers. Layers of silty sand, clayey sand, and fine sand occur in Borings 3.3a, 3.5a, and 3.7a. The sand layers are loose to medium dense based on SPT N-values. Washed sieve analysis results on select sand samples measured 46 and 47 percent passing the No. 200 sieve.

Bedrock. Auger refusal on apparent bedrock occurs at approximate depths of 20 to

49 feet in Borings 3.1a through 3.8a. Bedrock was cored in Borings 3.3a through 3.6a. The bedrock consists generally of hard to very hard, gray, very finely to finely crystalline limestone.

The limestone is thin- to medium-bedded and highly to slightly weathered. Bedrock core samples had recoveries of 86 to 100 percent and rock quality designation (RQD)6 values of 0 to 73 percent.

GROUNDWATER

Groundwater was observed during drilling in Boring 5.8a at an approximate depth of

18.5 feet. Groundwater was not observed during drilling in the other borings. Groundwater levels might not have stabilized before backfilling or beginning rock coring, which introduces water into the borehole and masks the groundwater level. Consequently, the indicated or lack of observed groundwater levels in a particular boring might not represent present or future levels. Groundwater levels could vary significantly over time due to local precipitation, the Mississippi River stage or other factors not evident at the time of exploration.

Piezometers. Temporary piezometers were installed in Borings 3.2a, 3.6a, and 5.7a to measure groundwater levels and collect groundwater samples. Groundwater depths of 47.2 and

23.4 feet were measured in the piezometers installed in Borings 3.6a and 5.7a, respectively. The piezometer in Boring B-3.2a was dry. Groundwater samples from Borings 3.6a and 5.7a were analyzed by Midwest Testing Laboratories for total phosphorus, soluble reactive phosphorus, total kjeldal nitrogen (TKN), nitrate plus nitrite, and total ammonia (ammonia plus ammonium).

Analysis results are presented in Appendix E.

6 Rock quality designation is the ratio of the sum of the pieces of core measuring 4 inches or longer to the total length of the cored interval, expressed as a percentage.

SECTION V - DESIGN CONSIDERATIONS AND RECOMMENDATIONS

Geotechnical features that could influence site development include the condition of existing fill, the presence of expansive soils or soft soils, and the depth and quality of bedrock in the area of the proposed museum expansion. Discussions of site development and foundation systems are presented herein. Geotechnology should be provided grading and foundation plans for review to verify that recommendations have been correctly implemented. The client should recognize that if the building loads or locations vary from those stated herein, our recommendations could require modifications, and/or additional field exploration and related analysis could be required.

The existing fill is generally 15 to 30 feet deep in the borings. The field and laboratory data indicate that the fill is uncontrolled and includes layers of rubble, and should be remediated. Much of the fill will be removed during excavation of the museum expansion. However, any fill that remains presents a risk of detrimental settlement to the building and should, therefore, be entirely removed and replaced with compacted fill materials. The fill can be reused if the rubble is processed and any deleterious and compressible materials such as wood and organics removed and discarded. For low retaining walls and other lightly-loaded structures, partial depth remediation and ground improvement options are provided herein.

High plasticity clay was not generally observed in the borings, except for an occasional sample of existing fill and a thin layer above the bedrock. High plasticity clay soil observed in the floor of the excavation for the museum expansion could result in heaving and distress of the floor slab. Therefore, the floor slab subgrade of the museum expansion should be checked for the presence of high plasticity clay during construction. If observed, it should be entirely removed and replaced with compacted, well-graded crushed rock.

TEMPORARY EXCAVATIONS

Temporary excavation slopes and retention systems must be consistent with OSHA Health and Safety Standards for Excavations, 29 CFR Part 1926, or successor regulations. The soil materials encountered during excavations for the proposed project are anticipated to consist generally of silty clay and rubble fill underlain by silty clay and silt natural soils. For excavations less than 20 feet deep, the OSHA classification for the existing fill and natural soils can be considered as Type C. OSHA guidelines provide for temporary slopes in Type C soil to be constructed at one vertical on 1.5 horizontal (1V:1.5H) or flatter. Sloping, benching or shoring for excavations greater than 20 feet deep must be designed by a registered professional engineer.

Temporary shoring could be required to protect existing buildings, drives, and below-grade utilities. Methods of excavation support include timber lagging with internal bracing, steel sheet piles, and soldier piles and lagging, possibly anchored with tie-backs socketed into rock. Alternatively, systems that combine temporary and permanent retention such as secant pier walls or diaphragm (slurry) walls can be considered. Retention systems must be designed to resist anticipated lateral earth pressures plus any surcharge. Design of temporary retention systems must incorporate, as a minimum, lateral pressures based on the earth pressure distribution shown on Plate 3. Design of permanent retention systems must resist larger, at-rest earth pressures presented in the subsequent subsection, “Soil Lateral Loads.” Permanent systems must also resist hydrostatic pressures unless drainage is incorporated into the wall construction.

Temporary slopes left exposed more than 24 hours could undergo sloughing and result in an unstable situation. The contractor should evaluate stability and failure consequences before open cut slopes are made. If the slope is expected to remain open for an extended time, an impermeable membrane could be considered as a means to reduce the potential for slope degradation and instability.

It is important to note that soils encountered in the construction excavations could vary across the site and that even if the OSHA criteria are used, there is a potential for slope failure. If different subsurface conditions are encountered at the time of construction, Geotechnology recommends that it be contacted immediately to evaluate the conditions encountered.

SITE GRADING

Site Preparation. All cut areas and areas to receive fill and backfill should be stripped of topsoil, soft soil, rubble fill, and other deleterious materials. Topsoil can be stockpiled for later use during landscaping or removed from the site. Existing fill materials should be entirely removed and replaced from within and to a 5-foot horizontal distance beyond the footprint of the proposed museum expansion and any other buildings. Existing fill should also be removed to a depth of 2 feet below pavement subgrades and two times the footing width below low retaining walls and other lightly loaded structures. The overexcavations can be backfilled with well-graded crushed rock compacted to the density specified in the subsequent Compaction Summary.

Partial removal and replacement includes a risk of detrimental settlement that must be accepted by the client as balance for reduced construction costs.

The exposed subgrade should be proofrolled. Any soft soil or yielding areas should be excavated and backfilled with soil or crushed rock compacted to the density specified in the subsequent Compaction Summary. Soft subgrade conditions within the deeper fill and underlying soils could require a crushed rock and geogrid mat to support construction equipment.

Rock Removal. Bedrock elevations vary widely within the proposed museum expansion footprint. Bedrock occurs at relatively shallow depths (20 to 22 feet) in the east and south part of the proposed museum expansion. Bedrock is much deeper (36 to 49 feet) in other areas. These depths are based on drill rig auger refusal. Weathered rock, rock pinnacles, or boulders could be encountered at higher elevations. Hard rock excavation should be anticipated during excavation for the proposed museum expansion. Line drilling and splitting or chipping with a hydraulic hoe-ram could be required to remove competent limestone. Blasting would be more effective at removing the rock, but is not expected to be implemented due to the proximity of the existing museum.

Suitable Fill Materials. Fill materials should consist of low plasticity, cohesive soils or well-graded granular materials. Acceptable fill soils include non-organic materials designated CL, ML, CL-ML, SP, SW, GP, and GW by ASTM D 2487. Existing fill can be reused provided that compressible or other deleterious materials are removed. Oversized rubble and pavement should be processed to a maximum particle size of 3 inches for use in building areas and or 6 inches for use in general grading and pavement areas. Care should be taken so that the larger pieces are not placed in a concentrated manner such that voids develop between nested pieces. A sufficient quantity of fines should be blended with the large pieces to reduce this risk.

Fill and Backfill Placement. Fill or backfill should be placed in uniformly thick lifts and compacted. The loose lift thickness should not exceed 8 inches. The fill should be systematically compacted to the levels given in the Compaction Summary. Fill containing rubble that cannot be tested for field density should be compacted with a 10-ton vibratory roller until no subgrade yielding is observed. The soil should be placed at moisture contents compatible with the required density. Depending on the soil moisture at the time of construction, aeration or wetting could be required to achieve proper compaction. Deleterious material should not be included in fill, and the fill should not be placed on soft materials or frozen ground.

COMPACTION SUMMARY

Category Minimum Compactiona

General soil fill 90% Rock backfill 95%

Pavement and floor slab subgrade 90%b Pavement and floor slab rock base course 95% a Measured as a percent of the maximum dry density as determined by the modified Proctor test in laboratory (ASTM D 1557).

b Moisture content within 4% of optimum moisture content

Trench Backfill. Settlement of utility trench backfill can result in unsightly depressions and localized pavement failures. Settlement of trench backfill can be reduced by mechanically compacting the backfill in lifts to the minimum compaction levels given in the Compaction Summary. In this method, the soil or granular material is placed and compacted in horizontal layers. The degree of compaction should be similar to that required in the fill adjacent to the trench or as recommended in the Compaction Summary.

Permeable trench backfill should not be used. Permeable soils can collect water that, due to the presence of potentially expansive soils, could result in heaving and distress of lightly loaded footings, slabs, and pavements.

Subgrade Protection. Proper drainage of the construction areas should be provided to protect the foundation excavations, floor slab subgrades and temporary slopes from the detrimental effects of weather conditions during construction. Finished subgrades and foundation excavations should be kept free of standing water at all times. Concrete should be placed in foundations the same day they are excavated.

Floor slab and pavement areas could be exposed to weather and disturbances from installation of utilities and normal construction traffic. Disturbance is generally relatively easy to repair in summer and fall months by reworking of the upper soils. Considerably more difficulty will be experienced in the wetter seasons, such as spring and winter. We recommend minimizing construction traffic on prepared subgrades.

Collection and Disposal of Site Water. Proper handling of the site water is important in the successful pavement and foundation performance. Water from surface runoff, downspouts, and subsurface drains, if any, should be collected and discharged through an appropriately designed site drainage system. Control of surface runoff should be maintained in compliance with the rules and regulations set forth in the Federal Water Pollution Control Act (1977).

Additionally, any and all permits related to site grading activities and control of storm water during construction activities should be obtained from the appropriate governmental jurisdiction(s).

SEISMICITY

The site is located in a region of the country that has a significant seismic risk due to the presence of the New Madrid Seismic Zone (NMSZ) in southeastern Missouri and the Wabash Valley Seismic Zone (WVSZ) in southeastern Illinois and southwestern Indiana. The NMSZ is the site of three of the largest magnitude earthquake events (estimated surface-wave magnitudes greater than or equal to 8.0) to strike North America in recorded history (December 1811 through February 1812). Researchers predict that the WVSZ is capable of producing large earthquakes similar in magnitude to the 1811-1812 NMSZ earthquakes.

The site is within the City of St. Louis, under the jurisdiction of Ordinance 68788 for the adoption of the IBC 2009. The maximum considered earthquake spectral response acceleration at short periods (SS) is 60 percent gravity (0.60g), and at 1-second periods (S1) is 0.18g. Based on shear-wave velocity data from the MASW survey, the soil profile at the site can be defined as Class C, Very Dense Soil and Soft Rock Profile.

Liquefaction. Layers of silty sand, clayey sand, and fine-grained sand were observed in Borings 3.3a, 3.5a, and 3.7a located within the footprint of the proposed museum expansion.

The sand layers are approximately 3 to 10 feet thick. SPT N-values of 14, 15, and 6 blows per foot (bpf) were measured in the sand layers.

Liquefaction analyses were performed using SPT N-values and field and laboratory descriptions of the soil materials encountered in the borings. Analyses were performed using the design magnitude earthquake and peak acceleration coefficients contained in the IBC code. The analysis results indicate that the potential for liquefaction is generally low for the sand layers present beneath the site. In addition, the sand layers are of limited extent and thickness within the footprint of the proposed museum expansion.

FOUNDATIONS ON ROCK

The proposed museum expansion can be supported on drilled piers bearing in competent limestone bedrock. Spread footings bearing on rock can be used in the eastern part of the structure where the rock is relatively shallow and the main level of the museum is at El 424.5

Drilled Piers

Straight shaft piers bearing in competent limestone can be designed using an allowable bearing pressure of 80 kips per square foot (ksf). Based on the boring data, from 1 to 4 feet of rock coring could be required in each pier to expose rock capable of supporting the maximum bearing pressure. In addition, obstructions in the fill and limestone ledges or boulders could result in pier rig refusal at shallower depths than occurred in our borings.

Additional capacity can be obtained by socketing the drilled piers into sound bedrock. In this case, the pier capacity would be equal to the summation of the following: (1) the end area of the shaft multiplied by the allowable end-bearing pressure and (2) the competent rock socket surface area multiplied by the allowable skin friction value. Allowable side frictional resistance of 15 and 50 psi can be applied to weathered and unweathered limestone, respectively.

Drilled piers proportioned for an end-bearing pressure of 80 ksf will require a probe hole at each pier location. Probe holes are performed before drilled pier construction and consist of NQ-rock cores, or similar, drilled at each pier location. This eliminates the need for manned entry to drill and inspect pilot holes made in the bottom of pier excavating. Probe holes should be located near the center of the pier. The probe holes are used to evaluate the existence of voids or seams of soft rock and clay below the design bearing elevation of the pier. The rock in the probe hole must meet the soundness criteria given in the appropriate table below. If the soundness criteria are not met, the pier bearing elevation must be deepened until the required soundness is obtained. A qualified geotechnical engineer or his representative must observe the probe holes and rock cores to determine the appropriate bottom elevation of each drilled pier.

ROCK SOUNDNESS CRITERIA

Vertical Probe Holes

80 ksf End-Bearing Drilled Piers

Depth Below Bottom of Pier

(ft)

Maximum Seam or Void

(inches)

Maximum Summation of Seams or Voids

(within intervals) (inches)

0 – 1/2D* 0.2 0.4 1/2D* - D* 0.4 0.8 D* - 2D* 1.25 2.0

Uplift Resistance. Uplift resistance can be achieved by socketing the drilled piers into competent bedrock. Uplift resistance for drilled piers can be computed considering the dead weight of concrete and available shear between the concrete and the rock socket. An allowable frictional resistance of 35 psi can be applied to the rock socket in sound limestone. The values can be increased by 33 percent for transient loading conditions. Where appropriate, based on the anticipated maximum groundwater level, the buoyant unit weight of concrete and soil should be used in computing uplift resistance. Uplift resistance in soil should be neglected.

Lateral Resistance. The lateral resistance of drilled piers depends on the shaft length and diameter, and the near-surface soil types. The lateral resistance can be computed using a computer program such as LPILE. This program can be used to estimate the pier deflection by varying the pier diameter for a given ultimate axial and lateral loads. The following tables list soil and rock parameters that can be used in LPILE for this project.

SOIL PARAMETERS FOR LATERAL LOAD ANALYSIS

Soil Type Soil

Model

Angle of Internal Friction (degrees)

Undrained Shear

Strength (psi)

Static Soil

Modulus, k (pci)

Strain Parameter

E50

Effective Unit

Weight (pci)

Moist Unit

Weight (pci)

Existing Fill

Stiff Clay, No Free Water

NA 5 NA 0.010 0.033 0.069

Natural, Cohesive

Soils

Soft Clay

NA 3 NA 0.020 0.030 0.066

Silty Sand, Fine Sand

Sand 32 NA 60 NA 0.033 0.069

ROCK PARAMETERS FOR STATIC LATERAL LOAD ANALYSIS

Rock Type Soil

Model

Effective Unit

Weight (pci)

Moist Unit

Weight (pci)

Young’s Modulus, Er (psi)

Uniaxial Compressive

Strength (psi)

RQD

(Percent) krm

Weak Rock, Highly Weathered, Poor Quality Limestone

Weak Rock

0.045 0.081 100,000 300 0 0.0005

Strong Rock, Moderately

Weathered to Fresh, Fair Quality

Limestone

Strong Rock

0.055 0.092 NA 5,000 NA NA

The effects of group interaction must be taken into account when evaluating lateral movement of pile or drilled shaft groups. The lateral resistance of pier assemblages can be evaluated using the GROUP software.

Spread Footings

Spread footings bearing on competent limestone can be designed for an allowable bearing pressure of 20 ksf. Competent rock is that which cannot be removed by a Caterpillar 225 excavator or equivalent. The prepared bearing surface should be level and free of soil, boulders, loose rock ledges, scaly rock, and shale. As such, mechanical methods of rock removal could be needed to remove loose rock.

The rock should be sound and fresh to moderately weathered. Discontinuities (joints, fractures, crevices, etc.) should be less than one-quarter inch in width if open and less than one inch in width if filled with soil or rock debris. Larger discontinuities should be cleaned out to a depth of 4 times their width and filled with a sand-cement grout.

Lateral Resistance. Lateral loads can be resisted by frictional resistance between the base of the footings and the bedrock. Resistance to sliding can be computed assuming an ultimate coefficient of friction of 0.7. Ultimate passive resistance, if required, can be computed assuming an equivalent fluid pressure of 250 pounds per cubic foot. Appropriate safety factors should be applied to determine the allowable sliding and passive resistances.

Settlement

Settlement of foundations bearing on rock, designed and constructed in accordance with the recommendations given in this report, is expected to be less than 1/2-inch.

SHALLOW FOUNDATIONS

Low retaining walls (less than 6 feet tall) and other lightly loaded structures can be supported on shallow foundations as detailed herein. Partial removal and replacement of existing fill below these structures includes a risk of detrimental settlement that must be accepted by the client as balance for reduced construction costs.

Bearing Pressure. Strip and spread footings can be proportioned for net allowable bearing pressures of 1,500 and 2,000 psf, respectively, provided they bear on firm, natural soil or remediated fill. Fill remediation shall consist of removal and replacement with compacted, well-graded crushed rock to a depth of 2 times the footing width below the design bearing elevation. The remediation should extend at least 5 feet beyond the footing area on each side. The minimum lateral dimensions for strip and spread footings should be 18 and 24 inches, respectively. Exterior footings and footings in unheated interior areas should be embedded 30 inches below the lowest adjacent exterior grade to provide protection from seasonal moisture variations and frost penetration.

The silty clay soils are easily disturbed. Footing excavations should be made with a smooth-edged backhoe bucket, and foot traffic in the bottom of the excavations should be minimized. Localized soft zones could be encountered at bearing elevations. Footing excavations should be extended through soft zones to stiffer soil. The overexcavation can be backfilled with lean concrete or flowable fill.

Settlement. Shallow foundations, proportioned and constructed as recommended above, are expected to settle approximately 1 inch. Differential settlement between any two adjacent footings could be approximately 3/4-inch. Estimated values of settlement contained in this report are based on our experience with projects of a similar nature. Consolidation tests and corresponding settlement calculations were not performed.

Uplift Resistance. Uplift loads can be resisted with the dead weight of the footing and structure, and the weight of soil above the foundation.

Lateral Resistance. Resistance to sliding can be computed assuming a coefficient of friction of 0.3; however, the ultimate resistance must be limited to 500 psf. The ultimate passive resistance can be computed based on an equivalent fluid pressure of 250 pcf; however, the upper 30 inches should be neglected due to seasonal variations in moisture and frost penetration. The lateral resistance values are ultimate values; appropriate factors of safety must be applied.

FLOOR SLABS

Existing, uncontrolled fill below floor slabs must be removed and replaced with compacted well-graded crushed rock to a depth of 2 feet below planned subgrade. In areas where the subgrade consists of bedrock, we recommend installing a minimum 12-inch layer of compacted well-graded crushed rock below the floor slab. Crushed rock must be compacted as specified in the Compaction Summary. Constructed as such, floor slabs can be designed using a vertical subgrade modulus of 100 pounds per square inch per inch of deflection (pci).

A 6-mil or thicker plastic sheet should be placed below the floor to reduce the potential for moisture to permeate the slab and the potential for mold growth within the buildings.

Notwithstanding other structural considerations, slab-on-grade floors should be designed to allow for differential movements that normally occur between the floor slab, columns, and foundation walls.

SOIL LATERAL LOAD

Foundation walls, retaining walls, and permanent retention systems must be designed to resist lateral soil loads. Design lateral pressures from surcharge loads must be added to the lateral earth pressure load. Lateral earth pressures can vary with wall restraint conditions, type of backfill, slope of ground surface behind the wall, and method of backfill compaction.

Design values are given in the following table for soil lateral loads on walls with horizontal backfill, subject to active and at-rest conditions. For walls for which tilting or deflection required to develop active earth pressure is not tolerable, lateral earth pressure shall be computed assuming at-rest conditions.

SOIL LATERAL LOADS ON WALLS

Description of Backfill Design soil lateral load (psf per foot of depth) At-rest Active

Inorganic clays of low to medium plasticity (CL)

68h + 0.55q 47h + 0.38q

Well graded gravel-sand mix (GW/SW) (e.g. 1-inch-minus)

48h + 0.40q 30h + 0.25q

Poorly graded clean gravel or sand (GP/SP) (e.g. 1-inch-clean)

55h + 0.45q 35h + 0.30q

Where:

h = depth below adjacent grade, feet q = surcharge load, psf

For the above equations to be valid for sand or gravel backfill, the backfill should be placed, in a wedge drawn upward and away from the edge of the wall footing at a 45-degree angle or flatter. If sand and gravel are to be placed within a steeper wedge, the values for low plasticity soil given above should be used. High plasticity clay should not be used as wall backfill.

In giving these values, it is assumed that hydrostatic pressures will not develop behind the walls, and that the wall backfill will be compacted as recommended in the Site Grading subsection of this report. Therefore, the walls must be provided with a drain system to allow for dissipation of hydrostatic pressure. Undrained walls could be subjected to additional pressures from groundwater, perched water, pipe leakages, or surface water infiltration. Permanent retention systems must be designed to resist hydrostatic pressures unless drainage is incorporated into the wall construction.

SUBSURFACE DRAINAGE

Groundwater was measured above the bedrock in a temporary piezometer installed within the footprint of the proposed museum expansion. Groundwater levels will likely rise with precipitation and increased Mississippi River stages. We recommend constructing a subsurface drain system around the perimeter of the museum expansion, as shown on Plate 4. The subsurface drain system should consist of 6-inch diameter PVC or equivalent pipe with 1/4- or 3/8-inch perforations; the pipe should be laid with the perforations down and enveloped with drain filter having a gradation in the range shown on Plate 4. The drain filter should be surrounded with Mirafi 140N filter cloth or approved substitute. We recommend a 6-inch thick permeable granular backfill wrapped in filter fabric or commercially available drainage mat, as illustrated on Plate 4, be placed directly behind the wall to facilitate drainage. The drainage system should be routed to sumps for collection and disposal.

Design measures should also be taken to waterproof below-grade areas of the building.

These measures include installation of a moisture barrier beneath the floor slab and water stops between foundation walls and the slab.

SLOPES

The stability of slopes depends on many factors, including the height and geometry of the slopes, the types of soils contained in the slopes, effects of groundwater, and any surface pressures present. In general, permanent cut and fill slopes, constructed at 1V:3H have been observed to perform satisfactorily. Therefore, it is our opinion that permanent slopes should be constructed at 1V:3H or flatter.

SECTION VI - RECOMMENDED ADDITIONAL SERVICES

The conclusions and recommendations given in this report are based on interpretation of exploration data and Geotechnology's experience. The client must recognize that variations could occur from conditions observed in the borings, particularly within existing fills or previously developed areas. Design recommendations are based on data from borings, sampling, and related procedures. Actual subsurface conditions could vary from those encountered in the borings. Therefore, design recommendations are subject to adjustment in the field, based on subsurface conditions encountered during construction. Since the intent of the design recommendations is best understood by Geotechnology, it is imperative to involve Geotechnology in the final design and construction process. Construction observation services are viewed as a continuation of the design process. Geotechnology will not be responsible for improper use of recommendations or failure by others to recognize conditions that can be detrimental to the successful completion of the project, or its performance.

We recommend that Geotechnology be retained to review grading and foundation plans to observe that recommendations given in this report have been correctly implemented. On-site services are required during site grading since placement techniques can significantly impact performance of the completed project. Foundation and floor slab subgrades should be observed before placing concrete or base course, respectively, to establish that the soil or rock conditions are consistent with conditions encountered during the field explorations. Of particular concern is the presence of rubble fill below structures and poor quality rock in foundation excavations.

Construction observation is intended to enhance compliance with project plans and specifications. It is not insurance, nor does it constitute a warranty or guarantee of any type. In all cases, contractors, et al, are solely responsible for the quality of their work and for adhering to plans and specifications.

SECTION VII - LIMITATIONS OF REPORT

This report has been prepared on behalf of and for the exclusive use of the client for specific application to the named project as described herein. If this report is provided to prospective contractors, the client should make it clear that the information is provided for factual data only and not as a warranty of subsurface conditions included in this report. Unanticipated soil or rock conditions could require the expenditure of additional funds to attain a properly constructed project. Therefore, some contingency fund is recommended to accommodate such potential extra costs.

Geotechnology has attempted to conduct the services reported herein in a manner consistent with that level of care and skill ordinarily exercised by members of the profession currently practicing in the same locality and under similar conditions. The recommendations and conclusions contained in this report are professional opinions. No other representation, expressed or implied, is included or intended.

Unless specifically stated in our proposal or this report, the scope of our services for this phase of the project did not include any environmental assessment or investigation for the presence or absence of wetlands or hazardous or toxic material in the soil, surface water, groundwater or air, on or below or around this site. Any statements in this report or on the boring logs regarding odors noted or unusual or suspicious items or conditions observed are strictly for the information of our client. Our scope did not include any services to investigate or detect the presence of mold or any other biological contaminants (such as spores, fungus, bacteria, viruses, and the by-products of such organisms) on and around the site, or any services designed or intended to prevent or lower the risk of the occurrence of an infestation of mold or other biological contaminants.

The analyses, conclusions, and recommendations contained in this report are based on the data obtained from the subsurface exploration. The field exploration methods used indicate subsurface conditions only at the specific locations where samples were obtained, only at the time they were obtained, and only to the depths penetrated. Discrete sampling cannot be relied on to accurately reflect natural variations in stratigraphy that could exist between sample locations and/or intervals. Unless specifically noted, the scope of our services did not include an assessment of the effects of flooding and natural erosion on the project site.

The recommendations included in this report have been based in part on assumptions about natural variations in site stratigraphy that can only be completely evaluated during earthwork and foundation construction. Accordingly, Geotechnology should be retained to perform construction observation and complete its geotechnical engineering service using observational methods.

Geotechnology cannot assume liability for the adequacy of its recommendations when they are used in the field without Geotechnology being retained to observe construction.

The conclusions or recommendations…