W912P6-15-R-0006-McCookRockwallSlopeStabilizationIDIQ-00-31-32_Appendix_A_Geotechnical_Baseline_Report_(GBR).pdf

US Army Corps of Engineers®

CHICAGO DISTRICT

LEADERS IN CUSTOMER CARE

CHICAGOLAND UNDERFLOW PLAN

(CUP) McCOOK RESERVOIR

ROCK WALL AND OVERBURDEN

STABILIZATION IDIQ

GEOTECHNICAL BASELINE

REPORT (GBR)

7 JANUARY 2015

00 31 32 Appendix A

Chicagoland Underflow Plan (CUP) McCook Reservoir Rock Wall and Overburden Stabilization IDIQ Geotechnical Baseline Report (GBR)

TOC-1

Chicagoland Underflow Plan (CUP) McCook

Rock Wall and Overburden Stabilization IDIQ

Table of Contents

List of Acronyms ............................................................................................................................. i

1.0 Introduction and Background .......................................................................................... 1-1

1.1 Introduction ................................................................................................................... 1-1

1.2 Purpose .......................................................................................................................... 1-1

1.3 Relation to the Contract Documents ............................................................................. 1-2

1.4 Organization of this Report ........................................................................................... 1-2

2.0 Project Description........................................................................................................... 2-1

2.1 Main Tunnel System Components Summary................................................................ 2-1

2.2 Shafts ............................................................................................................................. 2-2

2.3 Tunnel............................................................................................................................ 2-2

3.0 Summary of Geological Data........................................................................................... 3-1

3.1 Sources of Information.................................................................................................. 3-1

3.1.1 Design Phase Subsurface Exploration and Laboratory

Testing Program (AECOM 2008).......................................................................... 3-1

3.1.2 Subsurface Investigations by Others (1970 – 2000) .............................................. 3-1

3.1.3 Criteria for Data Inclusion ..................................................................................... 3-1

3.1.4 Previous Underground Experience ........................................................................ 3-2

3.2 Regional Geology.......................................................................................................... 3-2

3.3 General Site Geology .................................................................................................... 3-2

3.3.1 Soil ......................................................................................................................... 3-2

3.3.2 Rock ....................................................................................................................... 3-2

3.3.3 Structure ................................................................................................................. 3-3

3.3.4 Groundwater Levels............................................................................................... 3-4

3.4 Soil Unit Properties ....................................................................................................... 3-4

3.4.1 General ................................................................................................................... 3-4

3.4.2 Fill .......................................................................................................................... 3-4

3.4.3 Alluvium and Glacial Deposits .............................................................................. 3-4

3.5 Rock Unit Properties ..................................................................................................... 3-4

3.5.1 General ................................................................................................................... 3-4

3.5.2 Rock Weathering ................................................................................................... 3-5

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3.5.3 Equivalent Hydraulic Conductivity ....................................................................... 3-5

4.0 Characterization and Behavior of Engineering Geological Units.................................... 4-1

4.1 Properties and Behavior of Engineering Units – Soil ................................................... 4-1

4.1.1 Soil Classification .................................................................................................. 4-1

4.2 Properties and Behavior of Engineering Units – Rock ................................................. 4-2

4.2.1 Engineering Rock Unit .......................................................................................... 4-3

4.2.2 Discontinuity Orientation....................................................................................... 4-3

4.2.3 Joint Spacing .......................................................................................................... 4-4

4.2.4 Excavation and Support Classes ............................................................................ 4-4

5.0 Construction Considerations for Construction Shaft (Contractor Option) ...................... 5-1

5.1 Construction Shaft......................................................................................................... 5-1

5.1.1 Drill and Blast for Shaft Excavation ...................................................................... 5-1

5.1.2 Ground Support...................................................................................................... 5-1

5.2 Groundwater.................................................................................................................. 5-2

6.0 Construction Considerations for Tunneling..................................................................... 6-1

6.1 Anticipated Tunneling Conditions ................................................................................ 6-1

6.1.1 Drill and Blast Tunneling....................................................................................... 6-1

6.2 Ground Support ............................................................................................................. 6-1

6.3 Estimated Groundwater Inflows.................................................................................... 6-1

6.4 Grouting ........................................................................................................................ 6-2

7.0 References........................................................................................................................ 7-1

Tables

Table 4-1 Soil Engineering Unit Baselines................................................................................ 4-2 Table 4-2 Engineering Rock Unit – Baseline Intact Rock Properties ....................................... 4-3 Table 4-3 Summary of Joint Set Baselines ................................................................................ 4-3 Table 4-4 Summary of Joint Spacing Classes............................................................................ 4-4 Table 4-5 Summary of Joint Set Spacing Observations ............................................................ 4-4 Table 4-6 Relationship between E&S Classes and RMR .......................................................... 4-4 Table 6-1 Estimated Support Class Quantities .......................................................................... 6-1

Attachments

Attachment A Construction Shaft – Contractor Option – Ground Profile i

List of Acronyms

B&V Black & Veatch

BTS Brazilian tensile strength

CCD Chicago City Datum

CUP Chicagoland Underflow Plan

DSC differing site conditions

E&S Excavation and Support

GBR Geotechnical Baseline Report

GDR Geotechnical Data Report

HPU hydraulic power unit

ID inside diameter

LASMA Lawndale Avenue Solids Management Area

MGS Main Gate/Access Shaft

MTS Main Tunnel System

MWRDGC Metropolitan Water Reclamation District of Greater Chicago

RMR Rock Mass Rating

RQD Rock Quality Designation

SWRP Stickney Water Reclamation Plant

TARP Tunnel and Reservoir Plan

UCS unconfined compressive strength

USACE United States Army Corps of Engineers

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1.0 Introduction and Background

1.1 Introduction

This Geotechnical Baseline Report (GBR) describes geotechnical conditions that can be assumed during construction under the Rock Wall and Overburden Stabilization IDIQ Contract. This work may include but not be limited to rock high-wall stabilization, overburden slope stabilization, rock reinforcement, instrumentation installation, pavement of ramps and miscellaneous civil construction associated with the CUP McCook Reservoir. The project is designed by the USACE, Chicago District.

Refer to the project drawings and the Geotechnical Data Report for the McCook Reservoir System for the project location, tunnel alignment and shaft location figures.

1.2 Purpose

This GBR provides information relevant to subsurface conditions, referred to as the baseline conditions. The purpose of the GBR is to:

• Set baselines for geotechnical conditions and material behavior assumed to be encountered during construction shaft excavation and tunnel excavation.

• Identify important construction considerations, key project constraints, and selected requirements to be addressed by the Contractors during bid preparation and construction.

The contractual baselines do not represent warranties by the Government of the actual subsurface conditions that will be encountered by the Contractor. Rather, the purpose of the baselines is to translate the results of geotechnical investigations into clear descriptions of subsurface conditions. Nothing in this GBR limits the rights of the Government should a claim arise for differing site conditions (DSC).

The GBR is based upon several assumptions regarding the sequence of construction, the means and methods, and workmanship to be employed by the Contractor. The anticipated behavior of subsurface materials as described herein will be influenced by the means and methods selected and used during construction by the Contractor; and therefore, behavior may vary from that described in this report. The Contractor must evaluate the soil and groundwater conditions described herein as they relate to, and interact with, the means and methods selected by the Contractor for construction.

Any means and methods proposed by the Contractor where the Contractor believes the baseline becomes invalid or requires modification must be raised and discussed during the bid phase prior to bid opening. The Contractor has a duty to inform the Government of the baselines the Contractor believes are invalid, or require modification during the bid phase.

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1.3 Relation to the Contract Documents

This GBR references the GDR for the McCook Reservoir MTS and the GDR for this project prepared. The GDRs present details of the project field investigation completed in 2008 by AECOM and results of twenty previous investigations completed at or near the McCook Reservoir site. Also included as part of the GDR are the results of the laboratory testing performed on soil and rock samples collected during the investigation(s), including detailed descriptions of the field and laboratory testing data, methods. Boring logs and a summary table of laboratory test results and histograms depicting the distribution of various laboratory testing data are presented in the GDR. This GBR and the GDR are provided as information for the Contractor and are included in the Contract Documents. If there are any inconsistencies between the GBR and the GDR, the GBR shall take precedence. Individual Task Orders may contain supplemental information specific to the aspects of work included, and any assumptions that apply based upon that information.

This GBR is not intended to present the minimum required design and standards of construction contained in the Plans and Specifications. Nothing in this GBR should be construed as amending or altering the Plans and Specifications or applicable FAR clauses, or relaxing the standards of construction

The technical concepts, terms, and descriptions in this report follow standards commonly used in geotechnical engineering/engineering geology which have specific meaning pertaining to the work. Bidders should have a qualified geotechnical engineer or qualified engineering geologist carefully review this GBR so that a complete understanding of the information presented in this report is developed prior to submitting a bid.

1.4 Organization of this Report

This GBR broadly follows the principles contained in the ASCE document entitled “Geotechnical Baseline Reports for Construction”, dated 2007 and is comprised of an Introduction and Background (Section 1.0) and the following six sections (Section 2.0 to Section 6.0) as detailed below:

• Section 2.0 (Project Description) presents detailed descriptions about the project location, purpose, components, and requirements.

• Section 3.0 (Summary of Geological Data) describes the project setting including geological considerations and a summary of the available data from the GDR.

• Section 4.0 (Characterization and Behavior of Engineering Units) presents the characterization and behavior of material types present along the project alignment, including behavior of the different engineering units classified on the project.

• Section 6.0 (References).

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2.0 Project Description

The purpose of the McCook Reservoir project is to reduce flood damages in the greater Chicago combined sewer system area. The McCook Reservoir is part of the larger CUP, which includes tunnels for storm water storage and conveyance, and reservoirs for storm water storage. The CUP is also known as the Tunnel and Reservoir Plan (TARP) in MWRD documents.

McCook Reservoir will be located in a limestone/dolomite quarry, with nearly vertical pre-split perimeter walls. The reservoir will have two stages (Stage 1 invert at El. -284 CCD, Stage 2 invert at El. -279 CCD), separated by a weir (top El. -200 CCD). Minor storm events will be contained in the tunnel system (Mainstream and Des Plaines Tunnels).

The major work features under the Rock Wall and Overburden Stabilization IDIQ contract will include the construction and completion of slope stabilization and related elements of the reservoir.

2.1 R o c k W a l l a n d S l o p e S t a b i l i z a t i o n Components Summary

The major elements include the following:

a. Rock Wall Stabilization – Scaling, removal of loose or detached rock and soil materials from the reservoir highwall and surrounding areas; sealing, paving, constructing drainage for and stabilizing the top of rock bench surrounding the reservoir; drilling and installation activities associated with rock dowels, rock bolts, drain holes, rock cable bolts; rockfall control mesh, shotcrete applications on rock high wall and overburden slopes.

b. Overburden Slope Stabilization – Stabilization of sloped, vertical and near-vertical overburden overburden surfaces surrounding the reservoir using methods including but not limited to structural concrete block walls, soil nail walls, gabion walls associated drainage, footings and support.

c. Instrumentation Installation – Construction and installation of geotechnical instrumentation on horizontal and inclined and or vertical surfaces, including high walls.

d. Miscellaneous Elements – Construction activities associated with the preparation of the CUP McCook Stage 1 and Stage 2 Reservoir areas for operation, including but not limited to installation of guardrails, grading, access features, drainage features and controls, and vegetation control.

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3.0 Summary of Geological Data

Twenty subsurface investigations from 1970 to 2000 have been conducted within or near the McCook Reservoir. A summary of the data including the design subsurface investigation conducted specifically for the MTS (AECOM 2008) is included below.

3.1 Sources of Information

3.1.1 Design Phase M a i n T u n n e l S y s t e m Subsurface Exploration and Laboratory Testing Program (AECOM 2008)

The design phase subsurface exploration program was completed in July 2008 and consisted of three test borings designated LB-121-08, LB-122-08, and LB-123-08. The design phase subsurface exploration program consisted of drilling conventional test borings, performing downhole geophysical (acoustic and optical televiewer) logging, field conductivity tests, and installing groundwater monitoring wells and piezometers. Locations of test borings completed during the design phase exploration program are included in the project GDR and are shown on the Contract Drawings. For the results of the design phase subsurface exploration and laboratory testing program, refer to the project GDR.

3.1.2 Subsurface Investigations by Others (1970 – 2000)

Twenty subsurface investigations in the general vicinity of the proposed MTS have been completed since 1970 to aid in the design and construction of the McCook Reservoir and MTS.

Refer to the project GDR for a complete listing of the previous subsurface explorations and laboratory testing programs.

3.1.3 Criteria for Data Inclusion

Roughly 419 borings and numerous reports for various geotechnical/geological investigations have been completed to gather subsurface information in the general vicinity of the McCook Reservoir. For purposes of this report, the data has been culled and analyzed, as follows.

• All 419 borings were utilized for soil and rock unit properties.

• Eight borings; (as described in the project GDR) LB 121-08, LB 122-08, LB-123-08, 156-

B1, LB 101-98, LB 106-98, MW-1-99, and OW-1 and their associated in situ and laboratory test data were utilized for lithology, groundwater, engineering unit baselines, RMR, and RQD. The eight borings were chosen based on their proximity (within 650 ft) to the MTS project site and their penetration into rock.

• The McCook Haul Tunnels Design Project Report dated September, 2001 and prepared by URS Corporation was utilized for purposes of defining and baselining structural and discontinuity data.

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Refer to the project GDR for the individual borings logs and in situ, laboratory and structural data referenced above.

3.1.4 Previous Underground Experience

Refer to the McCook Final Reservoir Preparation GDR for a listing of previous underground construction experience near the McCook Reservoir project site.

3.2 Regional Geology

The project site lies on the eastern flank of the northwestward trending Kankakee Arch and is covered by a sequence of glacial drift deposits underlain by approximately 4,000 ft of Cambrian-to Silurian-aged sedimentary rock which in turn is underlain by Precambrian-aged crystalline rock.

The Cambrian- to Silurian-aged sedimentary rock of the Kankakee Arch consist of various dolomite, shale and sandstone formations underlain by Precambrian-aged crystalline rock which is located significantly below the floor of the quarry/reservoir.

The rock in the project vicinity is generally overlain by a sequence of fill, alluvial deposits, and glacial drift deposits (youngest to oldest).

3.3 General Site Geology

3.3.1 Soil

In general, the soil stratigraphy in the project area consists of Fill, Alluvium, and Glacial deposits. Fill has been placed overlying the native materials as a result of channelization, dredging, and construction of the Metropolitan Water District of Greater Chicago’s (MWRDGC) Lawndale Avenue Solids Management Area (LASMA), and other local construction.

The rock surface in the vicinity of the project site is generally classified as “slightly weathered” to “fresh”.

Detailed descriptions of the Fill, Alluvium, and Glacial deposits (including glacial till) are presented in Section 3.4.

3.3.2 Rock

3.3.2.1 Lithology

The rock underlying the project alignment consists of lithologies belonging to the Racine, Sugar Run, Joliet, Kankakee, Elwood, Wilhelmi, Brainard and Fort Atkinsons Formations. A detailed description of the formations and their properties are presented in the McCook Main Tunnel System GDR.

3-3

Racine Formation – the primary lithology of the Racine Formation as seen from the borings is a moderately hard to hard, slightly weathered, fine-grained, light gray-to-gray dolomite. This formation contains stylolites and stylolitic joints, chert bands and nodules, vugs, and pits.

Sugar Run Formation – The primary lithology of the Sugar Run Formation as seen from the borings is a hard, fresh, fine-grained, massive, light gray dolomite with stylolites, clay partings, and few to trace vugs and chert nodules.

Joliet Formation – The primary lithology of the Joliet Formation as seen from the borings is a medium hard, fresh, very fine-grained, thickly-bedded, gray to dark gray dolomite, with vugs and occasional stylolites.

Kankakee Formation – The primary lithology of the Kankakee Formation as seen from the borings is a medium hard to hard, slightly weathered, fine-to-medium grained, dark brown to gray dolomite with clay partings, vugs, chert nodules and bands, and fossils.

Elwood Formation – The primary lithology of the Elwood Formation as seen from the borings is a moderately hard, fresh, fine to medium grained, thinly-banded, gray to brownish-gray dolomite with black clay partings, fossils and occasional chert nodules. The Elwood Formation was considered to be the upper portion of the Edgewood Formation (in maps, reports and logs for previous projects.)

Wilhelmi Formation – The primary lithology of the Wilhelmi Formation as seen from the borings is a moderately hard, fresh, very fine-grained, thinly bedded, argillaceous, dark gray to black dolomite. The Wilhelmi Formation previously was reported as the lower part of the Edgewood Formation (in maps, reports and logs of previous projects.)

Brainard Shale – The Brainard Shale is the uppermost formation in the Maquoketa Group and is a gray-green thin-bedded dolomitic shale and/or mudstone.

Fort Atkinson Formation - The Fort Atkinson Formation is a thin to medium-bedded gray coarse to medium crystalline shaley dolomite with frequent shale partings.

3.3.3 Structure

Structure of the rock in the project area is defined by bedding and jointing discontinuities with bedding being the more prominent of the two (URS, 2001).

For purposes of this report, bedding is defined by a change in formation type through the stratigraphic sequence. Formations are presented in Section 3.3.2.1 and are generally defined by similar characteristics (mineralogy, depositional environment, fossil type). Bedding changes are frequently gradational rather than distinct and commonly occur within the same vertical

3-4 elevation (approximately 10 to 20 ft) across the project site.

Since 1991 two major joint sets have been extensively mapped and recorded in the project area.

For purposes of this report the two joint sets will be labeled J1 and J2 and their orientation, dip and spacing is presented in Section 4. Refer to the project GDR for more detailed description of the joints.

3.3.4 Groundwater Levels

Groundwater levels, from the eight borings (Section 3.1.3), ranged from El. -1.5 to -42.1 CCD and were generally obtained at the start of the drilling operations each day.

Groundwater level fluctuations occur with time and seasonal change due to variations in precipitation, evaporation, surface water runoff, and local dewatering.

3.4 Soil Unit Properties

3.4.1 General

A general description of the various soil units and their engineering properties is provided in this section. Anticipated behavior of the various soil units relative to optional Construction Shaft is described in Section 4. Soil sampling was conducted on the eight borings (Section 3.1.3) near the project site.

3.4.2 Fill

Man-made Fill near the project site is generally associated with dredging neighboring water bodies and previous construction or paving activities. Onsite Fill generally consists of asphalt, limestone base course, silty clay, silty sand, sand and trace gravel, roots and organic materials.

3.4.3 Alluvium and Glacial Deposits

Alluvium and Glacial deposits are present below the Fill and were seen in all the design phase borings. These deposits generally consist of organic clay, silty clay, fine to coarse sand and gravel, silt, sandy silt, silty sand, sandy clay, gravel, sandy gravel, cobbles and boulders.

Differentiating between the Alluvium and Glacial deposits in the borings was not always possible and for purposes of the GBR they are grouped together. Deposits generally varied in thickness from 21 ft (LB-122-08) to 36 ft (LB-101-98).

3.5 Rock Unit Properties

3.5.1 General

Data from laboratory tests conducted on samples of intact rock from design phase borings, and from previous laboratory testing on past borings, are presented in the project GDR. The purpose of this testing was to obtain information on the unconfined compressive strength (UCS) and the Brazilian tensile strength (BTS) tests. All the laboratory data is summarized in tabular form in the project GDR. Also presented in the GDR are a series of scatter plots for the various

3-5 laboratory tests, including RQD. Analysis of these histograms shows intact rock properties do not vary significantly by formation or by location within the project area. Baseline values for the intact rock properties are presented in Section 4.

3.5.2 Rock Weathering

In general, the weathering profile of the top of rock shows slight weathering grading to fresh with depth.

For purposes of this report, the top of rock is defined as the elevation or depth at which continuous rock mass is encountered. Rock and top of rock for construction purposes are defined in Section 31 00 00 – Earthwork.

3.5.3 Equivalent Hydraulic Conductivity

Equivalent rock mass hydraulic conductivity (k) was evaluated based on the results of 66 water pressure tests conducted in the design phase test borings as summarized in the project GDR.

Review of k values relative to geologic formation, depth below top of rock, and location along the tunnel alignment was undertaken to determine if correlations existed to facilitate predictions of water inflow during construction. Evaluation shows no clear correlations between geologic formation and equivalent hydraulic conductivity, or depth below top of rock and equivalent hydraulic conductivity. No tests showed a k value greater than 10-3 cm/sec and twelve tests (18%) measured k values greater than 10-4 cm/sec.

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4.0 Characterization and Behavior of Engineering Geological Units

4.1 Properties and Behavior of Engineering Units – Soil

The material descriptions of the soil units designated for this project, which include Fill, Alluvium, and Glacial deposits, are the same as presented in Section 3.4.

Behavior of soils during construction may impact the Contractor’s selection of means and methods. Ground behavior depends upon several factors including: gradation and texture of soil materials (e.g. the percentage and plasticity of fine materials), groundwater conditions, soil formation, depositional environment and structure, and the construction means and methods employed. The anticipated ground behavior for the soil units encountered during project construction has been classified in accordance with the Tunnelman’s Ground Classification.

Ground classification based on the behavior of soft ground tunnels was first proposed by Terzaghi in 1950 and has been modified by several authors, most notably by Heuer in 1974. The Tunnelman’s Ground Classification system is used in this GBR to describe the anticipated behavior of the soil units present.

For purposes of defining characteristics and behaviors of the soil profile, the materials present along the alignment have been classified into the following two Engineering Units for ground classification purposes:

• Coarse-Grained Soils - Includes fine to coarse sand and gravel, silty sand, and boulders in varying proportions

• Fine-Grained Soils – Includes silt, sandy silt, clay, silty clay, sandy clay, silty sandy clay, and organic clay in varying proportions

Both Engineering Units contain Fill, Alluvium, and Glacial materials as described in Section 3.

The following sections describe the behavioral characteristics of engineering soil units at the project site.

4.1.1 Soil Classification

No soil will be encountered during tunnel excavation. Soil will only be encountered during excavation at or near the ground surface outside the reservoir perimeter. Soil behavior at a particular location will depend upon the type of material being excavated and whether the material is above or below groundwater. The material behavior will vary depending on the magnitude of the hydraulic gradient providing the acting driving force. The types of ground behavior to be expected when excavating though soil materials comprising cohesive soils (lean clay, fat clay, silt, elastic silt) and granular soils (clayey sand and silty sand) shall include the following:

• Fine-Grained Soil materials above groundwater level – Slow Raveling

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• Fine-Grained Soil materials below groundwater water level – Slow to Fast Raveling

• Coarse-Grained Soil materials above groundwater level – Running

• Coarse-Grained Soil materials below groundwater level – Flowing

For baseline purposes the natural soil material shall be expected to contain rock fragments, cobbles, and boulders within 40 ft of the soil rock interface, derived from the weathering of the underlying rock. The Contractor should consider these rock fragments as having intact rock properties the same as the native rock and use the baseline material parameters considered in Section 4.2 for bid purposes.

The baseline properties for design and for excavation of each soil type to be encountered during excavation are presented in Table 4-1 below.

Table 4-1 Soil Engineering Unit Baselines

Parameter

Unit

Soil

Fine-Grained Coarse-Grained

Unit Weight (In Situ) pcf 145 145

Cohesion psf 2,000 0

Friction Angle degrees 0 35

Permeability cm/sec 1x10-7 1x10-4

4.2 Properties and Behavior of Engineering Units – Rock

Based upon the available data for each rock type presented in Section 3.3.2 it has been determined that the intact rock properties show moderate variation across the project. For this reason we have presented the data from studies and will provide supplemental information for individual Task Orders if warranted.

The Silurian bedrock on site has been divided based upon Rock Mass Rating (RMR) into a series of three Excavation and Support (E&S) Classes for drill and blast excavations.

• E&S Class I = RMR > 60;

• E&S Class II = RMR 40 – RMR 60; and

• E&S Class III = RMR < 40.

4.2.1 Rock Behavior During Prior Construction

The Elwood Formation has demonstrated a tendency to spall along bedding planes when exposed in the crowns of excavations constructed during previous work on the project. During portions of the excavation of Tunnel C in the Distribution Tunnels contract rockfall consisting

4-2 of blocks of up to approximately 10-pounds from the crown of the tunnel necessitated a sequence of construction consisting of:

1. Drill and shoot a round of closely-spaced shot holes 8 to 12 feet deep

2. Remove shot rock/muck

3. Scale rock surface with high pressure air and pry bars

4. Apply 2-inches of fiber-reinforced shotcrete

5. Repeat steps 1-4

6. Install permanent rock support one round behind the working face as the heading proceeded.

The same properties exhibited by the Elwood Formation were encountered in excavating Tunnel C through the Wilhelmi Formation, and the same excavation sequence was used to mitigate rockfall concerns.

The Brainard Shale has been known to cause serious problems of slaking in underground excavations in Northern Illinois. During excavation of the TARP tunnels and mainstream Pump Station chambers, this problem was avoided by application of shotcrete within 48 hours after excavation. Where uncovered and exposed to water and air after excavation it deteriorated to mud resulting in over excavation to a depth of up to three feet in the invert of Tunnel C during the Distribution Tunnels project.

4.2.2 Engineering Rock Unit Characteristics

The baseline intact rock properties are presented in Table 4-2. Rock material baselines are presented using arithmetic average and a value that 90% of the rock does not exceed. It should be noted that the UCS baseline value determination includes only direct UCS testing.

Table 4-2 Engineering Rock Unit – Baseline Intact Rock Properties

Parameter

Unit Engineering Unit

Average 90%

Unconfined Compressive Strength (UCS) psi 15,000 25,000

Brazilian Tensile Strength (BTS) psi 1,500 2,300

4.2.3 Discontinuity Orientation

The predominant horizontal discontinuity set in the bedrock are bedding planes. For baseline purposes the bedding dip angles will range from 0 to 5 degrees, generally in a southerly direction

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The baseline ranges in orientation of the two essentially vertical joint sets (J-1 and J-2) are summarized in Table 4-3.

Table 4-3 Summary of Joint Set Baselines

Feature

Dip Angle

Range (degrees)

Dip Direction

Range (azimuth)

Mean Plane Dip Angle (degrees)

Mean Plane Dip

Direction (azimuth)

J-1

80-90

315-325

135-145 140

J-2

80-90 35-45

215-225 220

4.2.4 Joint Spacing

The joint spacing classification used for the project is summarized in Table 4-4 (Brown, 1981).

Table 4-4 Summary of Joint Spacing Classes

Feature Joint Spacing Range

From (in.) To (in.)

Extremely Close 0.0 0.75

Very Close 0.75 2.5

Close 2.5 8

Moderately Wide 8 24

Wide 24 60

Very Wide 60 >60

The baseline ranges for joint spacing of the two joint sets are summarized in Table 4-5.

Table 4-5 Summary of Joint Set Spacing Observations Feature Joint Spacing Range (in.) Typical Joint Spacing

J-1 12 to >60 Moderately wide to very wide

J-2 12 to >60 Moderately wide to very wide

4.2.5 Excavation and Support Classes

The Engineering Rock Unit is divided based upon Rock Mass Rating (RMR) into a series of three E&S Classes for drill and blast mined tunnel support. Ratings for six parameters (UCS, RQD, joint spacing, joint condition, groundwater condition, and joint orientation) were used to classify the rock mass using the RMR system in accordance with Bieniawski (Bieniawski 1989).

The ratings for each of the six parameters are summed to provide a value of RMR between 0 and

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100. A summary of the project E&S Classes assigned based upon RMR’s for the engineering units is presented in Table 4-6 and baselined in Section 5.

Table 4-6 Relationship between E&S Classes and RMR

E&S Class RMR RMR Rock Description

E&S Class I > 60 Good to Very Good

E&S Class II 40 to 60 Fair

E&S Class III < 40 Poor to Very Poor

5.0 References

• Bieniawski, Z.T., Engineering Rock Mass Classifications, 1989, Wiley, New York.

• Brown, E.T., Rock Characterization Testing and Monitoring, 1981, Pergamon Press, Oxford, England.

• Heuer, R., Estimating Rock Tunnel Water Inflow, 1995 RETC Proc., June 1995, San

Francisco, CA.

• Heuer, R., Estimating Rock Tunnel Water Inflow – II, 2005 RETC Proc., June 2005, Seattle, WA.

• Heuer, R., Important Ground Parameters in Soft Ground Tunnels", Proceedings of Eng.

Found. Conf. on "Subsurface Exploration for Underground Excavation and Heavy Construction", August, 1974, Henniker, New Hampshire, ASCE.