MEMO Tetra Tech 17885 Von Karman Ave., Suite 500, Irvine, CA 92614 Tel 949-809-5121 Fax 949-809-5010 Insert optional entity website tetratech.com To: Sam Tieu, PE Cc: Ali Fayad, PE; Chitta Gangopadhyay, PE; Scott Vose; Wilbert Cho, PE From: Ike Pace, PE Date: December 5, 2014 Subject: Fullerton Creek Shoring and Construction Assessment Fullerton Creek Shoring Objectives: The Orange County Public Works Department (OCPW) is proposing to replace approximately 1,800 lineal feet of the north wall of Fullerton Creek Channel, from downstream of Western Avenue to upstream of Beach Boulevard. The design of the north wall is currently being performed by OCPW. The south wall of the channel was previously replaced and will remain in place. Tetra Tech has been contracted to provide a review assessment of five shoring alternatives that were presented by OCPW. In discussions with OCPW, the main goals for the shoring of the north wall are the following: Vibration effects to the adjacent homes should be minimal. The proposed shoring should not significantly impede the channels ability to carry a runoff of 6,700 cfs during a major storm event. The removal of the existing north wall and the required excavation to construct the new north wall should not impact the sliding stability of the existing south wall. The existing right-of-way should not be exceeded for construction of any shoring. Construction of shoring should not impact the existing bridges at Western Avenue and Beach Boulevard. The proposed shoring should minimize access conflicts during construction of the north wall. Fullerton Creek Shoring Review Assessment: The shoring methods (Attachment 1), along with their anticipated construction sequences, as presented by OCPW include the following: 1. Method 1: 50-feet deep sheet pile using Giken Silent Piler: • Insert pile • Excavate old wall • Build new retaining wall • Remove pile • No segmental restrictions are associated with this method. 2. Method 2: 25-feet +/- deep sheet pile using Giken Silent Piler: • Insert pile • Segmentally excavate wall • Use existing retaining walls as “H-piles- equivalent” to the stay-in-place sheet pile behaving as lagging • Stay-in-place sheet piles used as forms for back of new stem wall EXHIBIT V
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MEMO
Tetra Tech 17885 Von Karman Ave., Suite 500, Irvine, CA 92614
Tel 949-809-5121 Fax 949-809-5010 Insert optional entity website tetratech.com
To: Sam Tieu, PE
Cc: Ali Fayad, PE; Chitta Gangopadhyay, PE; Scott Vose; Wilbert Cho, PE
From: Ike Pace, PE
Date: December 5, 2014
Subject: Fullerton Creek Shoring and Construction Assessment
Fullerton Creek Shoring Objectives:
The Orange County Public Works Department (OCPW) is proposing to replace approximately 1,800 lineal feet of the north wall of Fullerton Creek Channel, from downstream of Western Avenue to upstream of Beach Boulevard. The design of the north wall is currently being performed by OCPW. The south wall of the channel was previously replaced and will remain in place.
Tetra Tech has been contracted to provide a review assessment of five shoring alternatives that were presented by OCPW. In discussions with OCPW, the main goals for the shoring of the north wall are the following:
Vibration effects to the adjacent homes should be minimal. The proposed shoring should not significantly impede the channels ability to carry a runoff of 6,700 cfs
during a major storm event. The removal of the existing north wall and the required excavation to construct the new north wall should
not impact the sliding stability of the existing south wall. The existing right-of-way should not be exceeded for construction of any shoring. Construction of shoring should not impact the existing bridges at Western Avenue and Beach Boulevard. The proposed shoring should minimize access conflicts during construction of the north wall.
Fullerton Creek Shoring Review Assessment:
The shoring methods (Attachment 1), along with their anticipated construction sequences, as presented by OCPW include the following:
1. Method 1: 50-feet deep sheet pile using Giken Silent Piler: • Insert pile • Excavate old wall • Build new retaining wall • Remove pile • No segmental restrictions are associated with this method.
2. Method 2: 25-feet +/- deep sheet pile using Giken Silent Piler:
• Insert pile • Segmentally excavate wall • Use existing retaining walls as “H-piles- equivalent” to the stay-in-place sheet pile behaving
as lagging • Stay-in-place sheet piles used as forms for back of new stem wall
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3. Method 3: This is similar to method 2 but with 25-feet +/- deep steel plate using the ABI Hydro-Press System.
4. Method 4: This is similar to method 2 but with 25-feet +/- deep Secant Pile Walls built with an auguring
machine within the channel. Secant Pile walls act as lagging between existing retaining walls.
5. Method 5 – Soldier Piles and Lagging
Installation
Methods 1 and 2 are similar, since they both use sheet piles as the main shoring component and utilize a Giken Silent Piler which essentially presses in the steel sheet pile. This method generates less noise and vibration than conventional hammering or vibrating sheet piles into the ground. The main difference between the two methods is that Method 1 utilizes a more conventional shoring technique which the sheet piles provide the cantilevered support for the construction and would be removed at the completion of the new wall. Method 2 installs the sheet piles in segments so that the existing wall can be used as "soldier piles" to support the sheet pile shoring. The sheet piles would be left in place to act as forms for the new north wall. Method 3 is similar to Method 2, with the exception of using steel plates in lieu of sheet piles and the installation uses an ABI Hydro-Press System to install the steel sheets. The ABI Hydro-Press is similar to the Giken Silent Piler in the way it installs the sheets. Method 4 is similar to Method 2 except it uses secant piles instead of sheet piles or steel sheets as the shoring component. The fifth method proposes to use conventional soldier pile and lagging to shore the area behind the existing north wall. It is assumed that the soldier piles would be drilled in and not driven in to minimize any vibration impact to the adjacent properties.
All of the methods presented above should create similar vibration and noise levels for the adjacent properties and considered equal in this respect.
As far as the construction of the proposed north wall is concerned, Methods 1 and 5 would have the least impact on the current design. Both of these methods use conventional shoring methods which would be removed after the completion of the new wall, so they would have minimal impact on the current wall design. The other three methods call for the shoring to be left in place to act as stay-in-place forms for the new wall. The shoring would need to be built approximately 3 feet behind the existing wall to allow for the drainage blanket behind the wall as well as avoiding the existing wall heel. At that distance, the shoring may be too far back to act as a stay-in-place form for the current wall design. The other requirement with these three methods (Method 2, 3 & 4) is that they are proposed to be constructed segmentally. The second phase of construction may encounter some coordination issues with its installation.
OCPW has stated that the existing south wall may not have adequate factors of safety for sliding if the existing north wall invert slab and the associated soil beneath it are removed, thus any proposed shoring needs to address the stability of the south wall. It is understood that the south wall depends on the invert slab and the passive resistance of the soil to provide adequate resisting force against sliding. Method 1 calls for the complete removal and excavation of the north wall without any means of providing added sliding resistance. This could create an unsafe condition for the south wall. Methods 2 through 4 require segmental construction with approximately 8-foot wide panels of the existing north wall to be removed at a time, while leaving the adjacent sections in place to act as "soldier piles". The remaining wall sections would provide resistance against the sliding of the south wall while the north wall is being constructed in segments. Once the newly constructed walls are complete, additional sheet piles or sheeting would be installed and the remaining portions of the walls constructed. Method 5 utilizes soldier piles and lagging and would be similar to Method 1 in its ability to provide sliding resistance for the south wall.
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Flow Conveyance and Construction Access
As far as conveyance of the anticipated water flows during a storm event and obstructing construction access, all of the methods are consider equal since none of them impede into the channel. The existing north wall could be removed for long lengths for Methods 1 and 5 which could expose risk of failure along the channel during a major flood. The segmental construction of Methods 2 through 4 would limit the risk of failure due to at a minimum half of the wall will be in place.
Right-of-Way
As far as easement encroachments are concerned, all of the methods would require the sheet pile, lagging or soldier piles to be installed approximately 3 feet behind the existing wall. It appears that the right-of-way is approximately 10 feet in width, so there should not be any issues with the proposed sheet pile shoring or lagging. Installation of the sheet piles or soldier piles would need to be performed from the channel invert.
Stability of the South Wall
The issue of providing sliding resistance for the south wall could be alleviated by constructing a sacrificial key adjacent to the existing south wall footing that would be deep enough to engage adequate passive pressure to resist the sliding of the south wall.
A short length sheet pile wall or plate installed and left in place along the toe of the south wall could provide adequate stability of the south wall against sliding. The pre-augured holes to install the sheet pile must be backfilled with crushed stone or similar materials. Design calculations would be necessary for the depth of the sheet pile penetration.
As an alternative, the "box" section of the new north wall may provide enough lateral capacity to resist the sliding of the south wall. The construction sequence would have to be so that the "box" section is constructed first and then the rest of the north wall.
Another method of providing more lateral resistance would be to have the contractor stockpile soil on the south side so the added weight would create enough friction to offset the sliding force. The amount of soil needed to increase the friction resistance is estimated to exceed 5.5 feet of depth assuming horizontal placement across the entire invert. However, the soil would have to be placed in a manner such that it would not slide into the new construction (i.e. set back and/or sloped from the center), which would likely create a wedge shape that may not leave enough room for movement of construction equipment along the south side. In addition, this soil stockpile would impact the channel's ability to carry the storm flows and should only be considered as an option during the dry season.
Use of horizontal struts or braces supported between north and south walls could also provide adequate safety factor against sliding. Design calculations would be necessary for the scheme. However, this may impact the movement of construction equipment or pace of construction due to the obstructions that would occur from the bracing.
Cost Comparisons
Preliminary construction costs for each of the five methods have been developed (Table 1). The costs are comprised of fixed costs, which are bid items that are not expected to be impacted by changes to the shoring method, and variable costs, those expected to change due to the shoring method. The cost estimates are based on the bid schedule provided in the plans and specifications along with calculated quantities for each bid item. Several general assumptions were utilized in calculating the costs used for the bid items of each method:
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Mobilization/Demobilization costs are estimated as a percentage of construction costs that ranges between 5% and 6% for the variable cost items, and is a set 5% for the fixed cost items.
The bid items for Class “B” Field Office, Dewatering, Maintain Traffic & Detours, and Dust Control all are calculated using an estimated construction duration for each method.
For all methods that require temporary sheet piling, it is assumed that the contractor would be able to re-use the sheeting three times, and therefore would only purchase the requisite number of sheets needed.
For all permanent sheeting, it is assumed that the contractor would purchase all the material required for the entire channel improvement length.
Methods 1 and 5 are assumed to be constructed in 100-lf sections, while Methods 2, 3 and 4 are assumed to be constructed in alternating 8-lf sections.
Methods 1 and 5 include costs for stabilizing the south wall during construction. Unit costs for Methods 2, 3 and 4 were modified from the original costs to reflect the lower productivities
assumed to be incurred due to the 8-lf segmenting of construction.
Table 1. Opinion of Probable Costs of Shoring Methods
Method
No. Shoring Method Description Fixed Costs Variable Costs Total Costs
5 50-vlf Soldier Piles and Lagging $275,000 $11,237,000 $11,512,000
Table 2 presents a simplified summary of the review assessment of the methods presented by OCPW. The higher number means a better result.
Table 2. Shoring Method Summary
Method
No.
Minimize
Vibration
Flood
Conveyance Flood Risk
South wall
Sliding
Easement
Encroachment
Impact on north
wall design Cost Total Score
1 4 5 2 3 3 5 4 26
2 4 5 4 4 4 2 3 26
3 4 5 4 4 4 2 3 26
4 4 5 4 4 2 2 2 23
5 4 5 2 3 2 4 1 21
Other Alternative Methods:
Tetra Tech briefly reviewed other possibilities for shoring during construction of the north wall (Attachment 2). These alternatives included:
1. Adding diagonal braces to the proposed shoring to provide sliding resistance for the south wall. This is similar to the way the shoring was performed when the south wall was constructed. This method would
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create some reduction in the channels ability to carry the 6,700 cfs runoff during a storm event. The construction access would also be hampered slightly due to constraints created by the bracing.
2. The use of tie-backs or soil nails. This method would require OCPW obtain construction easements from the adjacent property owners. The feasibility and time to obtain the easements may be prohibitive. This would also involve opening up a limited lower portion of the wall at a time to accommodate the structural element connecting the wall and the new base slab. A determination of adequate reinforcing steel in the existing stem would be required.
3. Adding horizontal braces from the top of the proposed shoring to the top of the south wall. This method
would likely also require stockpiled soil on the south invert and a vertical support at the center of the channel. This would provide sliding resistance for the south wall, but minimize the impact on the channel's ability to carry storm flows. Construction access may still be hampered by the constraints from the stockpiled soil, and vertical and horizontal braces. This method would not be recommended where there is a building adjacent to the top backfill of the south wall.
4. The north wall may be built using methods used to underpin foundations for buildings and retaining walls.
OCPW may elect to preserve the stem of the wall, and lower its foundation and the base slab by smaller segmental construction. This would involve opening up a limited lower portion of the wall at a time to accommodate the structural element connecting the wall and the new base slab. A determination of adequate reinforcing steel in the existing stem would be required. Close monitoring for wall top movement and ground settlement behind the wall is required for this method.
5. Sheet piling driven in behind the existing concrete channel wall. The sheet piling would be left in place as the permanent channel wall and the existing concrete channel removed. The invert would be cast against the sheet pile with the addition of nelson studs or similar. A concrete cap would be cast along the top of the sheet pile wall.
Alternative Methods Cost Comparisons
Preliminary construction costs for each of the five alternative methods have been developed (Table 3). The costs were developed in the same manner as the previous five methods referenced above. The same general assumptions were applied with addition of the following:
For Alternative Methods 1 and 3, it is assumed that the bracing would be 18-in steel piping that would be placed every ten feet. Enough piping would be purchased to work on approximately 200-lf at one time. The piping is assumed to be re-used as the construction progresses.
Alternative Method 2 assumes 25-lf soil nails would be installed. Alternative Method 4 is assumed to be constructed in alternating 4-lf sections to allow for arching of the
soils. Alternative Methods 2 and 5 include costs for stabilizing the south wall during construction.
Table 3. Opinion of Probable Costs of Alternative Shoring Methods
Altern.M
ethod No. Alternative Shoring Method Description Fixed Costs Variable Costs Total Costs
To facilitate a design scheme at bridge locations, additional soil and water information behind the north and south walls would be necessary. Also, the lateral and vertical extents of the slurry concrete behind the existing walls at the bridge locations, reportedly placed during a high flood, should be determined to evaluate construction problems with any design scheme. This could be accomplished by probing through the existing walls. If this evaluation determines that the slurry concrete can support the soil pressure behind it, it is conceivable that the existing north and south invert under the bridges could be removed and replaced, apparently without any shoring system. However, it would be preferable to use a segmental construction because of the element of uncertainty in the soil-supporting coverage of the slurry concrete. Note that the slurry concrete itself may not be laterally stable and could move during and upon removal of the north and south invert under the bridges. Also, buildup of any water pressure behind the existing wall could cause concentrated seepage through any openings in the slurry concrete with potential for erosion, ground loss and the consequent settlement of the road. Segmental construction may provide a precaution against ground loss and lateral movement. It may be prudent to also utilize horizontal struts or bracings for added safety, if needed. Design calculations would be necessary for the scheme.
Monitoring Recommendations
1. A condition survey should be performed before and after construction. 2. Lateral deflection/movement of sheet pile walls and the south wall should be measured and documented
for the entire duration of construction. Any progressively increasing movement with time should immediately be reported for remedial action.
3. Piezometers or observation wells are to be used at the top of the banks to ensure that the groundwater control system maintains the water level at least eighteen inches below the excavation bottom and that water pressure does not build up behind the walls during continuous and heavy precipitation.
4. The settlement of the road at the bridges and the ground behind north wall, especially for the Alternate Method No. 4 for north wall construction as presented above, should be monitored.
5. Contractor should submit a monitoring plan for above.
Conclusion
Based on our review and analysis, it appears that Method 1 of installing sheet piles for temporary shoring and then removing it provides the best alternative for the construction of the north wall. This is a conventional method of shoring and should be the most cost-effective.
The north wall may also be built using methods used to underpin foundations for buildings and retaining walls (Alternative Method 4). It may not require sheet pile installation behind the existing north wall; however construction duration would likely be significantly longer.
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Cursory Review of 75% Plans and 67% Specifications:
OCPW has requested that a cursory review of their 75% plans and 67% specifications be reviewed. The following are our comments on the plans and specifications:
1. Verify the constructability of the wall at Beach Boulevard. Can the existing footings be removed with the existing walls remaining in place?
2. Verify the connection moment capacity at the "step" of the new wall and existing wall at Beach Boulevard. 3. Can a "stepped" channel, similar to the section at Beach Boulevard be used for the entire length of the
project? 4. The construction notes for the typical section at Beach Boulevard on sheet 9 conflicts with the details
shown on sheet 14B. Sheet 9 indicates the removal of north wall and its replacement. Sheet 14b shows that the concrete wall stem for the north wall will stay and be structurally supported by the L shaped element of its new base slab matching the existing slab of the south wall.
5. Sheets 9 and 11 show a side inlet to be constructed under the Beach Boulevard Bridge through the north wall, but the existing north wall is protected in place and re-used. Please verify that this detail is correct.
6. The side inlet detail also shows a junction to be built under the approach to the Beach Boulevard Bridge; we understand that this portion of the bridge has been backfilled with a concrete slurry. This needs to be indicated on the plans since the work to remove it will be more difficult.
7. Verify that there will be adequate space to construct the side inlets for the 30 and 36 inch pipes. Sheet 11 calls for "L" to be shoring limits minus "C" and RC collar length. The shoring is estimated to be about 3 feet behind the existing wall. The collar length will be 24" for this size pipe and the "C" distance is 2'-6" on the plan. This is more than the estimated shoring limit.
8. The 12" (T3) walls at the top of the typical section shown on Sheet 14 are not thick enough for the hooks of the B1 bars (#9). Standard hook length for a #9 bar is 1'-7". The B4 bar (#8) has a similar issue.
9. Verify the reason for the "box" at the end of the invert slab. If this is for conveyance of water, there are no inlets found on the plans.
10. There are no details for the transition between the "box" and sections without a "box". 11. The channel detail under the Western Avenue Bridge shown on sheet 14A does not match the typical
section shown on sheet 4. 12. The cantilevered wing wall shown on sheet 14C needs to be checked for additional reinforcing at the top
to act as a cantilever. 13. Construction notes should indicate that the groundwater level should be maintained at least eighteen
inches below the excavation bottom with an adequately designed and installed groundwater control system.
14. The specifications do not require a submittal and approval of the contractor's shoring plan. Any shoring system finally adopted must be supported by design calculations for review.
15. The specifications need to define the limits for shoring. For example, driven piles will not be allowed due to noise and vibration restrictions, tie-backs will not be allowed due to easement restrictions, etc.
16. The specifications and construction notes should also include the monitoring requirements. 17. The specifications do not mention that there is a possibility of a 6700 cfs storm flow that the contractor
should to be aware of. 18. Section F-7 of the specifications should also include submittal and approval of their shoring plan. 19. Section F-31.7 should refer to Section 51-1.03E(3). The latest Caltrans spec (2010) has the drill and bond
