City of Laguna Beach Project No Forest Avenue Report No r Laguna Beach, California 92651

Transcription

1 81 Glenneyre St. Suite F Laguna Beach CA (949) FAX (949) November 8, 11 April 19, 12 (Revised) City of Laguna Beach Project No Forest Avenue Report No. 11-7r Laguna Beach, California Attention: Subject: References: Mr. Wade Brown Revised Geotechnical Update Report for Foundation Design Proposed Lifeguard Headquarters Facilities 175 Pacific Coast Highway Laguna Beach, California 1. Geofirm, 8, Geotechnical Update Report for Foundation Design, Proposed Lifeguard Headquarter Facilities, 175 Pacific Coast Highway, Laguna Beach, California, Project No. 718-, Report No , dated December 5. INTRODUCTION 2. Geofirm,, Excavation and Shoring Options, Proposed Lifeguard Headquarter Facilities, 175 Pacific Coast Highway, Laguna Beach, California, Project No , Report No , dated February 9. This revised report presents updated geotechnical conclusions and recommendations pertinent to the proposed new lifeguard headquarters facilities in Laguna Beach, California. Analysis for this investigation is based upon our previous referenced work and a review of conceptual architectural plans prepared by Whitfield Associates, Inc. As site conditions are generally similar to those previously investigated (Reference 1), the descriptions of existing conditions and earth materials are not duplicated herein. Accompanying Illustrations Figure 1 Typical Retaining Wall Subdrain Detail Plate 1 Updated Geotechnical Plot Plan Plate 2 Updated Geotechnical Cross Sections LH-1 through LH-4R

2 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: 2 Project Description Based on a review of recent plans prepared by Whitfield Associates, Inc., the proposed site improvements generally include the demolition of existing facilities at the site including the existing lifeguard facility, subterranean sewer lift station, detached public restroom building, and various exterior walkways and stairs. The proposed new lifeguard facility will be constructed in the same general location as the existing structure, and will include main and subterranean basement levels. The basement and first floor elevations are proposed to be at 2.66 and feet, NAVD88. Extensive hardscaping and landscaping are proposed to accommodate public access. A new sewer lift station is currently under construction adjacent to the existing facilities. The proposed lifeguard headquarters are anticipated to be supported on a waterproofed mat slab foundation supported by engineered compacted fill. Remedial grading and construction of basement-level foundations and retaining walls will require temporary shoring. We understand that a secant shoring system will be used around the exterior of the proposed lifeguard station. Exterior, non-structural improvements are anticipated to utilize conventional foundations embedded in competent existing soils or new engineered fill. CONCLUSIONS 1. The proposed lifeguard headquarters improvements are considered feasible from a geotechnical perspective, provided the recommendations herein are integrated into design, construction, and long-term maintenance. Proposed construction should not adversely affect adjacent properties provided appropriate construction methods and care are utilized during construction. 2. No active faults are known to transect the site and therefore the site is not expected to be adversely affected by surface rupturing. It will, however, be affected by ground motions from earthquakes during the design life of the structure. Secondary seismic hazards such as liquefaction and lateral spreading in the vicinity of the site are likely to occur in a major earthquake. However, these hazards will be mitigated within the proposed lifeguard station footprint by utilizing secant shoring around the structure, and by removing the liquefiable soils. Some damage may occur to improvements not supported on engineered fill over bedrock such as flatwork and utilities. 3. The site is underlain by artificial fill, and variably distributed landslide deposits, beach sand, alluvium, colluvium and Topanga Formation bedrock. Proposed foundation systems are recommended to be constructed in new engineered fill or bedrock. It is anticipated that onsite soils will be suitable for use as engineered fill pending environmental approval. Other backfill materials may also be used such as gravel and sand. Import should be approved by Geofirm prior to transporting to the site. 4. The proposed lifeguard headquarters building may be supported on a mat slab foundation with integrated retaining walls, supported on engineered fill over bedrock. Exterior

3 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: 3 improvements may be supported on conventional foundations in new engineered fill or may be deepened to competent existing soils. Some earthquake induced damage may occur to improvements not supported on engineered fill over bedrock such as flatwork and utilities. 5. Basement-level construction will require excavations that should be shored to retain caving-prone deposits and protect adjacent properties. Possible trenches for utilities will likely require shoring and bracing. 6. Onsite materials should excavate with conventional earthmoving equipment; however, difficult drilling conditions may be encountered in bedrock and possible lag deposits overlying the bedrock. Caving conditions are highly likely below groundwater. Casing of drilled excavations should be anticipated. 7. It should be anticipated that construction of proposed subterranean improvements will occur below groundwater. The proposed secant shoring will likely reduce the required dewatering, however, a dewatering contractor should be consulted to design and construct an appropriate system. Similarly, a waterproofing consultant or architect should design adequate waterproofing for the slabs and retaining walls. For design purposes, we recommend using a design groundwater elevation equal to the maximum tide elevation, which is estimated to be +8 feet (NAVD88). 8. The results of our laboratory testing and on-site observations reveal near-surface artificial fill materials have a low expansion potential, negligible soil soluble sulfate levels, and a severe potential for corrosion of buried metal. 9. No gross slope instability is anticipated over the design life of the structure. Shallow instability in the seacliff and the recent shallow landslide located in the southwest corner of the site may occur during seismic shaking or saturated conditions; however, no proposed improvements are currently planned for this area. UPDATED RECOMMENDATIONS Site Preparation and Grading 1. General Grading should be performed in accordance with the Standard Grading Specifications in Appendix D of the Reference 1 Report. Existing structures, underground improvements, vegetation and/or construction debris should be removed and disposed of offsite. Overexcavation and recompaction, where necessary, should be observed and approved in writing by a representative of this firm.

4 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: 4 2. Remedial Grading In order to mitigate the potential for liquefaction within the proposed lifeguard station footprint, we recommend removing the liquefiable alluvium soil to the bedrock contact within the secant pile shoring excavation, and backfilling the excavation with compacted fill. It is anticipated that the removals will extend approximately to 13 feet below the proposed finished floor elevation of 2.66 feet. We also recommend a minimum of 3 feet of existing, near-surface soils under proposed hardscape and landscape is removed and replaced with new engineered fill. Locally deeper removals may be recommended by the geologist during grading to remediate unsuitable soils. 3. Compaction Standard On-site soil materials are anticipated to be suitable for re-use as compacted fill, except for rubble or contaminated soil. Such materials should be placed at 1 percent of optimum moisture content and compacted under the observation and testing of the soil engineer to at least 9 percent of the maximum dry density as determined by ASTM D Imported Soils Imported soils for retaining wall backfill must be predominantly granular and nonexpansive, with a sand equivalent of at least. Imported materials should be approved by Geofirm prior to transport to the site. 5. Temporary Construction Slopes Temporary slopes exposing onsite materials should be cut in accordance with Cal/OSHA Regulations. It is anticipated that non-bedrock soils may be classified as Type B, and temporary cuts of 1:1 (horizontal:vertical) may be appropriate; bedrock may be classified as Type A where intact, and temporary cuts of ¾:1 may be appropriate. However, the soils exposed in temporary excavations should be evaluated by the contractor during construction. Shoring is anticipated around the footprint of the proposed lifeguard station, or where space limitations, wet soil or groundwater conditions preclude temporary slope layback. The safety of temporary construction slopes is deferred to the general contractor, who should implement the safety practices as defined in Section 1541, Subchapter 4, of Cal/OSHA T8 Regulations (6).

5 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: 5 Structural Design of Foundations 1. General It is anticipated that the structure will utilize a mat slab foundation founded in engineered fill over bedrock. Hardscape improvements may utilize conventional foundations in competent existing soil or new engineered fill. Deepening of foundations into competent soil may be necessary during construction. Laboratory test results indicate that the on-site materials have a low expansion potential. The following recommendations are based on the geotechnical data available and are subject to revision based on conditions actually encountered in the field. Our recommendations are considered to be generally consistent with the standards of practice. They are based on both analytical methods and empirical methods derived from experience with similar geotechnical conditions. These recommendations are considered the minimum necessary for the likely soil conditions and are not intended to supersede the design of the structural engineer or criteria of governing agencies. 2. Mat Slab Design It is anticipated that construction for the proposed structure will utilize a structural mat slab. The proposed mat slab should be designed by the structural engineer utilizing a coefficient of subgrade reaction of pounds per cubic inch. Mat slabs that will be constructed at a depth of 5 feet or more below the adjacent finished grade, and that will be supported by engineered compacted fill may be designed for an allowable bearing value of 25 pounds per square foot. Mat slabs should be at least 12 inches thick, and should be waterproofed below the groundwater table. 3. Conventional Foundations Conventional spread footings in geotechnically reviewed competent existing soil or compacted fill may be designed for an allowable bearing value of pounds per square foot, with a minimum width of 15 inches and a minimum embedment of 18 inches into competent material. This value may be increased by one-third for short duration wind or seismic loading. Settlement is anticipated to be less than approximately 3/4 inch in alluvium or fill. Lateral loads may be resisted by passive pressure forces and by friction acting on the bottom of footings. The allowable passive pressure forces may be computed using an equivalent fluid density of pounds per cubic foot for competent soil or compacted fill. The passive pressure should not exceed pounds per square foot. A coefficient of friction of.25 may be used in computing the fictional resistance.

6 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: 6 Conventional spread footings in geotechnically reviewed competent bedrock may be designed for an allowable bearing value of pounds per square foot. This value may be increased by one-third for short duration wind or seismic loading. Settlement is anticipated to be nil in bedrock. The allowable passive pressure forces may be computed using an equivalent fluid density of pounds per cubic foot for bedrock. The passive pressure should not exceed pounds per square foot. A coefficient of friction of.35 may be used in computing the fictional resistance for bedrock. To resist adverse effects of tension cracking due to seismic shaking effects, a minimum of two No. 4 bars should be placed at the top and bottom of continuous footings. Structural Design of Retaining Walls 1. Lateral Loads Active pressure forces acting on level backfilled retaining walls which support imported granular, non-cohesive material may be computed based on an equivalent fluid pressure of pounds per cubic foot. Walls supporting 2:1 slopes should be designed for an equivalent fluid pressure of 55 pounds per cubic foot. Possible topographic or structural surcharges should be addressed by the structural engineer. Restrained walls should be designed for 6 pounds per cubic foot equivalent fluid pressure. Limited wall deformations normally occur and should be considered in design of finished surfaces. Walls below the design groundwater elevation of +8 feet (NAVD88) should include hydrostatic pressure. In addition, if no subdrains are planned for the upper wall portion above the groundwater table, we recommend including an additional but separate hydrostatic pressure above the design groundwater elevation to account for possible shallow perched groundwater conditions. 2. Subdrains The drainage scheme depicted on Figure 1 or an approved alternative should be used to reduce the potential for seepage forces behind retaining walls. The details of such subdrain systems are referred to the wall designer, builder or waterproofing consultant. The subdrain is not a substitute for waterproofing. 3. Waterproofing A waterproofing consultant should be retained to provide appropriate recommendations to provide acceptable performance of construction below groundwater.

7 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: 7 Secant Shoring The proposed secant shoring will consist of caissons, some with structural steel and some without reinforcement. Shoring caissons with a diameter of at least twenty-four inches and a minimum bedrock embedment of 5 feet may be designed for a live plus dead load end bearing value of 6 pounds per square foot and skin friction of 5 pounds per square foot for bedrock only. No skin friction may be assumed for overlying materials. The values may be increased one-third for wind or seismic forces. Lateral resistance may be computed utilizing pounds per cubic foot equivalent fluid pressure for bedrock only, acting on a tributary area of twice the caisson diameter. Caissons used for shoring should be designed to resist potential lateral loading of 45 pounds per cubic foot equivalent fluid pressure within the deposits overlying the bedrock above the groundwater table. Shoring below the groundwater table should be designed for a total equivalent fluid pressure of 85 pounds per cubic foot, including hydrostatic pressure. Settlement in bedrock is anticipated to be nil. Sheeting, Shoring, and Bracing of Trenches for Storm Drain Replacement Trenches shall have sheeting, shoring, and bracing conforming to CAL/OSHA requirements. Lateral pressures for design of trench sheeting, shoring, and bracing shall be based on type of soil exposed in the trench, groundwater conditions, surcharge loads adjacent to the trench, and type of shoring what will be used in the trench. For preliminary design purposes, the following soil parameter values may be utilized for shoring designs; these may require modification to meet specific conditions at varying locations. Active Pressure Lateral Loading = 45 pounds per cubic foot equivalent fluid pressure Passive Pressure Lateral Resistance = 25 pounds per cubic foot equivalent fluid pressure Friction Coefficient =.35. Plans for shoring and bracing should be provided as a part of the plan submittal and should be reviewed by the geotechnical consultant and civil engineer. Concrete Laboratory test results indicate on-site soils have negligible soluble sulfate content. However, as the concrete is in a marine environment, a moderate sulfate exposure should be used for design purposes. The concrete mix should be designed by a concrete expert in consideration of structural requirements. In lieu of a specific design, recommendations as presented in the California Building Code, Section should be utilized, which refer to Tables and of ACI 318, which recommends Type II cement, a maximum water-cement ratio of., and a minimum unconfirmed compressive strength of 5, psi.

8 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: 8 Seismic Structural Design Based on the geotechnical data and site parameters, the following is provided by the USGS (NEHRP, 3) to satisfy the CBC design criteria: Foundation Plan Review Site and Seismic Design Criteria for CBC Design Recommended Parameters Values Site Class C Site Longitude (degrees) Site Latitude (degrees) Ss (g) B S1 (g) B.621 SMs (g) C SM1 (g) C.539 SDs (g) C SD1 (g) C.539 Fa 1. Fv 1.3 Seismic Design Category D In order to review conformance with the recommendations of this report and as a condition of the use of this report, the undersigned should review final foundation plans and specifications prior to submission of such to the building official for issuance of permits. Such review is to be performed only for the limited purpose of checking for conformance with the design concept and the information provided herein. This review shall not include review of the accuracy or completeness of details, such as quantities, dimensions, weights or gauges, fabrication processes, construction means or methods, coordination of the work with other trades or construction safety precautions, all of which are the sole responsibility of the Contractor. Geofirm s review shall be conducted with reasonable promptness while allowing sufficient time in our judgment to permit adequate review. Review of a specific item shall not indicate that Geofirm has reviewed the entire system of which the item is a component. Geofirm shall not be responsible for any deviation from the Construction Documents not brought to our attention in writing by the Contractor. Geofirm shall not be required to review partial submissions or those for which submissions of correlated items have not been received. Observation and Testing The California Building Code, Section requires geotechnical observation and testing during construction to verify proper removal of unsuitable materials, that foundation excavations are clean and founded in competent material, to test for proper moisture content and proper degree of compaction of fill, to test and observe placement of wall and trench backfill

9 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: 9 materials, and to confirm design assumptions. It is noted that the CBC requires continuous verification and testing during placement of fill, pile driving, and pier/caisson drilling. A Geofirm representative shall visit the site at intervals appropriate to the stage of construction, as notified by the Contractor, in order to observe the progress and quality of the work completed by the Contractor. Such visits and observation are not intended to be an exhaustive check or a detailed inspection of the Contractor s work but rather are to allow Geofirm, as an experienced professional, to become generally familiar with the work in progress and to determine, in general, if the work is proceeding in accordance with the recommendations of this report. Geofirm shall not supervise, direct, or have control over the Contractor s work nor have any responsibility for the construction means, methods, techniques, sequences, or procedures selected by the Contractor nor the Contractor s safety precautions or programs in connection with the work. These rights and responsibilities are solely those of the Contractor. Geofirm shall not be responsible for any acts or omission of the Contractor, subcontractor, any entity performing any portion of the work, or any agents or employees of any of them. Geofirm does not guarantee the performance of the Contractor and shall not be responsible for the Contractor s failure to perform its work in accordance with the Contractor documents or any applicable law, codes, rules or regulations. These observations are beyond the scope of this investigation and budget and are conducted on a time and material basis. The responsibility for timely notification of the start of construction and ongoing geotechnically involved phases of construction is that of the owner and his contractor. Typically, at least 24 hours notice is required. Jobsite Safety Neither the professional activities of Geofirm, nor the presence of Geofirm s employees and subconsultants at a construction/project site, shall relieve the General Contractor of its obligations, duties and responsibilities including, but not limited to, construction means, methods, sequence, techniques or procedures necessary for performing, superintending and coordination the work in accordance with the contract documents and any health or safety precautions required by any regulatory agencies. Geofirm and its personnel have no authority to exercise any control over any construction contractor or its employees in connection with their work or any health or safety programs or procedures. The General Contractor shall be solely responsible for jobsite safety. LIMITATIONS This investigation has been conducted in accordance with generally accepted practice in the engineering geologic and soils engineering field. No further warranty is offered or implied. Conclusions and recommendations presented are based on subsurface conditions encountered, and are not meant to imply a control of nature. As site geotechnical conditions may alter with

10 November 8, 11 Project No: April 19, 12 (Revised) Report No: 11-7r Page No: time, the recommendations presented herein are considered valid for a time period of one year from the report date. The recommendations are also specific to the current proposed development. Changes in proposed land use or development may require supplemental investigation or recommendations. Also, independent use of this report in any form cannot be approved unless specific written verification of the applicability of the recommendations is obtained from this firm. Thank you for this opportunity to be of service. If you have any questions, please contact this office. Sincerely, GEOFIRM Erik R. Hilde, PG Erick J. Aldrich, RCE, GE Senior Engineering Geologist, EG 23 Senior Geotechnical Engineer, GE 2565 Registration Expires Registration Expires Signed / / ERH/EJA:fp Distribution: Addressee (5)

11 Onsite Native Soil Cap (1.5-2.' thick) H Typical Retaining Wall Select Noncohesive Granular Backfill (SE > ) 1/2 H Geotextile Filter Fabric Limit of Wall Excavation Geotextile Filter Fabric 8" Lap Single-sized 1/2"- 3/4" Drain Rock (1 cubic foot per lineal foot) Retaining Wall Footing 4" Perforated Plastic Collector Pipe, (Below Slab Elevation) Notes: This system consists of a geotextile fabric-wrapped gravel envelope. Collection is with a 4- inch diameter perforated plastic pipe embedded in the gravel envelope and tied to a 4-inch diameter non-perforated plastic pipe which h discharges at convenient locations. The outlet t pipe should be placed such that the flow gradient is not less than 2. percent. The geotextile fabric-wrapped gravel envelope should be placed at a similar gradient All drain pipes should be Schedule PVC or ABS SDR-35. Perforations may be either bored 1/4- inch diameter holes or 3/16-inch slots placed on the bottom one-third of the pipe perimeter. If the pipe is to be bored, a minimum of holes should be uniformly placed per foot of length. If slots are made, they should not exceed 2-1/2 inches in length and should not be closer than 2 inches. Total length of slots should not be less than 5 percent of the pipe length and should be uniformly spaced. The fabric pore spaces should not exceed equivalent mesh openings or be less than equivalent mesh openings. The fabric should be placed such that a minimum lap of 8-inches exists at all splices. Typical Retaining Wall Subdrain Detail JOB NO.: DATE: FIGURE: APRIL 12 1

12 LH-4R' LH-3 GFB-3 LH-3' LHB-1 EXPLANATION LHB-1A CPT-2 22 Qlsr CPT-1 LH-2 LH-4R APPROXIMATE LOCATION OF GEOFIRM BORING (1985) APPROXIMATE LOCATION OF FAULT TRACE, DOTTED WHERE BURIED, QUERIED WHERE UNCERNTAIN APPROXIMATE LOCATION OF GEOLOGIC CONTACT, DOTTED WHERE BURIED, QUERIED WHERE UNCERTAIN 27 MEASURED STRIKE AND DIP OF BEDDING 26- MEASURED STRIKE AND DIP OF SHEAR 28 A MEASURED STRIKE AND DIP OF FAULT SURFACE, ARROW INDICATES STRIA DIRECTION A' LOCATION OF GEOTECHNICAL CROSS-SECTION LHB-3 BEDROCK: TOPANGA FORMATION GFB-3 LHB-2 LH-1 CIRCLED WHERE BURIED ALLUVIUM/COLLUVIUM, UNDIFFERENTIATED APPROXIMATE LOCATION OF GEOFIRM BORING (5) LH-2' BEACH SAND DEPOSITS LHB-3 RECENT LANDSLIDE DEPOSITS APPROXIMATE LOCATION OF GEOFIRM CONE PENETROMETER (9) CPT-2 ARTIFICIAL FILL LH-1' Qlsr 85 UPDATED GEOTECHNICAL PLOT PLAN LIFEGUARD HEADQUARTERS 175 PACIFIC COAST HIGHWAY LAGUNA BEACH, CALIFORNIA JOB NO.: REPORT NO.: R DATE: PLATE: APRIL 12 1

13 LH-1 LH-1' LH-2 LH-2' 5 5 TEMPORARY EXCAVATION PROFILE (TYP); 1:1 (HORIZ:VERT) MAXIMUM IN NON-BEDROCK SOILS EXISTING GRADE PROPOSED GRADE SUBDRAINS PER FIG. 1 PROPOSED HARDSCAPE 3' MIN. OVER-EXCAVATION BELOW EXISTING GRADE UNDER PROPOSED EXTERIOR IMPROVEMENTS BORING LHB-2 PROPOSED GRADE ELEVATION IN FEET BORING LHB-3 (PROJ.) T.D. 7' EXISTING PUBLIC RESTROOM POSSIBLE BURIED SLAB (EXISTING) TP-1 (PROJECTED) EXISTING GRADE ELEVATION IN FEET EXISTING 24" STORM DRAIN (APPROX.) TO BE REPLACED EXISTING GRADE ELEVATION IN FEET EXISTING 24" STORM DRAIN (APPROX.) TO BE REPLACED - APPROXIMATE GROUNDWATER ELEVATION LH-3 P L LH-3' LH-4R LH-4R' PACIFIC COAST HIGHWAY GFB-3 (4--85) PROPOSED STRUCTURE PROPOSED STRUCTURE P L EXISTING INN AT LAGUNA HOTEL LHB-1 LHB-1A EXISTING LIFEGUARD HEADQUARTERS BUILDING PROPOSED HARDSCAPE EXISTING HEADQUARTERS BUILDING ELEVATION IN FEET - EXISTING 24" STORM DRAIN (APPROX.) TO BE REPLACED T.D. 32' EXISTING PUMP ROOM EXISTING WET WELL REMOVE AND REPLACE NON-BEDROCK SOILS UNDER NEW SLABS APPROXIMATE GROUNDWATER ELEVATION T.D. 5'8" EXISTING LIFT STATION - ELEVATION IN FEET - Qal/ col REMOVE AND REPLACE NON-BEDROCK SOILS UNDER NEW SLABS EXISTING PUMP ROOM EXISTING WET WELL Qal/ col APPROXIMATE GROUNDWATER ELEVATION - - ANTICIPATED TEMPORARY SECANT-PILE SHORING, DESIGN PER STRUCTURAL ENGINEER EXISTING SECANT-PILE SHORING - - ANTICIPATED TEMPORARY SECANT-PILE SHORING, DESIGN PER STRUCTURAL ENGINEER - UPDATED GEOTECHNICAL CROSS SECTIONS LH-1 THROUGH LH-4R LIFEGUARD HEADQUARTERS 175 PACIFIC COAST HIGHWAY LAGUNA BEACH, CALIFORNIA JOB NO.: REPORT NO.: DATE: PLATE: R APRIL 12 2