Appendix D Rock Blasting Report

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Myra Black
5 years ago
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1 Appendix D Rock Blasting Report

3 May 20, 2005 Frank Arciero Jr. Fallingstar Homes Burbank Foothill Ranch, California Subject: ANTICIPATED ROCK EXCAVATION FRAZIER PARK ESTATES DEVELOPMENT FRAZIER PARK, CALIFORNIA Mr. Arciero: In order to provide Mark Dawson (Cornerstone Engineering) with some additional information regarding the possibility of blasting at the site, our firm contacted a local excavation contractor who has worked in the Frazier Park area for approximately 45 years. His experience in the general project area has been that conventional excavation techniques have been able to rip and remove the upper 40 feet of native soils and rock. He does not recall any areas that required blasting to remove the fractured rock. However, almost all of the contractor s experience with cuts has been under 40 to 50 feet in height and most likely through the softer Hungry Valley Formation. The large depths of cuts (up to 163 feet) for this project far exceed what the contractor has accomplished for earthwork jobs in the Frazier Park area. Based on the September 2, 2004 Grading Plan, it appears that the maximum depth of cuts in the Hungry Valley Formation are approximately 163 feet in height. The maximum depth of this cut is located approximately 200 feet east of the Frazier Mountain High School property line (in Area 12). The estimated area where blasting may be required in this formation is approximately 12 acres. The actual school buildings are located in excess of approximately 450 feet northwest of the west extent of the estimated blasting area. Without additional investigations (additional borings and/or seismic refraction lines), it is unknown whether blasting will be required to remove the lower portions of this unit. Another area where rock excavation and blasting may be required is the approximately 85- foot cut planned in Area 3. This cut slope will be accomplished in the gneiss rock formation. It is likely that the upper portions of this rock can be excavated with conventional techniques. However, it is very likely that rock excavation techniques will be required to remove the lower portions of the gneiss rock formation. The estimated area where blasting may be 612 NW Third Street, Grants Pass, Oregon Phone (541) Fax (541)

4 Page 2 required in this formation is approximately 2 acres. This cut is located approximately 3200 feet northwest of the property line for the Frazier Mountain High School. This considerable distance to the site will tend to dampen any ground accelerations created by the rock blasting. The change in geologic units (from gneiss rock to the Hungry Valley Formation) will also tend to dampen the ground accelerations felt by the school. Our experience and discussion with blasting experts regarding blasting programs which remove hard rock units indicates the following: 1. Conventional excavation techniques can be used to remove all or the majority of the soil and fractured rock from the blasting site. 2. The drilling contractor then drills small diameter holes in a grid pattern to a set depth into the hard rock with an air-track drill rig. The grid pattern and depths of drilling are generally selected based on rock hardness, natural fractures, depth of excavation, the goal of the finish product and other site and environmental factors. 3. Specific charges and detonation cords and are typically placed in the individual holes in a very specific and planned sequence. The charges within the holes can be detonated at specific time intervals to maximize their effect on the rock and to minimize its environmental impact to adjacent parcels and the public. The actual blast event(s) typically occurs over a time period of several seconds. The blast contractor is generally responsible to ensure the safety of the public and to ensure that the site is clear for blasting. 4. The fractured and pulverized rock is then removed from the blast site by conventional excavation equipment such as excavators, loaders and dump trucks in order to prepare the site for additional drilling and blasting (if needed). Many times a site will utilize a series of blast events to accomplish the required rock removal with minimal impact outside the blast area. This entire process (for an individual blast event) can range from several days to several weeks, depending on the size of the area planned for each individual blast event. Based on our discussions with blasting contractors and explosive distributors, we understand that typical blast events are utilized to pulverize from approximately 8,000 to 40,000 cubic yards of in-place rock. The drilling contractor generally utilizes 3 or 4-inch diameter holes and spaces the drill holes in a 9-foot by 9-foot grid pattern. Depending on the project grade requirements, each lift of blasting can vary in depth from 10 to 40 feet. A local contractor indicated that the typical blast event size for a project such at this generally covers an area of approximately 110 feet square and removes approximately 20 feet of material (9,000 cubic yards). The individual blast events will vary significantly in size and depth depending on the final product (cut slopes versus general material removal) desired by the blast event. For a blast size of approximately 9,000 cubic yards of in-place rock, we understand that approximately 21,000 pounds of ANFO powder would be required in the drill holes. We have conservatively estimated that approximately 628,000 cubic yards of rock blasting may be required between Areas 3 and 12 at the site. Based on an average yield of 9,000 cubic yards per blast event, this will require 70 individual blast events. Based on discussions 2500ltr2 Rock Blasting The Galli Group

5 Page 3 with blasting contractors, we understand that it is likely that 1 to 5 blast events could occur during a typical work week. The contractor will need time to remove the pulverized rock material and to drill for the next shot. Based on these extremely rough estimates, it is possible that the blasting program for this project could vary in length from 3 to 6 months. Based on our review of groundwater levels at the site (which are generally greater than 100 feet in depth), we anticipate that the drill holes will be relatively dry. Therefore, it is likely that the blasting contractor will utilize ANFO series of blasting agent ( powder ). It is our understanding that the ANFO product consists of a mixture of ammonium nitrate and fuel oil with various additives which can be utilized to enhance its water resistance. However, if standing water is encountered during the drilling, the blasting contractor will most likely switch to an emulsion/anfo blend which is specifically designed for detonation in wet conditions. PETN (Pentaerythritol Tetranitrate) boosters and a blasting cap are generally utilized to enhance and detonate the ANFO powders. Based on our discussions with local explosives distributor, trucks can generally carry from 16,000 to 23,000 pounds of ANFO powder. We understand that the ANFO powder can be placed and mixed in the drill holes directly from the truck (which minimizes spillage on the site). For a site such as this, it is prudent to perform test shots prior to finalizing the blasting program. Test shots usually consist of small charges (5% to 10% of the regular blast charges) in a series of 2 or 3 holes. These will help reveal natural fractures that can create excessive fly rock. They will also help the blasting contractor determine how best to lay out the production blasting. It also helps him determine the hole depth, charge size and depth of burial (stemming) for the charges. The stemming depth relates to the amount of sand placed over the charge in the hole to decrease fly rock. All together the test blast results will allow the blast contractor to provide a blasting program which minimizes the potential for damage at or adjacent to the site. It has been our experience that people tend to be much more sensitive to the noise and the air percussion that is caused during the blast event than are structures to the actual blast shock. The actual ground accelerations caused by blasting typically do not damage structures when the blasting contractor plans his blasting program to take into account the presence of nearby structures. Our firm has previously provided blast monitoring for a blast event which was within 100 feet of an existing home which experienced no damage or adverse effects from the blasting. The test program also allows us to monitor vibrations near the school structures. The data gathered will be used by the blast contractor to verify his final blast program will not damage adjacent structures. In order to reduce the impacts from blasting on the students and faculty of Frazier Mountain High School, we recommend the individual blast events be planned for after-school hours, during the weekends or during times when the school is not occupied. The contractor and 2500ltr2 Rock Blasting The Galli Group

6 Page 4 their blasting subcontractor can coordinate the blast events to minimize its impact on the public. The US Bureau of Mines (USBM) and the Office of Surface Mining Reclamation and Enforcement (OSMRE) have provided guidelines for damage to structures due to blasting and various mining operations. These guidelines are utilized to measure the blast events and compares it to thresholds of Peak Particle Velocities (PPV) which typically damage structures. We recommend that we provide seismic and air blast monitoring with seismographs during some or all of the blast events. This will provide documentation of peak particle velocities close to structures. The data will show that the properly laid out blast program results in PPV s well below the damage threshold for structures. We hope this meets your needs at this time. Please do not hesitate to call if you have any questions. Respectfully Submitted, THE GALLI GROUP ENGINEERING CONSULTING Paul A. Sellke, P.E. Senior Project Engineer 2500ltr2 Rock Blasting The Galli Group

IV. ENVIRONMENTAL IMPACT ANALYSIS G. GEOLOGY AND SOILS

IV. ENVIRONMENTAL IMPACT ANALYSIS G. GEOLOGY AND SOILS The following section is a summary of the geotechnical report conducted for the proposed project. The Report of Geotechnical Investigation Proposed