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HomeMy WebLinkAboutT-5010 7 TERRA ASSOCIATES, Inc. Consultants in Geotechnical Engineering, Geology and Environmental Earth Sciences I October 8, 2001 Project No. T-5010 Mr. Keith Davis 14609— 142nd Avenue SE Renton, Washington 98059 DEVELOP tv1EN-p'pl9A„.:. Subject: Coal Mine Hazard Evaluation Davis Property d 1815 Talbot Road South Renton, Washington al / Dear Mr. Davis: As requested, we have completed a Coal Mine Hazard Evaluation on the subject prop included review of available literature documenting historical mining activities in the Re (� subsurface investigation and visual reconnaissance of the subject site, and review of p: on property located immediately east of the subject site. The following discussion de study and presents our conclusions. r Z 0- BACKGROUND INFORMATION _ The subject site is a residential lot located northwest and adjacent to the intersection JI rI r' Talbot Road in Renton, Washington. King County tax records indicate that the site residence since about 1915. The original house was recently demolished, and a new construction near its location. This general region of Renton is known to have been actively mined for coal in the l, This site is in the general vicinity of the Patton mine, which was opened in 1872 and at O C to 1912. Historical records on the workings of the Patton mine are limited. Infon C/1 workings were confined to a single six- to eight-degree incline down the dip of one coal stratum, from which coal was mined along two levels. The entrance to the mine was located on the eastern side of Morris Avenue South at the right-of-way for South 16th Street, approximately 800 feet north-northwest of the subject site. It is reported that the Patton mine was not extensively developed, possibly because of groundwater and roof support problems. The overburden above the coal seam that was mined was relatively thin, estimated to be generally less than 100 feet. 12525 Willows Road, Suite 101, Kirkland, Washington 98034 Phone (425) 821-7777 9 Fax (425) 821-4334 9 terra@terra-associates.com r TERRA ASSOCIATES, Inc. Consultants in Geotechnical Engineering, Geology and Environmental Earth Sciences October 8, 2001 Project No. T-5010 Mr. Keith Davis 14609— 142nd Avenue SE Renton, Washington 98059 DEVC'TMOFRE O'N 4dG Subject: Coal Mine Hazard Evaluation Davis Property NOV 0 1 2001 1815 Talbot Road South r„m Renton, Washington '" ' � Dear Mr. Davis: As requested, we have completed a Coal Mine Hazard Evaluation on the subject property. Our scope of work included review of available literature documenting historical mining activities in the Renton, Washington area, a subsurface investigation and visual reconnaissance of the subject site, and review of previous work by our firm on property located immediately east of the subject site. The following discussion describes the results of our study and presents our conclusions. BACKGROUND INFORMATION The subject site is a residential lot located northwest and adjacent to the intersection of South 19th Street and Talbot Road in Renton, Washington. King County tax records indicate that the site has been occupied by a residence since about 1915. The original house was recently demolished, and a new house is currently under construction near its location. This general region of Renton is known to have been actively mined for coal in the late 1800s to early 1900s. This site is in the general vicinity of the Patton mine, which was opened in 1872 and abandoned some time prior to 1912. Historical records on the workings of the Patton mine are limited. Information indicates that the workings were confined to a single six- to eight-degree incline down the dip of one coal stratum, from which coal was mined along two levels. The entrance to the mine was located on the eastern side of Morris Avenue South at the right-of-way for South 16th Street, approximately 800 feet north-northwest of the subject site. It is reported that the Patton mine was not extensively developed, possibly because of groundwater and roof support problems. The overburden above the coal seam that was mined was relatively thin, estimated to be generally less than 100 feet. 12525 Willows Road, Suite 101, Kirkland, Washington 98034 Phone (425) 821-7777 9 Fax (425) 821-4334 • terra@terra-associates.com t avis Mr. Keith D October 8, 2001 In reviewing available records, there was one reported incidence of surface subsidence related to coal mining activities from the Patton mine. This was on property located at 320 South 19th Avenue, approximately one- fourth mile west of the subject site. In 1984, this site was extensively studied by the Morrison-Knudsen Company, Inc. (Morrison-Knudsen) under contract with the Office of Surface Mining. The reported problems and damage to the home included cracking of the interior and exterior fireplace chimney, a 1.5-inch sag in the kitchen floor, cracking of concrete walks and driveways, and ground subsidence below a rear deck and floor joist support. Extensive field exploration performed by Morrison-Knudsen revealed that the overburden above the coal seam mine in this area was relatively thin, less than 35 feet. Test borings performed above the mined tunnel noted that the overburden $oils were disturbed, possibly indicating slumping or subsidence of the soil zone. However, Morrison-Knudsen concluded that the settlements at the residence were not related to subsidence or collapse phenomena associated with the mining activities, but are more likely due to extensive and probably poorly placed fill materials at that location. FIELD EXPLORATION RESULTS On September 17, 2001, we investigated subsurface conditions at the site by excavating 4 backhoe test pits to ' maximum depths of 8 to 9 feet below the ground surface, and in a 75- to 80-foot long, approximately 5-foot deep trench that extended across the southeastern portion of the site. In addition, we reviewed a boring log from previous work by our firm, located approximately 75 to 80 feet east of the subject site. The surface elevation at the location of this boring is about Elev. 189, approximately 6 feet lower than the elevation along the southern margin of the subject site. The approximate locations of the on-site test pits and trench, and the off-site boring, ' are shown on the Exploration Location Plan,Figure 2. The soils observed in the on-site test pits and trench consist of eight to ten inches of sod and topsoil overlying about four to five feet of medium dense to dense, native silty sand to sandy silt. We observed glacial till consisting of dense to very dense silty sand/sandy silt with varying amounts of fine gravel beneath the upper weathered soils. We did not observe groundwater seepage or indications of disturbed soils in any of the test pits. The test boring located approximately 75 to 80 feet east of the subject site encountered very dense glacial till to a depth approximately 80 feet below the ground surface. The glacial till at this location is underlain advance outwash sands with silt and gravel to a depth approximately 105 feet below the ground surface. Our visual examination of the soil samples collected from the boring did not find any evidence of disturbance. A void was encountered beneath the outwash soils about 105.5 feet below the existing surface grade. The presence of this void was detected by a complete loss of drilling fluid once the void was penetrated. Sounding indicated that the void had a height of about 2.5 feet. Beneath the void, we encountered a very dense fine- to medium-grained sand. This sand is likely soft sandstone of the Renton formation. The void is indicative of mine workings, and it is likely that the sand formation encountered beneath the void is roof collapse following extraction of the coal. The preceding discussion is intended as a general review of subsurface conditions encountered at the locations of the on-site test pits and trench, and the off-site test boring. Detailed descriptions of the conditions encountered in the on-site test pits and trench, and in the off-site boring, are presented on the attached Test Pit Logs, Off-Site Boring Log, and Exploration Trench Log. Project No. T-5010 Page No. 2 Mr. Keith Davis October 8, 2001 DISCUSSION Available information indicates that the lower level of the Patton mine workings drove from west to east beneath the subject property, and then veered a short distance to the southeast. Conditions encountered in our off-site boring appear to confirm this recorded location of the mine workings. Based on review of the available mine records and the conditions observed in our off-site boring, it appears that the mine workings extended beneath the subject site. Therefore, the site would be subject to a coal mine hazard that involves the potential for surface subsidence to occur if the void or opening closes by natural processes. In our opinion, the only subsidence mechanism that could potentially affect the site is trough subsidence. Trough subsidence is time-dependent and occurs as a result of gradual bending of the soil strata overlying the opening, causing the roof to sag and eventual closure of the opening. This type of subsidence can result in both vertical and lateral displacements, the surface extent of which could extend beyond the horizontal dimension of the mine opening. The potential for development of a subsidence trough is dependent on many factors, including the dimensions of the mine workings and the strength and deformation characteristics of the overlying strata. The dimensions of the mine workings in this area are undocumented. However, in their previous study of the mine, Morrison- Knudsen speculated that the mine width along this lower level was likely five to eight feet. The sandstone that overlies the coal seam is a weak formation and, as reported, caused considerable difficulty during the mining operation with respect to roof collapse. The sand encountered beneath the void at Boring B-1 is likely roof collapse material, which occurred during or shortly following extraction of the coal. The overlying glacial sediments exhibit high strength characteristics, and based on visual examination of the soil samples and the penetration test results, do not appear to have been affected or disturbed by this roof collapse. There are no surface features present that would suggest trough subsidence has occurred. Given the conditions observed, it is more probable that the mine workings are relatively narrow and that the glacial sediments are arching or bridging the void that developed following collapse of the sandstone formation. Arching is a natural characteristic of the granular formation and is often relied upon in tunnel and shoring design. CONCLUSIONS Based on our study, it is our opinion that the hazard and associated risk to public health and safety associated with the presence of the coal mine workings beneath the site is minimal. Currently, there are no surface features that would suggest surface subsidence has occurred or is occurring. The results of our exploration indicate that the glacial sediments are currently bridging or arching above a void that likely resulted following roof collapse upon coal extraction. Given the likely narrow width of the mine workings, it is our opinion that this arching effect will continue. In the event of an earthquake, additional stress generated by ground shaking could affect the balance of this current equilibrium. Historically, since closing of the mine, the Puget Sound region has been subjected to three major earthquakes that occurred in 1949, 1965, and 2001. There are no surface expressions that would suggest the ground motions during these earthquakes had any effect on the current mine stability. However, a strong motion earthquake could result in additional collapse of soil into the void, the results of which may be reflected at the ground surface. Project No. T-5010 Page No. 3 Mr. Keith Davis October 8, 2001 We trust the information presented is sufficient to meet your current needs. If you have any questions or need additional information, please call. Sincerely yours, TERRA ASSOCIATES, INC. 4on .-SadIt,CR P;G: Project Engineerit�gYGeolog t f TletdoreJ,'Sghep�er',aP: Princip'IE igineer,i ' JG�'3S�ae Encl: Figure 1 —Vicinity Map Figure 2 Exploration Location Plan Figure 3 —Unified Soil Classification System Figures 4 through 5 —Test Pit Logs Figure 6—Off-Site Boring Log ' Figure 7 —Exploration Trench Log I I 1 Project No. T-5010 IPage No. 4 SUN ,j 'A� 5 S u 4T►+ <' SST`<' "$ cFQW CF i f ST SN sTN CT p TM n Ao FREO JS4 C� w¢x NT , W 14EYER . 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No. 5010 Date OCT 2001 Figure 1 37 - - - TP-4 � aT 1 NEW RESIDENCE _z UNDER CONSTRUCTION z Q 19 SE v / q / TP-1 A,41 �. o A: TP- / i i TP-2 / FIRE. / �)HYD fl SOUTH 19 STREET P w0 20 40 }ps, !E' APPROXIMATE SCALE IN FEET J OJ~ B-1 LEGEND:' 19 APPROXIMATE TEST PIT LOCATION APPROXIMATE BORING LOCATION 194 f z NOTE: THIS SITE PLAN IS FOR REFERENCE PURPOSES ONLY AND IT SHOULD NOT BE USED FOR CONSTRUCTION OR DESIGN PURPOSES. REFERENCE: SITE PLAN PROVIDED BY HANSEN SURVEYING,DATED JUNE 13,200E EXPLORATION LOCATION PLAN Terra DAVIS PROPERTY .� .•• ••• ASSOCIateS,` �rIC. RENTON, WASHINGTON • • Geotechnical Consultants Proj. No: 5010 Date OCT 2001 Figure 2 MAJOR DIVISIONS LETTER TYPICAL DESCRIPTION SYMBOL Clean GW Well-graded gravels, gravel-sand mixtures, little or no GRAVELS Gravels fines. i m (less than GP Poorly-graded gravels, gravel-sand mixtures, little or O N More than 5% fines) no fines. U) 'N 50% of coarse Silty gravels, gravel-sand-silt mixtures, non-plastic traction is GM o a) a with fines fines. Lli larger than No. nes z E �, 4 sieve GC Clayey gravels, gravel-sand-clay mixtures, plastic fines. 0 O - Clean SW Well-graded sands, gravelly sands, little or no fines. o SANDS Sands 0 Ca Z (less than Poorly-graded sands or gravelly sands, little or no c More than 5/o fines) SP fines. < s cz 50% of coarse Q as-C O o " I fraction is SM Silty sands, sand-silt mixtures, non-plastic fines. U g smaller than Sands No. 4 sieve with fines SC Clayey sands, sand-clay mixtures, plastic fines. Inorganic silts, rock flour, clayey silts with slight j `�O SILTS AND CLAYS MIL Inorganic a) O O C N CL Inorganic clays of low to medium plasticity, (lean clay). E o a) Liquid limit is less than 50% LIJ o c U) OL Organic silts and organic clays of low plasticity. Z cn cis a) Q c 0 MH Inorganic silts, elastic. o SILTS AND CLAYS CU W as E CH Inorganic clays of high plasticity, fat clays. Z_ 0 Liquid limit is greater than 50% �- OH Organic clays of high plasticity. ' HIGHLY ORGANIC SOILS PT Peat. DEFINITION OF TERMS AND SYMBOLS cn Standard Penetration 2* OUT w DensityResistance in Blows/Foot I SPOONSIDE SAMP ERETER SPLIT ' z Very loose 0-4 T 2.4" INSIDE DIAMETER RING SAMPLER Loose 4-10 OR SHELBY TUBE SAMPLER = Medium dense 10-30 Dense 30-50 1 WATER LEVEL (DATE) 0 Very dense >50 Tr TORVANE READINGS, tsf Standard Penetration Pp PENETROMETER READING tsf LU> Consistency Resistance in Blows/Foot DD DRY DENSITY, pounds per cubic foot > Very soft 0-2 LL LIQUID LIMIT, percent = Soft 2-4 0 Medium stiff 4-8 PI PLASTIC INDEX U Stiff 8-16 N STANDARD PENETRATION, blows per foot Very stiff 16-32 IHard >32 Terra UNIFIED SOIL CLASSIFICATION SYSTEM DAVIS PROPERTY Associates, Inc. RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-5010 Date OCT 2001 Figure 3 Test Pit No. TP-1 Logged by: JCS Approximate Elev. 192 Date: 9/17/01 Depth Moisture (ft ) Content Soil Description 00 12 inches SOD and TOPSOIL. Mottled grayish-brown silty SAND to sandy SILT,fine grained, medium dense, moist. (SM/ML) (Weathered glacial till) Gray to brownish-gray silty SAND,fine grained,dense to very dense, moist. With occasional fine gravel. (SM) (Glacial till) Test pit terminated at 8 feet. No groundwater seepage enountered. 10 Test Pit No. TP-2 Logged by: JCS Approximate Elev. 195 Date: 9/17/01 Depth Moisture (ft ) Soil Description Content 8 inches SOD and TOPSOIL. Tan silty SAND to sandy SILT,fine grained,medium dense, moist. (SM/ML) Mottled grayish-brown silty SAND to sandy SILT, fine grained, medium dense to dense, moist. (SM/ML) (Weathered glacial till) 5 Gray to brownish-gray silty SAND to sandy SILT, fine grained,dense to very dense, moist. With occasional fine gravel. (SM/ML) (Glacial till) Test pit terminated 9 feet. 101 No groundwater seepage encountered. TEST PIT LOGS Terra DAVIS PROPERTY i Associates, Inc. RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-5010 Date OCT 2001 Figure 4 l Test Pit No. TP-3 Logged by: JCS Approximate Elev. 194 Date: 9/17/01 Moisture Depth eft ) Content Soil Description ` 12 inches SOD and TOPSOIL. I Mottled grayish-brown silty SAND to sandy SILT,fine grained, medium dense to dense, moist. With occasional fine gravel. (SM/ML) (Weathered glacial till) '5 Gray to brownish-gray silty SAND to sandy SILT,fine grained, dense to very dense, moist. (SM/ML) (Glacial till) Test pit terminated at 9 feet. 10 1 No groundwater seepage encountered. Test Pit No. TP-4 Logged by: JCS i Approximate Elev. 188 Date: 9/17/01 Depth Moisture Content eft ) Soil Description Cont 10 inches SOD and TOPSOIL. Mottled grayish-brown silty SAND to sandy SILT,fine grained, medium dense to dense, moist. (SM/ML) (Weathered glacial till) Gray to brownish-gray silty SAND to sandy SILT, fine grained, dense, moist. (SM/ML) (Weathered glacial till) 5 Gray to brownish-gray silty SAND to sandy SILT, fine grained, dense to Ivery dense, moist. With occasional fine gravel. (SM/ML) (Glacial till) I Test pit terminated at 9 feet. 10 No qroundwater seepage encountered. I TEST PIT LOGS l Terra DAVIS PROPERTY I Associates, Inc. RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-5010 Date OCT 2001 Figure 5 l I Boring No. B-1 ' Logged by: MFS Approximate Elev, 189 Date; 1/31/96 - 2/5/96 Water Graph/ Relative Depth E Blow)s/ Content USCS Soil Description Density (ft ) ° foot (%) SM Red-brown to gray-brown silty Dense = 58 SAND, moist, mottled. Gray silty SAND, moist, trace Very Dense = 50/6" SM of gravel. (TILL) i 0 1 • • Gray-brown silty sandy GRAVEL, Very Dense = 50/4" GM moist. • Dark gray silty SAND with = 50/4" gravel/cobble, moist. Very Dense 20 = 60/6" Becomes gray medium SAND, Very Dense moist, with trace of silt. SM 0 50/6" * = 50/0" Dark gray silty SAND with Very Dense gravel/cobble, moist. = 80/6" 40 Gray sandy SILT with gravel, moist. Ve ]rd = 60/6" ML i [O J � I Gray silty SAND with gravel/ SM cobble, moist. Ve _ ! � 50/0 * Page 1 of 2 * No recovery OFF-SITE BORING LOG Terra DAVIS PROPERTY Associates, Inc. RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-2970-1 Date OCT 2001 Figure 6 Boring No. B-1 (Continued) Logged by: MFS Date: 1/31/96 - 2/5/96 Approximate Elev. 189 Graph/ Relative Depth E (N) Water Reave USCS Soil Description Density et o Blows/ Content foot (%) (As above) I SM Note: Drilling through cobble/ 70 = 50/3" gravel 58.5 to 63.5, 66 to 68.5, 3 to 78 feet. I I Gray medium SAND with Very v Dense QO = 93/6" silt and gravel/cobble. i i 90 �L 71/6" SM SP I 100 Void 105.5 to 108 feet. I"ALight GRAY fine to medium sand, 70 10" moist, with some organic spiSpaminations. Renton Formation Page 2 of 2 Boring terminated at 108.8 feet. Boring drilled with hollow stem auger to 13.5 feet, mud rotory 13.5 to 108.8 feet. OFF-SITE BORING LOG Terra DAVIS PROPERTY Associates, Inc. RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-2970-1 Date OCT 2001 Figure 6 ,1 r' tf SOUTH A 1 200 ' I EXISTING G 5 W W •. O 190 F. ........... Q J w BOTTOM OF TRENCH 180 SCALE 1" .6 :•A 4 w� t: t� NORTH )SURFACE 200 LU LL 190 p Q Uj 180 LEGEND: O A mottled gray-brown silty SAND to sandy SILT fine grained,medium dense to dense,moist(SM)(Weathered Glacial Till) © gray to brownish-gray silty SAND to sandy SILT fine grained,dense to very dense,moist,with occasional fine gravel(SM)(Glacial Till) NOTE: No groundwater seepage. EXPLORATION TRENCH LOG #,-- Terra DAVIS PROPERTY 9RENTON, WASHINGTON Associates, Inc. otechnical Consultants Proj. No. 5010 Date OCT 2001 Figure 7