More PG&E Tree Killing

Search the internet and see how many communities just like ours are losing their trees to PG&E. What PG&E is not telling anyone is that it is more dangerous to cut the trees down. The roots are helping the integrity of the pipe. "PG&E Pipe Stiffness and Soil Stiffness and Earthquake failure". Article below: Soil Stiffness Look online for: https://pgjonline.com/2016/06/01/report-card-has-pge-passed-the-test/ “San Francisco-based PG&E, one of the nation’s largest investor-owned utilities with 6,700 miles of high pressure transmission pipeline and 42,000 miles of distribution main, had to conduct critical safety pressure tests on segments of the line running through Santa Cruz in 2015 as part of an accelerated testing and replacement effort that the combination utility has been conducting the past five years in the wake of the San Bruno, CA tragedy that killed eight residents and injured scores more. The testing was to take several weeks, involving time-consuming, worker-intensive hydrostatic tests that are designed to detect and repair problems before they happen.” Look online for: Buried Pipe Failures Dependent on Soil Stiffness Agostino Napolitano “The amount of deflection induced by installation that will occur in any buried pipe depends on three factors: pipe stiffness, soil stiffness, and earth load and surface load due to construction equipment. Measurements made by Marston and Spangler equations reveal the load on a flexible pipe is substantially less than that on a rigid pipe. The level of lateral earth load also depends on the nature of the backfill and its level of compaction, as well as the stiffness of the side walls of a trench, if the pipe sits in a trench rather than in an embankment fill.” “Therefore, it should be readily appreciated that the backfill and its construction are vital to the performance of a flexible pipe. Unfortunately, designers have placed too much attention on the structural properties of the pipe rather than on the soil.” “There are many pertinent variables in the complex interaction of pipe and soil. For pipes, one widely recognized variable is pipe flexibility, D/t, which is an inverse form of pipe stiffness, EI/D3, and may be used for analyses involving pipe stiffness of plain steel pipe (no mortar linings or coatings).” “Pipe flexibility (D/t) normally ranges between 30 and 100 for oil and gas onshore pipelines. Another common variable is pipe deflection, Dx/D. For soil, the most pertinent variables are the friction angle f and the vertical strain of sidefill embedment, e. An approximation of strain is given by e = s/E’ where s is the vertical soil stress, and E’ is the soil stiffness modulus.” “Sidefill soil, on the opposite, is compressed vertically, compressed horizontally (radially) and confined longitudinally (biaxial compression) for which the compression (vertical strain) is less than it is for confined compression tests. To define if the behavior of a pipe is flexible or rigid, it is convenient to consider the stiffness ratio Rs as the ratio between soil stiffness and pipe stiffness: Rs = E’ / (EI/D3) = E’D3/EI Where: E’ is the soil stiffness modulus of the soil (slope of a secant on the stress strain diagram); EI/D3 = E/12(D/t)3 is the pipe stiffness, where I is the transverse moment of inertia per unit length of individual pipe wall components. Soil stiffness E’ can vary from 100 kPa for damped soil to 50-100 Mpa for well-compacted, coarsegrained soil. Pipe stiffness EI/D3 is inversely related to pipe flexibility D/t and reduces progressively to zero for high D/t values. Usually pipe stiffness contributes significant resistance to pipe deflection if Rs is less than about 200, or D/t less than 50 (Figure 2). Conversely, soil stiffness is crucial for flexible pipes and Rs is usually greater than 200.” Look online for: https://mceer.buffalo.edu/pdf/report/99-MN03.pdf in Google Chrome “Pipelines can be categorized as either continuous or segmented. Steel pipelines with welded joints are considered to be continuous while segmented pipelines include cast iron pipe with caulked or rubber gasketed joints, ductile iron pipe with rubber gasketed joints, concrete pipe, asbestos cement pipe, etc. The earthquake safety of buried pipelines has attracted a great deal of attention in recent years. Important characteristics of buried pipelines are that they generally cover large areas and are subject to a variety of geotectonic hazards. Another characteristic of buried pipelines, which distinguishes them from above-ground structures and facilities, is that the relative movement of the pipes with respect to the surrounding soil is generally small and the inertia forces due to the weight of the pipeline and its contents are relatively unimportant. Buried pipelines can be damaged either by permanent movements of ground (i.e. PGD, Permanent Ground Displacement) or by transient seismic wave propagation.” “Permanent ground movements include surface faulting, lateral spreading due to liquefaction, and landsliding. Although PGD hazards are usually limited to small regions within the pipeline network, their potential for damage is very high since they impose large deformation on pipelines. On the other hand, the wave propagation hazards typically affect the whole pipeline network, but with lower damage rates (i.e., lower pipe breaks and leaks per unit length of pipe). For example, during the 1906 San Francisco earthquake, the zones of lateral spreading accounted for only 5% of the built-up area affected by strong ground shaking. However, approximately 52% of all pipeline breaks occurred within one city block of these zones, according to T. O’Rourke et al., (1985). Presumably the remaining 48% of pipeline damage was attributed to wave propagation. Hence, although the total amount of damage due to PGD and wave propagation was roughly equal, the damage rate in the small isolated areas subject to PGD was about 20 times higher than that due to wave propagation.” Here we are looking at the relationship between dead tree roots, pore pressure, soil liquefaction, and pipeline failure in an earthquake. Look online for: http:\\www.nap.edu\read\2269\chapter\7#140 “Experience during the Loma Prieta earthquake confirmed the ruggedness of buried, welded steel pipeline systems located in competent soils.” The PG&E high-pressure transmission system suffered only two cracked welds in a 12-inch-diameter, 1930s vintage pipeline, which were repaired without interruption of service. Of the 25 distribution main repairs made in San Francisco, 23 were to older cast-iron pipe, and 20 were in areas known to have experienced permanent ground deformation (Phillips and Virostek, 1990; Honegger, 1991)” “Damage from to gas distribution lines in the city of San Francisco was largely limited to areas that experienced permanent ground deformation resulting from liquefaction, slope failure and settlement of alluvial sediment.” Note: liquefaction, slope failure, and settlement are all examples of excessive water accumulation. Look online for: https://mceer.buffalo.edu/pdf/report/99-MN03.pdf in Google Chrome “For a pipeline located in a liquefied layer as opposed to a competent layer, Suzuki et al. (1988) and Miyajima and Kitaura (1989) have shown that the pipe response is very sensitive to the stiffness of the equivalent soil springs. This subsection will discuss the equivalent stiffness of soil springs for a pipe in liquefied soil. Combining experimental data with analytical solutions based on a beam on an elastic foundation approach, Takada et al. (1987) developed an equivalent soil spring for a pipe in a liquefied soil. They indicate that the equivalent stiffness ranges from 1/1000 to 1/3000 of that for non-liquefied soil. On the other hand, Yoshida and Uematsu (1978), Matsumoto et al. (1987), Yasuda et al. (1987), and Tanabe (1988) suggest that the stiffness ranges from 1/100 to 3/100 of that for non-liquefied soil based on their model experiments.” “Miyajima and Kitaura (1991) also conducted model tests which indicated that the stiffness is related to the effective stress in the liquefied soil. That is, the soil spring constant is an increasing function of effective stress and hence, a decreasing function of excess pore water pressure ratio.” “These mitigation techniques involve various types of field treatments to reduce the potential for lateral spreading. The methods include increasing the density and strength of sand, lowering the ground water level and increasing the dissipation of pore water pressure. For example, Miyajima et al. (1992) proposed a vertical gravel drain system along the pipeline right-of-way which reduces the maximum pore water pressures. Fujii et al. (1992) suggest sand and compaction as a technique to increase soil density and strength, and thereby reduce the potential for liquefaction. Iwatate et al. (1988) performed experiments on buried culverts which drain ground water away from the pipeline. Finally, one could replace liquefaction soils in the vicinity of the pipe with nonliquifiable materials such as gravel to reduce the potential for liquefaction.” Or in our particular case the best desiccator available, live tree roots. Look online for: PIPELINES PIPA-Report-Final-20101117 Page 65 “Runoff drains and gutters should not funnel water directly into the transmission pipeline ROW, as excess water could erode pipeline soil cover and subsurface pipeline support and could impact pipeline corrosion protection systems.” Look online for: LANDSLIDES Processes, Prediction, and Land Use Roy C. Sidle Hirotaka Ochiai Chapter 6 “Almost all of the effects of forest harvesting discussed in this section are related to shallow, rapid landslides, where the deterioration of woody roots greatly affects the observed or modeled increases in landslide frequency and erosion. Although evidence has already been presented that indicates clearcutting may predispose shallow soil mantles to higher pore pressures during moderate storms following clearcutting...” Look online for: PublicReviewDraft2042.Pdf ASME/ANSI 401.2.3.1 Earthquakes. The following effects shall be considered when designing for earthquakes: (a) direct effects due to ground vibrations (b) induced effects (liquefaction, landslides) (c) effects due to crossing of active faults at the surface One final note. Roots have been shown to exert a root pressure on their of compacted earth of greater than 1MPa (145psi), the loss of which can dramatically effect soil stability, leading to subduction or liquefaction. The cutting of a tree results in the gradual breakdown of soil stiffness, loss of desiccating ability, and the deep root desiccation of potential liquefaction layers. The loss of such stiffness, should be of great concern, since it will not be immediate, but most assuredly it will have a dramatic, if not, catastrophic effect in future years.