Source: China’s Thousands of Small Dams Struggle to Stay Afloat Chen Tai’an poses for a photo atop the Hongsha Hydropower Station dam in Liuyang, Hunan province, 2021. Diao Fanchao for Sixth Tone For decades, rural areas along the Yangtze River depended on small hydropower stations. Now, amid rising ecological costs and safety concerns, the government wants to make them more sustainable. Early in April, continuous rain lashed the central city of Liuyang, Hunan province for days. As the Yangtze River Basin entered its major flood season and its banks swelled, Chen Tai’an stood inside the hydropower plant he partly owns, listening to the rumble of its turbines. He says it’s the best time of the year to generate hydropower since most turbines operate at full capacity. But this year has been different. Chen says his Hongsha Hydropower Station’s annual revenue fell by more than 30,000 yuan ($4,600) as its output was cut by 100,000 kilowatts per hour. The reduced power generation stemmed from new, and more stringent, government guidelines for maintaining “ecological water flow” — the level and quality of water in rivers to sustain the local ecosystem. According to a 2018 government policy mandated for small hydropower stations, Chen couldn’t store water during the dry spell between August and March — meaning river water could no longer be fully stored to generate electricity as in previous years. So he was given until August of last year to install a floodgate on the dam to release one-tenth of the annual runoff into the river, with which he complied. “All that water wasted… such a shame,” says Chen, looking at the river and furrowing his brow. He’s still pondering what the government meant by “ecological water flow.” To him, all river water is a valuable resource, and using turbines to turn it into [...]
Geo-Congress 2014, Atlanta, Booth 105 Join us at Geo-Congress 2014 in Atlanta starting Sunday, February 23rd and running through Tuesday, February 25th, 2014. We're excited to be a part of this historic gathering, the first Geo-Institute conference focused on sustainability. CPT is an important part of structural design, including sustainably focused projects. It is also a vital technology for ground water monitoring, protection and soil remediation which are essential to sustainable development. Vertek CPT is excited to be sharing the latest breakthrough CPT tools including the new S4 quick attach CPT system! We'll be planning our spring product demo schedule that is kicking off in May. So stop by booth #105 to arrange a time and place to experience these products first hand and see how Vertek CPT can help you to be successful in the CPT business. Hope to see you there!
Shear strength is the ability of a material to resist shear forces—that is, forces that produce a sliding failure in the material parallel to the direction of the force. The diagram at right demonstrates shear stress, along with tensional and compressional stress. (What's the difference between a stress and a force? Stress is defined as force per area.) How is this relevant to soil testing? Well, consider a sliding failure in soil, such as occurs along a fault plane in an earthquake. Shear strength tells us a great deal about how the soil will behave under shear forces and during changes in stress, for example due to an earthquake or excavation. The in-situ shear strength of soil is difficult to measure, and many methodologies for doing so have been proposed. In general, estimating undrained shear strength--that is, the shear strength of the soil with in-situ moisture--using the CPT is accomplished via the relationship between overburden stress and cone resistance, as shown in the equation below. su = (qc – σvo)/Nk Where: su = undrained shear strength (unitless) qc = cone resistance (psi) σvo = overburden stress (psi) Nk = empirical cone factor (a unitless constant) Nk is determined in the lab, for example via triaxial compression tests. The exact value varies based on the type of reference test used, so it is important to be consistent in this regard. Most test methods return values between 10 and 30, varying with factors such as OCR (over-consolidation ratio), pore pressure, and soil plasticity. Several alternative methods may be used to estimate undrained shear strength via CPT, depending on the test conditions and available data. One such method uses pore pressure at u2 (directly behind the cone) in place of overburden stress: su = (qc – u2)/Nk The disadvantage of this method is [...]
Did you know that our CPTSND Data Acquisition program can average repeat seismic strikes? Once you have a strike on the screen, simply accept (retain) the strike and then add another strike of the same type ( A strike for example). This second strike will display below the first strike and when the second strike is accepted (retained) it will be averaged with the first strike and only the averaged strike will remain on the screen. If a third strike is added and then accepted (retained) it will be averaged with the result of the first two. (NOTE: Our software does not retain all the individual strikes- once they are averaged only the average is on file) Averaging strikes is recommended by some of the top GeoTechs in the nation!