رئوس مطالب

  • چکیده
  • کلیدواژه ها
  • مقدمه
  • خاک مرکز شهر سیاتل و خاک رس سیاتل
  • دستگاه فشارسنج و فرآیندهای آزمایش
  • تکنیک های تخمین تنش جانبی در محل
  • روش های بررسی منحنی اولیه
  • کاربرد مدل ساختاری
  • آزمایش خزش فشار متعادل در محل
  • رابطه K0.ocr و k0.PI
  • بحث در مورد نتایج
  • خلاصه و جمع بندی

Abstract

Pressuremeter testing was conducted for the State Route (SR) 99 Bored Tunnel project in Seattle, Washington, to estimate in situ soil stress-deformation parameters along the tunnel alignment. Many of the tests were conducted in a very stiff to hard glaciolacustrine clay known as Seattle clay. This unit is historically known for deep-seated slope failures and many of these failures have been attributed to the release of high, locked-in lateral stresses. Estimation in situ lateral stresses along the tunnel alignment was a primary focus of the exploration program. Due to the hard consistency of this unit and the potential for cobbles, neither self-boring pressuremeter nor dilatometer testing was feasible; therefore, prebored pressuremeter testing was used. Using several lateral stress estimation techniques, including a novel in situ creep testing approach, the in situ lateral stresses in the Seattle clay were estimated to be significantly higher than what would be expected by assuming a simple, laterally constrained, vertical loading and unloading stress path due to glaciation. Deformational features commonly encountered in Seattle clay indicate its stress history also has included significant lateral shearing. The memory of this shearing within the fabric of the clay may influence the in situ stress state and response to lateral unloading.

Keywords: - - - - - - -

Conclusions

A novel technique for estimation of in situ lateral stresses, BPC testing, was performed in 10 PMTs during the geotechnical exploration program for the SR-99 Bored Tunnel project. The BPC technique was experimental during the SR-99 Bore Tunnel project exploration program and continues to be under development. Improved testing procedures for the BPC technique that attempt to control for possible loading rate and duration effects have been implemented in subsequent projects. Pore pressures develop during undrained PMT loading and also may have some influence on the creep behavior. However, because the pressuremeter membrane is impermeable, these pressures would need to dissipate into the formation. Further, the creep tests are held only for approximately 2 min. The authors anticipate that cavity creep movement is driven by an unbalanced pressure field and not dissipation of porewater. Future experimental studies with pore pressure measurements in a laboratory-controlled environment would be greatly beneficial to help better understand the relationship between cavity expansion creep movement and in situ lateral confining stress.

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