تعيين پارامترهاي رفتاري آبرفت درشت دانه‌ي تهران به كمك آزمايش‌هاي پرسيومتري برجا و آزمايشگاهي

Evaluation of Coarse Grained Alluvium Behavior Based on Pressuremeter tests

يكي از مهم‌ترين مسايل در مهندسي ژيوتكنيك، پيش بيني رفتار آبرفت درشت دانه است، كه در گذشته تلاش‌هاي زيادي براي مدل‌سازي آن انجام شده است. رفتار ژيوتكنيكي آبرفت درشت دانه در مسايل مختلف مهندسي ژيوتكنيك همواره مورد توجه پژوهشگران مختلف بوده است. هدف اصلي اين نوشتار تعيين پارامترهاي موثر در رفتار آبرفت درشت دانه به كمك دستگاه چمبر و آزمايش پرسيومتري است. طراحي و ساخت دستگاه چمبر جهت انجام آزمايش پرسيومتري در اين پژوهش انجام شده است. به منظور بررسي اثر سيمانتاسيون تعدادي آزمايش پرسيومتري بالغ بر 100 آزمايش در محل، در اعماق مختلف در آبرفت درشت دانه انجام شده است. همچنين با شبيه سازي شرايط محل در محيط آزمايشگاه بدون سيمانتاسيون، تعدادي آزمايش پرسيومتري در دستگاه چمبر انجام شده است. در نهايت، نتايج آزمون‌هاي انجام‌شده با يكديگر مقايسه و پارامترهاي رفتاري مختلف ژيوتكنيكي آبرفت درشت‌دانه گزارش شده است.

The pressuremeter test can be considered one of the most important in situ tests in geotechnical engineering projects. The pressuremeter consists of two main elements: a radially extendable cylindrical probe, which is placed inside the borehole at the desired test depth, and a monitoring unit, which remains on the ground surface. These two parts are connected by cables and hoses. Coarse grained alluvium layers are major subsurface layers in urban areas, such as Tehran, the capital of Iran. Prediction of the behavior of these layers in geotechnical engineering problems is very important. Based on this, and for better predicting the constitutive behavior of coarse grained alluvium with cementation, physical modeling has been undertaken. For this evaluation, we used the pressuremeter test (PMT) in a laboratory chamber designed and constructed for this purpose. In-situ tests play an important role in any geotechnical engineering investigation. This test is capable of properly estimating the geotechnical and deflection parameters of soil. These parameters are the elasticity modules (E), the shear modules (G), the in situ horizontal stress (?h), limit pressure (PL), undrained shear strength (Cu) for clay, over the consolidated ratio (Em/PL) and the reaction modules (Ks). Furthermore, the number of parameters of these constitutive models (in many cases) inhibits their incorporation into general purpose numerical codes, thus, restricting their usefulness in geotechnical engineering practice. There are several different kinds of pressuremeter that differ mainly by the way the probe is placed in the ground. These pressuremeter tests have been done using a preboring method. Then, for assisting the cementation effect on the behavior of these layers, some pressuremeter tests have been undertaken in a laboratory chamber constructed for this purpose. This instrument was constructed for modeling under in situ conditions without cementation to inspect the effects of cementation on the coarse grained alluvium layers. Afterwards, the results of the pressuremeter tests on the chamber are compared with each other and the geotechnical parameters of the coarse grained alluvium are reported. These pressuremeter stress-strain curves are compared with the field test curves, and the constitutive parameters have been recalculated. Based on these curves, the elasticity modules and limit pressure were presented. Other parameters have been calculated in this paper. Finally, the results of the pressuremeter tests in the field and the PMT in the chamber are compared with each other and the cementation effect is reported.