ارزيابي رفتار ماسه‌ي زهكشي نشده با استفاده از پارامتر حالت

Evaluating Sand Behavior through State Parameters

مطالعات تجربي نشان داده اند كه رفتار خاك هاي دانه‌يي از نسبت تخلخل و تنش همه جانبه‌ي تحكيم اوليه تاثير مي-پذيرند. بنابراين لزوم تدوين روابطي براي تعريف تاثير آنها در رفتار ماسه در چگالي‌ ها، تنش هاي همه جانبه و برشي مختلف ديده مي شود. در اين نوشتار با معرفي 4 پارامتر حالت: نسبت تنش همه جانبه، نسبت تنش همه جانبه‌ي ابتدايي، نسبت تنش برشي ابتدايي و شاخص فشار اوليه، دو فضاي تنش جديد جهت تعريف رفتار ماسه تحت بارگذاري زهكشي-نشده و يكنواخت در تمامي محدوده هاي تنش همه جانبه و چگالي پيشنهاد و دو رابطه بر اساس اين فضاها ارايه شده است. در ادامه، با استفاده از داده هاي آزمايشگاهي ديگر پژوهشگران، تمامي مسيرهاي تنش و مسيرهاي تنش- كرنش براي وضعيت‌هاي مختلف ماسه از حالت هاي شل تا متراكم تحت بارگذاري زهكشي نشده و يكنواخت شبيه سازي شده است. در نهايت، جهت صحت سنجي روابط پيشنهادي، نتايج حاصل با داده هاي آزمايشگاهي مربوط به آزمايش هاي سه محوري زهكشي نشده‌ي فشاري مقايسه و مورد بحث و ارزيابي قرار گرفته‌اند.

It has been understood from experimental studies that granular soil behavior can be highly affected by density and mean principal effective stress. The effect of these factors on sand behavior is of great significance, and defining the nature of the link between them and their controls on the behavior of sand, is carried out in this study. Sand, in its loose or dense state, before approximating its critical state, obtains a constant stress ratio. Therefore, changes in the stress ratio of shear stress to mean effective stress may be ignored. It is worth mentioning that in loose sand, it is corresponded to phase transformation, but, it happens next to phase transformation in dense sand. The point at which the constant ratio initiates is of great importance and is called Initial Failure Point. The present study tries to outline two noble state parameters; early confining stress ratio, , and early shear stress ratio, . Early confining stress ratio and early shear stress ratio are defined as the stress ratio of the current mean effective stress to the mean effective stress of the early point of the failure line, and as the stress ratio of the current shear stress to the shear stress of the early point of the failure line. Furthermore, another state parameter, confining stress ratio, , is defined as the stress ratio of the current stress to the initial mean effective stress. Finally, through introducing four state parameters including: initial state pressure index, , confining stress ratio, , early confining stress ratio, , early shear stress ratio, , two stress spaces of early confining stress ratio-early shear stress ratio and axial strain-early confining stress ratio, are introduced to define sand behavior under undrained monotonic loading in all ranges of confining stress and density, from loose state to dense state. Subsequently, according to these spaces, two relations are offered. Thus, undrained monotonic loadings are simulated. Eventually, in order to evaluate the accuracy of the proposed relations, the resulting simulations are compared with other laboratory tests in the literature of undrained triaxial compression. The results show very good agreement, indicating that the proposed relations are capable of simulating undrained sand behavior under monotonic loading.