fa بررسی موردی عملکرد ستون‌های جت‌گروتینک در بهسازی بستر پی گسترده ژئوتکنیک (مکانیک خاک و سنگ) Geotecnic مطالعه موردی Case-Study <p dir="RTL"><span style="font-family:b lotus;"><span style="font-size:10.0pt;">جت&rlm;گروتینگ یکی از روش&rlm;های بهسازی بستر و پایدارسازی شیب&rlm;ها است که به‌کمک آن می&rlm;توان ظرفیت باربری قائم یا جانبی زمین موردنظر را از طریق تزریق دوغاب سیمان تحت ‌فشار افزایش داد. در این تحقیق، بهسازی خاک با المان&rlm;های جت&rlm;گروت در یکی از شهرهای ساحلی شمال ایران بررسی می‌شود. نتایج تزریق دوغاب سیمان به‌روش تک‌سیالی به‌همراه شرایط ژئوتکنیکی</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">خاک</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">محل</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">ارائه می‌شود.</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">قطر</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">ستون&rlm;های جت&rlm;گروت، مقاومت تک‌محوری مغزه&rlm;های</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">گرفته‌شده</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">و</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">درصد</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">بازیابی</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">مغزه&rlm;ها</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">به‌عنوان</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">مهم‌ترین</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">پارامترهای</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">ارزیابی</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">عملکرد</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">بهسازی در معیارهای موجود، استفاده شده و بر اساس نتایج آن، طرح اولیه اصلاح و اجرا شده است. هم‌چنین</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">مشاهده شد</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">که در</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">صورت</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">تأمین</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">فشار</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">تزریق</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">450 بار</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">در</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">ماسه</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">سیلتی</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">اشباع و</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">غیراشباع با اعداد </span></span><span dir="LTR"><span style="font-size:9.0pt;">SPT</span></span><span style="font-family:b lotus;"><span style="font-size:10.0pt;"> متوسط به‌ترتیب 13 و</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">20، با سرعت بالا آمدن راد 5/0</span></span> <span style="font-family:b lotus;"><span style="font-size:10.0pt;">سانتی‌متر برثانیه و چگالی دوغاب </span></span><span dir="LTR"><span style="font-size:10.0pt;">gr/cm³</span></span><span style="font-family:b lotus;"><span style="font-size:10.0pt;"> 1600، به‌ترتیب ستون&rlm;هایی با قطر </span></span><span dir="LTR"><span style="font-size:10.0pt;">cm</span></span><span style="font-family:b lotus;"><span style="font-size:10.0pt;"> 80 و </span></span><span dir="LTR"><span style="font-size:10.0pt;">cm</span></span><span style="font-family:b lotus;"><span style="font-size:10.0pt;"> 100 به‌دست می&rlm;آید که مغزه&rlm;های استخراجی از ستون&rlm;های اجراشده در ماسه سیلتی اشباع دارای مقاومت تک&rlm;محوری </span></span><span dir="LTR"><span style="font-size:10.0pt;">kg/cm²</span></span><span style="font-family:b lotus;"><span style="font-size:10.0pt;"> 40 است. با توجه به زمان اجرای کوتاه نسبت به حجم عملیات بهسازی، روش جت&rlm;گروتینگ روشی مناسب و اقتصادی در زمین&rlm;های ماسه&rlm;ای اشباع و غیراشباع برای تأمین ظرفیت باربری موردنیاز است و معیار نرخ بهسازی در ارزیابی مقاومت تک‌محوری مغزه&rlm;های استخراجی از خاک بهسازی شده و تصحیح ظرفیت باربری ستون&rlm;های جت&rlm;گروت کارایی مناسبی از خود نشان داده است.</span></span><br> &nbsp;</p> <strong>Introduction</strong><br> Jet-grouting is a soil improvement technique which was originated in Japan. Jet-grouting method consist of disaggregation of soil or weak rock and its mixing with, and partial replacement by, a cement agent; the disaggregation is achieved by means of a high energy jet of a fluid which can be the cement agent itself. Jet-grouting techniques can be grouped into three main systems, which are named single, double and triple fluid, depending on the number of fluids injected into the subsoil, namely, grout (usually water&ndash;cement mixture), air and grout, and water plus air and grout. In the beginning, jet grouting was mostly viewed as a means of improving the subsoil properties for the foundations of large structures. Nowadays, its application are diversified for use in foundations, excavations, tunneling, water barriers and underpinning. This paper studies foundation improvement by jet-grouting in one of Iran northern cities and seeks the optimum design parameters for jet-grout columns in saturated and unsaturated sand. Results of cement grouting as one-fluid jet-grouting method together with site geotechnical characteristics are presented. Diameters of jet-grouted columns, uni-axial strength of soil-cement cores and core recovery index are surveyed as the most important parameters for performance assessment of improved foundation and the primary design is modified and the project completed based on the results.<br> <strong>Material and methods</strong><br> Design parameter of jet-grout columns were assumed according to guidelines and previous expertise as follows<s>ed</s>: single-fluid jet-grout method with 450 bar injection pressure and rod withdrawal speed of 0.5 cm/sec with a grout density of 1600 gr/cm³. Monitor rotation speed was set to 30 rpm. Soil strata consists of a 5 meter sand with some gravels followed by a 7 meter clayey silt with the average SPT numbers of 30 and 7, respectively. To investigate the effectiveness of design parameters, jet-grout columns head were uncovered by excavating its nearby soil and columns diameter were measured. Several core samples were prepared from columns with a L/D ratio of 2 and an average diameter of 74 mm by means of a triple tube core barrel after 28 days of columns installation. The volume of core samples were calculated by multiplying its length to its average cross section (calculated from the average diameter of cores) and their unit weight were obtained by dividing its weight to its volume. Uniaxial compression test conducted in the deformation-control mode with the strain rate of 1 percent on all samples. Core samples were tested in different ages from 34 to 85 days and uniaxial compression strength (UCS) of samples were corrected by age correction factor according to soil type suggested by Sližytė et al.<br> <strong>Results and discussion</strong><br> It is observed that the average diameter of columns that are constructed in unsaturated sand with design parameters mentioned in material and methods section, is one meter and the average diameter of columns that are constructed in saturated sand with the same density as unsaturated sand is 0.8 meter. This could be due to the dissipation of fluid jet energy under the water.<br> The modified obtained values from uniaxial compression test show that the strength of samples varies from 28 to 90 kg/cm². By omitting the lower, an upper 5 precent of the data as irrelevant data, the average UCS of the remaining part is equal to 57 kg/cm². By applying a geotechnical safety factor of 2.5 to the modified <s>a</s> filtered UCS values, a UCS of 40 kg/cm² is obtained as the structural strength of get-grout column.<br> <strong>Conclusion</strong><br> -It is observed that utilizing one-fluid jet-grout method with 450 bar injection pressure in saturated silty sand with mean SPT number 30, rod withdrawal speed of 0.5 cm/sec and grout density of 1600 gr/cm³ will result in 80 cm diameter jet-grout columns, while the same parameters will result in a 100 cm column in unsaturated sand which can be due to fluid jet energy dissipation under water.<br> -Considering the common design parameter for jet-grout columns in Iran, which are the same as the design parameters discussed in this paper, the UCS of get-grout columns in near shore silty sand with a safety factor of 2.5 is about 40 kg/cm².&nbsp;<br> <a href="./files/site1/files/123/6Extended_Abstract.pdf">./files/site1/files/123/6Extended_Abstract.pdf</a> بهسازی بستر, جت‌گروتینگ, تزریق پرفشار, معیار ارزیابی عملکرد, مقاومت فشاری محصور نشده 467 486 http://jeg.khu.ac.ir/browse.php?a_code=A-10-1411-1&slc_lang=fa&sid=1 Mohsen Sabermahani محسن صابرماهانی msabermahani@iust.ac.ir 10031947532846003609 10031947532846003609 Yes دانشگاه علم و صنعت ایران Valiollah Ghalehnovi ولی اله قلعه نوی v_ghalehnovi@civileng.iust.ac.ir 10031947532846003610 10031947532846003610 No دانشگاه علم و صنعت ایران Hamidreza Elahi حمیدرضا الهی hrelahi@yahoo.com 10031947532846003611 10031947532846003611 No دانشگاه علم و فرهنگ Shaham Atashband شهام آتش بند shaham1_at@yahoo.com 10031947532846003612 10031947532846003612 No دانشگاه آزاد اسلامی اراک