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Ground improvement using jet grouting column
- 1. GROUND IMPROVEMENT USING JET GROUTING COLUMN Carrefoursa ShoppingCenter – Izmit,Turkey
- 2. Contents ■ Objective ■ Introduction ■ Procedure ■ Site Layout and Soil Conditions ■ Liquefaction Analysis of Site ■ Design Parameter ■ Performance during Earthquake ■ Conclusion ■ References
- 3. Introduction ■ Jet grouting is a method of soil stabilization which involves the injection of a stabilizing fluid into the subsoil under high pressure under high velocity. ■ The soil stabilization by jet grouting is occurs due to the hardening of grouted fluid within the soil. ■ These hardened bodies forms like cemented columns which are grouted in numerous numbers as per requirement, thus stabilizing the soil.
- 4. Procedure
- 5. Location ■ The Carrefoursa complex covers an area of about 55,000 m2 and was designed to house a shopping mall. ■ The Carrefoursa Shopping Center is located in Izmit, approximately 5 kilometers from the fault rupture. ■ The shopping center, under construction at the time, was subjected to strong ground shaking during the Mw=7.4.
- 6. Objective ■ Jet-grout columns were also in- stalled to provide increased bearing support and to mitigate the effects of anticipated liquefaction.
- 8. ■ The Carrefour ShoppingCenter is situated in a low ground elevation. ■ The relatively flat area was recently reclaimed from Izmit Bay using gravelly fills. ■ The site is underlain by soft alluvial sediments consisting of alternating strata of soft clays, silt-clay mixtures, and silty sands. ■ The depth to firm rock is not known, but deep geological profiles from nearby sites suggest a depth of 80 to 100 m. ■ The water table is within 2 m of the surface.The site encompasses an area of about 55,000 m2
- 10. ■ The Cone PenetrationTest (CPT) tip resistances are low. ■ The values average about 1 MPa throughout the upper 25 m of the profile. ■ Standard Penetration Test (SPT) N1,60 blow counts average 5 blows/ft. in most strata. ■ Shear wave velocities measured by seismic CPTs are 110-140 m/sec throughout the upper 25 m.
- 12. ■ A simplified liquefaction analysis for the site was performed as Idriss (1998). ■ Peak accelerations in rock were estimated 0.5g. ■ Estimated cyclic stress ratios in the loose sand layer were found to be 0.5 ■ Design ground motions of M=7.5 ■ It was found that a high potential for liquefaction exists for the sand stratum. ■ This stratum varies from 2 to 4 m in thickness across the site and contains and average of 30% non-plastic fines.
- 14. ■ The jet-grout columns were installed using a single-fluid jet-grouting system. ■ The injection pressure was 450 bars. ■ Cement at a 1:1 water/cement ratio was used as the grouting agent to form the 0.6m diameter columns. ■ Two nozzles 2 mm in diameter were used on each rod.The rod rotation speed was 20 rpm. ■ The rods were lifted at the rate of 50 cm/minute.
- 15. Grid Pattern ■ Jet grout columns were installed in primary and secondary grids of rectangular pattern to provide blanket treatment beneath the structure. Primary Grid: ■ The columns in the primary grid are 0.6 m in diameter with a center- to-center spacing of 4.0 m. ■ These columns extended to a depth of 9.0 m from the ground surface.
- 16. Grid Pattern Secondary Grid: ■ The secondary grid consisted of shorter, 2.5-m long grouted columns installed in between the primary columns. ■ The center-to-center spacing of 2.0 m to further increase the liquefaction resistance of the sand stratum by means of solidification. ■ The short secondary columns were installed only within the sand stratum, extending from a depth of 6.5 m to 9.0 m in this area.
- 18. Quality assurance and quality control ■ Tests on the completed columns included integrity tests, pullout tests, compression strength tests on core samples, and visual field inspection. ■ Average 7- and 28-day unconfined compressive strengths from core samples were 2.0 MPa (280 psi) and 4.8 MPa (690 psi), respectively . ■ These values are typical of single-fluid jet-grout columns in fine-grained soils.
- 20. ■ During 1999 Kocaeli Earthquake (M7.4) the shopping center was about 60% complete and was the only area that had been jet-grouted. ■ No settlements or signs of ground damage were found beneath the supermarket building unlike in unimproved sections at the site. ■ Parking garage section suffered estimated settlements of 8-10 cm, and water was ponded on the surface ■ Warehouses located on about 25 m from the supermarket suffered about 5 cm of settlement.
- 22. PONDINGOFWATER AT PORTIONSOFTHE PARKING STRUCTUREAREA THAT WERE NOTYETTREATEDWITH JET GROUT COLUMNS
- 23. Typical CPT soundings before and after treatment
- 24. Conclusion ■ Conditions appropriate for liquefaction were present at the Carrefoursa ShoppingCenter site. ■ A loose sand layer 3.0 m in thickness was found to be liquefiable under relatively low levels of accelerations. ■ No settlements or signs of ground damage were found beneath the supermarket building unlike Parking garage. ■ Jet grout columns were effective in mitigation of liquefaction and liquefaction-related settlements of the loose sand stratum
- 25. References ■ https://www.researchgate.net/publication/265319014_SOIL_IM PROVEMENT_WITH_JET- GROUT_COLUMNS_A_CASE_STUDY_FROM_THE_1999_KOC AELI_EARTHQUAKE ■ https://link.springer.com/chapter/10.1007/978-3-540-79846- 0_98 ■ https://www.semanticscholar.org/paper/ON-METHODS-OF- GROUND-IMPROVEMENT-Khan- Yadav/01f303f201d56829136ddbf9672e7882b5fc9b74
- 26. THANKS!!
Editor's Notes
- Initially, the area where the soil has to be treated is chosen and a hole is drilled to the required depth. The depth depends upon how deep the weak subsoil exist. The hole drilled may be small of approximately 10 to 20 cm. Drilling can be done by rotating drilling system under high pressure to the desired depth. The next step is to place the equipment over the drill hole to conduct the injection process. The equipment consists of a jet grouting string of almost 7 to 10 cm diameter. At the end of this string, it possesses a nozzle in order have an injection at a higher velocity. The nozzle is small of diameter ranging from 1mm to 10mm. Now at the start, the string is raised and rotated slowly to seal the whole column surface with soil and the fluid system that has to be injected. Now the main jetting starts. As it progresses the fluid is injected (through a rotary motion) and the string is raised. Now between the process, a part of mud within the pit created and the fluid mix rises to the top, which is called as spoil. This gives an indication that the bottom is fully sealed with the grout and soil mix. The raising of the string is done in between the process at a distance of 40 to 100mm depending upon the depth of treatment. For each raising, a rotation is performed. There are certain systems in which raising is a continuous process along with the rotation of the string.
- The Kocaeli Earthquake of August 17, 1999 occurred in north- western Turkey with a magnitude of Mw=7.4. Seismic moment is a quantity used by seismologists to measure the size of an earthquake. The scalar seismic moment {\displaystyle M_{0}} M_{0} is defined by the equation M=u AD, where u is the shear modulus of the rocks involved in the earthquake (in pascals (Pa), i.e. newtons per square meter) A} is the area of the rupture along the geologic fault where the earthquake occurred (in square meters), and D} is the average slip (displacement offset between the two sides of the fault) on {\displaystyle A} (in meters
- The site is underlain by a gravelly sand fill that extends from the ground surface to a depth of about 2.5 m. The fill is underlain by a medium clay stratum that extends from a depth of 2.5 m to 6.0 m. Below the clay, a stratum of fine silty sand is encountered at a loose-to-medium density. The thickness of this sand layer ranges from 4 m to 1 m across the site. Below the sand, is a layer of medium silty clay that extends from 10 m to a depth of more than 30 m, where the exploration was terminated. The ground water table was found within 2.6 m of the ground surface throughout the site.
- Seismic CPT or SCPT is a method of calculating the small strain shear modulus of the soil by measuring shear wave velocity through the soil. The small strain modulus is an important quantity for determining the dynamic response of soil during earthquakes
- Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. the earthquake induced loading is expressed in terms of cyclic shear stress The capacity of soil to resist liquefaction represented by Cyclic Resistance Ratio (CRR). If the cyclic stress ratio caused by the earthquake is greater than the cyclic resistance ratio of in situ soil then liquefaction could occur during an earthquake.
- The jet-grout columns were installed using a single-fluid jet-grouting system. The injection pressure was 450 bars. Neat cement at a 1:1 water/cement ratio was used as the grouting agent to form the 0.6m diameter columns. Two nozzles 2 mm in diameter were used on each rod. The rod rotation speed was 20 rpm, and The rods were lifted at the rate of 50 cm/minute.
- Sonic Echo (SE) and Impulse Response (IR) are employed for the integrity test on deep foundation and piles. The test results can be used for evaluation of the pile cross-sectional area and length, the pile integrity and continuity, as well as consistency of the pile material;