Application of mechanically stabilized earth wall to construct sai gon river wall

lity to the system. Inclusions have been used since prehistoric times to improve soil. The use of straw to improve the quality of adobe bricks dates back to earliest human history. Many primitive people used sticks and branches to reinforce mud dwellings. During the 17th and 18th centuries, French settlers along the Bay of Fundy in Canada used sticks to reinforce mud dikes. Some other early examples of man-made soil reinforcement include dikes of earth and tree branches, which have been used in China for at least 1,000 years and along the Mississippi River in the 1880s. Other examples include wooden pegs used for erosion and landslide control in England, and bamboo or wire mesh, used universally for revetment erosion control. Soil reinforcing can also be achieved by using plant roots. The modern methods of soil reinforcement for retaining wall construction were pioneered by the French architect and engineer Henri Vidal in the early 1960s. His research led to the invention and development of Reinforced Earth, a system in which steel strip reinforcement is used. The first wall to use this technology in the United States was built in 1972 on California State Highway 39, northeast of Los Angeles. In the last 25 years, more than 23,000 Reinforced Earth structures representing over 70 million m2 (750 million ft2) of wall facing have been completed in 37 countries. More than 8,000 walls have been built in the United States since 1972. The highest wall constructed in the United States was on the order of 30 meters (98 feet). Currently, most process patents covering soil-reinforced system construction or components have expired, leading to a proliferation of available systems or components that can be separately purchased and assembled by the erecting contractor. The remaining patents in force generally cover only the method of connection between the reinforcement and the facing. Geogrids for soil reinforcement were developed around 1980. The first use of Geogrid in earth reinforcement was in 1981. Extensive use of Geogrid products in the United States started in about 1983, and they now comprise a growing portion of the market. 3.3.2 Current Usage of Mechanically Stabilized Earth Walls It is believed that MSE walls have been constructed in every State in the United States. Major users include transportation agencies in Georgia, Florida, Texas, Pennsylvania, New York, and California, which rank among the largest road building States. It is estimated that more than 700,000 m2 (7,500,000 ft2) of MSE retaining walls with precast facing are constructed on average every year in the United States, which may represent more than half of all retaining wall usage for transportation applications. The majority of the MSE walls for permanent applications either constructed to date or presently planned use a segmental precast concrete facing and galvanized steel reinforcements. The use of Geotextile faced MSE walls in permanent construction has been limited to date. They are quite useful for temporary construction, where more extensive use has been made. Recently, modular block dry cast facing units have gained acceptance due to their lower cost and nationwide availability. These small concrete units are generally mated with grid reinforcement, and the wall system is referred to as modular block wall (MBW). It has been reported that more than 200,000 m2 (2,000,000 ft2) of MBW walls have been constructed yearly in the United States when considering all types of transportation related applications. The current yearly usage for transportation-related applications is estimated at about 50 projects per year. In Vietnam, the constructions are reinforced by the traditional materials have been made at Lach Tray, Hai Phong Nga Tu Vong, Hanoi, Hue. Nowadays, the Mechanically Stabilized Earth Walls are developed in our country. So, they may be mentioned the retaining wall works: path to the bridge of Nuoc Man canal, Tan Duc bridge, Hung Vuong bridge in Long An, or retaining wall projects in Da Nang, Binh Duong, Ho Chi Minh City. We can say, with many of their outstanding characteristics, Mechanically Stabilized Earth Walls are innovative solutions for many different requirements in Viet Nam. In this thesis, I would introduce two solutions for retaining wall design works to stabilize Sai Gon River bank –Thanh My Loi residential area project, which will be clearly the advantages of this new material. 3.4 THEORETICAL BASIS FOR MECHANICALLY STABILIZED EARTH WALLS 3.4.1 Analysis theories Figure 3.31 The structure of mechanically stabilized earth wall It includes the four major components: (1) Facing: There are so many choices for the aesthetic and architectural requirements of investors. - Modular block was precast with many different models. - Precast panels of various sizes and different shapes. (2) Drainage: Using of crushed-stone aggregate and drainage-pipes. (3) Reinforcement: Uni-Axial Geogrid used for reinforcing. (4) Soil: Any filling soil at local. Geogrids are responsible for anchoring soil mass easily slip into the land mass itself is stable, wall surface can only beautify and keep the soil from erosion. Principles of calculation: MSEW based on two main factors to determine the type of Geogrids, embedded length and reinforcement spacing. Sizing for external stability. Sizing for internal stability. Currently, there are many standards in the world of design with MSEW. The contents of this thesis used AASHTO 2002/NHI 043-ASD standard of the United States to implement my design. 3.4.2 Determination of Basic Parameters The active coefficient of earth pressure Ka (Coulomb): It is calculated for vertical walls (defined as walls with a face batter of less than 8 degrees) and a horizontal backslope from: Ka= tan2(45-φ2) (3.1) For an inclined front face equal or greater than 8 degrees, the coefficient of earth pressure can be calculated from the general Coulomb case as: Ka=sin2θ+φsin2θsinθ-δ1+sinφ+δsinφ-βsinθ-δsinθ+β2 (3.2) Where φ : Friction angle of the soil. θ : The face inclination from a horizontal. δ : Wall friction angle. β : Surcharge slope angle. Figure 3.32 The active earth pressures (Coulomb analysis) Wall parameters: Vertical force due to earth pressure: V1=γrHL (3.3) Vertical force due to traffic surcharge: V2=qL (3.4) Resultant of vertical forces: R = V1 + V2 (3.5) The lateral force due to earth pressure: F1=12γbH2Ka (3.6) The lateral force due to traffic surcharge: F2=qHKa (3.7) 3.4.3 External Stability Analysis External stability evaluations for MSEW structures treat the reinforced section as a composite homogeneous soil mass and evaluate the stability according to conventional failure modes for gravity type wall systems. Differences in the present practice exist for internal stability evaluations which determines the reinforcement required, principally in the development of the internal lateral stress and the assumption as to the location of the most critical failure surface. As with classical gravity retaining structures, four potential external failure mechanisms are usually considered in sizing MSE walls. They include: Sliding on the base. Limiting the location of the resultant of all forces (overturning). Bearing capacity. Deep seated stability (rotational slip-surface or slip along a plane of weakness). Define wall geometry and soil properties Select performance criteria Preliminary sizing Evaluate static external stability Settlement/ lateral deform Overall slope stability Bearing capacity Overturning Sliding Establish reinforcement length Figure 3.33 External stability computational sequences are schematically illustrated above Direct Sliding: Figure 3.34 Sliding Check the preliminary sizing with respect to sliding at the base layer, which is the most critical depth as follows: FS sliding = Horizontal resisting forcesHorizontal driving forces= PRPd=V1tanφ(F1+F2) ≥1.5 (3.8) Where: FS sliding: Factor of safety for Sliding. Overturning (eccentricity): Figure 3.35 Overturning Overturning factor of safety: FOSov=MROMO ≥1.5 (3.9) Resisting moment: MRO=V1L2 (3.10) Driving moment: MO=F1H3+F2H2 (3.11) Bearing Capacity Failure: Figure 3.36 Bearing Capacity The concept of the wall base as a shallow foundation, resultant of vertical forces (R) will effect a tilt and the eccentricity is e. Based on the stress distribution at foundation base (Mayerhof), case of eccentric loading, the foundation size will scale to the conventional value (L-2e). Figure 3.37 External analysis: earth pressures/eccentricity; horizontal backslope with traffic surcharge Two modes of bearing capacity failure exist, general shear failure and local shear failure. Local shear is characterized by a "squeezing" of the foundation soil when soft or loose soils exist below the wall. General Shear: To prevent bearing capacity failure, it is required that the vertical stress at the base calculated with the Meyerhof-type distribution, does not exceed the allowable bearing capacity of the foundation soil determined, considering a safety factor of 2.5. σV≤qa=qultFS (3.12) A lesser FS of 2.0 could be used if justified by a geotechnical analysis which calculates settlement and determines it to be acceptable. Calculation steps for an MSE wall with a sloping surcharge are as follows: Obtain the eccentricity e of the resulting force at the base of the wall. Remember that under preliminary sizing if the eccentricity exceeded L/6, the reinforcement length at the base was increased. Calculate the vertical stress σv at the base assuming Meyerhof-type distribution: σV=V1+V2L-2e (3.13) Determine the ultimate bearing capacity qult using classical soil mechanics methods, e.g. for a level grade in front of the wall and no groundwater influence: qult=cfNc+0,5L-2eγfNγ (3.14) Where: qult: the ultimate bearing capacity (kN/m2) cf : The cohesion (kN/m2); γf : The unit weight (kN/m3); Nc,Nγ: Bearing capacity coefficients (dimensionless). Check that: σV≤qa=qultFS As indicated in step (2) and step (3), σv can be decreased and qult increased by lengthening the reinforcements. If adequate support conditions cannot be achieved or lengthening reinforcements significantly increases costs, improvement of the foundation soil is needed (dynamic compaction, soil replacement, stone columns, pre-compression. Local Shear: To prevent large horizontal movements of the structure on weak cohesive soils: γH≤2c (3.15) If adequate support conditions cannot be achieved, ground improvement of the foundation soils is indicated. Overall Stability: Figure 3.38 Deep seated stability (Rotational) Overall stability is determined using rotational or wedge analyses, as appropriate, which can be performed using a classical slope stability analysis method. The reinforced soil wall is considered as a rigid body and only failure surfaces completely outside a reinforced mass are considered. For simple structures with rectangular geometry, relatively uniform reinforcement spacing, and a near vertical face, compound failures passing both through the unreinforced and reinforced zones will not generally be critical. However, if complex conditions exist such as changes in reinforced soil types or reinforcement lengths, high surcharge loads, sloping faced structures, significant slopes at the toe or above the wall, or stacked structures, compound failures must be considered. If the minimum safety factor is less than the usually recommended minimum FS of 1.3, increase the reinforcement length or improve the foundation soil. Settlement Estimate: Conventional settlement analyses should be carried out to ensure that immediate, consolidation, and secondary settlement of the wall are less than the performance requirements of the project. This can be accomplished by increasing the top of wall elevations during design, but more practically, by delaying the casting of the top row of modular concrete blocks to the end of erection. The required height of the top row, would then be determined with possible further allowance for continuing settlements. Where the anticipated settlements and their duration, cannot be accommodated by these measures, consideration must be given to ground improvement techniques such as wick drains, stone columns, dynamic compaction, the use of lightweight fill or the implementation of multistage construction in which the first stage facing is typically a wire facing. 3.4.4 Internal Stability Analysis Internal stability is treated as a response of discrete elements in a soil mass. This suggests that deformations are controlled by the reinforcements rather than total mass, which appears inconsistent given the much greater volume of soil in such structures. Therefore, deformation analyses are generally not included in current methods. Maximum load level Load level at connection to face Equate allowable stress to applied connection stress Assess backfill develop allowable strength calculations Equate allowable stress to applied max.tensile stress Adjust soil reinforcement density to meet both max. and connection strength requirements Calculate reinforcement length required to be stable against pullout Assess backfill develop allowable strength calculations Design facing elements for the stress at wall face Design details for wall Evaluate static internal stability Select wall facing and backfill reinforcement type Reinforcement load level calculation by Figure 3.39 The design process can be illustrated above Reinforcement spacing: V1 = d1+ ½ (d2 – d1) (3.16) V2 = ½ (d2 – d1) + ½ (d3 – d2) Vi = ½ (di – di-1) + ½ (di+1 – di) Vend = ½ (dend – dend-1) + (H – dend) Calculation of Maximum Tensile Forces in the Reinforcement Layers Nghe Đọc ngữ âm Từ điển - :Xem từ điển chi tiết Geogrids are bearing tensile strength caused by the load itself and the external load. The tensile strengths are calculated independently and resultant of tensile strength will effect on each layer of Geogrids. Figure 3.40 The breakage of Geogrids Horizontal stress σH=Karσv+∆σh (3.17) σv=γrZ+σ2+q+∆σv (3.18) Where: Z: The depth referenced below the top of wall (m). ∆σv: The increment of vertical stress due to concentrated vertical loads (kN/m2). ∆σh: The increment of horizontal stress due to horizontal concentrated surcharges (kN/m2). For wall face batters of less than 80: Kar=tan2(45-φr) (3.19) For wall face batters equal to or greater than 80from the vertical: Kar=sin2(θ+φr)sin3θ1+sinφrsinθ2 (3.20) The maximum tension Tmax in each reinforcement layer per unit width of wall: Tmaxi=σHSV (3.21) Long-term tensile strength on a load per unit width of reinforcing basis. Tavailable=TULTRFD.RFID.RFCR (3.22) The design long-term reinforcement load. Tallowable=TavailablexRCFs (3.23) Where: TULT: Ultimate (or yield) tensile strength from wide strip test (ASTM D 4595) (kN/m). RFD: Durability rebate factor. It can vary typically from 1.1 to 2. RFID: Installation Damage reduction factor. It can range from 1.05 to 3.0. RFCR: Creep Reduction Factor Polymer Type Creep Reduction Factors Polyester 2.5 to 1.6 Polypropylene 5 to 4.0 High Density Polyethylene 5 to 2.6 Fs: Overall factor of safety to account for uncertainties in the geometry of the structure, fill properties, reinforcement properties, and externally applied loads. For permanent, MSEW structures only, a minimum factor of safety of 1.5 has been typically used. The safety factor of breakage tension: FOSST=TallowaleTmaxi≥1,5 Internal Stability with Respect to Pullout Failure: Figure 3.41The pullout of Geogrids Tmax≤1FOSPOF*γZpLeCRcα (3.24) Where: Rc : Coverage ratio as 1. Zp : The overburden pressure, including distributed dead load surcharges, neglecting traffic loads (m). Le : The length of embedment in the resisting zone (m). If Le ≤ 1, value as 1 If Le > 1, value as Le C : 2 for strip, grid, and sheet type reinforcement. α : Scale correction factor as 1. Tmax : Maximum reinforcement tension (kN/m). Pullout resistance factor: F*=tanφr Ci (3.25) Where: Ci : Interaction coefficient between the soil and reinforcement as 0.8 Safety factor against pullout: FOSPO≥1.5 Calculation of connection strength: FOSCO=bodkin joint strengthmaximum tensile force=TacTmaxi≥1.5 (3.26) Tac ≤ TULTRFDxFS Where: Tac: The connection strength (kN/m) by manufacturer (3.27) 3.5 Detailed instructions for using MSEW software For more advantages in the calculation as well as shorten the design time, I use MSEW software in the Geogrids design work. Basically, the theoretical calculations are similar as section 3.4. In this section, I just use some illustrated figures about using MSEW software. Figure 3.42 The flow chart for the procedure of simulation in MSEW YES NO Adjust reinforcement analysis Accept End Input the soil-reinforcement interaction parameters Start Create geometry wall/surcharge Input connection characteristic Input the engineering properties of the soil types Input specified heights, lengths and strengths of reinforcement Figure 3.43 The screens for input of design information and requirements These include the PROGRAM MANAGER, the GEOMETRY/URCHARGE, SOILS AND SEISMICITY, and REINFORCEMENT. Figure 3.44 Input required properties of he modular concrete block facing Figure 3.45 Calculations for the connection parameters. Figure 3.46 Connection strength Figure 3.47 Input the engineering properties of the reinforced soil, retained soil and foundation soil Figure 3.48 Input the reinforcement requirement from the design Figure 3.49 Input the technical characteristics of the Geogrids Figure 3.50 The results of height, length and type of Geogrids Figure 3.51 Input the interface fiction information for the geogrid reinforcement Figure 3.52 Determination of the earth pressure Figure 3.53 Results of the safety factors Figure 3.54 Results of detailed geogrids analysis CHAPTER 4: THE DESIGN SOLUTION FOR MECHANICALLY STABILIZED EARTH WALL AT THANH MY LOI PROJECT. 4.1 INTRODUCTION TO THANH MY LOI RESIDENTIAL AREA PROJECT 4.1.1 Project Overview Sai Gon river wall-Thanh My Loi project is responsible for protecting the residential area. So, according to the works classification standards, this works is level III. Figure 4.1 Location of Saigon river wall at Thanh My Loi project Works with the following design criteria: Wall Length: 633.28m (non-parking and canoes parking area) . The vertical wall height: 2.3m. The wall facing from a horizontal: 90 degrees. Peak load of wall: 0.1kg/cm2. The construction includes the following main categories: River wall. Drainage. Lighting. 4.1.2 Topography Topography of site is empty land, not populated, with natural elevation changes from 1.82m to 0.09m (According to Hon Dau elevation level). Along the river bank is serious erosion. Figure 4.2 Preparation of building site 4.1.3 Hydrological Characteristics The project area has a tropical monsoon climate, near the equator, hot, humid and rainy. There are two seasons in a year: rainy season from May to November with the prevailing southeast winds and dry season from December to April is the season winds towards the West - Southwest. The average wind speed is 2.9 m/s. Maximum water level with P = 1.0%: Hmax = +1.56 m. Minimum water level corresponding to P = 95%: Hmin = -2.55 m. Tidal amplitude (largest) average: 2.5 m to 3.0 m. Coastal flow velocity: 1.1 m/s. Average annual temperature and relatively stable, with approximately 28.10C: Absolute maximum temperature: 380C. Absolute minimum temperature: 140 C. Evaporation in the relatively high, reaching 1.642 mm. Humidity varies inversely with temperature, reached the highest in the rainy season and lower in the dry months. The average humidity for many years to reach 77.2%. Precipitation from 1.321mm to 2.729mm/year, average rainfall is 1.929mm. Focusing mainly on the rainy months 6, 7, 8, 9 and 10 and 90% annual rainfall. Dry season rainfall accounted for 10% of total annual rainfall. The hours have sunshine is 2,580 hours, about 29% of the time in a year. The construction is adjacent the Saigon River. So, they are directed from tidal regime of the river. There are two times of high tide and low tide per day and to interfere with drainage problems in areas where flood tides meet. 4.1.4 Result of Geotechnical Investigation. Based on the boring log at site and laboratory testing results, soil foundation is classified into 6 layers as followed: Layer 1: Soil classification: Yellow fillling finer sand. This layer is placed as below: Table 4.1 Soil classification of layer 1 Symbol of BH Depth of layer’s surface (m) Depth of layer’s bottom (m) Thickness of layer (m) SPT (hammer) HKBS1 0.0 0.2 0.2 - HKBS2 - - - - HKBS3 0.0 0.1 0.1 - Layer 2: Soil classification: Very soft state, blackish grey mud. This layer is placed as below: Table 4.2 Soil classification of layer 2 Symbol of BH Depth of layer’s surface (m) Depth of layer’s bottom (m) Thickness of layer (m) SPT (hammer) HKBS1 0.2 10.2 10.0 0-6 HKBS2 0.0 8.5 8.5 0 HKBS3 0.1 9.3 9.2 1-3 Physical and mechanical properties of the soil: Moisture content W = 74.61 % Wet unit weight γw = 1.48 g/cm3 Dry unit weight γd = 0.85 g/cm3 Specific gravity G = 2.56 Initial void ratio e0 = 2.86 Porosity n = 0.66 % Saturation degree S = 94.93 % Atterberg limit  Liquid limit WL = 62.39 % Plastic limit Wp = 31.64 % Plasticity index Ip = 30.75 % Index Liquid B = 1.4 Cohesion c = 0.059 kG/cm2 Angle of friction j = 03057’ Compressive index a1-2 = 0.11 cm2/kG Standard pressure Rtc = 0.76 kG/cm2 Layer 3: Soil classification: Stiff state bluish grey, reddish brown clay. This layer is placed as below: Table 4.3 Soil classification of layer 3 Symbol of BH Depth of layer’s surface (m) Depth of layer’s bottom (m) Thickness of layer (m) SPT (hammer) HKBS1 10.2 21.5 11.3 4 – 13 HKBS2 8.5 18.3 9.8 5 – 19 HKBS3 9.3 13.1 3.8 9-10 Physical and mechanical properties of the soil: Moisture content W = 27.7 % Wet unit weight γw = 1.92 g/cm3 Dry unit weight γd = 1.51 g/cm3 Specific gravity G = 2.69 Initial void ratio e0 = 2.36 Porosity n = 0.43 % Saturation degree S = 95.43 % Atterberg limit  Liquid limit WL = 41.89 % Plastic limit Wp = 22.39 % Plasticity index Ip = 19.54 % Index Liquid B = 0.72 Cohesion c = 0.21 kG/cm2 Angle of friction j = 18025’ Compressive index a1-2 = 0.028 cm2/kG Standard pressure Rtc = 4.56 kG/cm2 Layer 4: Soil classification: Very stiff state, yellowish grey, bluish grey sandy clay. This layer is placed as below: Table 4.4 Soil classification of layer 4 Symbol of BH Depth of layer’s surface (m) Depth of layer’s bottom (m) Thickness of layer (m) SPT (hammer) HKBS1 21.5 22.5 1.0 16 HKBS2 18.3 19.0 0.7 - HKBS3 13.1 14.5 1.4 8 Physical and mechanical properties of the soil: Moisture content W = 22.55 % Wet unit weight γw = 1.9 g/cm3 Dry unit weight γd = 1.55 g/cm3 Specific gravity G = 2.68 Initial void ratio e0 = 0.73 Porosity n = 0.42 % Saturation degree S = 82.6 % Atterberg limit  Liquid limit WL = 31.3 % Plastic limit Wp = 17.4 % Plasticity index Ip = 13.9 % Index Liquid B = 0.35 Cohesion c = 0.15 kG/cm2 Angle of friction j = 16059’ Compressive index a1-2 = - cm2/kG Standard pressure Rtc = 4.15 kG/cm2 Layer 5: Soil classification: Very stiff to hard state, bluish grey, reddish brown clay. This layer is placed as below: Table 4.5 Soil classification of layer 5 Symbol of BH Depth of layer’s surface (m) Depth of layer’s bottom (m) Thickness of layer (m) SPT (hammer) HKBS1 22.5 ≥30.0 ≥7.5 21-27 HKBS2 19.0 36.5 17.5 23-43 HKBS3 15.2 ≥30.0 ≥14.8 19-35 Physical and mechanical properties of the soil: Moisture content W = 21.18 % Wet unit weight γw = 1.98 g/cm3 Dry unit weight γd = 1.64 g/cm3 Specific gravity G = 2.69 Initial void ratio e0 = 0.64 Porosity n = 0.39 % Saturation degree S = 88.36 % Atterberg limit  Liquid limit WL = 41.41 % Plastic limit Wp = 20.78 % Plasticity index Ip = 20.14 % Index Liquid B = 0.02 Cohesion c = 0.31 kG/cm2 Angle of friction j = 18005’ Compressive index a1-2 = 0.019 cm2/kG Standard pressure Rtc = 8.84 kG/cm2 Layer 6: Soil classification: Medium dense state yellow finer and medium sand. This layer is placed as below: Table 4.6 Soil classification of layer 6 Symbol of BH Depth of layer’s surface (m) Depth of layer’s bottom (m) Thickness of layer (m) SPT (hammer) HKBS1 - - - - HKBS2 36.5 ≥50.0 ≥13.5 11-27 HKBS3 - - - - Physical and mechanical properties of the soil: Moisture content W = 20.56 % Wet unit weight γw = 1.91 g/cm3 Dry unit weight γd = 1.58 g/cm3 Specific gravity G = 2.67 Initial void ratio e0 = 0.68 Porosity n = 0.41 % Saturation degree S = 80.18 % Atterberg limit  Liquid limit WL = - % Plastic limit Wp = - % Plasticity index Ip = - % Index Liquid B = - Cohesion c = 0.066 kG/cm2 Angle of friction j = 27040’ Compressive index a1-2 = 0.015 cm2/kG Table 4.7 Statistical table of physical and mechanical properties of soil layers results Physical – mechanical properties Unit Layers 1 2 3 4 5 6 Grain size cobble % - 0.0 0.0 0.0 0.0 0.0 Gravel % - 0.0 0.0 0.0 0.0 0.0 Sand % - 19.22 22.1 42.95 21.64 80.33 Silt % - 30.23 28.97 29.15 27.47 11.29 Clay % - 50.55 48.93 27.90 50.89 8.38 Moisture W % - 74.61 27.7 22.55 21.18 20.56 Wet unit weight γw g/cm3 - 1.48 1.92 1.9 1.98 1.91 Dry unit weight γd g/cm3 - 0.85 1.51 1.55 1.64 1.58 Specific gravity G - - 2.56 2.69 2.68 2.69 2.67 Initial void ratio e0 - - 2.86 2.36 0.73 0.64 0.68 Porosity n % - 0.66 0.43 0.42 0.39 0.41 Saturation degree  S % - 94.93 95.43 82.6 88.36 80.18 Liquid limit  WL % - 62.39 41.89 31.3 41.41 - Plastic limit  WP % - 31.64 22.39 17.4 20.78 - Plastic index IP % - 30.75 19.54 13.9 20.14 - Index Liquid   B - - 1.4 0.72 0.35 0.02 - Cohesion c kG/cm2 - 0.059 0.21 0.15 0.31 0.066 Angle of friction  j Degree - 03057’ 18025’ 16059’ 18005’ 27040’ Compressive index a1-2 cm2/kG - 0.11 0.028 - 0.019 0,015 SPT value N - - 0-6 4-19 8-16 15-43 11-27 Conclusion: The investigation result shows that the geological conditions of area are rather complex, the soil layers are much varied from place to place. Investigation result also shows that at site have 6 soil layers as belows: Layer 1: Yellow fillling finer sand. This layer appears at borehole HKBS1 and HKBS3 with 0.2 and 0.1m depth. Layer 2: Very soft state, blackish grey fat clay. Average thickness: 9.3m. This layer has low physical – mechanical properties. Layer 3: Stiff state bluish grey, reddish brown clay. Average thickness: 8.3m. Layer 4: Very stiff state, yellowish grey, bluish grey sandy clay. Average thickness: 1.03m. Layer 5: Very stiff to hard state, bluish grey, reddish brown clay. Average thickness: 13.3m. Layer 6: Medium dense state yellow finer and to medium sand. This layer only appears at drilling holes HKBS2, with a depth of 50.0m. Layer thickness is 13.5m. Borehole HKBS3 appears dense sand lens at the depth of 14.5 – 15.2m, lens thickness: 0.7m. The site is influenced by the semi tidal regime. Therefore, it’s necessary to consider the influence of hydro dynamic pressure to the soil strength during construction. Recommendation: For construction loading, it’s suggested to use at least 18.0m pile for reinforce. To prevent erosion, it’s suggested to use rock gabion, rock mattress … To reinforce the bank, it’s suggested to apply mechanical stabilized earth walls with using Geosynthetic products such as: Geogrids, Geotextiles, Geocell… 4.1 PROPOSED SOLUTION FOR DESIGN 4.2.1 The Use of Mechanically Stabilized Earth Wall Currently, this solution provides both technical efficiency and economic benefits. In addition, the wall face has much choice with the requirements about the aesthetic of the project. Figure 4.3 The typical section for non-parking area Using mechanically stabilized earth wall with modular concrete block wall face: Geogrids are spread horizontally and they are connected with modular concrete blocks against the shear force of potential failure mass. Two types of Uni-Axial Geogrid are used: There are the three lower layers with E’GRID 65R and at the five upper ones with E’GRID 50R. The anchoring length is 5 meters and decrease slightly 4 meters. The thickness for each reinforced soil layer is 0.4 meters. Using a modular concrete block (20x20x40cm), placed on reinforced concrete beam with size: (60x60cm), placed on prestressed concrete piles D350, with spacing between two piles is 4.5 meter, with pile length is 22 meter. Inner wall face, there is an aggregate layer close it to drain with thickness of 30 centimeters close. At the bottom of the reinforced area is an 30-cm-in-thickness-aggregate layer, which is placed on a 10-cm-medium-grained sand layer with Geogrid E’Grid 3030. Outside of wall face used stone mattress (0.3x1x2m), placed on wooden piles (9piles/m2) against erosion at wall base. Some photos of the actual work Figure 4.4 Site cast modular concrete blocks Figure 4.5 Preparation of wooden piles Figure 4.6 Construction of concrete beam Figure 4.7 Segment of finished concrete beam Figure 4.8 Wooden piles driving at construction site 4.2.2 The Basis of Calculations and Estimations Internal stability analysis The establishment of types, vertical spacing and anchoring length Geogrids Standard use: TCN 272-05 Software support: MSEW 3.0 The global stability analysis To determine the global safety factor Slope/W Settlement TCN 262 – 2000 Microsoft Excel Table 4.8 Soil data γ (kN/m3) C (kPa) φ (degree) Reinforced Soil 20 0 30 Retained Soil 20 0 30 Foundation Soil 20 20 15 Table 4.9 Recommended minimum factors of safety with respect to failure modes are as follow (AASHTO 2002/NHI 043 – ASD) Types Minimum safety factors External Stability Direct Sliding FSmin=1.5 Eccentricity e ≤ L6 or eL ≈ 0.1666. Overall FSmin=1.5 Bearing Capacity FSmin=2.5 Internal Stability Breakage of Geogrids FSmin=1.5 Pull out resistance FSmin=1.5 Connection strength FSmin=1.5 Table 4.10 The layout of the Geogrids Layer Geogrid Elevation (m) Geogrid Length (m) Product name 1 0.20 5.00 E’GRID 65R 2 0.60 5.00 E’GRID 65R 3 1.00 5.00 E’GRID 65R 4 1.40 5.00 E’GRID 50R 5 1.80 5.00 E’GRID 50R 6 2.20 4.00 E’GRID 50R 7 2.60 3.00 E’GRID 50R The active coefficient of earth pressure Ka Ka (internal stability) = 0.3333 Ka (external stability) = 0.3333 Sizing for external stability Table 4.11 Bearing capacity calculated Static Units Ultimate bearing capacity (qult) 277.7 kPa Mayerhoof stress (σv) 68.15 kPa Eccentricity (e) 0.12 m Eccentricity (e/L) 0.023 - Fs calculated 4.07> 2.5 - Base length 5.00 m Table 4.12 Direct sliding for given layout Layer Geogrid Elevation (m) Geogrid Length (m) FS Static Minimum safety factors Product name Result 1 0.20 5.00 3.550 1.5 E’GRID 65R Y 2 0.60 5.00 4.040 1.5 E’GRID 65R Y 3 1.00 5.00 4.686 1.5 E’GRID 65R Y 4 1.40 5.00 5.578 1.5 E’GRID 50R Y 5 1.80 5.00 6.891 1.5 E’GRID 50R Y 6 2.20 4.00 7.209 1.5 E’GRID 50R Y 7 2.60 3.00 7.810 1.5 E’GRID 50R Y Note: Y: The factor of safety is satisfactory for AASHTO. N: The factor of safety is unsatisfactory for AASHTO. Table 4.13 Eccentricity for given layout Layer Geogrid Elevation (m) Geogrid Length (m) e/L e/L Maximum Result Product name 1 0.20 5.00 0.0221 0.166 Y E’GRID 65R 2 0.60 5.00 0.0168 0.166 Y E’GRID 65R 3 1.00 5.00 0.0122 0.166 Y E’GRID 65R 4 1.40 5.00 0.0084 0.166 Y E’GRID 50R 5 1.80 5.00 0.0052 0.166 Y E’GRID 50R 6 2.2 4.00 0.0043 0.166 Y E’GRID 50R 7 2.6 3.00 0.0043 0.166 Y E’GRID 50R Note: Y: The factor of safety is satisfactory for AASHTO. N: The factor of safety is unsatisfactory for AASHTO. Sizing for internal stability Table 4.14 Results for strength Layer Geogrid Elevation (m) Tavailable (kN/m) Tmax (kN/m) Actual calculated Fs-overall Minimum safety factors Result 1 0.20 23.7 7.47 3.171 1.5 Y 2 0.60 23.7 6.40 3.700 1.5 Y 3 1.00 23.7 5.33 4.440 1.5 Y 4 1.40 18.6 4.27 4.362 1.5 Y 5 1.80 18.6 3.20 5.817 1.5 Y 6 2.2 18.6 2.13 8.725 1.5 Y 7 2.6 18.6 1.20 15.511 1.5 Y Note: Y: The factor of safety is satisfactory for AASHTO. N: The factor of safety is unsatisfactory for AASHTO. Table 4.15 Results for pullout Layer Geogrid Elevation (m) Coverage ratio Tmax (kN/m) Le (m) La (m) Actual Static Fs Minimum safety factors Result 1 0.20 1.00 7.47 4.88 0.12 27.072 1.5 Y 2 0.60 1.00 6.40 4.65 0.35 25.789 1.5 Y 3 1.00 1.00 5.33 4.42 0.58 24.510 1.5 Y 4 1.40 1.00 4.27 4.19 0.81 23.232 1.5 Y 5 1.80 1.00 3.20 3.96 1.04 21.949 1.5 Y 6 2.2 1.00 2.13 2.73 1.27 15.126 1.5 Y 7 2.6 1.00 1.20 1.50 1.50 7.381 1.5 Y Note: Y: The factor of safety is satisfactory for AASHTO. N: The factor of safety is unsatisfactory for AASHTO. Table 4.16 Results for connection Layer Geogrid Elevation (m) Connection force (kN/m) Reduction factor for connection Available connection strength (kN/m) Fs-overall connection Minimum safety factors Result 1 0.20 7.5 1.00 24.9 3.33 1.5 Y 2 0.60 6.4 1.00 24.9 3.89 1.5 Y 3 1.00 5.3 1.00 24.9 4.66 1.5 Y 4 1.40 4.3 1.00 19.5 4.58 1.5 Y 5 1.80 3.2 1.00 19.5 6.11 1.5 Y 6 2.2 2.1 1.00 19.5 9.16 1.5 Y 7 2.6 1.2 1.00 19.5 16.29 1.5 Y Note: Y: The factor of safety is satisfactory for AASHTO. N: The factor of safety is unsatisfactory for AASHTO. Settlement Figure 4.9 Stresses diagram Figure 4.10 Time-settlement diagram They are detailed in Appendix-II. The global stability analysis Figure 4.11 Safety factor of river wall when reinforced with Geogrids. The global Stability analysis calculated by Geo-Slope software to determinate the most dangerous sliding curve: Using Geo-Slope software: Kmin = 1.816 > 1.4 (according to 22TCN 262-2000. There are not the deep-sliding curves from results above. So, wall will ensure the technical requirements with the large safety factor. The Limitation in Calculation Results. MSEW design must accord with AASHTO which has been used in many projects in our country (without any standards for design in Vietnam). We can say that the calculations of Geogrids are quite easy because there are available analysis theories and design software. Currently, MSEW software is a good support for the design. Morever, the supporting software is very useful for calculations such as RESSAA, GeoStudio and Plaxis software with a support for Geosynthetics. However, some typical case for the river wall design which is theories and calculation tools revealed limitations at Thanh My Loi residential area project. Those are the calculation limitations of parameters with wooden piles. The Plaxis and GeoSlope can display the wooden material parameters correctly, MSEW is relative with ones. The replacement of mud is reinforced with wooden piles by another, is a subjective determination based primarily on experience. However, this error does not significantly affect to stabilize wall because the calculated safety factors are quite large. 4. 3 OPTION FOR THE BEST SOLUTION Sloping Embankment with the Self-Inserted Hexagon Concrete Slabs Surface Figure 4.12 The typical section for sloping embankment solution. Reinforced concrete, which is quite popular material, is used widely in construction. This is a product of the combination between concrete and steel reinforcement to create load-bearing structures in construction. This combination offers many advantages for reinforced concrete. Concrete and steel approximate with a coefficient of thermal expansion, to avoid the influence of environmental temperature. Concrete protect steel reinforcement against the erosion of the environment. Basically, the reinforced concrete structure as steel reinforcement can resist tensile stress well while concrete is tensile resistance. Advantages: The Sloping Embankment with the Self-Inserted Hexagon Concrete Slabs Surface has become popular in the construction field in the world and Vietnam. Therefore, a solution has many advantages: relatively easy to design construction procedures have become familiar with available materials. Disadvantages: The frequent disadvantage of the Sloping Embankment with the Self-Inserted Hexagon Concrete Slabs Surface is the cost and construction conditions. Cost of materials: cement, steel, sand ... always been affected from the factor market, cause difficulties in calculating the costs for the project. In addition, materials used for reinforced concrete walls are natural materials. In the current trend, people are trying to use manufactured, renewable and safe natural environment products. Mechanically Stabilized Earth Wall Advantages: Use simple and rapid construction procedures and do not require large construction equipment. Do not require experienced craftsmen with special skills for construction. Require less site preparation than other alternatives. Need less space in front of the structure for construction operations. Reduce right-of-way acquisition. Do not need rigid, unyielding foundation support because MSE structures are tolerant to deformations. Are cost effective. Are technically feasible to heights in excess of 25 m (80 ft). Disadvantages: Require a relatively large space behind the wall or outward face to obtain enough wall width for internal and external stability. MSEW require select granular fill. (At sites where there is a lack of granular soils, the cost of importing suitable fill material may render the system uneconomical). Requirements for RSS are typically less restrictive. Suitable design criteria are required to address corrosion of steel reinforcing elements, deterioration of certain types of exposed facing elements such as Geosynthetics by ultra violet rays, and potential degradation of polymer reinforcement in the ground. Table 4.8 Compare advantages and disadvantages of two solutions Contents Solution 1 Marks Solution 2 Marks Technical Requirements Ensure. 4.5 Ensure. 5 Cost for the entire project. 7,905,560,000 VND. 5 11,721,954,120 VND. 3 Construction Junction of hexagonal concrete slabs are easily damaged. Controlling of quality construction is quite complex. 3 Construction quality control easier by using materials supplied from the factory passed quality inspection. 5 Construction time About 98 days. 5 About 135 days. 4 Service life About 30 years. 3 About 120 years. 5 Aesthetics Hexagonal concretes bring to aesthetic for the project. 4.5 There are many choices wall surface, creating aesthetic for the project 5 Total marks 25 27 Note: The maximum score is 5 marks. Conclusions Saigon river wall are constructed with a fairly large scale - residential at Thanh My Loi project. Construction must ensure about technical requirements, economic efficiency, construction time and aesthetics. After analysis and evaluation, solution - Using mechanically stabilized earth wall is chosen design. This solution ensures the technical requirements, reasonable price, construction time, aesthetic elements. Also this plan is very flexible in construction solution, to meet the requirements of investors. 4.4 CONSTRUCTION SEQUENCE Step 1: Preparation of subgrade This step involves removal of unsuitable materials from the area to be occupied by the retaining structure. All organic matter, vegetation, slide debris and other unstable materials should be stripped off and the subgrade compacted. In unstable foundation areas, ground improvement methods, such as dynamic compaction, stone columns, wick drains or other foundation stabilization/improvement methods would be constructed prior to wall erection. Step 2: Placement of a leveling concrete beam for the erection of the facing elements This generally unreinforced concrete beam is often only 300 mm (1 ft) wide and 150 mm (6 inches) thick and is used for MSEW construction only, where modular concrete blocks are subsequently erected. Figure 4.13 This concrete beam is to serve as a guide for facing block erection Step 3: Erection of the first row of facing blocks on the prepared concrete beam. Facings may consist of either precast concrete panels, metal facing panels, or dry cast modular concrete blocks. For construction with modular concrete blocks which is full dimensions are used throughout with no shoring. The erection of facing panels and placement of the soil backfill proceed simultaneously. Figure 4.14 The block first row is erected on concrete beam Step 4: Placement and compaction of backfill on the subgrade to the level of the first layer of reinforcement and its compaction The fill should be compacted to the specified density, usually 95 to 100 percent of AASHTO T-99 maximum density and within the specified range of optimum moisture content. Compaction moisture contents dry of optimum are recommended. Figure 4.15 Lighter compaction equipment is used near the wall face Lighter compaction equipment is used near the wall face to prevent buildup of high lateral pressures from the compaction and to prevent facing panel movement. Because of the use of this lighter equipment, a backfill material of good quality in terms of both friction and drainage, such as crushed stone is recommended close to the face of the wall to provide adequate strength and tolerable settlement in this zone. Step 5: Placement of the first layer of reinforcing elements on the backfill The reinforcements are placed and connected to the facing blocks, when the compacted fill has been brought up to the level of the connection they are generally placed perpendicular to back of the facing panels. Geogrids which are ensured the minimum distance of 50 mm to junctions, are cut to length design. We must make sure that all the grid cells are inserted in the connector. Figure 4.16 Cutting Geogrids process Geogrids are placed in the modular concrete blocks and the installation between Geogrids and modular concrete blocks by connector. Figure 4.17 The installation of the modular concrete blocks Geogrids are laid between layers of blocks and held in place by the weight of the blocks above.We should avoid excessive bending Geogrids. Figure 4.18 Geogrids are spread on each filling soil layer Step 6: Placement of the backfill over the reinforcing elements to the level of the next reinforcement layer and compaction of the backfill Figure 4.19 Geogrids are always stretched during building operations The previously outlined steps are repeated for each successive layer. Spread and compacted filling materials. We still continue with the above steps until they are reached to height design. Filling materials should be sprayed by excavators, shovels ... as for the soil grains in the fixed Geogrids.Nghe Đọc ngữ âm Step 7: Wall facing finishing The compaction requirements of backfill are different in close proximity to the wall facing (within 1.5 to 2 m) and they are free construction operations from that position to end of length design. Vehicles and machinery are not allowed to move directly on the Geogrids Figure 4.20 Track type construction equipment should not travel directly on Geogrids materials 4.5 THE ERRORS OFTEN OCCUR DURING CONSTRUCTION PROCESS. Concrete beam Concrete beam is relatively easy construction. However, if the concrete beam is not properly with the design, it will affect to the installation of modular concrete block face and will be very hard to fix this problem. Concrete beam should be used with suitable concrete to ensure the concrete strength which is calculated previously. Figure 4.21 Concrete beam must be constructed carefully Modular concrete blocks They were installed in concrete beam to create the wall face with no shoring. So, each modular concrete block should be made accurately to achieve uniformity in the dimension. If not, it will cause difficulties for building the wall face and time-consuming. Besides, concrete strength as well as the aesthetics should be ensured. Nghe Đọc ngữ âm Figure 4.22 Irregularity in the modular concrete block dimensions. Compaction The road roller is too heavy weight. If it does not keep the standard distance to the wall face (2m), wall will be damaged in the construction phase. Nghe Đọc ngữ âm Figure 4.23 Construction means too close to the wall surface Placement of the reinforcing layer on the backfill Geogrids must be stretched in the process of spread ones. Besides, they must be installed to length design properly. If not, the Geogrid effect is reduced significantly. Figure 4.24 Geogrid is not stretched on the backfill CHAPTER 5: CONCLUSIONS AND RECOMMENDATION 5.1 Conclusions The application of mechanically stabilized earth wall to construct Saigon river wall at Thanh My Loi residential area project has shown the great advantages in comparison with traditional method-Using concrete wall. Technical factors are secured, the wall will be protected and it will be sustained before the impact factors from nature in a long time. Construction costs are also reduced significantly, the clear advantages compare with the former solution, which saves significant to investors. The construction of the new solution is relatively simple, even without the use of machinery, which are the outstanding advantages of this method. The construction time was shortened, thus creating favorable conditions for the progress of the entire project. The service life is very high and can be more than 120 years; the maintenance, as well as building renovation are not too strictly required. Another highlight of this new solution is the aesthetic, the work with so many options in the design of the wall face. We can choose the modular concrete block face, panel with a variety of shapes and colors of the wall surface which all help the work remain in such a long time. The construction of the river wall to construct the Saigon River is one of the most important work, affecting to entire Thanh My Loi residential area project-one of the major projects for economic development in District 2, HCMC. Because of that, I would like to recommend the optimal solution-Using mechanically stabilized earth wall to construct Saigon river wall at Thanh My Loi residential area project. 5.2 Recommendation Viet Nam has regularly occurred the erosion, landside, flood phenomena which are enormous impacts to people's life, as well as country's economy. So, finding solutions to reduce the harmful effects are the urgent requirements. Therefore, potential applications of Geosynthetics are very large, consistent with conditions in our country. Any product has its advantages and disadvantages, therefore we need to do further research to develop of advantages and to overcome the disadvantages of them or we may develop the new products which are preeminent to replace the old ones. There are not any technical solutions, which are the optimum for all cases. So designers must carefully consider before deciding what solution to be used. Geogrids are not an exception. They are not able to replace the traditional solutions such as sand piles, wick drains… when the soft soil thickness is large and degree of consolidation is slow. REFERENCES [1] US Department of Transportation Federal Highway Administration (2001). Publication No.FHWA-NHI-00-043 “Mechanically Stabilized Earth Walls and Reinforced Soil Slopes- Design and construction guidelines.” [2] US Department of Transportation Federal Highway Administration (2001). Publication No.FHWA-NHI-00-043 “Corrosion/Degradation of Soil Reinforcement for Mechanically Stabilized Earth Walls and Reinforced Soil Slopes- Design and construction guidelines” [3] Sanjay Kumar Shukla, Jian-Hua Yin  (2008). “Fundamentals of Geosynthetic Engineering”. [4] Tuấn, P.M (2010). “Ứng dụng Geogrids và Geocell trong dự án Phước Nguyên Hưng-Huyện Nhà Bè-TP.Hồ Chí Minh”. Luận văn đại học, Đại Học Bách Khoa Tp.HCM. [5] Chính, Đ.T (2007). “Ứng dụng lưới địa kỹ thuật trong thiết kế tường chắn có cốt – áp dụng cho cầu Đắk Nông – thị xã Gia Nghĩa – tỉnh Đắk Nông”. Luận văn đại học, Đại học Bách Khoa Tp. HCM. [6] Tân, Đ.Q (2010). “Ứng dụng lưới địa kỹ thuật trong thiết kế tường chắn có cốt cho công trình đường dẫn đầu cầu Kênh Nước Mặn-Huyện Cần Giờ-Tỉnh Long An”. Luận văn đại học, Đại Học Bách Khoa Tp.HCM. [7] Phiệt, P.T (2001). “Áp lực đất và tường chắn đất”. Nhà Xuất Bản Xây Dựng. [8] Việt, V.V (2004). “Cẩm nang dùng cho kỹ sư địa kỹ thuật”. Nhà Xuất Bản Xây Dựng. [9] Hải, D.H (2004). “Thiết kế và thi công Tường chắn đất có cốt”. Nhà Xuất Bản Xây Dựng. [10] Hồ sơ báo cáo “Kết quả khảo sát địa chất” của công ty TNHH Hoàng Trung Chính lập vào tháng 12 năm 2009. [11] BOSTD & NEWGRIDS Limited (2009). “The World of E’GRID”. Integral Geogrids The New Force in Geotechnical Engineering. [12] Vân, Tùng. (Monday, October, 2010 ). [13] Presto Geosystems. (Thursday, July 8, 2010). [14] Miracell. (Sunday, December 26, 2010). APPENDIX I APPENDIX II APPENDIX III APPENDIX IV