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HAPPY NEW YEAR 2018 APPLICATION OF THE HOLLOW STRUCTURE FOR RIVER TRAINING IN FORM OF GROIN NGUYEN VAN NGOC, LE THI HUONG GIANG Faculty of Hydraulic Engineering, Vietnam Maritime University Abstract There are two common kinds of foundations at present: shallow and deep foundations. Shallow foundations are gravity structures built directly on natural base or with a buffer layer. Deep foundations are piled structures supported by pilework and deep-driven piling system. An applicable solution is the hollow structures, in which they are used as piles driven into soil through the main mechanism of gravity. It is suitable and effective in case of soft soil without base treatment, unlike the conventional gravity structures. Keywords: Hollow structure, gravity mechanism, groins. Tóm tắt Kỹ thuật nền móng hiện nay cơ bản có hai loại: Móng nông, công trình đặt trực tiếp trên nền thiên nhiên hoặc thông qua lớp đệm; công trình làm việc theo nguyên lý trọng lực. Móng sâu, công trình đặt trên nền cọc cắm sâu vào trong đất, công trình làm việc theo nguyên lý móng cọc. Giải pháp kết cấu rỗng, công trình cắm vào đất như một cây cọc, song làm việc chủ yếu theo nguyên lý trọng lực. Giải pháp kết cấu này sẽ có hiệu quả cao khi xây dựng trên nền địa chất yếu, vì xây dựng công trình trên nền địa chất yếu không phải xử lý nền như đối với công trình trọng lực truyền thống. Từ khóa: Kết cấu rỗng, nguyên lý trọng lực, kè mỏ hàn. 1. Introduction The hollow structure was researched and proposed to apply for the 10.000DWT marginal quaywall in Hai phong's soft soil area by Ngoc. N. V et al in 1998 [4]. In 2015-2016, this structure was contuniously proposed to Tien lang's land-reclaiming coffer-dam [3], Lach huyen International Gateway Port's breakwater with a saved cost up to 190% [5]. This is the premise for research on groins-one type of river training work. 2. The main hollow structures Six-hollow block structures have been registered at National office of Intellecture Property of Viet Nam by Ngoc. N. V et al (according to the decison No. 73929/QĐ-SHTT), and they are shown in Figure 1. d b) t h h t c) a D a b D a t h a) a a d) e) a f) d ' f ) a a t h h h A t D h t t A A A b B b B A Figure 1. The main hollow structures a) hollow structure in shape of parallelepiped; b) hollow structure in shape of cubic; c) hollow structure in shape of circle post; d) hollow structure in shape of frustum of pyramid with 4 slope sides; e) hollow structure in shape of frustum of cone; f, f’) hollow structure in shape of frustum of pyramid with two or one slope sides a a Journal of Marine Science and Technology No. 53 - January 2018 55 HAPPY NEW YEAR 2018 3. Overview on river training work in form of groins So far, there are four common kinds of river training works: earthen river training work (Figure 2a); rock river training work (Figure 2b); earthen river training work armored with rocks (Figure 2c) and piled ones. a) b) d) c) Figure 2. Cross-section of some groins Structurally, groins have a cross-section of slope one working according to closed groins' mechanism (It means that no current passes through); the piled groins' functioning mechanism is the opened ones which allow current to flow through. It is easy for the granular structures (rock or soil) to be unstable locally because during excutive process, the slope and rock size are not normally the same as in design. Pile groins whose toes reinforced by rocks have the same disadvantage. a) b) Figure 3. Pictures of some broken goins a) Groin KT2; b) Groin KT 10+11 [1] 4. Proposing an innovative structural solution based on the hollow structure's functioning mechanism The new structural solution is eco-technically calculated and compared with the rubble-mound groin H5 - Kenh Giang - Kinh Thay river, Hai Duong. Figure 4a is the cross section of the rubblemound groin H5 - Giang Canal; Figure 4b is the cross section of the new structure proposed. 56 Journal of Marine Science and Technology No. 53 - January 2018 HAPPY NEW YEAR 2018 a) 150 + 1 .6 9 + 0 .6 5 m =1 m ,5 =1 ,5 40 -0 .8 1 220 380 200 380 220 1400 b) 1 .5 0 .2 0 .5 0 .2 1 .1 0 .2 0 .5 0 .2 1 .5 0 .2 0 .2 + 1 .6 9 2 .5 + 0 .6 5 5 :1 5 :1 1 .0 0 .3 0 .3 0 .3 0 .1 -0 .8 1 0 .4 0 .2 0 .2 0 .4 0 .1 0 .1 2 .9 Figure 4. Cross-section of proposed groin structure a) Kenh Giang Rubble mound groin H5; b) Proposed groin's structure 5. Technical calculations 5.1. Input data In this paper, authors would like to calculate for groin number H5 with the following design parameters [2]: - Current velocity: V = 2m/s; - Mass density: ɣw = 1.67 t/m3; - Uplift density: ɣdn = 0.71 t/m3; - Angle of internal friction: φ = 2o73'; - Adhesive force: C = 07 t/m2. 5.2. Content of calculation [6] 5.2.1. Loads on strucsture 1 .5 H 5 :1 1 .0 5 :1 2 .5 G bt ECc E c E b Gd Nk F E bc On Nn Figure 5. Diagram of loads on new structure Journal of Marine Science and Technology No. 53 - January 2018 57 HAPPY NEW YEAR 2018 As for this kind of structure, authors would like to calculate for one meter long (as the same other gravity ones), and the result as the following: - Gravity load of structure: Gbt = 1.27 t/m; - Hydrodynamic pressure: H = 0.78 t/m; - Gravity load of soil: Gđ = 2,06 t/m - Active earth pressure caused by ɣ: Ecɣ = 0.32 t/m; - Active earth pressure caused by C: EcC = 0.7 t/m; - Passive earth pressure caused by  : Ebɣ = 0.39 t/m; - Passive earth pressure caused by C: EbC = 0.77 t/m; - Sliding resistance caused by friction and adhesive force: F = 1.18 t/m; - Tensile force (k = 1.8): Nk = - 0,45 t/m; - Compressive force (k = 1.8): Nn = -1.87 t/m. 5.2.2. Content of stability calculation a) Testing the structure' s embedding depth: kNn  Pc  RF  u  ili  60 x0.116  2.12 x0.2  7.38(t / m) k (1) Pc 7.38   2.68  [K]=1.6 N n 2.75 (2) Where: - R: Reaction at the bottom of structure; - F: Cross-section area of structure; - u: Cross-section perimeter of structure; - ‫ﺡ‬i: Lateral friction factor; - li: Soil layer thickness in corresponding to ‫ﺡ‬i . b) Testing of the planar shearing stability: Egiu Etruot  0.7  1.18  0.39  0.77 3.04   2.76  [K ]  1.68 0.78  0.32 1.1 (3) c) Testing of the overturning stability at point O n: 1 1 1 2.9 0.7  0.39  0.77  1.27  0.25 x2.85 3.33 3 3 2 2    1.87  [K ]  1.2 1 Ml 1.87 0.78 x2.25  0.32 3 Mg (4) Conclusion: With the 1-meter embedding depth of the structure, the structure's stability is ensured. 6. Economic efficiency comparison with real structure - H5 groin - Kenh Giang - Hai Duong To clarify the economic efficiency of newly-proposed structure, the authors executed recalculating for rubble mound groin H5 of Kenh Giang - Hai Duong. We also calculate for one meter long of new structure [6], and the result can be summarized as the following: - Rubble mound groin H5 of Kenh Giang - Hai Duong: 9,079 million VND/1m; - The hollow structural goin: 6,457 million VND/1m. The construction cost of hollow structure groin is only 71.14% of rubble mound groin, saving 2,622 million VND/1m. 7. Conclusion The new structural solution proposed demonstrates the following effects: 58 Journal of Marine Science and Technology No. 53 - January 2018 HAPPY NEW YEAR 2018 - Technical Efficiency: The stability is much better than he rubble-mound groins, because the reinforced concrete structures are designed with greater stability and higher capaccity of mechanical construction; the constructional work quality can be controlled. This remarkable advantage has overcome the disadvantages of known structure. - Economic Efficiency: Save up to 29% compared to traditional rubble-mound types, even higher if compared with the piling ones. Using hollow-structure solution to build groins is highly economically and technically efficient, therefore it worth being considered for application. REFERENCES [1] Technical & Economical Report of Tam Xa’s embankment - Hong River, 2017. [2] Designed Drawings of H5 Kenh Giang groin in 2002. [3] Nguyen Van Ngoc, Study on some forms of sea dykes, applied for Tienlang dyke - Hai Phong, 06/2016. [4] Nguyen Van Ngoc, Research project at the Viet Nam Maritime University: Research on gravity works for deep water, Soft soil and island area, 1998. [5] Nguyen Van Ngoc, Research project at the Viet Nam Maritime University: Researching and proposing new structural solutions for rubble-mound breakwater in soft soil area, 2017. [6] Nguyen Van Ngoc, Research project at the Viet Nam Maritime University: Research on the hollow structural solution for construction of river training works, 2017-2018. [7] TCVN 207:92, Vietnamese Standards, Design of Sea Port, 1992. Received: Revised: Accepted: 11 January 2018 22 January 2018 28 January 2018 Journal of Marine Science and Technology No. 53 - January 2018 59