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MINISTRY OF EDUCATION UNIVERSITY OF TRANSPORT AND COMMUNICATIONS LE DUC TIEN RESEARCH ON BEARING CAPACITY OF DRILLED SHAFT INTO WEARTHERED ROCK LAYER Specialization: Transport Construction Engineering Code: 958.02.05 DOCTOR OF PHILOSOPHY THESIS Hanoi - 2020 The thesis was completed at: University of Transport and Communications Academic supervisors : Assoc Prof.Dr Nguyen Ngoc Long Assoc Prof.Dr Bui Tien Thanh Reviewer 1: …………………………………………… Reviewer 2: …………………………………………… Reviewer 3: …………………………………………… The dissertation will be presented at the university-level dissertation assesment council at the University of Transport Communications Time ……… hour, day …… month …… year……… … The dissertation can be found at: - National Library - University of Transport and Communications Library and INTRODUCTION Rationale of the Research In current design standards, the calculation of the bearing pile capacity is divided into two cases, when the pile is placed in the soil, the formulas related to the resistance of the ground are used; while the pile is attached to the rock, it is possible to apply the compressive strength of qu rocks However, in areas where the thickness of the weathered rock is relatively large, the weathering intensity is smaller than that of rock but much larger than that of soil, this fractured weathered rock is called IGM leading to many difficulties in applying calculation standards as well as checking The design standards of drilled shafts in Vietnam and the transportation industry have not mentioned specifically the method of calculating the resistance of piles when they are through Intermediate Geomaterials (IGM) but considered as soil layers following semiexperimental fomulas (cohensive soil) or formula based on SPT experiments (sandy soil) Static compression test to measure deformation along the pile’s body has been applied in many countries around the world to determine the level of friction mobilization along the pile’s body Currently, the highway bridge design standard named TCVN 1182310: 2017 has included the definition of fractured weathered rocks, but there has been no experimental study for the bearing capactity of drilled shafts when they are placed into weathered fractures rocks in Vietnam For those reasons, the implementation of this thesis is necessary Objective of the Research This thesis focuses on estimating the bearing capacity of drilled shafts pierced into fractured weathered rocks strata in the Central of Vietnam and Quang Tri Province by summarizing formulas and calculation theory for this type of ground In additon, the project conducted static pile compression test combined with stress measurement, displacement at the pile’s body, pier tip to determine the exact behavior of drilled shafts when they are used on this rock layer Subject and scope of the Research - Subject of the research: the bearing capacity of drilled shafts pierced into fractured weathered rocks in the Central region - Scope of the research: empirical research and modeling to determine the load capacity of drilled shafts pierced into fractured weathered rock layers in the Central region, focusing on Quang Tri area Research Methodology - Theoretical research methods such as: analysis and synthesis theory; - In-situ tests: static compression test and pull out test of drilled shaft with real dimensions pierced into fractured weathered layers - Finite elements method determines the bearing capacity of drilled shafts pierced into fractured weathered layers Scientific, practical significance and contribution of the thesis - Scientific significance of the thesis: The thesis has scientific significance in conducting in-situ experiments both compression and pull-out tests, attaching modern measuring devices to determine side resistance and tip resistance of drilled shaft into weathered rock layer in Central region in Vietnam - Practical significance of the thesis: Products of the project contribute to quantify the bearing capacity of drilled shafts into fractured weathered rock layers - New contributions of the thesis: - The thesis has carried out static compression test and pull out test for drilled shaft at the site Strain gages, extensionmeter and other devices are along the drilled shaft to determine the side and tip resistance of pile, giving the judgment on the behavior of drilled shaft placed in fractured weathered rock - FEM model using FB-pier software is proposed to calculate calculation of the bearing capacity of drilled shaft into the weathered rock layer - Pull-out test results and FEM (FB-pier) results are new contributions for estimating the bearing capacity of the drilled shaft placed into into the weathered rock layer in Quang Tri area Contents of the thesis The thesis includes : Introduction, chapters, conclusion and recommendation as follow: Chapter 1: Overview Chapter 2: Theoretical and experimental basis for assessing the bearing capacity of drilled shafts in Intermediate Geomaterials Chapter 3: Experimental study of static compression and pull-out tests of drilled shafts placed in Wearthered rock Chapter 4: Analysis of the load bearing capacity of drilled shafts in Wearthered rock by Finite Element Method and compare with the in-situ tests’ findings Conclusion and Proposal CHAPTER OVERVIEW OF BEARING CAPACITY DRILLED SHAFT INTO WEARTHERED ROCK LAYER 1.1 General introduction of drilled shaft Drilled shafts are a solution for works with large loads Drilled shafts are widely applied to various types of buildings such as tall buildings, bridges, tunnels and seaport projects Construction technology of drilled shafts requires contractors who have sufficient capacity and experience in human resources, equipment, construction processes and behaviors when incidents occur during the construction of drilled shafts The choice of Drilled shafts technology is the selection of hole technology The selection of the type of drilling technology depends on the following criteria: ground conditions of the construction site, hydrogeological conditions, capacity of machinery and equipment 1.2 Geological summation of the central region is characterized by fractured weathered rocks To summarize the geology of the central region, the research team conducted surveys and collected data and documents for Da Nang and Quang Tri province Usually stones are classified according to Table 1-1 based on their intensity When considering the degree of weathering of rocks in Danang area, it is possible to base on criteria of RQD as in Table 1-2 [2] Table 1-1: Classification of rocks by intensity according to Attewell & Farmer 1976 Classify Very weak Weak Unconfined compression test (MPa) 10~20 20~40 Typical stone form The sedimentary rocks are weathered and compacted Schist rocks, poorly linked sedimentary rocks medium 40~80 Solids 80~160 Very Solids 160~320 Compressed sedimentary rocks and some coarse, coarse-grained rocks Compressed magma rocks and some metamorphic rocks and finegrained sandstone Quartzite, dense fine-grained magma 1.3 Definition and characteristics of the IGM intermediate soil layer The following table summarizes the definitions of IGM from multiple sources using either horizontal compressive strength or N –SPT values Table 2: Definitions of soil types according to the authors [13, 42] Author (Year) IGM soil type Define Compressive strength All types of Clarke and Smith (1993) of hip expansion rock 50 hammers Non-draining adhesive Marinos (1997) All types rock of force> 0.3 MPa Compressive strength of hip expansion> Johnston (1989) All types rock of Gannon et al (1999) All types rock of of O’Neill et al (1995) All types rock All types rock Mayne Harriss (1993) Sticky soil De Freitas (1993) Sand originates from sedimentary rocks Akai (1997) of MPa Hips compressive strength> 0.5 MPa The strength of compression of the hips is> 0.6 MPa Compressive strength at hip 1-10 MPa Compressive strength of hip expansion 0.5-5 MPa SPT value, N> 50 hammers Compressive strength of hip expansion from to 25 MPa The strength of hip expansion in saturation state is 0.5-20 MPa Thus, in principle, cracked weathered rocks can be considered as IGM soil From that, the formula can be applied to calculate the bearing capacity of drilled shafts when placed in this fractured weathered rock Dobereiner de Freitas (1986) Sandstone 1.4 Overview of some methods for calculating the bearing capacity of drilled shafts in fractured weathered rock in Vietnam Currently in our country, the design of drilled shafts is applied according to LRFD (USA) standard for the transportation industry or according to Vietnam standards In these standards, the calculation of the pile's bearing capacity is divided into two cases, when the pile is placed in the soil, the formulas related to the soil resistance such as internal friction angle of loose soil, compression resistance is not expanded in qu drainage conditions for cohesive soils, using field test results such as CPT, SPT, etc., and when piles are attached to rocks, the compressive resistance of qu stones can be used Calculate the resistance according to the ground and deformation of drilled shafts in weathered fractured layers according to TCVN 11823-10: 2017 1.5 Conclusion of chapter - Overview of the geology of the study area, the weathering layer from strong to medium, affecting the estimation of pile bearing capacity is the layer representing geology of the Central Region and Quang Tri with a relatively large thickness due to It should be studied when designing to calculate the bearing capacity of piles when placed into this geological layer - Da Nang, Quang Tri and Quang Binh have weathered rock layer with RQD value: 0-30% intensity from 2.5Mpa ÷ 25Mpa with a thickness of 4.5m ÷ 25m belonging to IGM Group III stratigraphy when calculated by Vietnam Road Bridge design standard TCVN 11823-10: 2017 - Theoretical and experimental formulas for drilled shafts during the construction of fractured weathered beds have also been studied in the world recently CHAPTER THEORETICAL AND EXPERIMENTAL BASIS FOR ASSESSING THE BEARING CAPACITY OF DRILLED SHAFTS IN WEARTHERED ROCK 2.1 Overview of methods for determining the bearing capacity of drilled shafts with measuring devices along the pile body in Vietnam In our country, the first researches on static compressive tests combined with deformation measurement along the pile body were conducted by the authors Nguyen Minh Hai and Tran Thanh Quang at the Royal Tower in District 7, Ho Chi Minh City This study applied the method of backward analysis suggested by Fellenius Recently, O-cellmounted experiments have been applied to a number of drilled shafts projects on rocks in Danang [6] Hoang Thanh Hai's thesis proposes a procedure for determining the tz rule of the pile as well as processing the deformation data along the pile body according to the method of determining the normalizing elastic module for some drilled shafts in Hanoi [7] The two studies only stopped at establishing the transmission line in the pile without making comparisons with the methods of calculating analytes or finite elements to propose the choice of a reliable method of calculating the bearing capacity of the pile high and consistent with our country's geology Le Phuong analyzed the load transmission line in the pile by static compression test combined with deformation measurement along the pile body [10] These testing devices are similar to pile static compressive testing equipment, but they incorporate strain gauges along the pile body Strain gauges are known as straingages (Sister bar) 2.2 Overview of methods for determining the bearing capacity of drilled shafts with measuring devices along the pile body in the world Static compression test to measure deformation along the pile body has been applied since 1969 for precast reinforced concrete piles in many places around the world to determine the level of friction mobilization along the pile body [32] Later empirical studies on drilled shafts were also conducted to determine pile resistance as well as pile resistance [13, 21-27, 29, 30, 33, 35-39, 42, 44, 47, 51, 53] The load capacity of the pile driven into the IGM layer has been analyzed by the Montana Department of Transport (9) [31] For IGM, it can be determined by the value of 1-axis compression resistance for rock, or SPT hammer index for loose soil Each project was analyzed by design report, construction data and CAPWAP software Many experiments in the US showed that just using static compression test is not enough to assess pile behavior [13, 26, 28, 40] For example, the drilled shafts are 1.2 m in diameter and about 15.6 m long and are constructed through sand layers and mountings into weak limestone layers in Tampa, Florida Experimental results show that important information can be obtained from the mounting of measuring devices, if only using conventional static compression testing will not be determined 3.2.2.5 Load process Order of increasing and reducing the load: The load applied to the pile head with each load level is different with% of the design load The load is increased to the next level after the settlement of the pile head is stable at the previous load level with the following load sequence: Checking devices: 0% % 0% Cycle 1: 100% Increase the load: 0% 25 % 50% 75% 100% Reduce the load: 100% 50% 0% Procedure 2: 150% Increase the load: 0% 25 % 50% 75% 100% 125% 150% Reduce the load: 150% 100% 50% 0% 3.2.3 Pull-out experiment 3.2.3.1 Experimental methods Pile extraction test is performed by applying axial load so that the piles spit out of the ground Actual loads are carried out by a hydraulic jack system operating under a hydraulic pump, with a jet system of test beams and supports made of concrete blocks 3.2.3.2 Experimental equipment and installation methods Installation equipment includes: • Load system: Jack, hydraulic pump; • Displacement measurement system: Dipslacement gauges, standard beams; • Jet system: Experimental beams, supports, anchor links 3.3 Research according to reverse analysis combines theory and measurement results during experiments 3.3.1 The bearing capacity of the pile according to theory The results of the calculation of tip resistance and side resistance according to TCVN 111823 - 10: 2017 are summarized as in the following table 15 Table 3-3: Friction resistance of piles at weathered cracked rock Calculation results Side friction (MPa) Calculated according to TCVN 11823 – 10:2017 unit 0,1728 Tip Resistance (MPa) 0,7094 3.3.2 Bearing capacity of pile under experiment 3.3.2.1 Static compression test results Experimental results of drilled shafts Table 3-4: Summary of results of settlement of drilled shafts Depo sit name Displacement Leng th of pile (m) Required experime ntal load (T) Pile head T6-1 Middle of the pile 14 229.5 Nose pile Displacem ent correspon ding to the largest casualty at each location (mm) The remaining Displacem ent correspon ding to the downstrea m process at each position (mm) 1.43 0.4 0.5 0.13 0.01 Displacem ent allowable limit (mm) 80 Conclude: - Experimental piles T6-1, D800mm are tested to a load of 229.5 tons The settlement with the largest load is 1.43mm smaller than the permissible limit prescribed in Articles 4.4.11 - 4.4.12 of TCVN 9393: 2012 (10% of pile diameter: 800x10% = 80mm) - Based on Article 4.5.3 of TCVN 9393: 2012, experimental piles T6-2, D800mm have a limited load capacity of 229.5 tons Therefore, the expected design of the 153 ton pile load capacity is grounded 16 Experimental results measuring stress deformation of the drilled shaft body - From the internal force of the two elevations, it is possible to calculate the frictional resistance of the soil layer around the pile section between the two elevations Fmsi = Qi-Qi + - From Fmsi friction resistance, it is possible to calculate fmsi = Fmsi / Sxqi friction resistance, Sxqi is the surrounding area of the pile segment between two elevations.Nếu tính sức kháng ma sát tất lớp đất xung quanh tính sức kháng mũi lớp đất đáy cọc Friction resistance of soil layer around pile section from elevation is 11.8m from bottom of cage and 10.5m from bottom of cage F1= F11.8 – F10.5 = 188,23– 185,89 = 2,34 ( T ) - Friction resistance unit: f1 = F1 / Sxqi = (2.34 x10) / (2,512 x 1.3) = 0.0072 MPa Friction resistance of soil layer around pile section from elevation 10.5m from cage bottom and 2.4m from bottom of cage F2= F10.5 – F2.4 = 185,89 – 86,56 = 99,33 ( T ) - Friction resistance unit: f2 = F1 / Sxqi = (99.33 x 10) / (2,512 x 8.1) = 0.0488 MPa Friction resistance of soil layer around pile section from elevation 2.4m from bottom of cage and bottom of cage F3= F2.4 – F0 = 86,56 – 19,15 = 67,41 ( T ) - Friction resistance unit: f3 = F1 / Sxqi = (67.41 x 10) / (2,512 x 2.4) = 0.11181 MPa 3.3.2.2 Experimental results spit Table 3-11: Summary of results of measurement of displacement of drilled shafts 17 The remainin Len Require Depo Subsidence gth d sit track of experim name subsidence pile ental (m) load (T) Relocatio g n displace correspo ment Subsid nding to correspo ence the nds allowa largest the ble downstr limit each eam (mm) position process (mm) at LF at to each position (mm) Pile head 11.32 3.04 5.73 4.18 0.9 0.3 T6-2 Middle the pile of 14 260 80 T6-3 Nose pile Conclude: - Experimental pile T6-2,3; D800mm tested to a load of 260 tons The displacement corresponding to the maximum load level is 11.32mm smaller than the permissible limit prescribed in Articles 4.4.11 - 4.4.12 of TCVN 9393: 2012 (10% of pile diameter: 800x10% = 80mm) 18 Figure 3-6: Side resistance versus depth for static loading test Figure 3-7: Side resistance versus depth for pull out test 19 3.4 Ultrasonic experiment The results of ultrasonic tests for T6-1, T6-2 and T6-3 piles show that the concrete is homogeneous (Table 3-14), v> 3000m/s Details of charts can be found in the appendix Table 3-6 Results of the ultrasonic testing of the pile at T6 post Deposit name Section Velocity (m / s) 1-2 Pile - Head 2-3 T6 3-1 3000 – 4450 1-2 3150 – 4400 3200 - 4550 3000 - 3950 Pile - Head T6 2-3 3300 – 3800 3-1 1-2 3650 – 4250 3250 – 4550 Pile - Head 2-3 T6 3-1 3100 – 4150 3050 - 4250 Comment Concrete meets requirements homogeneity the for Concrete meets requirements homogeneity the for Concrete meets requirements homogeneity the for 3.5 Conclusion of chapter - This chapter presents the results of tensile and compression tests for drilled shafts constructed in the fractured weathered rock layer of Ai Tu bridge in Quang Tri province, giving the order of installing the measuring heads, necessary equipment, Collect data and process results - The experimental results allow to draw the chart of unit friction resistance at the pile body and the tip of the pile - Comparison of calculation results according to the design standards TCVN 11823-10: 2017 between the load capacity at the pile tip and the pile body for drilled shafts into cracked weathered rock layer and actual test results Unit resistance to experimental pile is 14% larger than 20 calculated The resistance of experimental pile tip units is 38% larger than calculated - Pile extraction test with measuring heads along the pile body is the first new test applied to determine the load bearing capacity (lateral resistance) of drilled shafts in Vietnam - Ultrasonic experiments have shown that these piles have homogeneous concrete 21 CHAPTER ANALYSIS OF THE LOAD BEARING CAPACITY OF DRILLED SHAFT IN WEARTHERED ROCK BY FINITE ELEMENT METHOD AND COMPARISON WITH THE IN-SITU TEST FINDING 4.1 Selecting software to calculate the bearing capacity of drilled shafts in the IGM FB Pier software has a description of IGM cracked soil, so it can simulate pile compression and piling experiments better than other methods In addition, FB-pier software can simulate the interaction between pile and soil according to p-y curve and t-z curve in accordance with TCVN 11823-2017 Thus, the proposal of using FB-pier software to calculate 4.2 Calculation according to FB-Pier software model Load (ton) 50 100 150 200 250 300 150 200 250 300 0.0 Settlement (mm) 0.5 1.0 1.5 Top of pile Center of pile Pile tip 2.0 50 100 Figure 4-1: The load-settlement curve for static loading test 22 Load (ton) 50 100 150 200 250 300 150 200 250 300 Displacement (mm) Top of pile Center of pile Pile tip 10 12 50 100 Figure 4-7: The load-settlement curve for pull-out test 4.3 Compare calculation results between FB-Pier and actual experimental results Load (ton) 50 100 150 200 250 300 150 200 250 300 0.0 0.5 Settlement (mm) 1.0 1.5 2.0 2.5 Top of pile (measured) Ceter of pile (measured) Pile tip (measured) Top of pile (modeled) Ceter of pile (modeled) Pile tip (modeled) 3.0 3.5 4.0 50 100 Figure 4-8: Comparison between the results of FB-Pier software and actual results for static loading experiments 23 Load (ton) 50 100 150 200 250 300 150 200 250 300 Displacement (mm) Top of pile (measured) Center of pile (measured) Pile tip (measured) Top of pile (modeled) Center of pile (modeled) Pile tip (modeled) 10 12 50 100 Figure 4-9: Comparison between the results of FB-Pier software and actual results for static loading experiments Table 4-2 Comparison of pull-out test results with calculation results based on FB-pier When calculated according Method of to FB-pier software Calculated according to actual experiments calculation Resistance to pile qs (MPa) Tip resistance qp (MPa) Top of Center pile of pile Pile tip Top of Center pile of pile Pile tip 0.00828 0.0514 0.1096 0.0072 0.0488 0.1118 0.48 0.5542 24 Bảng 4-3 So sánh kết thí nghiệm nhổ với kết tính tốn theo FB-pier When calculated according Method of to FB-pier software Calculated according to actual experiments calculation Resistance to pile qs (MPa) Top of Center pile of pile 0.0095 0.015 Pile tip 0.1511 Top of Center pile of pile 0.0068 0.0145 Pile tip 0.1662 Comparison of FB-pier software calculation results and actual experimental results: + The resistance value of pile unit qs: the experimental result is 15.5% bigger than the software + Resistance value of pile tip qp: experiment result is 10% larger than software at 7C cracked weathered rock 4.4 Conclusion of chapter Based on the results of static compression test and pile extraction test with measuring devices along the pile body and the pile test model according to FB-pier software, some conclusions can be drawn as follows: - Pile compression and compression testing along the pile body allows more accurate calculation of the load capacity of drilled shafts into the weathered layer 25 - The Fb-pier software allows the estimated load bearing capacity to be quite similar to the actual static compression test and pile extraction when the loads are applied at small and medium levels.So sánh kết tính tốn phần mềm FB-pier kết tính tốn theo thí nghiệm thực tế: + The resistance value of pile unit qs: the experimental result is 15.5% bigger than the software + Resistance value of pile tip qp: experiment result is 10% larger than software at 7C cracked weathered rock 26 CONCLUSIONS AND PROPOSALS - From the study of geological data in the Central region through the synthesis of geological survey results from the actual bridge constructions, especially in Quang Tri province, it can be confirmed that the geological layer of weathered rock is cracked This area is classified as IGM-III geological layer according to the road bridge standards 11823-10: 2017 - The province compression test, pile extraction combined with deformation measurement along the pile body is a highly reliable method to determine the bearing capacity of drilled shafts placed in weathered rock fractures during design and construction work; The calculation of the resistance of drilled shafts placed in the cracked weathered stratum according to the current road bridge design standards TCVN 11823-10: 2017 gives results close to the experimental results - The results of static compression test and pile extraction into the weathered fractured layer at Cau Ai Tu showed that the resistance of the experimental unit to the pile was greater than calculated by 14% The resistance of experimental pile tip units is 38% larger than calculated - Using FB-pier software to simulate the process of compressing and pulling for drilled shafts when placed in cracked weathered stratum to ensure closeness, consistent with pile behavior Comparison of FB-pier software calculation results and actual experiment results at the experimental positions show the following results: + The resistance value of pile unit qs: the experimental result is 15.5% bigger than the software 27 + Resistance value of pile tip qp: experiment result is 10% larger than software at 7C cracked weathered rock Proposal - When the test determines the load-bearing capacity along the drilled shaft shaft placed in the fractured weathered rock layer, compared with the traditional static compression method, the pile extracting test has the advantage of being conducted quickly, requiring little counterbalance , can consider to use to determine the load capacity of the pile (lateral resistance) and check the load capacity of the pile during design and construction - When applying the "Road Bridge Design Standard TCVN 1182310: 2017" to calculate the load capacity of drilled shafts for IGM soil types, it is necessary to adjust by the formulas to suit the regional geological conditions However, studies are needed: + Carry out additional studies on pile extraction with deformation measuring equipment along the pile body with critical tension to determine the maximum lateral resistance of the pile, combined with the calculation of pile resistance according to TCVN 11823 -10: 2017 when the pile is placed on the cracked weathered rock layer to give the adjustment coefficient in the calculation formula of the current standard close to the actual bearing capacity of the pile + Further studying the construction works in the weathered fractured rock layer in the future, collecting compression data and extracting piles to determine the appropriate length of the pile piles into the weathered weathered rock 28 LIST OF PUBLICCATIONS Lê Đức Tiến; Nguyễn Châu Lân; Bùi Tiến Thành; Nguyễn Ngọc Long (2019) “Nghiên cứu thí nghiệm nén tĩnh thí nghiệm nhổ cọc cọc khoan nhồi đặt vào tầng phong hóa nứt nẻ khu vực Quảng Trị” (Hội thảo cục giám định Quảng Ninh tháng năm 2019) Lê Đức Tiến; Nguyễn Châu Lân; Bùi Tiến Thành; Nguyễn Ngọc Long; Nguyễn Đức Bình (2019) “Nghiên cứu sức chịu tải dọc trục cọc khoan nhồi đặt vào tầng phong hóa nứt nẻ khu vực Quảng Trị” Tạp chí Cầu đường tháng năm 2019 Tr 10-14 Nguyen Chau Lan, Le Duc Tien, Bui Tien Thanh, Nguyen Ngoc Long (2019) “Estimation of bearing capacity for drilled shafts installed in the weathering rock in central Vietnam” Proceedings of “The Third International Conference on Transport Infrastructure and Sustainable Development (TISDIC2019)” 31/8-1/9/2019 in Da nang Tiến, L Đức, Dương, Đặng H., Lân, N C., Thành, B T., & Long, N (2019) “Đánh giá sức chịu tải cọc khoan nhồi lớp đá nứt nẻ từ kết thí nghiệm mơ hình phần tử hữu hạn” Tạp Chí Khoa Học Cơng Nghệ Xây Dựng (KHCNXD) - ĐHXD, 13(3V), 55-63 https://doi.org/10.31814/stce.nuce2019-13(3V)-06 ... (2019) Nghiên cứu sức chịu tải dọc trục cọc khoan nhồi đặt vào tầng phong hóa nứt nẻ khu vực Quảng Trị” Tạp chí Cầu đường tháng năm 2019 Tr 10-14 Nguyen Chau Lan, Le Duc Tien, Bui Tien Thanh, Nguyen... Châu Lân; Bùi Tiến Thành; Nguyễn Ngọc Long (2019) Nghiên cứu thí nghiệm nén tĩnh thí nghiệm nhổ cọc cọc khoan nhồi đặt vào tầng phong hóa nứt nẻ khu vực Quảng Trị” (Hội thảo cục giám định Quảng... Long, N (2019) “Đánh giá sức chịu tải cọc khoan nhồi lớp đá nứt nẻ từ kết thí nghiệm mơ hình phần tử hữu hạn” Tạp Chí Khoa Học Công Nghệ Xây Dựng (KHCNXD) - ĐHXD, 13(3V), 55-63 https://doi.org/10.31814/stce.nuce2019-13(3V)-06
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