Performance of Slurry TBM Tunnelling in Sandy Cobble Ground – A Case Study in Lanzhou

Shunze Cao,Jian Cui,Yongfang Jia,Ruyong Deng 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.7

The slurry tunnelling boring machine (TBM) was used to construct the tunnel of the Lanzhou Metro Line 1 undercrossing the Yellow River, China. The ground is characterized by sandy cobble with high cobble content. There are many challenges for slurry TBM tunnelling in sandy cobble ground because the cobble is hard to break and transport. This paper focuses on the performance of slurry TBM tunnelling, summarizes the lessons of shield driving and suggests countermeasures for the cobble breaking and disposal including cutterhead improvement, double pebble crusher and clasts collection tank. The chamber pressure and grouting pressure during the driving process were recorded and compared with the theoretical ground stress. The key parameters including the thrust force of cylinders, advance rate, torque and rotation speed of the cutterhead were recorded and analysed. Field test results show that the surface settlement induced by slurry TBM tunnelling in sandy cobble ground can be well controlled and the longitudinal surface settlement can be predicted by the Attewell formula and modified Attewell formula. This paper provides a good reference for slurry TBM tunnelling in sandy cobble ground.

불연속면을 포함한 사질토 지반에서 터널 굴착에 따른 하중전이

이상덕 사단법인 한국터널지하공간학회 2003 한국터널지하공간학회논문집 Vol.5 No.3

본 연구에서는 활동성 불연속면을 포함하고 있는 모래지반에 터널을 굴착할 때에 터널 주변의 원지반에 발생되는 아칭을 규명하기 위하여 터널 상부의 토피고와 불연속면의 위치 및 각도를 변화시켜가며 모형실험을 수행하였다. 모형실험기의 중앙에 수직으로 이동이 가능한 가동판을 설치하고 모래지반 조성 후에 가동판을 강하시켜서 터널 굴착을 모형화 하였고, 토조의 바닥판에 로드셀을 부착하여, 아칭에 의한 하중전이를 측정하였다. 굴착에 의한 지표면의 침하거동은 변위측정센서를 지표면에 설치하여 측정하였으며, 실험 중에 연속사진촬영을 실시하고 지반조성시 일정한 간격으로 설치한 측점의 움직임을 관측하여 굴착에 의한 지반이완형태를 측정하였다. 본 연구 결과 터널굴착시 불연속면의 각도와 위치, 그리고 터널 상부의 토피고에 따라서 하중전이 형태와 이완영역이 변화하는 것을 확인하였으며 지반의 이완영역이 터널과 인접해 있는 불연속면을 따라 주변지반으로 점차 확대되어 가는 것을 알 수 있었다. This study is focused on the finding out load transfer mechanism in the ground near the tunnel during tunnel excavation in the jointed sandy ground. Laboratory model tests were performed on various cases of the overburden heights above tunnel crown, location, and degree of discontinuity planes. For model tests, a movable plate was installed in the midst of the bottom of sandy ground. This plate, moving downwards, was intended to model the stress relaxation during tunnel excavation. The load transfer was measured at the fixed separated bottom plates adjacent to the movable plate. As the result, the loosening zone and the load-transfer form around the tunnelling site were affected by the overburden height and the characteristics of discontinuous planes. And large loosening zone was developed along the discontinuous planes which were close to the tunnel.

Evaluation of the grouting in the sandy ground using bio injection material

Kim, Daehyeon,Park, Kyungho Techno-Press 2017 Geomechanics & engineering Vol.12 No.5

This study was intended to evaluate the improved strength of the ground by applying the bio grouting method to a loose sandy ground. The injection material was prepared in the form of cement-like powder, with the bio injection material produced by microbial reactions. The grouting test was conducted under the conditions similar to the field where the bio injection material can be applied. In addition, the injection materials (cement and sodium silicate No. 3) used for Labile Waterglass (LW) method and the conventional grouting methodwere prepared through a two-solution one-step process. The injection into the specimens was done at a pressure of 150 kPa and then, with a bender element, their moduliof elasticity were measured on the 7th, 14th, 21st and 28th curingdays to analyze their strengths according to the duration of curing. It was confirmed that in all injection materials the moduli of elasticity increased over time. In particular, when 30% of the bio injection material was added to 100% cement, the modulus of elasticity tended to increase by about 15%. This confirmed that the applicability became higher when the bio injection material was used in place of the conventional sodium silicate.

강성저면위 유한한 두께의 모래지반에 놓인 얕은기초의 지지력

전상현,유건선,유남재 한국지반공학회 2011 한국지반공학회논문집 Vol.27 No.6

In this paper the method of estimating the bearing capacity of shallow foundation on a finite layer of sandy ground underlain by a rigid base was proposed by assessing results of the model test and the numerical analyses. For model experiments, the centrifuge tests under 1g and 20 g of gravitational levels were performed with sandy soils sampled from the field, changing the relative density of sandy soil and the ratio of thickness of sand layer (H) to the width of strip footing (B). As results of tests, bearing capacity tends to increase with the value of H/B while settlement for a given load intensity decreases. Bearing capacity also increases with relative density of the soil. In order to propose the method of estimating the bearing capacity of thin sandy layer underlain by a rigid base, values of bearing capacity factors from test results were compared with the values of modified bearing capacity factor by Mandel & Salencon (1972) considering the effect of H/B value on bearing capacity. The relation of bearing capacity factor ratio, normalizing friction angle of sandy soil, with the value of H/B was suggested so that this relation could be applied to design in the safe side. The results of numerical analyses obrained by changing the layout of footing, relative density of sandy soil and the value of H/B, were in good agreements with the suggested relation.

강성지반위 사질토층에 위치한 얕은기초의 침하량특성분석

황희석(Hwang, Hui-Seok),김동건(Kim, Dong-Geon),유남재(Yoo, Nam-Jae) 강원대학교 산업기술연구소 2014 産業技術硏究 Vol.34 No.1

In this paper the settlement characteristic of shallow foundation on sandy soil overlained by rigid ground was investigated by analyzing results of model tests. For model experiments, model tests were performed with sandy soils sampled from the field, changing the relative density of sandy soil and the ratio of thickness of sandy layer(H) to the width of model strip footing(B). As result of tests, settlement of sandy soils increases as the value of H/B increases, whereas it increases with relative density of soil. Bearing capacity decreases as the thickness of the sand layer relative to the footing width increases. In order to analyze the settlement characteristics of sandy ground, the results of model tests were compared with the predicted values using the empirical formulas proposed by Terzaghi, De Beer and Schmertmann. The method by De Beer was found to be in good agreements with test results.

도심지 깊은 굴착으로 발생하는 인접 지반 지표침하 분석

양구승,김명모 한국지반공학회 1997 지반 : 한국지반공학회지 Vol.13 No.2

풍화토 및 모래질 충적토가 암반위에 쌓인 형태로 구성된 국내 수도권 도심 지역에서, 깊은 굴착 공사로 인하여 발생하는 인접 지표의 침하에 대해 현장 측정을 중심으로 연구를 수행하였다. 먼저, 토류벽 설치, 중간 말뚝 설치 등 본격적인 굴토 공사가 진행되기 이전의 공정으로 인한 인접 지표침하량, 침하 영향거리 등을 측정, 분석하였으며 다음으로, 본격적인 굴토로 인하여 발생하는 인접 지표의 침하에 대해 침하량, 침하 영향거리 등을 측정, 분석하고 균질한 사질토 지반이나 단단한 점토 지반에 대해 기존에 제시된 연구 결과와 비교하였다. 또한 굴착 공사시 과도한 변형으로 인하여 인접 지표 및 구조물에 균열 등의 피해가 발생한 7개 현장 사례를 통하여 굴착 공사로 인한 인접 지표의 균열 발생 범위에 대하여 분석하였다. Adjacent ground surface settlements by deep excavations are analyzed by field observations in the areas where excavations are performed in sandy soils or weathered soils underlain by rocks, First, the magnitude and the distribution of ground surface settlements, which are developed before main excavation activities (e. g., diaphragm wall installation and center pile installation) , are measured and analyzed. Secondly, the magnitude and the distribution of ground surface settlements by main excavation are measured and analyzed. And the results are compared with the predictions obtained by the empirical methods. Through case studies performed on the excavation sites where adjacent ground surfaces or structures are damaged by excavation activities, upper limit location of ground surface cracks are investigated.

사질지반 NATM 터널의 강관보강 효과에 대한 모형실험

임종철,장지건,홍석우 釜山大學校生産技術硏究所 1998 生産技術硏究所論文集 Vol.55 No.-

사질지반에서 얕은 터널 굴착시 지표면의 침하억제와 막장의 안정은 필수적이다. 이를 위해 적정한 보조공법을 사용하여 지반을 개량하여야 한다. 그러나 이러한 보조공법에 관한 메터니즘이 아직 명확하게 밝혀지지 않고 있다. 본 연구에서는, 강관을 사용한 보조공법의 메커니즘을 연구하기 위해 모래로 지반을 조성하여 실험을 실시하엿다. 그 결과는 아래와 같다. 1) 주동상태는 건조모래(w=0.28%)에서는 ΔL/D≒0.0025일 때, 함수비 (w)=1.8% 에서는 ΔL/D≒0.005일 때 발생하였다. 여기서, D : 터널의 지름, ΔL : 막장의 후퇴변위 2) 모형지반의 함수비가 1.8%일 때는 보강재의 길이가 0.7D이상이면 충분한 지지력을 얻을 수 있다. 3) 막장전면에 작용하는 주동토압은 무라야마(村山)의 방법에 의한 이론값이 모형실험에서 구한 실측값보다 크게 나타났다. To excavate the shallow tunnel in sandy ground, it is essential to Keep stablity of face and to reduce the settlement of ground surface. For these purpose, we should improve the strength of the ground by using appropirate auxiliary method. But the effect and mechanism of the auxiliary method is not proved clearly yet. In this study, the model tests were preformed on the sandy ground to study the mechanism of auxiliary structure by steel pipe. Test results are as follows; 1) The active state occurred at ΔL/D≒0.0025 on dry sand and ΔL/D≒0.005 on wet sand (w=1.8%). where, D;diameter of tunnel, ΔL:backward displacement of tunnel face. 2) The enough bearing capacity was obtained. when the length of reinforcement is larger than 0.7D in the case of wet sand. 3) The active earth pressure on the face, the value by Murayama's method is larger than the measurement value by the model test.

모형실험을 활용한 저수심 사질토 지반에서 원형강관 설치 석션압 평가

신진화(Zhen-Hua Xin),김재현(Jae-Hyun Kim),이주형(Ju-Hyung Lee) 한국산학기술학회 2021 한국산학기술학회논문지 Vol.22 No.2

본 연구에서는 해상(수상) 교량기초 시공 시 석션압으로 간편하게 설치될 수 있는 원형관 공법을 개발하고자, 실내 모형실험을 통하여 저수심 모래지반에 원형관 관입 시 설치 석션압을 평가하였다. 포화된 사질토의 반복실험을 위해 3개의 진동발생기를 활용한 진동다짐 토조 시스템을 구축하였고, 지반강도 확인을 위하여 소형 콘관입 장비를 활용하였다. 진동다짐 토조 시스템은 내부의 모래지반에 반복적으로 진동을 가하여 효율적으로 균질한 모래지반을 확보할 수 있었다. 다양한 지름과 두께를 가지는 원형관 모형체를 제작하고, 다양한 수심조건에 대하여 석션관입 실험을 수행하였다. 실험을 통한 석션압 분석결과 원형관의 관입깊이가 커짐에 따라 석션압은 커지고 지름이 클수록 원형관을 관입시키는데 필요한 석션압은 작아지는 것을 확인하였다. 특히, 수위가 낮을수록 석션관입을 위해 원형관 내부에서 끌어 올려야 하는 수두가 커지는 반면, 높아진 수두에 의한 물의 무게는 원형관의 전체 자중을 증가시켜 관입에 필요한 석션압은 작아짐을 알 수 있었다. 따라서, 저수심 조건에서 석션압을 이용하여 원형관을 설치할 경우 수심의 영향을 고려하여 설계 석션압을 결정해야 할 것으로 판단된다. In this study, a circular pipe can be installed by suction pressure for construction on soft ground with a low-water level. A series of laboratory-scale model tests were conducted in sandy ground to comprehend the suction pressure of the circular pipe in low-water levels. For repeated tests on saturated sandy soil, a container was mounted with three vibration generators on the floor. A repetitive vibration was applied using the vibration system for ground compaction. In the model tests, different diameters and thicknesses on saturated sandy soil with a water depth were considered. The result showed that the suction pressure increased with increasing penetration depth of the circular pipe. Moreover, the suction pressure required to penetrate the pipe decreased with increasing diameter. In the low-water level, the total suction pressure measured at the top lid increased because additional suction pressure is required to lift the water column. On the other hand, this led to a decrease in suction pressure to penetrate the circular pipe because the weight of the water column is applied as a dead load. Therefore, it is necessary to consider the water level to design the required suction pressure accurately.

건조 사질토 지반에 설치된 석션 버켓기초의 장기 반복하중에 의한 누적회전각 산정

김성렬,이시훈,최창호 한국지반공학회 2016 한국지반공학회논문집 Vol.32 No.12

A suction bucket foundation has been considered to be a potential foundation type for offshore wind turbines. Asuction bucket foundation is usually installed in soft soil, so the accumulated displacement of the foundation may occurunder long-term cyclic loads. In this study, a series of 1-g model tests were performed to analyze the accumulatedrotation of suction bucket foundations under long-term cyclic horizontal loads. The dry model ground was prepared tohave two different soil densities by air-pluviation method. The model tests were performed varying the embedment depthof the suction bucket, the soil density, and the amplitude of cyclic load. A one-way horizontal cyclic load was appliedover 104cycles. Test results showed that the accumulated rotation of the suction bucket foundation increased with theincrease in the number of cycles and load magnitudes. Based on the model test results, a new equation was proposedto evaluate the accumulated rotation of the suction bucket foundations in dry sandy ground under long-term cyclichorizontal loads.

모래층 지반 안벽구조물의 탄성침하거동 연구

유남재,전상현,전진용 江原大學校 産業技術硏究所 2007 産業技術硏究 Vol.27 No.B

This paper is research results of investigating the elastic settlement behavior of the coastal caisson structure built on the sandy deposit by comparing results of centrifuge model experiments and those of existing methods of estimating elastic settlement. Basic soil property tests such as specific gravity test, grain size distribution test and organic content test with disturbed soil sampled from the site were carried out. The centrifuge experiment of model satisfying the required design criteria was performed under 50 of artificial accelerated gravitational force condition. The Centrifuge model experimental results were compared and analyzed with the current methods of estimating settlement based on the elastic modulus obtained from the results of odeometer tests and empirical methods from literature reviews.