Prediction of The Reinforcement Ground Behavior with The Vacuum Consolidation Method by Triaxial Model Test & FE Analysis H.Kawabata Y.Tanabashi Y.JiangT.Shiono Nagasaki University Maruyama Industry Co,Ltd

Soft ground Fill Soft ground Vacuum pomp P Background of research It forces the water draining away, and promotes the consolidation lateral flow upheaval of the ground Fill construction Field is constricted Vacuum consolidation  It is possible to support rapid construction  It can suppress lateral flow and upheaval of the ground  However, the ground behavior is not clarified enough, and the design and the site management depend very on the experienced technique. combination

Construction technique Airtight + protection sheet Vertical drain Horizontal drainPorous catchment tube Vacuum pomp flow of drainage

Fill construction Soft ground Different ground behaviors Vacuum consolidation Method Soft ground Vacuum consolidation Method Soft ground Vacuum consolidation Method settlement Vertical drain Vacuum pomp side contraction P 盛土施工 軟弱層 Fill lateral flow upheaval Fill construction

vacuum pressure settlement pore water pressure inclination drainage discharge The purpose is to predict the ground behavior of fill construction by using VCM Purpose of research Simulation of VCM Numerical analysis confirm the validity of modeling simulate the fill construction by using VCM Numerical simulation comparison Measurement item Field investigation ※ VCM ； Vacuum Consolidation Method

Field investigation Construction spot panorama Outline of field investigation  Construction period 20 November ～  Improved area About 3300m 2  Improved depth About 12m  Loading vacuum pressure About -69kPa 17.6m 187m th construction field

Cross section of field Fill -1.0m -2.0m -5.0m -11.9m Sand mat Surface soil Clay Sandy cilt Cilty clay Center of field 2.4m -5.1m S m S m S-3 8.0m -3.5m P m P m P-2 Differential settlement gauge Pore pressure meter 0.8m Field end

Vacuum Consolidation Method P Vacuum pomp Vertical drain Fill construction by using VCM Fill P Finite element (FEM)analysis

Outline of analysis Vacuum Consolidation Method The coupled analysis of soil and water SEKIGUCHI ･ OTA model force the water draining away, and promote the consolidation could express deformation behavior of pore water flow and soil skeleton at the same time could express the dynamic behavior of clay ground

Model of analysis 70m 8.8m 0.9m 11m Surface soil Clay 1 Clay ２ Clay ３ Cilty clay 1 Cilty clay 2 Cilty clay 3 Cilty clay 4 Cilty clay 5 Cilty clay 6 Sand mat Reinforcement part Sandy cilt Vertical drain Thickness ： 0.004m Drain pitch ： 0.8m Boundary of drainage （ It is set to the jointed part of vertical drain and horizontal drain ）  When the pump operates ⇒ Water head is -69kPa  When the pump stops ⇒ undrained

Input parameter Depth ( GL-m ) Name of soil layer Model γ t (kN/m 3 ) IPIP E (MPa) C (MPa) k (cm/sec) － FillLinear elastic18.00 － × ～ 1.00 Sand matLinear elastic18.63 － × ～ 2.00 Surface soil Sekiguchi ・ Ota －－ 3.100× ～ 3.00 Clay 1 Sekiguchi ・ Ota × ～ 4.00 Clay 2 Sekiguchi ・ Ota × ～ 5.00 Clay 3 Sekiguchi ・ Ota × ～ 5.50 Sandy ciltLinear elastic17.65 － × ～ 7.00 Cilty clay 1 Sekiguchi ・ Ota × ～ 8.00 Cilty clay 2 Sekiguchi ・ Ota × ～ 9.00 Cilty clay 3 Sekiguchi ・ Ota × ～ Cilty clay 4 Sekiguchi ・ Ota × ～ Cilty clay 5 Sekiguchi ・ Ota × ～ Cilty clay 6 Sekiguchi ・ Ota ×10 -8

Pore pressure analysis (GL-8.50m) field (GL-8.50m) analysis (GL-5.20m) field (GL-5.20m) analysis (GL-3.50m) field (GL-3.50m) Reason: → It is thought that drainage was promoted in field when the pump stopped, while undrained boundary is set in analysis. GL-3.5m

Settlement of the center field As a whole, a similar tendency is shown. However, the value of analysis exceeds the value of field as time passes. analysis field Fig.12 Reason: Pore pressure (GL-3.50m) ; analysis < field (Fig.12) → In analysis, vacuum pressure propagation was overestimated compared with field.

Surrounding displacement It is the result after vacuum pump operates for 94 days. analysis field A similar tendency Surrounding displacement(cm) The surrounding displacement of the ground can be predicted.

Side displacement Within reinforcement area It is the result after vacuum pump operates for 98 days. A similar tendency analysis field The side displacement of the ground can be predicted.

Vacuum Consolidation Method P Vacuum pomp Vertical drain Fill construction by using VCM Fill P Numerical simulation

Outline of numerical simulation Actual achievement Slow fill construction ： 3 ～ 5cm/day Fill construction by using VCM ： 10 ～ 20cm/day Rate of fill Numerical simulation Rate of fill Pay attention to the loading period of vacuum pressure in before filling, while filling, and after filling. Rapid fill construction ： 20cm/day Fill construction by using VCM ： 50cm/day

Analytical case Rate of fill ： 20cm/day ～ Height of fill is 5m ～ case Period of filling （ day ） Periods after stopping filling （ day ） Rate of fill ： 50cm/day ～ Vacuum pressure + Height of fill 5m ～ case Period of vacuum pressure （ day ） Periods after stopping vacuum pressure （ day ） BeforeFilling After 2 － 10 － － － 5 60 Comparison

Period of filling Period of Vacuum pressure Pattern diagrams 盛土高 (m) 真空圧 (kPa) 盛土高 (m) 真空圧 (kPa) Vacuum pressure (kPa) Height of fill (m) 5m 25days case1 360 days after filling 5m case2 10days -69kPa 360 days after filling case5 -69kPa 20days 30days 5m 90days 360 days after filling

Settlement in the center field Rate of fill ： 20cm/day In comparison with case1 and case5 The effect of the fill construction by using VCM is confirmed. case1 case2 case5 Fill Vacuum pressure case1 case2 case5 Rate of fill ： 50cm/day Rebound occurs after the vacuum pump stopped. In comparison with case2 and case5 It is thought that the influence of period of vacuum pressure is small.

It is result after filling or vacuum pump stopped after 360 days. In comparison with case2 and case5 It is thought that the influence of the period of vacuum pressure is small. Surrounding displacement Within reinforcement area Surrounding displacement(cm) case1 case2 case5 the center field In comparison with case1 and case2, case5 The suppressive effect to upheaval of the ground by the VCM is confirmed.

Within reinforcement area Side displacement case1 case2 case5 It is result after filling or vacuum pump stopped after 360 days. In comparison with case1 and case2, case5 The suppressive effect to lateral flow by the VCM is confirmed.

The numerical analysis is able to reflect the behavior of field using VCM. Conclusion ① comparison Field investigation The agreement was confirmed from the results of the Numerical analysis and Value of field on the items of pore pressure, settlement, surrounding displacement and side displacement. Numerical analysis

Conclusion ② The suppressive effect to lateral flow and upheaval of the ground by the VCM has been confirmed. Numerical simulation It is able to predict the behavior of field in fill construction by using VCM.

謝々

Experimental apparatus Triaxial room Displacement meter Load cell Control panel triaxial room Pore pressure meter Drain diameter ： 7.4cm height ： 15cm Specimen

lateral pressure axial pressure Initial condition It loads axial pressure and lateral pressure Excess pore pressure loss axial displacement, drainage discharge, and pore water pressure Automatic measuring water The vacuum pressure (-69kPa) is loaded Outline of triaxial test

： Specimen T‐7T‐7 T‐3T‐3 T-6 T-9 GL-5.0m GL-2.0m GL-7.0m GL-9.0m GL-12.0m 3m 2m 3m Way of reduction

settlement ＝ Σ （ axial strain ×each thickness of the ground ） Model test Field(center) Field （ avarage ） Settlement

Model test drainage discharge ＝ Σ （ bulk strain ×area ×thickness of the ground ） Field Drainage discharge

Field （ GL-3.5m ） Model （ T-3 ） Model （ T-7 ） Field （ GL-8.5m ） Pore water pressure Time (day) Pore water pressure(kPa)

Constitutive(SEKIGUCHI ･ OTA model) Yield function M = M : Limit strain ratio D : dalitancy coefficient

パラメータ決定フロー ( 関口・太田モデ ル ) 限界応力比 ダイレイタンシー係数 非可逆比 先行圧密時の静止土圧係数有効応力に基づくポアソン比 塑性指数