新疆中天山山區玉溪莫勒蓋隧道偏壓坍方處治技術分析研究

朱春生，楊曉華，房健宏，來弘鵬

(1.長安大學公路學院，西安710064;2.新疆維吾爾自治區交通運輸萬規劃設計管理中心，烏魯木齊830000;3.青海交通科學研究所，西寧810008)

0 Introduction

Along with the accelerating of the construction of the highway transportation in Xinjiang，Urumqi-WeiLi，WenSu-ZhaoSu highway project through the Tianshan mountains will be on the agenda step by step.The highway tunnels will grow up to be project control engineering.

At present，the number of highway tunnel operation in Xinjiang is not much，mainly along the highway such as G30，G217 in the TianShan mountains.In such a complex environment with high altitude，low temperature，crushing rock and rich groundwater，it is less experience to build a road tunnel in Xinjiang even no reliable reference in domestic.The operated SaiL-iMuHu tunnel in G30 line built alongside lake has encountered water gushing in its build progress.The project targetly studied the tunnel waterproof material and system.Haxilegen tunnel in G217 line studied the segregation and void treatment technology for dealing with lining seepage，local deformation，cracking and other diseases.The tunnel old G217 was built through Tianshan mountains scrapped soon due to improper collapse treatment coursed forming hollow water into ice frozen.Visibly，recent research focuses on the tunnel waterproof and drainage system，percolating water treatment technology，but it is less for collapse treatment technology research.［1-2］.

1 Project overview

In 2009，YuXiMoLeGai tunnel is rebuilt in G217 line highway with length 1 943 m.The tunnel exitmileage is K724+038 and export height is about 3 230 m.The K723+600～K724+038 section is through fault fracture zone with developed formation joint and rich groundwater.Tunnel K723+910～K723+940 section of surrounding rock grade is V，for weathering seriously，weak broken and overall poor.The strong to weak weathering chlorite schist is easy to be softened in water.

At 2:00 Am on 29th of July in 2010，tunnel K723 +911～K723+919 section is peeling off and crackingat at the right side of arch.After that a small amount of sprayed concrete block out.At 5:00 Am，the part sprayed concrete falling off the block.Subsequently，landslides off the block has been continued.Ended by a large landslide，collapse the entire body closed tunnel section，landslides volume 600～ 700 m3(Fig.1).

Fig.1 Tunnel collapse between K723+911～K723+919

2 Reason analysis and the mechanism of collapse

Analysis of force and deformation characteristics of lining structure:load and strain of tunnel supporting structure are shown in Fig.2，the rock pressure ratio (the left side of the wall:the right)is about 0.9∶1 with the strain ratio is about 0.6∶1;arch waist surrounding rock pressure ratio(the left:the right)is 0.4∶1 with the strain ratio is 0.3∶1.Visible，the tunnel pressure is significantly asymmetric and the top lining arch bears tensile stress significantly.Tunnel surrounding rock is biased severely.In Fig.3，K723+910 section vault settlement curves shows that the section settlement for 12 days of continuous accumulation rate increased.The biased surrounding rock has been threatening the safety of tunnel structure.

Fig.2 Stress and strain regime in the section of K723+910 before collapse

Fig.3 Changes of settlement with the date in the section of K723+91(unit:mm)

Analysis of topographic and geological conditions: Tianshan Mountains'average altitude is up to 5 000 m with an average altitude of 3 000 m snowline line.Tunnel elevation generally located below the snowline but very close to.Tianshan Mountain tunnel is usually buried deep，of rich water.According to the failure degree range and surface inclination，depth and the conditions of surrounding rock in tunnel，the greater ground obliquity scope is，the more destruction of deep buried side encounter，with the less damage range of shallow buried side.Biased degree decreases with depth increases;the damage range and bias degree decrease with increasing friction angle.In Fig.4，K723 +911 tunnel collapse has little effect for buried deeply，but the slope is steep and heading for surrounding rock rich water appears around the images with different characteristics are the main factors of tunnel surrounding rock collapse of bias(as shown in Fig.5).

Fig.4 Sketch map of geological profile in the section of K723+911

Fig.5 Schematic diagram of geological conditions K723+911

Analysis of hydrogeological features:tunnel face at K723+911 is the chlorite schist，with right part is of rich groundwater，presenting plastic flow state and poor stability.The softening of chlorite schist strength test results of the strength indexes of saturated and dry conditions are as follows:in chlorite schist dry state，the cohesion is 22.46 MPa and internal friction angle is 20.92°;in saturated NaCl solution saturation state，the cohesion is 6.06 MPa and internal friction angle is 16.69°;in distilled water saturated state，the cohesion is 5.95 MPa and internal friction angle is 10.98°［3］.According to the strength of eccentrically loaded the degree of friction angle range and surrounding rock that chlorite schist in water showed significant reduction characteristics is an important factor leading to the tunnel collapse［3］.

Based on the K723+911 bias voltage collapse of model test as the research object，when surrounding rock is V，tunnel right face is of weak broken surrounding rock，tunnel lining by the occurrence of stress and lining disease，tunnel collapse treatment technology of soft rock in Xinjiang Tianshan mountain environment，provide technical support for the treatment scheme，also can provide reference for similar engineering.

3 Model experiment［4-5］

3.1 Lining structure and geomechanical model similarity theory

1)The tunnel lining structure is an elastic cylindrical shell structure，both the bending stress，and axial force.The control equation of bending deformation and axial deformation is not the same，they apply different similarity criteria.When the model and the prototype of the same material，the similarity criterion of two kinds of stress conditions are satisfied at the same time.When the model material and the material of the prototype is not at the same time，two kinds of similarity criteria cannot be satisfied simultaneously.The bending deformation of tunnel structure is the structural safety control mode，should be based on the bending deformation of similarity criterion to determine the model thickness and model design，so that bending deformation and the prototype is similar，the bending deformation similarity criterion.The bending deformation of the lining shell is regarded as the similarity criterion of thin plate structure.A plate thickness of H，X and Y coordinates of cross section in two mutually perpendicular to the direction of.In the lateral uniform pressure under the action of q，meet the control equation of thin plate.

K—plate bending stiffness;E—elastic modulus; μ—Poisson ratio.

The scale set model(model Cl=1/n).The model and the prototype are required to satisfy(Type 1)， the similarity criterion can be derived.By(3)model of lining thickness of publicity(Type 4)

2)Destruction of geomechanical model test，similarity requires not only similar in elastic stage model of stress and deformation state and the prototype，and beyond the elastic stage until destroyed，model of stress and deformation state and prototype.In fact，to obtain complete similarity model is very difficult，the main problem is that model material density，density，elastic modulus，Poisson's ratio are independen.Therefore，destructive testing can only satisfy the similarity criterion mainly，is the basic model of similarity，the similarity model test.

3.2 Model similarity ratio

The PYD-50 three to plane strain loading geomechanics model experiment device for horizontal loading experiment，ignoring the model body weight.By the similarity criterion of Cσ/Cl，Cγ=1 can be seen，Cl and Cσcan be independently selected.Considering that the test device geometry models and model selection，model of section geometric similarity ratio is Cl =80，stress similarity ratio using Cσ=1.This test mainly similarity can be divided into the following categories:stress similarity ratio Cσ=1，such as E，σ，C etc.;geometric similarity ratio Cl=80，such as l，δ，u etc;dimensionless similarity ratio C=1，such as ε，μ etc;capacity similarity ratio:C will not be considered.

3.3 Material selection and parameter setting

The model size is 70 cm×50 cm×20 cm.The barite powder:quartz sand:plaster model:water= 1∶1∶0.27∶0.45 simulation of weakly weathered limestone(as V rock)，internal friction angle is 19°，cohesion is 0.09 MPa，elastic modulus 210 MPa，Poisson's ratio is 0.35.According to the dosage of gypsum water:1∶1 proportion of lining concrete material model，the elastic modulus is 3.5 GPa.

Table 1 The parameter value

Fig.6 Stress-strain curve of surrounding rock

Fig.7 Relationship between elastic modulus of lining material and water-gypsum ratio

3.4 Test plan and test process

The test in a stepwise loading to simulate stress effect on tunnel structure，sets 3 group test(M1～M3)were observed in stress field with the lateral pressure coefficient λ=0.5，λ=1，λ=1.5，the existence of weak surrounding rock，lining on the right side of the tunnel lining structure stress characteristic，disease development.

The experimental process includes two stages:the first stage is from the test load to tunnel lining crack resistance limit state.The distribution of weak surrounding rock tunnel on the right side of the lining structure under non-uniform surrounding rock pressure observation，record the occurrence，distribution characteristics of lining diseases.The second stage，the weak surrounding rock and tunnel face after grouting reinforcement，by crustal stress，lining structure reach the failure state completely.Observation on the surrounding rock grouting reinforcement，combined into a steady bearing ring lining，lining disease distribution law of development.

Fig.8 Experiment model

3.5 Test result

Shown in Fig.9-14 for the occurrence of lining structure disease M1～M3 and the distribution and the tangential stress and deformation trend graph.Part of the symbol graph representation for respectively:()ultimate bearing state，lining the outer tangential stress;［］for the structural strength of grouting reinforcement，recovery，lining the outer tangential stress;{} the final failure，lining the outer tangential stress;(unit:Mpa).The broken rock reinforcement before:○(peeling)，□(cracking)，☆(blocked).Disease occurrence sequence:ⅠⅡⅢHT……After grouting reinforcement:●(peeling)，■(cracking)，★(block)，as the disease occurrence sequence(1)(2)(3)……

M1(λ =0.5)occurrence and distribution as shown in Fig.9 tunnel lining，the lining structure of tangential stress and deformation trend as shown in Fig.10.

Fig.9 Occurrence and distribution of lining structure diseases with λ of 0.5

Fig.10 Tangential stress and deformation trend of the lining structure with λ of 0.5

The lateral pressure coefficient is 0.5，under the vertical pressure stress field.The lining right arch foot firstly crack，then inverted arch and the right side wall cracking.The disease is mainly distributed on the right side wall，the right arch foot and the inverted arc.From the aspect of structure stress，tunnel vertical is compressed Obviously，tensile stress are respectively 3.91 MPa and 2.98 MPa measured in vault and inverted arch.Because of weak broken surrounding rock，the right wall by the surrounding rock supporting insufficient resistance outward bulge deformation，the lining the outer tangential stress is 2.11 MPa，higher 12.8% than on the left wall of the lateral tangential stress (1.87 MPa).While the two arch waist of tangential stress is a negative and a positive.With weak surrounding rock，the tunnel lining structure is under bias.From the deformation trend，the overall changes present flat circular lining.

After grouting，disease distribution characteristics present multi-point blossom，scattered everywhere in the arch.The vault，the inverted arch with grouting，pressure tendency has not decreased but increased，tensile stress are respectively 6.97 MPa and 4.76 MPa measured on vault and invert，increased by 78.2% and 59.7%respectively.Both sides of the wall of the tangential stress were reduced by 68.4%and 56.3%，two arch waist regression compressive stress state.Lining deformation trend of flat Steamed buns shape.

Overall，the lining arch foot as the curvature is small，the force was the most sensitive，is the disease first district.The inverted arch inward deformation trend is clearly.On the right side of broken surrounding rock grouting can restrain tunnel by bias，the lining stress is uniform，but by the action of vertical stress in surrounding rock collapse treatment，when attention should be paid to the prevention of the vertical deformation of the lining.

M2(λ = 1)occurrence and distribution as shown in Fig.11 tunnel lining，the lining structure of tangential stress and deformation trend as shown in Fig.12.

Fig.11 Occurrence and distribution of lining structure diseases with λ of 1

Fig.12 The lining structure of tangential stress and deformation trend graph with λ of 1

When the lateral pressure coefficient is 1，form the disease occurrence and distribution，lining arch foot is still the first crack area，but overall disease mainly distributed in upper half arch.From the aspect of structure stress，left and right arch waist，side wall，arch foot tangential stress respectively，one positive and one negative，lining deformation presents“left to the convex shape”.In the lateral pressure coefficient is 1 of the stress field，the lining is biased role more obvious for the weak surrounding rock.The left arch foot is subjected to tangential stress at the largest，up to 3.36 MPa.

After grouting，the disease is mainly distributed in the left side of the arch.From the stress situation，side wall under tangential stress continues to increase，increased respectively by 90.2%and 193.3%，“left to the convex”lateral deformation trend more obvious，the area with relatively little change in the tangential stress.Overall，comparing with λ=0.5 stress field， the lining left arch foot first disease，invert inward deformation tendency is obvious，but the right side wall rock grouting on the left to curb the role of poor deformation.

M3(λ =1.5)occurrence and distribution as shown in Fig.13 tunnel lining，the lining structure of tangential stress and deformation trend as shown in Fig.14.

Fig.13 Occurrence and distribution of lining structure diseases with λ of 1.5

Fig.14 The lining structure of tangential stress and deformation trend graph with λ of 1.5

When the lateral pressure coefficient is 1.5，based on the horizontal pressure force field，lining arch foot is still the first crack，both sides of the wall cracks.From the stress of surrounding rock，by the bias，lining the right spandrel compression effect is obvious，the measured tangential stress is 6.36 MPa，is 1.5 times more than other parts of the arch.Arch pressed inward deformation trend remains similar with M1，M2.It presents arch vault，arch foot convex，arch waist and the inverted arch concave，general triangular deformation trend.

After grouting reinforcement，crack is mainly distributed in the arch plane of the first and third quadrant，namely the right arch waist and left arch foot region.The right arch waist tangential stress increased about 14.6%，deformation was under a certain control，lining triangle deformation trend more obvious.

From the analysis results based on M1～M3 test，we can get the following conclusions and suggestions:

First，in different stress field，the arch foot is the most sensitive areas and often the first crack place in disease.Treatment plan should focus on setting locking anchor pipe or the feet lock bolt arch foot reinforcement measures.

Second，in vertical pressure field，arch pressure significantly with serious vertical deformation.In the λ =1 and 1.5 stress field，the lining bias effect becomes more and more apparent，lining the lateral deformation is bigger，so it should be combined with the actual situation，set the horizontal vertical necessary to support the treatment scheme，curb deformation.

Third，by the horizontal pressure，caused by the right weak broken surrounding rock bias affects become the more obvious，even local grouting，arch waist，side wall is still serious deformation，arch ring is also easy to produce lateral or triangular deformation，vertical pressure and stress field，was no obvious bias effect.So in the treatment scheme，one should pay attention to strengthening grouting increased，the half or full face grouting，on the other hand，appropriately increasing the arch lining its strength，ensure the security of structure.

4 Treatmentplan and treatment effect

4.1 Treatment plan

According to the comprehensive analysis of the conclusions and recommendations of the tunnel collapse treatment measures，technical parameters and adjustment suggestion as shown in the following table:

Table 2 Comparison of treatment plan parameter

Continued table 2

4.2 Treatment scheme

1)Adopting the advanced small pipe grouting is to reinforce stratum.Using φ42 cm 3.5 m lone small duct grouting forepole，along the upper half arch ring，ranging from the original plan 120°to 150°，improve the ability of the surrounding rock stability.

2)As shown in Fig.16，at the beginning of the August and September，the second lining stress and strain monitoring results shows the force of the most disadvantaged right haunch pressure and strain monthly increases were 2.61% and 1.67%.The treatment scheme of the landslidebody stress and deformation are well controlled，the reasonable treatment scheme.

Fig.15 Schematic diagram of construction

Fig.16 Changes of settlement with the date in the section of K723+920

Fig.17 convergence curve of surrounding rock in the section of K723+920

Fig.18 Stress and strain of lining in the section of K723+915

5 Conclusions

This paper tunnel gives construction technology and treatment recommendations as following:

1)In the vertical pressure stress field，influence of bias effect on lining is relatively small.The greater Horizontal direction stress level is in pressure field，the more obvious lining bias effect is.But no matter what kind of working condition，arch waist is one of the most unfavorable position force，advanced small pipe grouting with the first half of the 150 degrees and above setting range can better improve the anti eccentric compression bearing capacity of lining.

2)In soft rock and the existence of bias tunnel，the arch of the foot is the most prone to the disease site，recommend the use of the feet lock catheter(anchor)reinforcement measures.

3)The level of the pressure stress field，easy to produce lateral arch or triangular deformation，vertical pressure and stress field，arch deformation rule is oblate.CRD method can be used to suppress lining deformation，suitable for the tunnel in cold regions bias，weak rock.

4)Increase the initial supporting shotcrete thickness，encryption two lining circumferential reinforcement spacing can be used jointly.

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