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In the construction of tunnels, some complex geological conditions, such as water-bearing rock masses, are sometimes encountered. If the water content of this rock mass is relatively large, the whole construction process cannot be carried out at all unless a self-drilling hollow bolt is used. Why is the support construction of water-bearing rock mass so difficult? How to construct self-drilling hollow bolts? How to support the water-bearing rock mass? Today, Sinorock will take a specific application case to explain in detail.

In a certain engineering tunnel, the stratum is dominated by water-bearing rock mass with developed fissures, and the rock mass is severely weathered and has strong water permeability. When the excavation passes through the rock mass karst cave, the broken cave section or the fault fracture zone, because the surrounding rock is under the fault, the daily water inflow is more than 2000m3 in the working face. The problem of stuck drilling and hole collapse, the construction process can no longer be carried out normally.

Self-drilling hollow bolt is composed of six parts: drill bit, hollow bolt body, connecting sleeve, backing plate, nut and centering device. Two problems arise.

The project adopts alloy drill bit, which has strong penetrating power. Under the action of the rock drill, all kinds of rock mass can be easily drilled. The drill bit has a number of slurry holes, which can be cleaned in the initial stage, and can be used to exhaust slurry during grouting.

The self-drilling hollow bolt body has continuous wave thread or trapezoidal thread, which can be connected with the drill bit to complete the drilling construction. At the same time, the rod body can be cut at any position, or it can be lengthened by connecting sleeves, which is very suitable for construction in relatively narrow space conditions such as tunnels.

The hollow design of the self-drilling hollow bolt body makes it have a grouting function. When the bolt body completes the drilling, it does not need to be pulled out, which avoids the problem of slurry loss caused by the traditional process of grouting and anchor pulling. When grouting the self-drilling hollow bolt, the hole is closed and the bottom of the hole is circulated. During grouting, several holes can be grouted at the same time according to the amount of grouting and the situation of grouting.

After the self-drilling hollow bolt is connected with the screw grouting machine, pressure grouting can be realized, which can make the grout more fully fill the rock mass cracks and drilling holes, increase the diameter of the anchor body, and improve the anchoring effect. In addition, the high-strength backing plate and nut can evenly transmit the stress of the deep surrounding rock to the hole wall, and achieve the purpose of mutual support with the rock mass.

The centralizer ensures that the self-drilling hollow bolt is always in the center of the borehole during the drilling and grouting process. The grout can completely and evenly wrap the rod body to avoid corrosion due to contact with the external environment, and the support time is longer.

With the increase of construction projects, it is inevitable to encounter sand layer geology during the support construction of some foundation pits. If the traditional support method is still used, the progress of the whole project will be slowed down a lot or even stagnant. It can perfectly solve various problems encountered in traditional support construction. So what are the characteristics of the sand geological structure? What are the problems encountered by traditional support methods? How does the self-drilling hollow bolt solve these problems?

Characteristics of the geological structure of the sand layer

The sand layer geology is mostly composed of medium sand and silty sand layers. Depending on the location of the project, some artificial fill, coarse sand, and silty clay may also be mixed. The most obvious feature of this kind of geology is that the soil is soft and easy to collapse.

Problems encountered by traditional support methods

In the support construction, the ordinary hollow bolts cannot be constructed at all when they encounter the sand layer geology that is difficult to form holes and easy to collapse after the holes are formed. Because the construction process of the ordinary hollow bolt is to drill first and then grouting, when the drill pipe is withdrawn, it is likely that the hole will collapse, and the subsequent bolt cannot be put in, resulting in the entire support construction cannot continue.

Self-drilling hollow bolt

Self-drilling hollow bolt is a kind of high-efficiency supporting material. It consists of high-strength alloy or all-steel drill bit, hollow bolt body, connecting sleeve, backing plate, nut and centering device. It integrates drilling, grouting and anchoring. It is very suitable for drilling construction under geological conditions that are easy to collapse holes and difficult to form holes. The self-drilling hollow bolt itself is both a drill pipe and an anchor rod. It does not need to be pulled out after drilling. After connecting the grouting machine, the grouting can be grouted from the inside to the outside through the hollow channel and the drill hole.

Construction technology of self-drilling hollow bolt

Drilling Rig Positioning: According to the length and drilling angle of a single self-drilling hollow bolt, move the special drilling rig for self-drilling bolts to an appropriate position.

Install the anchor rod and drill bit: according to the geological conditions, select the appropriate drill bit to connect with the hollow anchor rod body, ensure that the end and the tail are clamped and fixed firmly and in a straight line, and the tail end of the anchor rod is connected with the optional grouting adapter and grouting machine. connect. The length of the anchor rod is generally not less than 3 meters, and the clamping distance between the head and tail of the anchor rod is not more than 2 meters, so as to avoid too many joints affecting the connection quality, and the clamping distance is too long during the drilling process. and post-grouting.

Anchor rod drilling: In order to ensure the direction, slope and accuracy of the anchor rod, before drilling, the surveyor will stake out the position of the anchor rod. During the drilling process, check the drilling angle and direction, and correct the deviation in time.

Grouting: In sand layer geology, grouting is generally carried out in two steps, the initial pressure is generally 0.2Mpa ~ 1Mpa, and the water-cement ratio is about 1:1. When the bolt is drilled to the design depth, the secondary grouting is carried out. The secondary grouting pressure is 1MPa ~ 2.5MPa, and the water-cement ratio is controlled between 0.45~0.6:1, so that the grout can fully fill the rock mass cracks and expand. Anchor radius.

Reinforcement: Install backing plates and nuts on the exposed section of the self-drilling hollow bolt close to the rock surface to reinforce the bolt. When the rock mass is deformed, the deformation force is transmitted to the bolt and the anchor body through the backing plate and the nut to stabilize the rock mass.

Self-drilling rock bolt is an improvement and innovation on the basis of traditional anchors. It has many advantages over traditional anchors.

No Need Casing Pipes

The rock anchor can be drilled in a loose soil layer or a broken rock layer without the need of a casing pipe to protect the drilling hole collapsing. Since the self-drilling anchor system is drilling and grouting simultaneously, there is no worry about that the drilling hole collapses and the anchor cannot be installed.

Pressure Grouting

By means of pressure grouting, the cement mortar is evenly distributed in the borehole and penetrates into the surrounding soil or rock layer (the so-called filter cake effect). This results in higher bond strength while allowing the soil and hollow anchor bolt to be better integrated into the softer soil layer. What’s more, the slurry could fill into the cracks or the rock and soil to expand the diameter of the anchor. So, the anchoring effect is better than traditional anchors.

Thread Design

The stability of the high slope is mainly determined by the geological conditions of the slope formed in the natural environment, as well as the acquired artificial transformation and other factors. The fractured section of the rock mass on the high slope has the characteristics of broken rock formation, high-risk factors, and difficulty in supporting. When choosing the supporting method, it is necessary to choose a supporting method with a strong penetrating force and a good anchoring effect. I suggest self-drilling rock bolts to support the broken section of the high slope rock mass.

Characteristics of High Slope Rock Mass Crushing Section

It is very common for the slump in the upper part of the broken section of the rock mass on the high slope to cause hole collapse or stuck drill. Since the drill bit will be stuck in the narrow part, it is necessary to check whether the drill hole is displaced frequently during support and timely adjustment. High-slope rock fragmentation will cause high-abrasive support difficulties. Ordinary drill pipes are also prone to drilling difficulties when they pass through these formations. Self-drilling rock bolts are equipped with various types of drill bits, which are highly matched with the properties of rock formations and soil so that we can improve drilling efficiency in different geological conditions.

Supporting Method for Broken Section of Rock Mass on High Slope

Self-drilling anchor bolts can complete drilling, bolt installation, grouting, anchoring, and other processes in one construction process. Compared with conventional drill pipes, self-drilling hollow bolts are equipped with a variety of drill bits, including " There are various types of cross all-steel drill bits, "mud drill bits", "ball-tooth alloy drill bits", etc., which can be selected according to the properties of different rock layers and soil during construction.

The self-drilling hollow bolt is used in combination with the excavation and modification drilling rig. The construction work area is large, and the construction height is high, which can minimize the personal safety risk of the construction personnel. The rod body is made of high-strength alloy seamless threaded steel pipe, which can be cut or lengthened arbitrarily. It has the advantages of simple construction technology, high construction efficiency, and good economic benefits. The problems of shrinking collapsed holes, and difficulty in forming holes have played a good anchoring effect.

Advantages of Self-drilling Rock Bolt Support

High stability

The grouting of self-drilling rock anchors is from the inside to the outside through the inner hole of the rod. At the same time, the outer end of the anchor hole is provided with a grouting plug and a backing plate, which can effectively prevent the grouting from overflowing. If necessary, pressure grouting can also be carried out, so that the slurry can be pushed into the cracks of the rock and soil around the rod body, and the stability of the rock formation can be improved.

Strong Ability to Cope with the Environment

The self-drilling hollow bar combines the drill pipe and the hollow bolt body into one and can be used in the stratum that is weak and broken and difficult to form holes. An ordinary bolt is of poor adaptability, which generally needs a drilling hole in advance and then is put in the hole. However, the hole will often collapse when the drill pipe is pulled out in the broken and weak rock. Therefore, in the face of weak and broken rock mass construction, the self-drilling bolt has a stronger ability to cope with the environment.

The construction process is simple

The self-drilling bolt integrates drilling, bolt installation, and grouting. All construction procedures are completed in one process, reducing the process of pulling out the drill pipe, installing the bolt, and inserting the grouting pipe, and the process is simple. High construction efficiency.

The rock layers that the tunnel passes through may encounter complex geological conditions, and the pebble layer is one of them, which has the characteristics of broken rock and poor cohesion. The pebble layer support needs to adopt a method with strong permeability and strong cohesion. The self-drilling anchor bolt can realize the function of grouting while drilling, which is more conducive to the bonding of broken rock layers and is convenient for construction.

Reasons for the Support of the Tunnel Passing Through the Pebble Layer

The pebble stratum is loose, the cohesion is small, and the pores are large. Once excavated, it is easy to have a decline in bearing capacity, poor resistance, and then some unexpected situations such as instability and disintegration. The reasons for support are as follows.

Loose Structure

The structure of the pebble layer itself is loose. If the tunnel is in the area near the river or sea water, due to the submersion of groundwater, the fine particles will be eroded, and the mechanical properties of the rock mass with poor cementation will drop sharply under the action of excavation.

Sudden Deformation

The pebble layer is very sensitive to excavation and other actions. Once the excavation is disturbed, the stress is redistributed and the resistance capacity is reduced. The tunnel bearing arch will fail in a short period of time, causing instability failure, disintegration, and then collapse into the tunnel.

Face Crack

The pebble layer includes pebbles, boulders, large-diameter gravel, etc., and the mud-calcareous filler in the middle will become weak, which will lead to further loosening and cracking of the face. The phenomenon of falling blocks in the part above the arch waist of the face will lead to deformation of the surrounding rock, breaking through the reserved deformation, and squeezing the tunnel structure.

Support Method for Tunnel Crossing Pebble Layer

The geological structure of the pebble layer tunnel is loose, and the rock mass is seriously broken. It is difficult to form holes by using the general support construction method, resulting in the delay of the construction progress. The self-propelled anchor rod integrates drilling, grouting and anchoring, which can well bond the unstable rock formation and make the project achieve the expected anchoring effect.

Drilling Preparation

The drilling angle, length, mixing ratio of slurry, and selection of drill bits should be determined according to the rock formation. Most tunnel advance support will use 51, 76 self-propelled bolts. Adjust the drilling angle of the rock drill according to the terrain and geological conditions.

Drilling Grouting

When the self-propelled bolt is longer and needs to be spliced ​​together, a drill bit should be put on the front end of the first section of the bolt, and the tail end of the bolt should be connected to the grouting machine through the rotary grouting adapter. During drilling, grouting is carried out, and the slurry is pressed into the hole and into the cracks of the rock mass to consolidate the rock mass and stay in the deep stable rock mass, and bond together with the stable layer as the slurry solidifies.

Anchor Rod Extension

When the remaining 30 cm of the first section of anchor rod, stop drilling, put a connecting sleeve with artificial lubricant on the tail of the previous section of anchor rod, and then connect the latter section of anchor rod, and so on until drilling to the design length. At the end of the drilling, the anchor rod is exposed at least 10 cm, which is convenient for the installation of the arched backing plate and the ball nut.

Pull Test

After the self-propelled bolt is constructed, it is necessary to test the pull-out force value of the bolt to check whether it meets the design value of pull-out force. For every 300 bolts in the operation area, no less than 3 bolts should be randomly checked for pull-out force test to ensure that the construction effect meets the expected requirements.

The structure of the self-drilling micro pile consists of a hollow bolt with continuous threads, and an OPC cement slurry with a minimum strength of 25N/mm2, which can also transmit tensile and compressive forces to the ground. Also, self-drilling micro piles can transfer tensile and compressive loads to deeper load-bearing soil layers in the ground.

Compared with traditional piles, the advantages of self-drilling micro piles are:

Withstands compressive and tensile forces

No need for temporary casing

Improve the internal mechanical action of the floor / grout

Easy installation, greatly improve production efficiency

Small rotary impact equipment is enough to drill

Can be installed in narrow spaces

The working bearing capacity of self-drilling micro piles ranges from 110kN to 3660kN

Vibration-free drilling can be used, low vibration, low noise, minimal damage, and no damage to adjacent buildings.

Self-drilling micro piles offer great benefits for excavation and concrete plinth schemes, as well as great convenience for health and safety concerns. See below practical applications of self-drilling micro piles in building foundation engineering.

The foundation of the building is repaired. Since the foundation of the ancient building has no reinforced concrete supporting structure, the settlement occurs in the years. In order to restrain the deformation, self-drilling micro piles are used to control and restrain the development of the deformation.

Weak and broken surrounding rocks are often encountered during construction in tunnel engineering. Due to the nature of the rock mass itself, the weak and broken surrounding rock is easy to collapse and difficult to form holes, and it is difficult for ordinary bolts to support. Sinorock recommends using self-drilling hollow rock bolt in tunnel to support.

The self-drilling hollow rock bolt system is composed of a hollow anchor bar, coupler, nut, drill bit, plate, and centralizer. It can combine drilling, grouting, and anchoring in one process. The self-drilling anchor bolt system is safe, efficient, and convenient. It is suitable for broken rock, loose soil, and geological conditions where is difficult to drill holes. It helps to ensure the anchoring effect in complex ground conditions and achieve the best construction result.

Self-drilling hollow rock bolt systems are divided into R thread and T thread systems. The sizes of our self-drilling anchor bolt include R25, R32, R38, R51, T30, T40, T52, T73, T76, T103, T111, T127, T130, T150, and T200. We can choose different product sizes and types of self-drilling anchor systems according to different engineering requirements.

Self-drilling hollow rock bolt system, which combines drilling, grouting, and anchoring together, is suitable for broken rock and conditions which are difficult to drill holes. Casing pipe is omitted in construction, which greatly improves construction efficiency.

2. Self-drilling anchor bolt system has a rich variety of drill bits, and the drill bit can be selected according to the properties of rock and soil, which can improve the drilling efficiency.

Self-drilling hollow rock bolt system can fill cracks, consolidate rock mass and soil layer through pressure grouting, and has good grouting spreading radius and reliable anchoring quality.

The hollow bar can be cut arbitrarily and lengthened by the coupler. Therefore, the self-drilling anchor bolt is suitable for construction in the narrow space that the large equipment cannot enter.

During the construction process, the project management team adhered to the principles of short footage, weak blasting, strong support, early closure, and frequent measurement to organize the construction, and made full use of advanced geological forecasts to reinforce the surrounding rock in the cave in advance and strengthen the initial support.

When the tunnel passes through the weak and broken surrounding rock, the excavation disturbance will cause large deformation of the surrounding rock. If the initial support is not timely, the deformation of the surrounding rock may exceed its allowable range, and in severe cases, it will cause the instability of the face and the collapse of the tunnel, resulting in major economic losses. At this time, it is necessary to adopt the tunnel's advanced support measures to control the deformation of the surrounding rock, so as to achieve the purpose of ensuring the safety of the tunnel construction.

Self-drilling hollow bolt is an irreplaceable product for tunnel advance support, and plays a major role in geotechnical support:

Radially consolidating the tunnel circumference and supporting the rock mass, forming a load-bearing ring, allowing the rock mass to support itself (with shotcrete and other surface elements).

Umbrella shelters and advance braces are used as means of advance support in the case of inferior rock formations, shallow soil layers, and ultimate stress.

Reinforcement of end faces maintaining internal rock stress for tunneling of large cross-sectional areas.

Due to the limitation of the section form, surrounding environment and geological conditions of urban subway stations, the enclosure structure generally adopts the form of bolt support. At present, with the continuous increase of the excavation depth of the subway open cut station, the surrounding construction environment is becoming more and more complex, and the length and diameter of the rock bolt are also increasing and increasing.

Under the action of the maximum horizontal stress, the surrounding rock will appear interlayer dislocation, resulting in the deformation of the foundation pit. The role of the bolt is to restrain the shear dislocation of the rock stratum along the axial direction, so the main advantages of using the pile-anchor support type in this open-cut foundation pit are as follows:

The large-diameter self-drilling rock anchor bolt has good supporting effect, simple construction, and is conducive to mechanized operation, and the construction speed is fast.

The large diameter bolt has the advantages of high strength, high rigidity and high shear resistance in force.

The large-diameter self-drilling rock anchor bolt support works together with the surrounding rock to change the mechanical state of the surrounding rock to achieve a more stable foundation pit wall.

The large-diameter self-drilling rock anchor bolt support provides a large space for the construction of the internal structure of the foundation pit, avoids the safety risks caused by the replacement of the support, and effectively ensures the stability of the foundation pit during the construction process.

The successful application of the large-diameter rock anchor bolt in the subway open-cut foundation pit provides a safe and reliable space for the foundation pit excavation and structural construction and avoids the necessary switching support operation using inner braces. Under the premise of effectively saving the project cost, the construction risk is reduced, and the project construction period is ensured.

With the development of domestic engineering construction, highways, railways, mines, water conservancy and other projects will encounter a large number of slope terrain, and often face geological disasters such as high and steep slope collapse and landslides during construction. Therefore, the research, development and application of slope protection and reinforcement treatment technology has certain social and economic value. There are various forms of slope protection technology used internationally. Among them, self-drilling hollow bolt support is a safe, high-quality and efficient protection technology, which has been widely used in various slope protection and reinforcement projects.

Below we will introduce you a slope project supported by self-drilling hollow bolt.

The west side slope of the main plant area of ​​the project is a rock side slope. Due to the impact of rainwater erosion and blasting construction, the slope partially collapsed and fell off. In order to strengthen the local stability of the slope, plain concrete repair and self-drilling hollow bolt anchoring support structure were used in the construction. lengthened.

The mechanical action principle of self-drilling hollow bolt can be summarized in the following three points:

1. Suspension of anchor rod: The anchor rod passes through the weak and loose rock and soil mass and is anchored into the stable stratum to generate tension, overcome the self-weight and sliding force of the sliding rock and soil mass, and prevent the slope and cave wall from sliding and slumping.

2. Squeeze reinforcement: The compression zones of adjacent bolts under stress overlap each other to form compression bands. Enhance integrity and improve bearing capacity.

3.Combined beam (arch) action: After the bolt is inserted into the stratum to a certain depth, the strata under the action of the anchoring force squeeze each other, the friction among the layers increases, and the internal stress and deflection decrease, which is equivalent to a simple stack The combined beam (arch) becomes a composite beam (arch). The flexural rigidity and strength of the composite beam (arch) are improved, thereby enhancing the bearing capacity of the formation.

In tunnel construction, hollow rock bolts are often used to maintain the stability of surrounding rock and ensure construction safety. With the increase in the use of bolts in tunnel engineering, construction safety, and quality problems are also common. The angle and length of the bolt, as well as the installation and grouting of the bolt, are relatively common problems. Sinorock will show you some problems existing in the tunnel construction supported by rock bolts and how to prevent them.

The Preparation Before the Construction

Staffing of Quality Management Personnel

The tunnel construction supported by the rock bolts process is relatively complicated. In order to ensure the construction quality, it is necessary to provide monitoring personnel during the construction to monitor the drilling positioning, drilling angle, drilling depth, grouting, and inspection of the bolt construction.

Raw material inspection

The tunnel construction quality supported by rock bolts is closely related to the quality of raw materials. It is necessary to control the quality of raw materials, plan the inspection items and sampling ratios of raw materials, control the quality of raw materials from the source of manufacturers, and choose manufacturers with reliable quality.

Inspection of construction equipment

The tunnel construction supported by rock bolts mainly relies on labor and drilling rigs. The bolting rigs need to be selected according to the construction environment and construction design. The construction environment determines the area of ​​the construction rig and the convenience of construction. The design of construction drawings determines the drilling depth requirements that the rig needs to meet.

Problems in The Process of Anchor Construction

Anchor Rod Positioning

The rock bolt positioning includes steps such as laying out, marking, and fixing points. It cannot be positioned intuitively. If the anchor rod positioning deviates, the construction effect will not meet the requirements. Therefore, the construction site should strictly require the construction process of self-drilling hollow grouting bolts, and checking the positioning of the bolts for 10% of the number of bolts.

Drilling Angle

When designing, the drilling angle of the rock bolts will be set according to the geological and rock formation. During construction, due to the environmental conditions of the tunnel and the limitation of equipment adjustment, the drilling angle often deviates. Before drilling, manual observation and checking are required to ensure the accuracy of construction.

Anchor Rod Installation

When purchasing rock bolts, it is necessary to take into account the occurrence of unexpected situations, and purchase bolts that exceed the required amount, including their accessories. The purpose is to prevent the length, specification, and appearance of the rock bolt do not meet the requirements, and if the accessories are not complete during the installation of the bolt, which can be replaced immediately. When installing the stopper, if it is found to be loose or the distance from the orifice is too large or too small, it should be corrected immediately.

Grouting Problem

In tunnel construction, if hollow rock bolts are used, attention should be paid to grouting and grouting. When inspecting, it is necessary to pay attention to whether there is an overflowing slurry near the orifice stopper, and whether it is intentionally plugged with an anchoring agent at the grouting port, which is a false grouting phenomenon. If the steps of grouting and grouting are not done well, the slurry will not be full, resulting in excessive pores and affecting the anchoring effect.

Problems of Acceptance and Acceptance of Anchor Bolt Construction

Construction Effect of Anchor Rock Bolt

After the rock bolt grouting construction is completed, the length and grouting degree of the bolt needs to be checked. Unqualified bolts belong to failed bolts and need to be re-struck or grouted. The number of re-struck bolts is the same as the number of failed bolts, and the length should be 1.5 times that of the failed bolts.

Pull-out Test

According to relevant regulations, it is necessary to test the pull-out force value of the bolt after the construction of the bolt to check whether it meets the design value of the pull-out force. In the test, no less than 3 bolts should be randomly checked for pull-out force test in every 300 bolts in the operation area.

Slopes of soil with rock is a mixed slope composed of soil and fully weathered rock in the upper part and rock in the lower part. Due to its own structural characteristics, instability accidents often occur. It is necessary to select a scientific support method in combination with the actual situation of the project to ensure the stability of the soil-filled rock slope. Below, Sinorock will introduce the soil-filled rock slope to you. How to reinforce.

Difficulties in supporting soil and stone slopes

Geological complexity

The thickness of the covering layer of the slopes of soil with rock is large, and the mechanical properties of the upper soil layer are poor, so it is difficult to provide the required resistance of the retaining structure, and the conventional retaining structure is difficult to effectively play the supporting function. The soil-rock slope has different failure modes at different stages, and the later stage is more complicated and the failure modes are diverse.

Poor strength

When the slope rate is steep, due to the low mechanical strength of the soil and rock slope itself, during the continuous rainfall period, the shallow surface soil of the slope is prone to slump and slippage when it is saturated with water.

Slip instability

The weight of soil increases due to rainfall infiltration, and the shear strength of soil decreases. Because the soil-rock interface of the soil-rock slope is relatively steep, after the slope is excavated, the slope soil may slide along the soil-rock interface, and the arc-shaped sliding instability of the larger volume of soil is easy to occur in the deeper part. , and deep polyline-shaped slip failure.

Supporting method of soil-rock structure mixed slope

Clean up the slope

The upper layer of the soil and stone slope is mostly loose soil. It is necessary to clean the slope surface first, remove the scum, vegetation and loose stones on the slope surface, clean the slope surface, and prepare for the subsequent construction.

Slope classification

The support of soil and rock slope should consider not only the control of the deep sliding deformation of the slope, but also the control of the soil deformation in the middle and shallow parts. Therefore, it is necessary to classify the slope and design different support methods according to different depths.

Rig selection

Ordinary down-the-hole drilling rigs cannot realize the function of grouting while drilling. In the case of grouting without pressure, it is difficult for the cement to flow upward along the rod body, resulting in scarce or even no cement slurry around the rod body, resulting in limited slurry entering the surrounding rock. The added strength of the slope is also limited. Choosing a special drilling rig for self-drilling bolts for construction can better play the effect of self-drilling bolts.

Anchor rod drilling

When the mixed slope is constructed, it is difficult to form holes due to the loose soil. During drilling, it is necessary to carry out slag discharge back and forth, so as to avoid the occurrence of sticking problems and improve the drilling efficiency.

Drilling and Grouting Simultaneously

The self-drilling hollow grouting bolt can realize the function of grouting while drilling. During repeated drilling, the slope is fed with enough grout, and the bond strength between the anchor and the slope is greatly increased, which enhances the soil quality. strength, and also enhances the ability to resist slope deformation.

Drainage settings

Choose according to the local weather and environment, and increase the drainage setting. Many slopes are unstable because of excessive water content. If the construction is in the rainy season, it is necessary to close cracks, increase drainage ditches, and divert water to the outside of the slope to prevent water from infiltrating the slope and accelerating deformation.

Monitoring deformation

In the construction process, information construction can be implemented, and the construction can be better guided through monitoring data. It mainly monitors the displacement and settlement of the slope, records the dynamic changes, and ensures the safety after construction.

During the construction of domestic support projects, in the face of loose geology, many people choose to use traditional casing to drill into holes. The self-drilling rock bolt technology introduced from abroad can be a good substitute for casing drilling, and the overall cost is lower. So, what is the difference between casing drilling and self-drilling rock bolt? Today, Sinorock gives you a brief introduction.

Casing Drilling Construction Technology

There are many methods of casing drilling, which need to be comprehensively selected according to the type of drilling rig, construction requirements and formation conditions. Under normal circumstances, the casing is pressed into the casing while drilling, or the casing is pressed in ahead of time, and then the drilling tool follows. It is mainly divided into two methods: eccentric follow-up tube and concentric follow-up tube, which are different in process principle. Casing drilling can prevent the hole wall from collapsing or the quicksand filling the borehole during the drilling process, but the construction process is more complicated, and it is suitable for drilling loose strata and quicksand layers.

Construction Technology of Self-Drilling Rock Bolt

Self-drilling rock bolts need to be inspected for the drill bit, hollow bolt body, and drilling rig before starting construction. The hollow bolt body is connected to the drilling rig and grouting machine through a rotary grouting adapter. During construction, drilling rigs and grouting can be carried out at the same time. After grouting, install the backing plate and nuts to ensure the anchoring effect. Self-drilling rock bolts are mainly suitable for difficult-to-form surrounding rock, stratum fragmentation, etc., and can enter a narrow space for construction to shorten the construction period.

The Difference Between Casing Drilling & Self-Drilling Rock Bolts

The hollow bolt body used by the self-drilling rock bolt can be cut arbitrarily and can also be lengthened by connecting sleeves. It can be constructed in a narrow space where large equipment cannot enter, and the construction is more convenient.

The casing wall is omitted in the self-drilling rock anchor construction process, which greatly improves the construction efficiency, shortens the construction period, and reduces the overall construction cost.

The casing drilling grouting needs to put the bolt first and then connect to the grouting machine. The self-drilling hollow bolt can be connected to the grouting machine and the drilling rig through the rotary grouting adapter to realize the function of grouting while drilling.

Slope is a very common terrain in highway and railway engineering. During the construction process, it needs to be reinforced and supported by various methods to prevent it from collapsing, falling rocks, uneven slope stress distribution and other problems, reducing safety. hidden danger. There are many methods for slope support, including gravity retaining wall, thin-wall retaining wall, spray anchor support and self-drilling rock bolt support. Today, Sinorock will introduce and analyze the following methods in detail. Advantages and disadvantages of four common slope support methods.

Supporting the slope by the self-gravity of the retaining wall

Gravity retaining wall slope support is a relatively traditional and common slope support method. Its principle is to use the gravity of the slope body or the wall itself to resist the side pressure of the slope. Gravity retaining walls can be made of concrete, block stone, rubble, etc. as masonry, or concrete can be directly poured on the slope surface, and are often used in highways, harbors, railways, mines and other projects.

Advantages: easy to obtain materials and construction, low cost.

Disadvantages: large volume and weight, and it is difficult for weak geology to bear its weight.

Applicable situation: the height of the slope is not large, and the materials can be obtained locally

Slope Support with Thin Wall Reinforced Concrete

That is, the thin-walled retaining wall belongs to the light retaining wall, which is divided into buttress type and cantilever type.

Advantages: simple structure, convenient construction, light weight

Disadvantages: It needs to consume a certain amount of steel and cement. If the slope height is relatively large, the amount of steel will be doubled and the cost will be higher.

Applicable situation: small slope height

Ordinary bolt support (bolt shotcrete support)

Slope shotcrete support is a support method in which concrete and ordinary hollow bolts are combined to bear the slope weight together with the surrounding rock of the slope. Shotcrete support is a more complicated support method, and the construction process is also more complicated. Shotcrete anchor support is to drill holes on the slope first, then insert the bolts, and then use high pressure to drive the cement slurry into the drilled holes through the bolts to reinforce the surrounding rock mass together with the bolts. Although this support method can effectively limit the deformation of the surrounding rock, adjust the stress distribution of the rock mass, and prevent the rock mass from collapsing and falling, the construction process is too complicated and the efficiency is extremely low.

Advantages: strong adhesion, strong penetration, firm and reliable support

Disadvantages: complex construction process, difficult construction, low efficiency

Applicable situation: can be used for temporary support of engineering slopes

Self-drilling Rock bolt for slope support

The self-drilling rock bolt slope support is similar to the shotcrete support, but the efficiency is much higher than that of the shotcrete support. Most ordinary hollow bolts need to be drilled with drill pipes first, then the bolts are inserted, and then connected with the grouting machine for grouting, while the self-drilling rock bolts are both drill pipes and bolts. After the rotary grouting adapter is connected to the grouting machine, grouting can be performed at the same time as drilling, realizing the integration of drilling, grouting and anchoring functions, simplifying the construction process and shortening the construction time.

Advantages: convenient construction, strong anchoring force, high efficiency

Disadvantages: It is necessary to use a special drilling rig for self-drilling rock bolts for construction. There are few domestic manufacturers of self-drilling rock bolts, and there are also fewer self-drilling rock bolting rigs.

The Zhengwan high-speed railway is 818 kilometers long, connecting Zhengzhou, Henan and Wanzhou, Chongqing. It is an important part of the Beijing-Kunming corridor in my country's eight-horizontal and eight-vertical high-speed railway network, and it is also a newly planned railway included in the national "Twelfth Five-Year Plan" period. Construction started at the end of 2014 and is expected to open to traffic in 2022.

The Gaojiaping Tunnel of the ZWZQ-5 bid section of the Hubei section of the Zhengwan High-speed Railway has complex engineering geology, difficult construction and high safety risks. The inlet section is V-grade surrounding rock, mainly composed of medium-strong weathered shale, weak surrounding rock and high water-rich karst cave, broken rock mass and poor self-stability, and the lining type is Vcw composite lining. During the construction process of China Railway 11th Bureau, Sinorock R51 self-drilling bolts were used as advanced pipe shed support, instead of traditional steel pipe sheds.

There are 50 holes per ring at the top of the end face. The hole spacing is 400mm, and the hole depth is 25 meters. The hole is inclined upward at an angle of 7°. When drilling, we use R51/76 tungsten carbide button drill bit, and the hole diameter is 76mm. After the drilling is completed, the grouting shall be carried out. The water-cement ratio of the cement slurry is 1:1, and the grouting pressure is 0.5-2.0MPa. After the grouting is completed, the orifice shall be blocked with a grouting plug.

As we all know, bolt support needs to adopt different support methods according to different geology. Silty clay belongs to cohesive soil, which is relatively hard when dry and relatively sticky when wet. Silty clay will absorb immediately when it comes into contact with water, so there are problems such as serious material consumption in bolt support. Below, Sinorock will answer the question of whether silty clay can be bolted for support. this question.

Difficulties of silty clay support

The soil is viscous

Silty clay is generally brownish-yellow, hard plastic, with small soil particles, low moisture content, and high water absorption. In the support process, it is necessary to consider the difference between the actual pull-out force and the design pull-out force to see whether the tensile strength of the bolt can meet the pull-out force requirements.

Large pulp consumption

Since the silty clay has strong water absorption, and the soil will become viscous after absorbing water, in order for the bolt to be smoothly drilled into a hole, it is necessary to use the method of drilling, then pulling out, and then drilling. This will lead to long construction time, more slurry outflow, material loss, and large slurry consumption.

The water outlet is blocked

During the drilling process, because the clay will stick to the drill bit, it is easy to block the hole. Especially when the drilling depth is deep, this problem may not be obvious at the beginning, but as the drilling deepens, there may be a problem that the grouting pressure is insufficient and the grouting cannot be smoothly returned, which will lead to hole plugging.

Self-drilling bolt support solution

The self-drilling bolt has the functions of drilling and grouting at the same time, which can well solve the support problems of different complex geology. Let's take a look at how the self-drilling bolt solves the silty clay support.

Drilling method

Since the silty clay is easy to form agglomeration, it will stick to the rod body, connecting sleeve, drill bit and adapter of the self-drilling bolt, so it is necessary to slow down the drilling speed, let the slurry discharge the clay, and then drill deeply.

Slurry ratio

For the preparation of the water-cement ratio of the slurry, it is necessary to pay attention to the principle of thinning first and then thickening. First, use the slurry with a relatively large water-cement ratio, and inject a slurry with a relatively small water-cement ratio after drilling. And add a centralizer to make the hollow bolt body in the middle of the borehole to ensure that the slurry can wrap the rod body more evenly.

Power of grouting machine

In the early stage of drilling, it is necessary to pay attention to clearing the hole. While drilling, the hole should be cleaned with water, and the long anchor rod should be connected and sleeved in time, and the power of the grouting machine should be increased at the same time. Self-drilling rock bolts are drill rods, which do not need to be pulled out after drilling, so there is no problem of not forming holes, reducing the possibility of hole plugging and reducing slurry consumption.

At present, the more common supporting bolts on the market are finished-rolled rebar, steel strands, hot-rolled ribbed steel bars, and other materials. There are many successful cases of self-drilling hollow bolts that are widely used in the world. Compared with ordinary bolt materials, self-drilling hollow bolts have higher tensile strength and are applicable to more geological conditions. Below, Sinorock will introduce the difference between self-drilling hollow bolts and ordinary bolts in detail.

1. Differences in material properties

Self-drilling hollow bolts: Self-drilling hollow bolts have a wide range of diameters, with sizes ranging from 25 to 200 mm. The tensile strength and yield strength of the material are relatively high. The yield strength can reach more than 600MPa, and the tensile resistance value can reach 200- 14000kN.

Ordinary bolts: Ordinary bolts are generally made of hot-rolled ribbed steel bars, fine-rolled threaded steel bars, steel strands, and other materials. The strength levels are also from low to high, and the diameter size and tensile force value range are limited.

2. Differences in construction technology

Self-drilling hollow bolt: prepare drilling rig, materials → install bolt bit → connect bolt to drilling rig, grouting pump → drilling → flushing hole → extend bolt → drilling → complete drilling (grouting completed) → Install the backing plate nut

Ordinary bolts: prepare drilling rigs and materials → install drilling tools → place drilling rigs → drill holes → purge and discharge slag after forming holes → remove drilling tools and drill pipes → push and release bolts (cables) → pull out casing → anchors (cables) grouting → construction tensioner → tension lock → anchor seal

3. Difference in labor cost

Self-drilling hollow bolt: The construction of a self-drilling hollow bolt requires less personnel, about three people, and the labor cost is low.

Ordinary anchor rod: Ordinary anchor rod needs to be pressed into the casing while drilling, or the casing is pushed into the drilling tool ahead of time and drilled into a hole. When I introduced the difference between casing drilling and self-drilling, I also introduced the relevant content. The construction process of ordinary bolts is more complicated and requires more labor costs.

4. Differences in construction efficiency

Self-drilling hollow bolts: Self-drilling hollow bolts are generally drilled and formed at one time, and there are no problems such as hole collapse, sticking, and difficulty in inserting rods. The efficiency is 2-4 times that of ordinary bolts.

Ordinary bolts: In severely broken areas, there are problems such as hole collapse, stuck drilling, and difficulty in inserting rods. Ordinary bolts need to be grouted ahead of time and then solidified before making holes, resulting in low construction efficiency and even impossible construction.

5. Price difference

Ordinary geology: The cost of self-drilling hollow bolts is about 15% higher than that of ordinary hollow bolts, and about 60% higher than that of ordinary reinforced steel bolts. General broken geology: Self-drilling hollow bolts are 15% higher than ordinary hollow bolts, and about 30% higher than ordinary reinforced steel bolts.

Severely broken geology: Self-drilling hollow bolts are 15% higher than ordinary hollow bolts, but 10% lower than ordinary steel bars, so in severely broken surrounding rock areas, the economic advantages of self-drilling hollow bolts are more obvious.

6. Difference in inapplicability

Self-drilling hollow bolt: no need to make holes under bad surrounding rocks such as backfill area, weathered rock, broken rock, sand layer, clay layer, pebble layer, etc., bolt into one, the hollow bolt body can be used as a grouting channel, grouting from the inside to the outside.

Ordinary bolts: It can be applied in ordinary rock formations, but when encountering complex geology, it will face problems such as narrow construction space, inability to form holes, and difficult construction.

The pipe roofing is generally a supporting structure used in tunnel engineering, which forms a protective layer on the top of the tunnel to protect the safety of tunnel construction. Ordinary pipe umbrella generally is assembled of steel tubes with a transverse hole crossing. Self-drilling pipe umbrella is structured by self-drilling anchor bolts. Today Sinorock will introduce the difference between self-drilling pipe roofing and ordinary pipe umbrella.

Comparison Between Self-Drilling Pipe Roofing and Ordinary Pipe Umbrella

Difference in Construction Cost

Under the same construction environment, self-drilling anchor bolts can realize one-time drilling support. While the construction of ordinary pipe roofing requires drilling, hole cleaning, supporting and other processes. After drilling, the drill pipe will be pulled out and piped manually, which not only has low construction efficiency and long construction period, but also increases the cost of personnel and equipment. Therefore, compared with ordinary pipe umbrella, the self-drilling pipe roofing reduces the configuration of personnel and the construction cost.

Differences in Construction Efficiency

In the similar rock formation of tunnel construction, the self-drilling pipe umbrella and the ordinary pipe umbrella are compared for data detection and equipment usage tracking. After the actual case testing, the average construction efficiency of the self-drilling pipe umbrella reaches 1.42 m/min, while the construction efficiency of the ordinary pipe umbrella used is only 0.98 m/min.

Overall Benefit Difference

In the same project, due to the processing technology of the self-drilling pipe umbrella, the material cost is about 14% higher than that of the ordinary pipe roofing. However, the construction progress is about 45% higher than that of ordinary pipe roofing. Taking into account the installation and connection of multi-section anchor bolts, couplers and other components in the actual construction of self-drilling pipe sheds, we may make it 40%. Comprehensive evaluation of materials, mechanical equipment and construction progress shows that the overall benefit of self-drilling pipe umbrella is increased by about 22%.

Difference in Support Performance

According to the design and calculation comparison, when using in the project, the ultimate load and yield load of the self-drilling anchor bolt with a diameter about 30% smaller than the steel pipe are higher than that of the steel tube, and the mass is reduced by about 2% to 5%. In blasting construction, even the self-drilling pipe umbrella with insufficient grouting can still achieve a good supporting effect, which thanks to the high rigidity of the material of the Sinorock self-drilling hollow anchor bolt.

Advantages of Self-Feeding Pipe Umbrella

High Construction Efficiency

Ordinary pipe umbrella needs to be drilled with a drilling pipe first, and then the drill pipe is pulled out, and then the steel tubes with a transverse hole crossing will be topped into the hole for grouting. The self-drilling pipe umbrella can complete the construction by drilling and grouting at one time, with few construction steps and high construction efficiency.

Strong Adaptability

Ordinary pipe roofing has high requirements for drilling. If the drilling hole collapses or there is gravel staying in the hole, it is difficult for the ordinary steel tubes to be inserted into the hole. Therefore, the ordinary pipe roofing is only suitable for the projects with stable formation. The anchor bolt of the self-drilling pipe umbrella is the drill rod. It does not need to pull out the drill rod. It can still be constructed normally in the broken rock and loose soil. It is suitable for various types of rock formations and has stronger adaptability.

High Security

Self-drilling pipe umbrella can be constructed by bolting rigs, which are easier to mechanize. Compared with ordinary pipe umbrella, the labor intensity is lower and requires less labor. At the same time, workers can stay away from the construction site while processing to ensure their own safety.

Low Cost

Although the material cost of self-drilling pipe umbrella is slightly higher than that of ordinary pipe roofing, its construction efficiency is higher, and it can better adapt to various unpredictable rock conditions in tunnel construction. The self-drilling pipe umbrella can be constructed easily, shorten the construction period, and indirectly reduce the cost of capital and equipment renting.