Self-Drilling Hollow Bolt Supports Deep Foundation Pit in Sand Layer, Simple And Efficient

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the construction process of the ordinary hollow bolt is to drill first and then grouting, when the drill pipe is withdrawn, it is likely that the hole will collapse, and the subsequent bolt cannot be put in, resulting in the entire support construction cannot continue.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.

In the geological construction of sand layer, self-drilling hollow bolts are used for support, which is simple in construction, high in construction efficiency and strong in anchoring force. Self-drilling hollow bolts can be used not only in sandy geological formations, but also in many soft and broken rock formations, with a wide range of applications.